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Anatomy_Gray_2900 | Anatomy_Gray | Deep to the dura mater is the arachnoid (from the Greek word arachne meaning “spider’s web”) mater. The outer layer of the arachnoid mater is composed of several layers of flattened cells that lie adjacent to the meningeal layer of the dura mater (eFig. 9.19). Strands of connective tissue extend from this outer layer to form arachnoid trabeculae, which connect internally to the pia mater (eFig. 9.19). The pia mater forms a thin, veil-like layer that closely follows the gyri and sulci on the surface of the brain. The pia and arachnoid matter are separated by a subarachnoid space that contains CSF and the major blood vessels supplying the brain. | Anatomy_Gray. Deep to the dura mater is the arachnoid (from the Greek word arachne meaning “spider’s web”) mater. The outer layer of the arachnoid mater is composed of several layers of flattened cells that lie adjacent to the meningeal layer of the dura mater (eFig. 9.19). Strands of connective tissue extend from this outer layer to form arachnoid trabeculae, which connect internally to the pia mater (eFig. 9.19). The pia mater forms a thin, veil-like layer that closely follows the gyri and sulci on the surface of the brain. The pia and arachnoid matter are separated by a subarachnoid space that contains CSF and the major blood vessels supplying the brain. |
Anatomy_Gray_2901 | Anatomy_Gray | Vascular supply to the brain is divided into the anterior circulation arising from the internal carotid arteries and posterior circulation from the vertebral arteries (eFig. 9.20). The internal carotid arteries arise from the branching of the common carotid arteries at the level of the fourth cervical vertebra. Bilaterally the arteries course through the neck to enter the middle cranial fossa through the carotid canal. The arteries then make a series of turns to pass through the petrous portion of the temporal bone and cavernous sinus before entering the subarachnoid space just lateral to the optic chiasm. Upon exiting the cavernous sinus, the internal carotid artery gives rise to the ophthalmic artery and then continues superiorly to give off the posterior communicating artery and anterior choroidal arteries before terminating as the anterior and middle cerebral arteries (eFig. 9.21). | Anatomy_Gray. Vascular supply to the brain is divided into the anterior circulation arising from the internal carotid arteries and posterior circulation from the vertebral arteries (eFig. 9.20). The internal carotid arteries arise from the branching of the common carotid arteries at the level of the fourth cervical vertebra. Bilaterally the arteries course through the neck to enter the middle cranial fossa through the carotid canal. The arteries then make a series of turns to pass through the petrous portion of the temporal bone and cavernous sinus before entering the subarachnoid space just lateral to the optic chiasm. Upon exiting the cavernous sinus, the internal carotid artery gives rise to the ophthalmic artery and then continues superiorly to give off the posterior communicating artery and anterior choroidal arteries before terminating as the anterior and middle cerebral arteries (eFig. 9.21). |
Anatomy_Gray_2902 | Anatomy_Gray | The two anterior cerebral arteries anastomose proximally via the anterior communicating artery, anterior to the optic chiasm (eFig. 9.22). Distal to this connection, the anterior cerebral artery (ACA) courses along the medial aspect of the cerebral hemisphere within the longitudinal fissure and follows the superior border of the corpus callosum to the anterior portion of the parietal lobe. Along its course two large branches arise: the callosomarginal artery, which follows the cingulate sulcus, and the pericallosal artery, which is immediately adjacent to the corpus callosum (eFig. 9.23). Given its course and branches, the ACA perfuses most of the medial aspect of the brain from the frontal lobe to the anterior portion of the parietal lobe. | Anatomy_Gray. The two anterior cerebral arteries anastomose proximally via the anterior communicating artery, anterior to the optic chiasm (eFig. 9.22). Distal to this connection, the anterior cerebral artery (ACA) courses along the medial aspect of the cerebral hemisphere within the longitudinal fissure and follows the superior border of the corpus callosum to the anterior portion of the parietal lobe. Along its course two large branches arise: the callosomarginal artery, which follows the cingulate sulcus, and the pericallosal artery, which is immediately adjacent to the corpus callosum (eFig. 9.23). Given its course and branches, the ACA perfuses most of the medial aspect of the brain from the frontal lobe to the anterior portion of the parietal lobe. |
Anatomy_Gray_2903 | Anatomy_Gray | Branching laterally from the internal carotid artery, the middle cerebral artery (MCA) penetrates the lateral fissure and gives off the lenticulostriate striate arteries (eFig. 9.24) before bifurcating into superior and inferior divisions, which loop extensively along the insula and frontal operculum before emerging on the lateral convexity of the cerebrum. The superior division perfuses the cortex above the lateral fissure, including the lateral frontal lobe and a small portion of the anterior parietal lobe (eFig. 9.21). The inferior division perfuses the cortex below the lateral fissure, including the temporal lobe and the anterolateral portion of the parietal lobe. | Anatomy_Gray. Branching laterally from the internal carotid artery, the middle cerebral artery (MCA) penetrates the lateral fissure and gives off the lenticulostriate striate arteries (eFig. 9.24) before bifurcating into superior and inferior divisions, which loop extensively along the insula and frontal operculum before emerging on the lateral convexity of the cerebrum. The superior division perfuses the cortex above the lateral fissure, including the lateral frontal lobe and a small portion of the anterior parietal lobe (eFig. 9.21). The inferior division perfuses the cortex below the lateral fissure, including the temporal lobe and the anterolateral portion of the parietal lobe. |
Anatomy_Gray_2904 | Anatomy_Gray | The posterior cerebral cortex receives vascular supply from the vertebral-basilar system of arteries. This system begins with the vertebral arteries bilaterally, which arise from the subclavian arteries and ascend through the foramen transversarium of the cervical vertebrae in the neck. After entering the foramen magnum at the level of the pontomedullary junction, the arteries join to form the basilar artery, which courses along the midline of the ventral brainstem (eFig. 9.20). At the level of the midbrain, the basilar artery gives rise to the posterior cerebral artery (PCA), which turns posteriorly and gives rise to branches that perfuse the inferior and medial temporal and occipital lobes. Also at the PCA, a connecting artery, the posterior communicating artery, branches off and connects to the internal carotid artery (eFig. 9.22). | Anatomy_Gray. The posterior cerebral cortex receives vascular supply from the vertebral-basilar system of arteries. This system begins with the vertebral arteries bilaterally, which arise from the subclavian arteries and ascend through the foramen transversarium of the cervical vertebrae in the neck. After entering the foramen magnum at the level of the pontomedullary junction, the arteries join to form the basilar artery, which courses along the midline of the ventral brainstem (eFig. 9.20). At the level of the midbrain, the basilar artery gives rise to the posterior cerebral artery (PCA), which turns posteriorly and gives rise to branches that perfuse the inferior and medial temporal and occipital lobes. Also at the PCA, a connecting artery, the posterior communicating artery, branches off and connects to the internal carotid artery (eFig. 9.22). |
Anatomy_Gray_2905 | Anatomy_Gray | Venous drainage of the cerebral hemispheres follows a system of deep veins, superficial veins, and dural venous sinuses before reaching the internal jugular vein. Before reaching the internal jugular veins, the superficial and deep veins connect to the dural sinuses located between the periosteal and meningeal layers of the dura. None of the vessels in this network have valves present in their lumen. | Anatomy_Gray. Venous drainage of the cerebral hemispheres follows a system of deep veins, superficial veins, and dural venous sinuses before reaching the internal jugular vein. Before reaching the internal jugular veins, the superficial and deep veins connect to the dural sinuses located between the periosteal and meningeal layers of the dura. None of the vessels in this network have valves present in their lumen. |
Anatomy_Gray_2906 | Anatomy_Gray | Running along the superior edge of the falx cerebri is the superior sagittal sinus. The superior sagittal sinus continues posteriorly to drain into the transverse sinuses bilaterally (eFig. 9.25A). Each transverse sinus turns inferiorly to form the sigmoid sinus, which exits the jugular foramen to become the internal jugular vein. Along the inferior margin of the falx cerebri is the inferior sagittal sinus (eFig. 9.25B). Posteriorly, the inferior sagittal sinus joins the great vein of Galen to form the straight sinus. The point where the straight sinus, superior sagittal sinus, and occipital sinus join is known as the confluence of the sinuses (eFig. 9.25B). The confluence of sinuses is drained by the transverse sinuses. Located on either side of the hypophysial fossa is a plexus of veins referred to as the cavernous sinus (eFig. 9.26). In addition to receiving drainage from the other sinuses, the cavernous sinus also receives the ophthalmic veins. The cavernous sinus is drained by | Anatomy_Gray. Running along the superior edge of the falx cerebri is the superior sagittal sinus. The superior sagittal sinus continues posteriorly to drain into the transverse sinuses bilaterally (eFig. 9.25A). Each transverse sinus turns inferiorly to form the sigmoid sinus, which exits the jugular foramen to become the internal jugular vein. Along the inferior margin of the falx cerebri is the inferior sagittal sinus (eFig. 9.25B). Posteriorly, the inferior sagittal sinus joins the great vein of Galen to form the straight sinus. The point where the straight sinus, superior sagittal sinus, and occipital sinus join is known as the confluence of the sinuses (eFig. 9.25B). The confluence of sinuses is drained by the transverse sinuses. Located on either side of the hypophysial fossa is a plexus of veins referred to as the cavernous sinus (eFig. 9.26). In addition to receiving drainage from the other sinuses, the cavernous sinus also receives the ophthalmic veins. The cavernous sinus is drained by |
Anatomy_Gray_2907 | Anatomy_Gray | referred to as the cavernous sinus (eFig. 9.26). In addition to receiving drainage from the other sinuses, the cavernous sinus also receives the ophthalmic veins. The cavernous sinus is drained by the superior petrosal sinus into the transverse sinus and inferior petrosal sinuses into the internal jugular vein. | Anatomy_Gray. referred to as the cavernous sinus (eFig. 9.26). In addition to receiving drainage from the other sinuses, the cavernous sinus also receives the ophthalmic veins. The cavernous sinus is drained by the superior petrosal sinus into the transverse sinus and inferior petrosal sinuses into the internal jugular vein. |
Anatomy_Gray_2908 | Anatomy_Gray | Venous drainage from the superficial veins is primarily received by the superior sagittal sinus and cavernous sinus. Although the pattern of superficial veins coursing through the subarachnoid space from the cerebral cortex is quite variable, three veins appear to be fairly constant. Positioned in parallel to the lateral fissure is the superficial middle cerebral vein, which drains into the cavernous sinus from the temporal lobe (eFig. 9.25A). Connecting to the superficial middle cerebral vein perpendicularly is the superior anastomotic vein (of Trolard) (eFig. 9.25A). This vein courses superiorly across the parietal lobe to drain into the superior sagittal sinus. Also connecting to the superficial middle cerebral vein perpendicularly is the inferior anastomotic vein (of Labbé) (eFig. 9.25A). The inferior anastomotic vein passes inferiorly along the temporal lobe to drain into the transverse sinus. | Anatomy_Gray. Venous drainage from the superficial veins is primarily received by the superior sagittal sinus and cavernous sinus. Although the pattern of superficial veins coursing through the subarachnoid space from the cerebral cortex is quite variable, three veins appear to be fairly constant. Positioned in parallel to the lateral fissure is the superficial middle cerebral vein, which drains into the cavernous sinus from the temporal lobe (eFig. 9.25A). Connecting to the superficial middle cerebral vein perpendicularly is the superior anastomotic vein (of Trolard) (eFig. 9.25A). This vein courses superiorly across the parietal lobe to drain into the superior sagittal sinus. Also connecting to the superficial middle cerebral vein perpendicularly is the inferior anastomotic vein (of Labbé) (eFig. 9.25A). The inferior anastomotic vein passes inferiorly along the temporal lobe to drain into the transverse sinus. |
Anatomy_Gray_2909 | Anatomy_Gray | In contrast to the superficial veins, deep veins are more constant in their organization. Most of the deep veins eventually drain into the great cerebral vein (of Galen) before entering the dural venous sinuses (eFig. 9.27). Traveling adjacent to the ACA and MCA are the anterior cerebral vein and deep middle cerebral vein. These deep veins join to form the basal vein (of Rosenthal), which continues around the lateral aspect of the midbrain. Formed at the interventricular foramen by the joining of the septal and thalamostriate veins bilaterally are the internal cerebral veins (eFig. 9.27). Posterior to the midbrain, the internal cerebral veins and basal veins join to form the great cerebral vein (of Galen) (eFig. 9.27). From here the great cerebral vein joins the inferior sagittal sinus to form the straight sinus. Part III: Thalamus | Anatomy_Gray. In contrast to the superficial veins, deep veins are more constant in their organization. Most of the deep veins eventually drain into the great cerebral vein (of Galen) before entering the dural venous sinuses (eFig. 9.27). Traveling adjacent to the ACA and MCA are the anterior cerebral vein and deep middle cerebral vein. These deep veins join to form the basal vein (of Rosenthal), which continues around the lateral aspect of the midbrain. Formed at the interventricular foramen by the joining of the septal and thalamostriate veins bilaterally are the internal cerebral veins (eFig. 9.27). Posterior to the midbrain, the internal cerebral veins and basal veins join to form the great cerebral vein (of Galen) (eFig. 9.27). From here the great cerebral vein joins the inferior sagittal sinus to form the straight sinus. Part III: Thalamus |
Anatomy_Gray_2910 | Anatomy_Gray | Part III: Thalamus The thalamus (Greek for “inner chamber”) is a large, egg-shaped mass of gray matter derived from the diencephalon of the developing brain (see eTable 9.1). The most significant role of the thalamus is as a synaptic relay for pathways projecting to the cerebral cortex. However, the thalamus also acts as a gatekeeper to prevent or enhance information transfer, depending on the behavioral state. Sensory, motor, limbic, and modulatory signals from behavioral and arousal circuits all have synaptic relays within the thalamic nuclei. | Anatomy_Gray. Part III: Thalamus The thalamus (Greek for “inner chamber”) is a large, egg-shaped mass of gray matter derived from the diencephalon of the developing brain (see eTable 9.1). The most significant role of the thalamus is as a synaptic relay for pathways projecting to the cerebral cortex. However, the thalamus also acts as a gatekeeper to prevent or enhance information transfer, depending on the behavioral state. Sensory, motor, limbic, and modulatory signals from behavioral and arousal circuits all have synaptic relays within the thalamic nuclei. |
Anatomy_Gray_2911 | Anatomy_Gray | Because of its location deep within the brain, the thalamus is neighbored by several structures and also portions of the ventricular system. Anteriorly, the thalamus extends forward to contact the interventricular foramen, which connects the lateral and third ventricles (eFig. 9.28). Together, the thalamic nuclear masses and the ventrally located hypothalamus comprise the lateral walls of the third ventricle. Immediately lateral to the thalamus is the posterior limb of the internal capsule (eFig. 9.29). Related to the dorsal aspect of the thalamus is the body of the lateral ventricle, and extending caudally is the midbrain portion of the brainstem (eFig. 9.28). Across the midline of the third ventricle, the two thalamic masses are interconnected by the interthalamic adhesion. | Anatomy_Gray. Because of its location deep within the brain, the thalamus is neighbored by several structures and also portions of the ventricular system. Anteriorly, the thalamus extends forward to contact the interventricular foramen, which connects the lateral and third ventricles (eFig. 9.28). Together, the thalamic nuclear masses and the ventrally located hypothalamus comprise the lateral walls of the third ventricle. Immediately lateral to the thalamus is the posterior limb of the internal capsule (eFig. 9.29). Related to the dorsal aspect of the thalamus is the body of the lateral ventricle, and extending caudally is the midbrain portion of the brainstem (eFig. 9.28). Across the midline of the third ventricle, the two thalamic masses are interconnected by the interthalamic adhesion. |
Anatomy_Gray_2912 | Anatomy_Gray | Based on their relationship to the internal medullary lamina, a Y-shaped band of myelinated axons coursing rostrocaudally through the thalamus, the thalamic nuclei are classified into four groups: (1) anterior, (2) medial, (3) lateral, and (4) intralaminar (eFig. 9.30). In addition to this structural categorization, the nuclei are divided into three major functional classes: (1) relay, (2) intralaminar, and (3) reticular. As mentioned earlier, most of the thalamus is composed of relay nuclei, which have reciprocal excitatory connections with the cortex. Relay nuclei are further subdivided into specific and nonspecific based on their projections to specific areas of the primary sensory and motor cortex or more diffuse cortical projections. The majority of specific relay nuclei reside in the lateral thalamus—in fact, all sensory modalities, with the exception of olfaction, have relays in the lateral thalamus before reaching their primary cortical target. Details of specific and | Anatomy_Gray. Based on their relationship to the internal medullary lamina, a Y-shaped band of myelinated axons coursing rostrocaudally through the thalamus, the thalamic nuclei are classified into four groups: (1) anterior, (2) medial, (3) lateral, and (4) intralaminar (eFig. 9.30). In addition to this structural categorization, the nuclei are divided into three major functional classes: (1) relay, (2) intralaminar, and (3) reticular. As mentioned earlier, most of the thalamus is composed of relay nuclei, which have reciprocal excitatory connections with the cortex. Relay nuclei are further subdivided into specific and nonspecific based on their projections to specific areas of the primary sensory and motor cortex or more diffuse cortical projections. The majority of specific relay nuclei reside in the lateral thalamus—in fact, all sensory modalities, with the exception of olfaction, have relays in the lateral thalamus before reaching their primary cortical target. Details of specific and |
Anatomy_Gray_2913 | Anatomy_Gray | in the lateral thalamus—in fact, all sensory modalities, with the exception of olfaction, have relays in the lateral thalamus before reaching their primary cortical target. Details of specific and nonspecific nuclei and their cortical connections can be reviewed in eTable 9.4. | Anatomy_Gray. in the lateral thalamus—in fact, all sensory modalities, with the exception of olfaction, have relays in the lateral thalamus before reaching their primary cortical target. Details of specific and nonspecific nuclei and their cortical connections can be reviewed in eTable 9.4. |
Anatomy_Gray_2914 | Anatomy_Gray | Intralaminar nuclei reside within the internal medullary lamina and have numerous reciprocal projections, primarily with the basal ganglia and reticular formation (eFig. 9.30).There are two major functional regions of the intralaminar nuclei: rostral and caudal. The rostral intralaminar nuclei have reciprocal connections with the basal ganglia and also relay input from the ascending reticular activating system. Caudal intralaminar nuclei, which include the large centromedian nucleus, are predominantly involved in basal ganglia circuitry. | Anatomy_Gray. Intralaminar nuclei reside within the internal medullary lamina and have numerous reciprocal projections, primarily with the basal ganglia and reticular formation (eFig. 9.30).There are two major functional regions of the intralaminar nuclei: rostral and caudal. The rostral intralaminar nuclei have reciprocal connections with the basal ganglia and also relay input from the ascending reticular activating system. Caudal intralaminar nuclei, which include the large centromedian nucleus, are predominantly involved in basal ganglia circuitry. |
Anatomy_Gray_2915 | Anatomy_Gray | The reticular nucleus of the thalamus is a thin, sheet-like structure along the lateral aspect of the thalamus just medial to the posterior limb of the internal capsule (eFig. 9.30). Unlike the rest of the thalamic nuclei, the reticular nucleus does not send projections to the cerebral cortex, but rather receives input from other thalamic nuclei and the cortex, which project back to the thalamus. Functionally, this organization of inputs and outputs, along with the GABAergic neurons of the reticular nucleus, allows it to regulate thalamic activity quite effectively. Vascular supply to the thalamus arises from penetrating branches from the ACA, anterior choroidal artery branching from the internal carotid, lenticulostriate arteries of the middle cerebral artery and thalamoperforator arteries from the posterior cerebral arteries. Part IV: Brainstem | Anatomy_Gray. The reticular nucleus of the thalamus is a thin, sheet-like structure along the lateral aspect of the thalamus just medial to the posterior limb of the internal capsule (eFig. 9.30). Unlike the rest of the thalamic nuclei, the reticular nucleus does not send projections to the cerebral cortex, but rather receives input from other thalamic nuclei and the cortex, which project back to the thalamus. Functionally, this organization of inputs and outputs, along with the GABAergic neurons of the reticular nucleus, allows it to regulate thalamic activity quite effectively. Vascular supply to the thalamus arises from penetrating branches from the ACA, anterior choroidal artery branching from the internal carotid, lenticulostriate arteries of the middle cerebral artery and thalamoperforator arteries from the posterior cerebral arteries. Part IV: Brainstem |
Anatomy_Gray_2916 | Anatomy_Gray | Part IV: Brainstem The brainstem is a stalklike structure within the posterior cranial fossa of the skull connecting the forebrain and spinal cord (eFig. 9.31). From rostral to caudal, the brainstem consists of the midbrain, pons, and medulla oblongata. Broadly speaking, the brainstem has three main functions: (1) it is a conduit for tracts ascending and descending through the CNS; (2) it houses cranial nerve nuclei III to XII (note that the CNXI is in the cervical spinal cord); and (3) it is the location for reflex centers related to respiration, cardiovascular function, and regulation of consciousness. Externally, each portion of the brainstem has a distinct appearance and structural features that define its many functional roles. | Anatomy_Gray. Part IV: Brainstem The brainstem is a stalklike structure within the posterior cranial fossa of the skull connecting the forebrain and spinal cord (eFig. 9.31). From rostral to caudal, the brainstem consists of the midbrain, pons, and medulla oblongata. Broadly speaking, the brainstem has three main functions: (1) it is a conduit for tracts ascending and descending through the CNS; (2) it houses cranial nerve nuclei III to XII (note that the CNXI is in the cervical spinal cord); and (3) it is the location for reflex centers related to respiration, cardiovascular function, and regulation of consciousness. Externally, each portion of the brainstem has a distinct appearance and structural features that define its many functional roles. |
Anatomy_Gray_2917 | Anatomy_Gray | Approximately 2 cm in length, the midbrain connects the forebrain to the pons caudally and the cerebellum posteriorly (eFig. 9.32A). Along the midline of the anterior surface there is a deep depression, the interpeduncular fossa, which has several perforations on its surface where small vessels perforate through the floor of the fossa. On either side of the interpeduncular fossa are the crus cerebri (eFig. 9.32B). Projecting medially from the crus is cranial nerve III, the oculomotor nerve (eFig. 9.33A). The most prominent features on the posterior surface are the superior and inferior colliculi (eFig. 9.32A). Between the inferior colliculi, cranial nerve IV, the trochlear nerve, emerges, crosses the midline, and wraps around the lateral aspect of the midbrain (eFig. 9.32A). Laterally, the superior brachium and inferior brachium can be seen as they project in an anterolateral direction from the superior and inferior colliculi. | Anatomy_Gray. Approximately 2 cm in length, the midbrain connects the forebrain to the pons caudally and the cerebellum posteriorly (eFig. 9.32A). Along the midline of the anterior surface there is a deep depression, the interpeduncular fossa, which has several perforations on its surface where small vessels perforate through the floor of the fossa. On either side of the interpeduncular fossa are the crus cerebri (eFig. 9.32B). Projecting medially from the crus is cranial nerve III, the oculomotor nerve (eFig. 9.33A). The most prominent features on the posterior surface are the superior and inferior colliculi (eFig. 9.32A). Between the inferior colliculi, cranial nerve IV, the trochlear nerve, emerges, crosses the midline, and wraps around the lateral aspect of the midbrain (eFig. 9.32A). Laterally, the superior brachium and inferior brachium can be seen as they project in an anterolateral direction from the superior and inferior colliculi. |
Anatomy_Gray_2918 | Anatomy_Gray | Caudal to the midbrain, the pons is approximately 2.5 cm in length and connects the midbrain to the medulla (eFig. 9.32B). The midline of the anterior surface has a shallow groove, the basilar groove, where the basilar artery resides along its course (eFig. 9.32B). On either side of the basilar groove, the pons has a prominent convex shape as a result of the vast number of fibers bridging through the pons to the cerebellum through the middle cerebellar peduncle. Along the anterolateral surface of the pons, cranial nerve V, the motor and sensory root of the trigeminal nerve, emerges (eFig. 9.33B). At the junction of the pons and medulla, from medial to lateral, cranial nerves VI (abducent), VII (facial), and VIII (vestibulocochlear) emerge (eFig. 9.33C). The posterior surface of the pons faces the cerebellum and forms the floor of the fourth ventricle (eFig. 9.32A). Along the midline of the posterior surface is a prominent bump, the facial colliculus, which represents the relationship | Anatomy_Gray. Caudal to the midbrain, the pons is approximately 2.5 cm in length and connects the midbrain to the medulla (eFig. 9.32B). The midline of the anterior surface has a shallow groove, the basilar groove, where the basilar artery resides along its course (eFig. 9.32B). On either side of the basilar groove, the pons has a prominent convex shape as a result of the vast number of fibers bridging through the pons to the cerebellum through the middle cerebellar peduncle. Along the anterolateral surface of the pons, cranial nerve V, the motor and sensory root of the trigeminal nerve, emerges (eFig. 9.33B). At the junction of the pons and medulla, from medial to lateral, cranial nerves VI (abducent), VII (facial), and VIII (vestibulocochlear) emerge (eFig. 9.33C). The posterior surface of the pons faces the cerebellum and forms the floor of the fourth ventricle (eFig. 9.32A). Along the midline of the posterior surface is a prominent bump, the facial colliculus, which represents the relationship |
Anatomy_Gray_2919 | Anatomy_Gray | the cerebellum and forms the floor of the fourth ventricle (eFig. 9.32A). Along the midline of the posterior surface is a prominent bump, the facial colliculus, which represents the relationship between the facial nerve fibers as they wind around the nucleus of the abducent nerve (eFig. 9.33C). | Anatomy_Gray. the cerebellum and forms the floor of the fourth ventricle (eFig. 9.32A). Along the midline of the posterior surface is a prominent bump, the facial colliculus, which represents the relationship between the facial nerve fibers as they wind around the nucleus of the abducent nerve (eFig. 9.33C). |
Anatomy_Gray_2920 | Anatomy_Gray | The medulla is the longest portion of the brainstem, measuring approximately 3 cm in length (eFig. 9.32A). At the rostral connection of the medulla to the pons, it has a broad conical shape that tapers caudally before connecting with the spinal cord at the level of the foramen magnum. Along the midline of the anterior surface is the anterior median fissure, which continues on to the anterior surface of the spinal cord (eFig. 9.33B). Lateral to the fissure are the medullary pyramids composed of motor fibers descending from the cerebral cortex (eFig. 9.33B). Continuing caudally, the pyramids eventually give way to the decussation of the pyramids where the majority of motor fibers decussate to the opposing side. Lateral to the pyramids are the olives, which represent the underlying inferior olivary nuclei. It is at the junction of the pyramid and the olive that the rootlets of cranial nerve XII, the hypoglossal nerve, emerge (eFig. 9.33D). Oriented posterior to the olives are the | Anatomy_Gray. The medulla is the longest portion of the brainstem, measuring approximately 3 cm in length (eFig. 9.32A). At the rostral connection of the medulla to the pons, it has a broad conical shape that tapers caudally before connecting with the spinal cord at the level of the foramen magnum. Along the midline of the anterior surface is the anterior median fissure, which continues on to the anterior surface of the spinal cord (eFig. 9.33B). Lateral to the fissure are the medullary pyramids composed of motor fibers descending from the cerebral cortex (eFig. 9.33B). Continuing caudally, the pyramids eventually give way to the decussation of the pyramids where the majority of motor fibers decussate to the opposing side. Lateral to the pyramids are the olives, which represent the underlying inferior olivary nuclei. It is at the junction of the pyramid and the olive that the rootlets of cranial nerve XII, the hypoglossal nerve, emerge (eFig. 9.33D). Oriented posterior to the olives are the |
Anatomy_Gray_2921 | Anatomy_Gray | olivary nuclei. It is at the junction of the pyramid and the olive that the rootlets of cranial nerve XII, the hypoglossal nerve, emerge (eFig. 9.33D). Oriented posterior to the olives are the inferior cerebellar peduncles, which form a connection between the cerebellum and medulla (eFig. 9.33D). At the junction of the olive and inferior cerebellar peduncles from rostral to caudal, rootlets of cranial nerves IX (glossopharyngeal), X (vagus), and XI (spinal accessory) emerge. Like the pons, the posterior surface of the medulla forms the floor of the fourth ventricle (eFig. 9.32A). Coursing down the midline of the posterior medulla is the posterior median sulcus, which continues into the spinal cord. On either side of the sulcus are the gracile and cuneate tubercles, formed by the underlying gracile nucleus and cuneate nuclei (eFig. 9.32A). | Anatomy_Gray. olivary nuclei. It is at the junction of the pyramid and the olive that the rootlets of cranial nerve XII, the hypoglossal nerve, emerge (eFig. 9.33D). Oriented posterior to the olives are the inferior cerebellar peduncles, which form a connection between the cerebellum and medulla (eFig. 9.33D). At the junction of the olive and inferior cerebellar peduncles from rostral to caudal, rootlets of cranial nerves IX (glossopharyngeal), X (vagus), and XI (spinal accessory) emerge. Like the pons, the posterior surface of the medulla forms the floor of the fourth ventricle (eFig. 9.32A). Coursing down the midline of the posterior medulla is the posterior median sulcus, which continues into the spinal cord. On either side of the sulcus are the gracile and cuneate tubercles, formed by the underlying gracile nucleus and cuneate nuclei (eFig. 9.32A). |
Anatomy_Gray_2922 | Anatomy_Gray | Internal structures of the brainstem can be identified by their general location in the tectum (Latin for “roof”), tegmentum (Latin for “covering”), or basis (eFig. 9.34). To identify the structures present in each level of the brainstem, it is best to view serial sections stained for myelin. This way, nuclear groups and myelinated axons can be more easily distinguished from one another. | Anatomy_Gray. Internal structures of the brainstem can be identified by their general location in the tectum (Latin for “roof”), tegmentum (Latin for “covering”), or basis (eFig. 9.34). To identify the structures present in each level of the brainstem, it is best to view serial sections stained for myelin. This way, nuclear groups and myelinated axons can be more easily distinguished from one another. |
Anatomy_Gray_2923 | Anatomy_Gray | The tectum is the most obvious landmark of the midbrain, as it consists of the prominent superior colliculi, inferior colliculi, and underlying cerebral aqueduct. Given the short length of the midbrain, stained serial sections typically include either the superior colliculi, which are located rostrally, or the inferior colliculi, which are caudal. In addition to the superior colliculi, within a rostral section of the midbrain prominent nuclei such as the oculomotor nuclei, Edinger–Westphal nuclei, red nuclei, mesencephalic nuclei of cranial nerve V, and substantia nigra can be seen (eFig. 9.35). In caudal sections of the midbrain the inferior colliculus, trochlear nucleus, mesencephalic nuclei of cranial nerve V, and substantia nigra are present (eFig. 9.36). | Anatomy_Gray. The tectum is the most obvious landmark of the midbrain, as it consists of the prominent superior colliculi, inferior colliculi, and underlying cerebral aqueduct. Given the short length of the midbrain, stained serial sections typically include either the superior colliculi, which are located rostrally, or the inferior colliculi, which are caudal. In addition to the superior colliculi, within a rostral section of the midbrain prominent nuclei such as the oculomotor nuclei, Edinger–Westphal nuclei, red nuclei, mesencephalic nuclei of cranial nerve V, and substantia nigra can be seen (eFig. 9.35). In caudal sections of the midbrain the inferior colliculus, trochlear nucleus, mesencephalic nuclei of cranial nerve V, and substantia nigra are present (eFig. 9.36). |
Anatomy_Gray_2924 | Anatomy_Gray | Sections from the rostral pons are significant for pontine nuclei and multiple transversely oriented pontocerebellar fibers en route to the contralateral cerebellum. Interspersed among these horizontally running axon are longitudinally running corticospinal fibers (eFig. 9.37). Dorsal to this collection of fiber bundles, the medial lemniscus is oriented horizontally, forming a borderlike structure between the basal and tegmental portion of the pons (eFig. 9.37). At the lateral edge of the medial lemniscus, the spinothalamic tract can be seen, because it neighbors the superior cerebellar peduncle (eFig. 9.37). Near the midline, the medial longitudinal fasciculus resides just ventral to the periaqueductal gray matter. | Anatomy_Gray. Sections from the rostral pons are significant for pontine nuclei and multiple transversely oriented pontocerebellar fibers en route to the contralateral cerebellum. Interspersed among these horizontally running axon are longitudinally running corticospinal fibers (eFig. 9.37). Dorsal to this collection of fiber bundles, the medial lemniscus is oriented horizontally, forming a borderlike structure between the basal and tegmental portion of the pons (eFig. 9.37). At the lateral edge of the medial lemniscus, the spinothalamic tract can be seen, because it neighbors the superior cerebellar peduncle (eFig. 9.37). Near the midline, the medial longitudinal fasciculus resides just ventral to the periaqueductal gray matter. |
Anatomy_Gray_2925 | Anatomy_Gray | At mid-pontine levels the superior cerbellar peduncles form the lateral walls of the expanding fourth ventricle (eFig. 9.38). Also at this level, the prominent middle cerebellar peduncles can also be seen, along with the motor nucleus and principal sensory nucleus of cranial nerve V, the trigeminal nerve. In the caudal aspect of the pons, the abducent nucleus can be appreciated just lateral to the medial longitudinal fasciculus (eFig. 9.39). Also present at this level is the medial vestibular nucleus in addition to the anterior and posterior cochlear nuclei. | Anatomy_Gray. At mid-pontine levels the superior cerbellar peduncles form the lateral walls of the expanding fourth ventricle (eFig. 9.38). Also at this level, the prominent middle cerebellar peduncles can also be seen, along with the motor nucleus and principal sensory nucleus of cranial nerve V, the trigeminal nerve. In the caudal aspect of the pons, the abducent nucleus can be appreciated just lateral to the medial longitudinal fasciculus (eFig. 9.39). Also present at this level is the medial vestibular nucleus in addition to the anterior and posterior cochlear nuclei. |
Anatomy_Gray_2926 | Anatomy_Gray | From rostral to caudal the internal structures of the medulla will be briefly described from three levels: (1) level of the inferior olivary nucleus, (2) decussation of the internal arcuate fibers, and (3) decussation of the pyramids. Nuclei visible in a transverse section at the level of the inferior olivary nucleus include those associated with cranial nerves VIII (vestibulocochlear), IX (glossopharyngeal), X (vagus), XI (spinal accessory), and XII (hypoglossal) (eFig. 9.40). At this level, the medial lemniscus maintains a vertical position immediately adjacent to the midline. Dorsal to the medial lemniscus are the medial longitudinal fasciculus and hypoglossal nucleus. A large distinguishing structure at this rostral level is the laterally oriented inferior cerebellar peduncle, which connects to the cerebellum posteriorly. | Anatomy_Gray. From rostral to caudal the internal structures of the medulla will be briefly described from three levels: (1) level of the inferior olivary nucleus, (2) decussation of the internal arcuate fibers, and (3) decussation of the pyramids. Nuclei visible in a transverse section at the level of the inferior olivary nucleus include those associated with cranial nerves VIII (vestibulocochlear), IX (glossopharyngeal), X (vagus), XI (spinal accessory), and XII (hypoglossal) (eFig. 9.40). At this level, the medial lemniscus maintains a vertical position immediately adjacent to the midline. Dorsal to the medial lemniscus are the medial longitudinal fasciculus and hypoglossal nucleus. A large distinguishing structure at this rostral level is the laterally oriented inferior cerebellar peduncle, which connects to the cerebellum posteriorly. |
Anatomy_Gray_2927 | Anatomy_Gray | Continuing caudally at the level of the internal arcuate fibers, the dorsal aspect of the medulla is populated by the gracile nucleus medially, followed by the cuneate and spinal trigeminal nucleus laterally. Ventral to the cuneate and gracile nuclei, their neuronal axons can be seen decussating as internal arcuate fibers to form the medial lemniscus near the midline of the medulla. Lateral to the internal arcuate fibers and ventral to the spinal trigeminal tract, the spinocerebellar and anterolateral tracts can be seen along the perimeter of the medulla (eFig. 9.41). Before transitioning into the spinal cord, the pyramidal decussation can be observed along the midline of the caudal medulla (eFig. 9.36). Dorsal to these decussating fibers, the gracile and cuneate nuclei begin to emerge as their fasciculi continue rostrally. Note that the spinal accessory nucleus (CN XI) is located in the cervical spinal cord and not the medulla. | Anatomy_Gray. Continuing caudally at the level of the internal arcuate fibers, the dorsal aspect of the medulla is populated by the gracile nucleus medially, followed by the cuneate and spinal trigeminal nucleus laterally. Ventral to the cuneate and gracile nuclei, their neuronal axons can be seen decussating as internal arcuate fibers to form the medial lemniscus near the midline of the medulla. Lateral to the internal arcuate fibers and ventral to the spinal trigeminal tract, the spinocerebellar and anterolateral tracts can be seen along the perimeter of the medulla (eFig. 9.41). Before transitioning into the spinal cord, the pyramidal decussation can be observed along the midline of the caudal medulla (eFig. 9.36). Dorsal to these decussating fibers, the gracile and cuneate nuclei begin to emerge as their fasciculi continue rostrally. Note that the spinal accessory nucleus (CN XI) is located in the cervical spinal cord and not the medulla. |
Anatomy_Gray_2928 | Anatomy_Gray | Vascular supply to the brainstem, and other structures in the posterior cranial fossa, is provided by branches off of the vertebrobasilar system of arteries. As mentioned in the “Cerebral Vasculature” section, the vertebrobasilar system begins with the vertebral arteries bilaterally, which arise from the subclavian arteries and ascend through the foramen transversaria of cervical vertebrae C6 to C2 in the neck. At the pontomedullary junction, the vertebral arteries fuse to form the single basilar artery. The basilar artery continues rostrally and terminates as the paired posterior cerebral arteries at the pontomesencephalic junction. | Anatomy_Gray. Vascular supply to the brainstem, and other structures in the posterior cranial fossa, is provided by branches off of the vertebrobasilar system of arteries. As mentioned in the “Cerebral Vasculature” section, the vertebrobasilar system begins with the vertebral arteries bilaterally, which arise from the subclavian arteries and ascend through the foramen transversaria of cervical vertebrae C6 to C2 in the neck. At the pontomedullary junction, the vertebral arteries fuse to form the single basilar artery. The basilar artery continues rostrally and terminates as the paired posterior cerebral arteries at the pontomesencephalic junction. |
Anatomy_Gray_2929 | Anatomy_Gray | Before merging and forming the basilar artery, each vertebral artery gives rise to a posterior inferior cerebellar artery (PICA) and posterior spinal artery and contributes to the formation of the anterior spinal artery (eFig. 9.42). The PICA perfuses the lateral aspect of the medulla and the inferior portion of the cerebellum. The medial and anterior portions of the medulla receive vascular supply from the paramedian branches off of the vertebral and anterior spinal arteries. At the level of the caudal pons, the anterior inferior cerebellar artery (AICA) branches off of the basilar artery and perfuses the lateral portion of the caudal pons (eFig. 9.43A). Rostral levels of the lateral pons are perfused by circumferential branches of the basilar artery (eFig. 9.43A and B). Medial portions of the pons are perfused by paramedian branches off of the basilar artery as it continues rostrally toward the midbrain. | Anatomy_Gray. Before merging and forming the basilar artery, each vertebral artery gives rise to a posterior inferior cerebellar artery (PICA) and posterior spinal artery and contributes to the formation of the anterior spinal artery (eFig. 9.42). The PICA perfuses the lateral aspect of the medulla and the inferior portion of the cerebellum. The medial and anterior portions of the medulla receive vascular supply from the paramedian branches off of the vertebral and anterior spinal arteries. At the level of the caudal pons, the anterior inferior cerebellar artery (AICA) branches off of the basilar artery and perfuses the lateral portion of the caudal pons (eFig. 9.43A). Rostral levels of the lateral pons are perfused by circumferential branches of the basilar artery (eFig. 9.43A and B). Medial portions of the pons are perfused by paramedian branches off of the basilar artery as it continues rostrally toward the midbrain. |
Anatomy_Gray_2930 | Anatomy_Gray | Just before the midbrain, the superior cerebellar arteries branch off of the basilar artery and supply the superior cerebellar peduncles and caudal aspect of the dorsal midbrain before reaching the superior portion of the cerebellar hemispheres. Paramedian branches from the basilar artery supply the medial aspect of the midbrain (eFig. 9.43C). The final branches emerging from the top of the basilar artery are the PCAs, which perfuse the lateral aspect of the midbrain before reaching the thalamus, medial occipital, and inferior temporal lobes (eFig. 9.43C and D). Part V: Spinal cord | Anatomy_Gray. Just before the midbrain, the superior cerebellar arteries branch off of the basilar artery and supply the superior cerebellar peduncles and caudal aspect of the dorsal midbrain before reaching the superior portion of the cerebellar hemispheres. Paramedian branches from the basilar artery supply the medial aspect of the midbrain (eFig. 9.43C). The final branches emerging from the top of the basilar artery are the PCAs, which perfuse the lateral aspect of the midbrain before reaching the thalamus, medial occipital, and inferior temporal lobes (eFig. 9.43C and D). Part V: Spinal cord |
Anatomy_Gray_2931 | Anatomy_Gray | Part V: Spinal cord The spinal cord is continuous with the medulla oblongata near the foramen magnum at the base of the skull. Cylindrical in shape, it occupies the vertebral canal of the vertebral column to the LI and LII vertebral level in an adult (eFig. 9.44). Numerous ascending and descending axonal tracts course through the spinal cord and connect with the brain to convey sensory (afferent) and motor (efferent) information for facilitation of movement, reflexes, sensory input, and feedback mechanisms. | Anatomy_Gray. Part V: Spinal cord The spinal cord is continuous with the medulla oblongata near the foramen magnum at the base of the skull. Cylindrical in shape, it occupies the vertebral canal of the vertebral column to the LI and LII vertebral level in an adult (eFig. 9.44). Numerous ascending and descending axonal tracts course through the spinal cord and connect with the brain to convey sensory (afferent) and motor (efferent) information for facilitation of movement, reflexes, sensory input, and feedback mechanisms. |
Anatomy_Gray_2932 | Anatomy_Gray | Like the brain, the spinal cord is surrounded by three concentric meninges: the dura mater, arachnoid mater, and pia mater. The spinal dura mater is continuous with the inner meningeal layer of the cranial dura mater and extends inferiorly to the posterior surface of the vertebral body of S2 (eFig. 9.45). It is separated from the bony vertebral canal by the epidural/extradural space (eFig. 9.45). In addition, unlike in the cranial cavity, the underlying arachnoid mater is not tightly adherent to the dura mater, and instead has a theoretical plane or potential space called the subdural space. | Anatomy_Gray. Like the brain, the spinal cord is surrounded by three concentric meninges: the dura mater, arachnoid mater, and pia mater. The spinal dura mater is continuous with the inner meningeal layer of the cranial dura mater and extends inferiorly to the posterior surface of the vertebral body of S2 (eFig. 9.45). It is separated from the bony vertebral canal by the epidural/extradural space (eFig. 9.45). In addition, unlike in the cranial cavity, the underlying arachnoid mater is not tightly adherent to the dura mater, and instead has a theoretical plane or potential space called the subdural space. |
Anatomy_Gray_2933 | Anatomy_Gray | Although the arachnoid mater of the spinal cord has a less adherent relationship with the dura mater than in the cranial cavity, the overall structure of the arachnoid mater is the same (eFig. 9.46A). The subarachnoid space created by the loose relationship of the arachnoid and underlying pia mater extends inferiorly to the level of the SII vertebra (eFig. 9.45). Given that the spinal cord terminates near the LI–LII vertebrae, this lower termination point of the subarachnoid space creates a safe and enlarged space for accessing CSF in the clinical setting (eFig. 9.45). | Anatomy_Gray. Although the arachnoid mater of the spinal cord has a less adherent relationship with the dura mater than in the cranial cavity, the overall structure of the arachnoid mater is the same (eFig. 9.46A). The subarachnoid space created by the loose relationship of the arachnoid and underlying pia mater extends inferiorly to the level of the SII vertebra (eFig. 9.45). Given that the spinal cord terminates near the LI–LII vertebrae, this lower termination point of the subarachnoid space creates a safe and enlarged space for accessing CSF in the clinical setting (eFig. 9.45). |
Anatomy_Gray_2934 | Anatomy_Gray | The innermost pia mater is a highly vascular layer that is adherent to the surface of the spinal cord. Midway between the anterior and posterior roots the pia mater forms a flat continuous sheet, the denticulate ligament (eFig. 9.46B). At the posterior and anterior rootlets, sleevelike projections from the denticulate ligament extend out through the arachnoid mater to attach onto the dura mater. These delicate attachments anchor and position the spinal cord within the central area of the subarachnoid space. | Anatomy_Gray. The innermost pia mater is a highly vascular layer that is adherent to the surface of the spinal cord. Midway between the anterior and posterior roots the pia mater forms a flat continuous sheet, the denticulate ligament (eFig. 9.46B). At the posterior and anterior rootlets, sleevelike projections from the denticulate ligament extend out through the arachnoid mater to attach onto the dura mater. These delicate attachments anchor and position the spinal cord within the central area of the subarachnoid space. |
Anatomy_Gray_2935 | Anatomy_Gray | The anterior and posterior surfaces of the spinal cord have several longitudinally running fissures and sulci. Along the midline on the anterior surface of the spinal cord is a deep separation, the anterior median fissure (eFig. 9.47). Posteriorly the spinal cord has a shallower separation, the posterior median sulcus, which is flanked on either side by a posterolateral sulcus (eFig. 9.47). Emerging from the spinal cord are a series of rootlets, which coalesce to form anterior and posterior roots at the corresponding cord segment (eFig. 9.48). These anterior and posterior roots converge to form 31 pairs of spinal nerves, which extend the length of the spinal cord (eFig. 9.44). Along the length of the spinal cord two regions are enlarged to accommodate the numerous neurons innervating the upper and lower extremities. The cervical enlargement extends from C5 to T1 and innervates the upper extremities, whereas the lumbar enlargement extends from L2 to S3 and innervates the lower | Anatomy_Gray. The anterior and posterior surfaces of the spinal cord have several longitudinally running fissures and sulci. Along the midline on the anterior surface of the spinal cord is a deep separation, the anterior median fissure (eFig. 9.47). Posteriorly the spinal cord has a shallower separation, the posterior median sulcus, which is flanked on either side by a posterolateral sulcus (eFig. 9.47). Emerging from the spinal cord are a series of rootlets, which coalesce to form anterior and posterior roots at the corresponding cord segment (eFig. 9.48). These anterior and posterior roots converge to form 31 pairs of spinal nerves, which extend the length of the spinal cord (eFig. 9.44). Along the length of the spinal cord two regions are enlarged to accommodate the numerous neurons innervating the upper and lower extremities. The cervical enlargement extends from C5 to T1 and innervates the upper extremities, whereas the lumbar enlargement extends from L2 to S3 and innervates the lower |
Anatomy_Gray_2936 | Anatomy_Gray | the upper and lower extremities. The cervical enlargement extends from C5 to T1 and innervates the upper extremities, whereas the lumbar enlargement extends from L2 to S3 and innervates the lower extremities (eFig. 9.44). | Anatomy_Gray. the upper and lower extremities. The cervical enlargement extends from C5 to T1 and innervates the upper extremities, whereas the lumbar enlargement extends from L2 to S3 and innervates the lower extremities (eFig. 9.44). |
Anatomy_Gray_2937 | Anatomy_Gray | A cross-section of the spinal cord reveals an inner H-shaped gray matter consisting of neuronal cell bodies and an outer white matter composed of myelinated neuronal axons. The ventral or anterior horns of gray matter contain cell bodies of motor neurons, whereas the dorsal or posterior horns contain cell bodies receiving sensory information (eFig. 9.47). An enlargement of the lateral portion of the gray matter, termed the intermediolateral cell column, can be seen in the T1 to L2 region of the spinal cord (eFig. 9.49). This region enlarges to accommodate the preganglionic cell bodies of the sympathetic nervous system. To further define the diverse cytoarchitecture of the gray matter, it is divided into 10 zones known as Rexed’s laminae (eFig. 9.50). These will be referred to as they relate to later discussions of the ascending and descending tracts within the spinal cord. | Anatomy_Gray. A cross-section of the spinal cord reveals an inner H-shaped gray matter consisting of neuronal cell bodies and an outer white matter composed of myelinated neuronal axons. The ventral or anterior horns of gray matter contain cell bodies of motor neurons, whereas the dorsal or posterior horns contain cell bodies receiving sensory information (eFig. 9.47). An enlargement of the lateral portion of the gray matter, termed the intermediolateral cell column, can be seen in the T1 to L2 region of the spinal cord (eFig. 9.49). This region enlarges to accommodate the preganglionic cell bodies of the sympathetic nervous system. To further define the diverse cytoarchitecture of the gray matter, it is divided into 10 zones known as Rexed’s laminae (eFig. 9.50). These will be referred to as they relate to later discussions of the ascending and descending tracts within the spinal cord. |
Anatomy_Gray_2938 | Anatomy_Gray | The anterior funiculus of the white matter consists of motor axons, whereas the posterior funiculus consists of axons conveying sensory information (eFig. 9.47). The lateral funiculus has a mixture of axons conveying both sensory and motor information. | Anatomy_Gray. The anterior funiculus of the white matter consists of motor axons, whereas the posterior funiculus consists of axons conveying sensory information (eFig. 9.47). The lateral funiculus has a mixture of axons conveying both sensory and motor information. |
Anatomy_Gray_2939 | Anatomy_Gray | Sensory information entering the CNS from peripheral sensory receptors is conducted through a series of neurons that synapse with targets in the spinal cord, cerebral cortex, and other brain structures. The sensory modalities carried in these pathways include pain, temperature, tactile, and proprioceptive input. Conscious perception of sensory input is transmitted through neuronal pathways, which reach the primary somatosensory region of the cerebral cortex. In addition to conscious sensory input, there is subconscious sensory input, which is transmitted to other structures such as the cerebellum. For simplicity, in this section we will review the sensory pathways that reach conscious perception and discuss the pathways conveying subconscious sensory input in the section on cerebellum. | Anatomy_Gray. Sensory information entering the CNS from peripheral sensory receptors is conducted through a series of neurons that synapse with targets in the spinal cord, cerebral cortex, and other brain structures. The sensory modalities carried in these pathways include pain, temperature, tactile, and proprioceptive input. Conscious perception of sensory input is transmitted through neuronal pathways, which reach the primary somatosensory region of the cerebral cortex. In addition to conscious sensory input, there is subconscious sensory input, which is transmitted to other structures such as the cerebellum. For simplicity, in this section we will review the sensory pathways that reach conscious perception and discuss the pathways conveying subconscious sensory input in the section on cerebellum. |
Anatomy_Gray_2940 | Anatomy_Gray | Two somatosensory pathways ascend within the spinal cord to reach the cortex: (1) the anterolateral pathways, which convey sensations of pain, temperature, and crude touch; and (2) the posterior column–medial lemniscal pathway, which conveys sensations of discriminative or fine touch, vibration, and conscious proprioception (eFig. 9.51). Both of these pathways transmit information through a series of three neurons. We will review the anterolateral pathway first. | Anatomy_Gray. Two somatosensory pathways ascend within the spinal cord to reach the cortex: (1) the anterolateral pathways, which convey sensations of pain, temperature, and crude touch; and (2) the posterior column–medial lemniscal pathway, which conveys sensations of discriminative or fine touch, vibration, and conscious proprioception (eFig. 9.51). Both of these pathways transmit information through a series of three neurons. We will review the anterolateral pathway first. |
Anatomy_Gray_2941 | Anatomy_Gray | The anterolateral pathways are composed of three tracts: the spinothalamic, spinoreticular, and spinomesencephalic tract. Separate aspects of pain are conveyed through the spinothalamic tract, so we will follow the course of those neurons first. The first-order neuronal cell body of axons forming the spinothalamic tract is located in a spinal ganglion (eFig. 9.52). Axons then enter the spinal cord through the posterior root to reach the posterior horn. From here, axons have two courses: some synapse immediately on second-order neurons in the posterior horn gray matter (lamina I and V), and others have axonal collaterals that ascend or descend one to two spinal cord segments in the posterolateral tract of Lissauer before synapsing with the second-order neurons in the gray matter (eFig. 9.51). Axons of the second-order neurons then cross obliquely over two to three spinal cord segments within the anterior commissure of the spinal cord to join the anterolateral tract on the contralateral | Anatomy_Gray. The anterolateral pathways are composed of three tracts: the spinothalamic, spinoreticular, and spinomesencephalic tract. Separate aspects of pain are conveyed through the spinothalamic tract, so we will follow the course of those neurons first. The first-order neuronal cell body of axons forming the spinothalamic tract is located in a spinal ganglion (eFig. 9.52). Axons then enter the spinal cord through the posterior root to reach the posterior horn. From here, axons have two courses: some synapse immediately on second-order neurons in the posterior horn gray matter (lamina I and V), and others have axonal collaterals that ascend or descend one to two spinal cord segments in the posterolateral tract of Lissauer before synapsing with the second-order neurons in the gray matter (eFig. 9.51). Axons of the second-order neurons then cross obliquely over two to three spinal cord segments within the anterior commissure of the spinal cord to join the anterolateral tract on the contralateral |
Anatomy_Gray_2942 | Anatomy_Gray | Axons of the second-order neurons then cross obliquely over two to three spinal cord segments within the anterior commissure of the spinal cord to join the anterolateral tract on the contralateral side (eFig. 9.52). These second-order axons ascend through the CNS to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.52). Axons from the third-order neurons then project through the posterior limb of the internal capsule to reach the primary somatosensory cortex (eFig. 9.52). | Anatomy_Gray. Axons of the second-order neurons then cross obliquely over two to three spinal cord segments within the anterior commissure of the spinal cord to join the anterolateral tract on the contralateral side (eFig. 9.52). These second-order axons ascend through the CNS to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.52). Axons from the third-order neurons then project through the posterior limb of the internal capsule to reach the primary somatosensory cortex (eFig. 9.52). |
Anatomy_Gray_2943 | Anatomy_Gray | The spinoreticular and spinomesencephalic tracts have a similar beginning as the spinothalamic tract. The principal difference is the target structure of the second-order axons. Rather than project to the thalamus as the spinothalamic tract does, the spinoreticular tract projects to the reticular formation in the brainstem to convey the emotional and arousal aspects of pain (eFig. 9.52), and the spinomesencephalic tract projects to the periaqueductal gray matter and superior colliculi in the midbrain for the central modulation of pain (eFig. 9.52). | Anatomy_Gray. The spinoreticular and spinomesencephalic tracts have a similar beginning as the spinothalamic tract. The principal difference is the target structure of the second-order axons. Rather than project to the thalamus as the spinothalamic tract does, the spinoreticular tract projects to the reticular formation in the brainstem to convey the emotional and arousal aspects of pain (eFig. 9.52), and the spinomesencephalic tract projects to the periaqueductal gray matter and superior colliculi in the midbrain for the central modulation of pain (eFig. 9.52). |
Anatomy_Gray_2944 | Anatomy_Gray | First-order neuronal cells bodies of the posterior column–medial lemniscal pathway are located in a spinal ganglion (eFig. 9.53). Axons then enter the spinal cord through the posterior root to reach either the gracile fasciculus (gracile means “thin”), which carries information from the lower limb and trunk, or the cuneate fasciculus (cuneate means “wedge-shaped”), which carries information from the upper limb and neck. These first-order axons then ascend ipsilaterally to the caudal medulla and synapse with the second-order neuronal cell bodies within the nucleus gracilis and nucleus cuneatus (eFig. 9.53). Axons of these second-order neurons then cross over as the internal arcuate fibers to form the medial lemniscus in the contralateral medulla (eFig. 9.53). These second-order axons ascend through the brainstem to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.53). Axons from the third-order neurons then project through the | Anatomy_Gray. First-order neuronal cells bodies of the posterior column–medial lemniscal pathway are located in a spinal ganglion (eFig. 9.53). Axons then enter the spinal cord through the posterior root to reach either the gracile fasciculus (gracile means “thin”), which carries information from the lower limb and trunk, or the cuneate fasciculus (cuneate means “wedge-shaped”), which carries information from the upper limb and neck. These first-order axons then ascend ipsilaterally to the caudal medulla and synapse with the second-order neuronal cell bodies within the nucleus gracilis and nucleus cuneatus (eFig. 9.53). Axons of these second-order neurons then cross over as the internal arcuate fibers to form the medial lemniscus in the contralateral medulla (eFig. 9.53). These second-order axons ascend through the brainstem to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.53). Axons from the third-order neurons then project through the |
Anatomy_Gray_2945 | Anatomy_Gray | through the brainstem to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.53). Axons from the third-order neurons then project through the posterior limb of the internal capsule to reach the primary somatosensory cortex (eFig. 9.53). | Anatomy_Gray. through the brainstem to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.53). Axons from the third-order neurons then project through the posterior limb of the internal capsule to reach the primary somatosensory cortex (eFig. 9.53). |
Anatomy_Gray_2946 | Anatomy_Gray | Descending tracts through the spinal cord are involved in voluntary movements; postural movements; and coordination of head, neck, and eye movements. These pathways originate from the cerebral cortex and brainstem and are influenced by sensory input and feedback circuitry from the cerebellum and basal ganglia. Structures that influence regulation of motor planning and voluntary control will be discussed in subsequent sections. In this section we will review the tracts of the medial and lateral motor systems. The tracts in each of these systems are composed of an upper motor neuron with cell bodies located in the cerebral cortex or brainstem and a lower motor neuron with cell bodies located in the spinal cord gray matter. We will begin by exploring the tracts of the lateral motor system first. | Anatomy_Gray. Descending tracts through the spinal cord are involved in voluntary movements; postural movements; and coordination of head, neck, and eye movements. These pathways originate from the cerebral cortex and brainstem and are influenced by sensory input and feedback circuitry from the cerebellum and basal ganglia. Structures that influence regulation of motor planning and voluntary control will be discussed in subsequent sections. In this section we will review the tracts of the medial and lateral motor systems. The tracts in each of these systems are composed of an upper motor neuron with cell bodies located in the cerebral cortex or brainstem and a lower motor neuron with cell bodies located in the spinal cord gray matter. We will begin by exploring the tracts of the lateral motor system first. |
Anatomy_Gray_2947 | Anatomy_Gray | Tracts of the lateral motor system include the lateral corticospinal tract and rubrospinal tract. Both are located in the lateral column of the spinal cord white matter and synapse on lower motor neuronal cell bodies in the lateral aspect of the anterior horn gray matter. | Anatomy_Gray. Tracts of the lateral motor system include the lateral corticospinal tract and rubrospinal tract. Both are located in the lateral column of the spinal cord white matter and synapse on lower motor neuronal cell bodies in the lateral aspect of the anterior horn gray matter. |
Anatomy_Gray_2948 | Anatomy_Gray | Clinically, the most important tract is the lateral corticospinal tract, because it is responsible for controlling movement of the upper and lower extremities. Cell bodies of upper motor neurons forming this tract are located in the primary motor cortex (eFig. 9.54). Axons of these upper motor neurons converge in the corona radiata and descend through the posterior limb of the internal capsule to reach the crus cerebri of the midbrain. These axons continue through the anterior aspect of the pons as small bundles to accommodate the transverse pontocerebellar fibers, which are also present in this location. Once the fibers reach the medulla, they are again grouped together and form a large swelling known as the pyramid (eFig. 9.54). At the caudal medulla, before transitioning into the spinal cord, most of the axons decussate over to the contralateral side to form the lateral corticospinal tract (eFig. 9.54). The remaining axons will stay ipsilateral and form the anterior corticospinal | Anatomy_Gray. Clinically, the most important tract is the lateral corticospinal tract, because it is responsible for controlling movement of the upper and lower extremities. Cell bodies of upper motor neurons forming this tract are located in the primary motor cortex (eFig. 9.54). Axons of these upper motor neurons converge in the corona radiata and descend through the posterior limb of the internal capsule to reach the crus cerebri of the midbrain. These axons continue through the anterior aspect of the pons as small bundles to accommodate the transverse pontocerebellar fibers, which are also present in this location. Once the fibers reach the medulla, they are again grouped together and form a large swelling known as the pyramid (eFig. 9.54). At the caudal medulla, before transitioning into the spinal cord, most of the axons decussate over to the contralateral side to form the lateral corticospinal tract (eFig. 9.54). The remaining axons will stay ipsilateral and form the anterior corticospinal |
Anatomy_Gray_2949 | Anatomy_Gray | cord, most of the axons decussate over to the contralateral side to form the lateral corticospinal tract (eFig. 9.54). The remaining axons will stay ipsilateral and form the anterior corticospinal tract, a tract included in the medial motor systems. | Anatomy_Gray. cord, most of the axons decussate over to the contralateral side to form the lateral corticospinal tract (eFig. 9.54). The remaining axons will stay ipsilateral and form the anterior corticospinal tract, a tract included in the medial motor systems. |
Anatomy_Gray_2950 | Anatomy_Gray | After decussating and forming the lateral corticospinal tract, the axons descend through the spinal cord to synapse on the cell bodies of lower motor neurons in the lateral portion of the anterior horn gray matter. Axons of these lower motor neurons then exit the spinal cord through the anterior root (eFig. 9.54). The other lateral motor system pathway is the rubrospinal tract (eFig. 9.55). Cell bodies of upper motor neurons in this pathway begin in the red nucleus of the midbrain. After leaving the red nucleus, the axons cross the midline as the ventral tegmental decussation and descend as the rubrospinal tract through the brainstem and lateral column of the spinal cord white matter (eFig. 9.55). These axons only descend to cervical regions of the spinal cord, and axons synapse with interneurons in the anterior horn gray matter to facilitate flexor muscle activity and inhibit extensor muscle activity of the upper limb. | Anatomy_Gray. After decussating and forming the lateral corticospinal tract, the axons descend through the spinal cord to synapse on the cell bodies of lower motor neurons in the lateral portion of the anterior horn gray matter. Axons of these lower motor neurons then exit the spinal cord through the anterior root (eFig. 9.54). The other lateral motor system pathway is the rubrospinal tract (eFig. 9.55). Cell bodies of upper motor neurons in this pathway begin in the red nucleus of the midbrain. After leaving the red nucleus, the axons cross the midline as the ventral tegmental decussation and descend as the rubrospinal tract through the brainstem and lateral column of the spinal cord white matter (eFig. 9.55). These axons only descend to cervical regions of the spinal cord, and axons synapse with interneurons in the anterior horn gray matter to facilitate flexor muscle activity and inhibit extensor muscle activity of the upper limb. |
Anatomy_Gray_2951 | Anatomy_Gray | Tracts of the medial motor system regulate axial or truncal muscles involved in maintaining posture, balance, automatic gait-related movements, and orientating movements of the head and neck. Unlike the lateral motor system, the tracts in this system primarily project bilaterally on interneurons within the spinal cord. This makes it difficult to test each tract individually in the clinical system. We will briefly review the four tracts of the medial motor system beginning with the anterior corticospinal tract. | Anatomy_Gray. Tracts of the medial motor system regulate axial or truncal muscles involved in maintaining posture, balance, automatic gait-related movements, and orientating movements of the head and neck. Unlike the lateral motor system, the tracts in this system primarily project bilaterally on interneurons within the spinal cord. This makes it difficult to test each tract individually in the clinical system. We will briefly review the four tracts of the medial motor system beginning with the anterior corticospinal tract. |
Anatomy_Gray_2952 | Anatomy_Gray | The anterior corticospinal tract is formed by the remaining descending upper motor neurons that did not decussate in the caudal medulla to form the lateral corticospinal tract. These upper motor neurons, which remain ipsilateral to form the anterior corticospinal tract, descend through the medial aspect of the anterior spinal cord to the level of the upper thoracic region (eFig. 9.54). These axons project bilaterally to synapse on cell bodies of lower motor neurons in the medial portion of the anterior horn gray matter. Axons of these lower motor neurons then exit the spinal cord through the anterior root. | Anatomy_Gray. The anterior corticospinal tract is formed by the remaining descending upper motor neurons that did not decussate in the caudal medulla to form the lateral corticospinal tract. These upper motor neurons, which remain ipsilateral to form the anterior corticospinal tract, descend through the medial aspect of the anterior spinal cord to the level of the upper thoracic region (eFig. 9.54). These axons project bilaterally to synapse on cell bodies of lower motor neurons in the medial portion of the anterior horn gray matter. Axons of these lower motor neurons then exit the spinal cord through the anterior root. |
Anatomy_Gray_2953 | Anatomy_Gray | Tectospinal tract axons arise from cell bodies located in the superior colliculus of the dorsal midbrain (eFig. 9.56). These axons decussate in the dorsal tegmental decussation shortly after leaving the nucleus to form the tectospinal tract along the midline of the brainstem. The tectospinal tract continues through the brainstem near the medial longitudinal fasciculus and into cervical regions of the spinal cord near the anterior median fissure. Within the cervical spinal cord, axons project bilaterally to synapse on cell bodies of interneurons in the anterior horn gray matter. As the superior colliculus receives visual input, it is believed that the tectospinal tract modulates reflex postural movements in response to visual stimuli. | Anatomy_Gray. Tectospinal tract axons arise from cell bodies located in the superior colliculus of the dorsal midbrain (eFig. 9.56). These axons decussate in the dorsal tegmental decussation shortly after leaving the nucleus to form the tectospinal tract along the midline of the brainstem. The tectospinal tract continues through the brainstem near the medial longitudinal fasciculus and into cervical regions of the spinal cord near the anterior median fissure. Within the cervical spinal cord, axons project bilaterally to synapse on cell bodies of interneurons in the anterior horn gray matter. As the superior colliculus receives visual input, it is believed that the tectospinal tract modulates reflex postural movements in response to visual stimuli. |
Anatomy_Gray_2954 | Anatomy_Gray | Vestibulospinal tract axons arise from vestibular nuclei located in the pons and medulla. The medial vestibular nucleus gives rise to the medial vestibulospinal tract, which projects bilaterally to thoracic regions of the spinal cord, and the lateral vestibular nucleus gives rise to the lateral vestibulospinal tract, which descends ipsilaterally through the entire length of the spinal cord to synapse on interneurons in the anterior horn gray matter (eFig. 9.57). Given that the vestibular nuclei receive sensory input from the inner ear and cerebellum, this tract facilitates activity of extensor/antigravity muscles and inhibits activity of flexor muscles to maintain balance and an upright posture. As an example, the change in head position induced during tripping initiates extension of the upper limb and/or lower limb to prevent oneself from falling forward. | Anatomy_Gray. Vestibulospinal tract axons arise from vestibular nuclei located in the pons and medulla. The medial vestibular nucleus gives rise to the medial vestibulospinal tract, which projects bilaterally to thoracic regions of the spinal cord, and the lateral vestibular nucleus gives rise to the lateral vestibulospinal tract, which descends ipsilaterally through the entire length of the spinal cord to synapse on interneurons in the anterior horn gray matter (eFig. 9.57). Given that the vestibular nuclei receive sensory input from the inner ear and cerebellum, this tract facilitates activity of extensor/antigravity muscles and inhibits activity of flexor muscles to maintain balance and an upright posture. As an example, the change in head position induced during tripping initiates extension of the upper limb and/or lower limb to prevent oneself from falling forward. |
Anatomy_Gray_2955 | Anatomy_Gray | Reticulospinal tract axons arise from the reticular formation in the pons and medulla. The axons of the pontine and medullary reticulospinal tracts descend ipsilaterally through the length of the spinal cord in the anterior white matter and synapse with interneurons in the anterior horn gray matter. They are believed to function in regulating voluntary movements in reflex activity and autonomic outflow (eTables 9.5 and 9.6). | Anatomy_Gray. Reticulospinal tract axons arise from the reticular formation in the pons and medulla. The axons of the pontine and medullary reticulospinal tracts descend ipsilaterally through the length of the spinal cord in the anterior white matter and synapse with interneurons in the anterior horn gray matter. They are believed to function in regulating voluntary movements in reflex activity and autonomic outflow (eTables 9.5 and 9.6). |
Anatomy_Gray_2956 | Anatomy_Gray | Vascular perfusions to the spinal cord are supplied by three longitudinally running vessels and several segmental branches. The longitudinally running vessels are the anterior spinal artery and two posterior spinal arteries. The posterior spinal arteries originate in the cranial cavity as branches of either the vertebral artery or PICA. These arteries descend along the length of the posterior spinal cord on the posterolateral sulcus. The single anterior spinal artery originates within the cranial cavity from the union of two contributing branches from the vertebral arteries. The anterior spinal artery descends along the length of the anterior spinal cord on the anterior median fissure. | Anatomy_Gray. Vascular perfusions to the spinal cord are supplied by three longitudinally running vessels and several segmental branches. The longitudinally running vessels are the anterior spinal artery and two posterior spinal arteries. The posterior spinal arteries originate in the cranial cavity as branches of either the vertebral artery or PICA. These arteries descend along the length of the posterior spinal cord on the posterolateral sulcus. The single anterior spinal artery originates within the cranial cavity from the union of two contributing branches from the vertebral arteries. The anterior spinal artery descends along the length of the anterior spinal cord on the anterior median fissure. |
Anatomy_Gray_2957 | Anatomy_Gray | Reinforcing vascular supply to these longitudinally running vessels is provided by eight to ten segmental medullary arteries. The largest segmental medullary artery is the artery of Adamkiewicz in the lower thoracic or upper lumbar region. This vessel is typically on the left side and contributes significantly to perfusion of the lower portion of the spinal cord. Venous drainage of the spinal cord occurs through a series of longitudinally running channels that connect with the anterior and posterior spinal veins on the surface of the cord. Part VI: Basal nuclei | Anatomy_Gray. Reinforcing vascular supply to these longitudinally running vessels is provided by eight to ten segmental medullary arteries. The largest segmental medullary artery is the artery of Adamkiewicz in the lower thoracic or upper lumbar region. This vessel is typically on the left side and contributes significantly to perfusion of the lower portion of the spinal cord. Venous drainage of the spinal cord occurs through a series of longitudinally running channels that connect with the anterior and posterior spinal veins on the surface of the cord. Part VI: Basal nuclei |
Anatomy_Gray_2958 | Anatomy_Gray | Part VI: Basal nuclei The basal nuclei are a collection of gray-matter structures named for their location deep within the base of the forebrain. Functionally, the basal nuclei have a significant role in controlling posture and voluntary movement through connections to the thalamus, cortex, and neighboring basal nuclei structures. In addition to their role in posture and movement, the basal nuclei have connections to limbic system pathways, which govern the expression of various behaviors and motivational states. For the purposes of this section, we will focus on reviewing the structures of the basal nuclei and pathways involved in controlling posture and voluntary movement. | Anatomy_Gray. Part VI: Basal nuclei The basal nuclei are a collection of gray-matter structures named for their location deep within the base of the forebrain. Functionally, the basal nuclei have a significant role in controlling posture and voluntary movement through connections to the thalamus, cortex, and neighboring basal nuclei structures. In addition to their role in posture and movement, the basal nuclei have connections to limbic system pathways, which govern the expression of various behaviors and motivational states. For the purposes of this section, we will focus on reviewing the structures of the basal nuclei and pathways involved in controlling posture and voluntary movement. |
Anatomy_Gray_2959 | Anatomy_Gray | A variety of terminology is used to refer to the structures of the basal nuclei individually and based on their collective morphology. To appreciate the three-dimensional shape of the basal nuclei and their relationship to surrounding structures, it is best to view them in horizontal and coronal brain sections taken at different levels of the brain. The corpus striatum (Latin for “striped body”) includes the caudate nucleus and lentiform nucleus. This collection of structures received their name because of the striated appearance of bands that interconnect the caudate nucleus and putamen of the lentiform nucleus through the anterior limb of the internal capsule (eFig. 9.58). | Anatomy_Gray. A variety of terminology is used to refer to the structures of the basal nuclei individually and based on their collective morphology. To appreciate the three-dimensional shape of the basal nuclei and their relationship to surrounding structures, it is best to view them in horizontal and coronal brain sections taken at different levels of the brain. The corpus striatum (Latin for “striped body”) includes the caudate nucleus and lentiform nucleus. This collection of structures received their name because of the striated appearance of bands that interconnect the caudate nucleus and putamen of the lentiform nucleus through the anterior limb of the internal capsule (eFig. 9.58). |
Anatomy_Gray_2960 | Anatomy_Gray | The lentiform nucleus (Latin for “lens-shaped”) includes the globus pallidus and putamen, which appear lens-shaped when viewed laterally. Both of these structures are lateral to the internal capsule, which separates them from the thalamus and caudate nucleus medially (eFig. 9.58). Laterally, the putamen is bordered by the external capsule, a thin layer of white matter adjacent to a thin gray-matter layer called the claustrum. Beyond the claustrum is the external capsule, which borders the white matter of the insula (eFig. 9.58). | Anatomy_Gray. The lentiform nucleus (Latin for “lens-shaped”) includes the globus pallidus and putamen, which appear lens-shaped when viewed laterally. Both of these structures are lateral to the internal capsule, which separates them from the thalamus and caudate nucleus medially (eFig. 9.58). Laterally, the putamen is bordered by the external capsule, a thin layer of white matter adjacent to a thin gray-matter layer called the claustrum. Beyond the claustrum is the external capsule, which borders the white matter of the insula (eFig. 9.58). |
Anatomy_Gray_2961 | Anatomy_Gray | Medial to the internal capsule is the caudate nucleus. The caudate nucleus is a large C-shaped structure divided into a head, body, and tail, which closely follows the shape of the lateral ventricle (eFig. 9.58). Rostrally, the head of the caudate has a large rounded shape that contributes to the lateral wall of the anterior horn of the lateral ventricle (eFig. 9.58). Also at this level, the head of the caudate is continuous with the putamen (eFig. 9.59). Because of this close relationship the putamen and caudate are referred to collectively as the striatum. At the level of the interventricular foramen, the head of the caudate transitions to the body. The body of the caudate is long and narrows substantially as it transitions from the head to the tail (eFig. 9.59). Along its course the body contributes to the floor of the lateral ventricle. Near the posterior border of the thalamus the body of the caudate transitions into the tail. The tail continues anteriorly within the roof of the | Anatomy_Gray. Medial to the internal capsule is the caudate nucleus. The caudate nucleus is a large C-shaped structure divided into a head, body, and tail, which closely follows the shape of the lateral ventricle (eFig. 9.58). Rostrally, the head of the caudate has a large rounded shape that contributes to the lateral wall of the anterior horn of the lateral ventricle (eFig. 9.58). Also at this level, the head of the caudate is continuous with the putamen (eFig. 9.59). Because of this close relationship the putamen and caudate are referred to collectively as the striatum. At the level of the interventricular foramen, the head of the caudate transitions to the body. The body of the caudate is long and narrows substantially as it transitions from the head to the tail (eFig. 9.59). Along its course the body contributes to the floor of the lateral ventricle. Near the posterior border of the thalamus the body of the caudate transitions into the tail. The tail continues anteriorly within the roof of the |
Anatomy_Gray_2962 | Anatomy_Gray | contributes to the floor of the lateral ventricle. Near the posterior border of the thalamus the body of the caudate transitions into the tail. The tail continues anteriorly within the roof of the inferior horn of the lateral ventricle to terminate in the amygdaloid nucleus (eFig. 9.59). | Anatomy_Gray. contributes to the floor of the lateral ventricle. Near the posterior border of the thalamus the body of the caudate transitions into the tail. The tail continues anteriorly within the roof of the inferior horn of the lateral ventricle to terminate in the amygdaloid nucleus (eFig. 9.59). |
Anatomy_Gray_2963 | Anatomy_Gray | Input to the basal nuclei is primarily received by the striatum (caudate nucleus and putamen), and output predominantly leaves from the globus pallidus. Many structures send input to the striatum, including all areas of the cerebral cortex, thalamic nuclei, subthalamic nucleus, brainstem, and substantia nigra. To understand how the basal nuclei integrates all of this incoming information to influence motor activity, two simplified neuronal loops are described: the direct pathway and the indirect pathway. | Anatomy_Gray. Input to the basal nuclei is primarily received by the striatum (caudate nucleus and putamen), and output predominantly leaves from the globus pallidus. Many structures send input to the striatum, including all areas of the cerebral cortex, thalamic nuclei, subthalamic nucleus, brainstem, and substantia nigra. To understand how the basal nuclei integrates all of this incoming information to influence motor activity, two simplified neuronal loops are described: the direct pathway and the indirect pathway. |
Anatomy_Gray_2964 | Anatomy_Gray | The direct pathway has a series of connections through the basal nuclei, which result in an overall increase in motor activity. This pathway begins with input to the striatum, which sends axonal connections to the globus pallidus (eFig. 9.60A). The globus pallidus then has output connections to the thalamus, which completes the circuit with axonal connections back to the cortex. The indirect pathway has a similar course, with the addition of output connections to the subthalamic nucleus, which results in an overall decrease in motor activity (eFig. 9.60B). Part VII: Cerebellum | Anatomy_Gray. The direct pathway has a series of connections through the basal nuclei, which result in an overall increase in motor activity. This pathway begins with input to the striatum, which sends axonal connections to the globus pallidus (eFig. 9.60A). The globus pallidus then has output connections to the thalamus, which completes the circuit with axonal connections back to the cortex. The indirect pathway has a similar course, with the addition of output connections to the subthalamic nucleus, which results in an overall decrease in motor activity (eFig. 9.60B). Part VII: Cerebellum |
Anatomy_Gray_2965 | Anatomy_Gray | Part VII: Cerebellum The cerebellum is the largest structure of the hindbrain. It resides within the posterior cranial fossa and is composed of two large hemispheres, which are connected by the vermis in the midline (eFig. 9.61). Functionally, the cerebellum plays a role in maintaining balance and influencing posture and is responsible for coordinating movements by synchronizing contraction and relaxation of voluntary muscles. We will first examine the structural organization of the cerebellum and then review how these structures contribute to the circuitry of the cerebellum. | Anatomy_Gray. Part VII: Cerebellum The cerebellum is the largest structure of the hindbrain. It resides within the posterior cranial fossa and is composed of two large hemispheres, which are connected by the vermis in the midline (eFig. 9.61). Functionally, the cerebellum plays a role in maintaining balance and influencing posture and is responsible for coordinating movements by synchronizing contraction and relaxation of voluntary muscles. We will first examine the structural organization of the cerebellum and then review how these structures contribute to the circuitry of the cerebellum. |
Anatomy_Gray_2966 | Anatomy_Gray | Within the posterior cranial fossa, the cerebellum is covered by the tentorium cerebelli of the dura mater (eFig. 9.17) and connects to the posterior surface of the brainstem via the superior, middle, and inferior cerebellar peduncles (eFig. 9.62). Anteriorly, the cerebellum forms the roof of the fourth ventricle (eFig. 9.14). On its surface, the cerebellum has several convoluted folds, or folia, separated by fissures. Two of these fissures serve as landmarks to divide the cerebellum into three lobes. Superiorly, the primary fissure separates the anterior lobe from the posterior lobe (eFig. 9.61). Anteriorly and inferiorly, the posterolateral fissure defines the structures of the flocculonodular lobe, which includes the flocculus from each hemisphere and nodule of the vermis (eFig. 9.63). A third fissure, the horizontal fissure, borders the superior and inferior surfaces of the cerebellum (eFig. 9.64). | Anatomy_Gray. Within the posterior cranial fossa, the cerebellum is covered by the tentorium cerebelli of the dura mater (eFig. 9.17) and connects to the posterior surface of the brainstem via the superior, middle, and inferior cerebellar peduncles (eFig. 9.62). Anteriorly, the cerebellum forms the roof of the fourth ventricle (eFig. 9.14). On its surface, the cerebellum has several convoluted folds, or folia, separated by fissures. Two of these fissures serve as landmarks to divide the cerebellum into three lobes. Superiorly, the primary fissure separates the anterior lobe from the posterior lobe (eFig. 9.61). Anteriorly and inferiorly, the posterolateral fissure defines the structures of the flocculonodular lobe, which includes the flocculus from each hemisphere and nodule of the vermis (eFig. 9.63). A third fissure, the horizontal fissure, borders the superior and inferior surfaces of the cerebellum (eFig. 9.64). |
Anatomy_Gray_2967 | Anatomy_Gray | Each fold or folia of the cerebellar cortex has a central core of white matter covered by a thin layer of gray matter superficially. In sections parallel to the median plane, the branching pattern of the folia can be appreciated; this is often referred to as the arbor vitae (eFig. 9.28). Deep within the white matter of each hemisphere are four masses of cerebellar nuclei. From lateral to medial they are the dentate, emboliform, globose, and fastigial (eFig. 9.65). Note that the emboliform and globose are collectively referred to as the interposed nuclei. Output from the cerebellum originates from one of these four nuclear complexes before leaving through the superior cerebellar peduncle, predominantly. In general, the output from each cerebellar hemisphere coordinates movement on the ipsilateral side of the body. | Anatomy_Gray. Each fold or folia of the cerebellar cortex has a central core of white matter covered by a thin layer of gray matter superficially. In sections parallel to the median plane, the branching pattern of the folia can be appreciated; this is often referred to as the arbor vitae (eFig. 9.28). Deep within the white matter of each hemisphere are four masses of cerebellar nuclei. From lateral to medial they are the dentate, emboliform, globose, and fastigial (eFig. 9.65). Note that the emboliform and globose are collectively referred to as the interposed nuclei. Output from the cerebellum originates from one of these four nuclear complexes before leaving through the superior cerebellar peduncle, predominantly. In general, the output from each cerebellar hemisphere coordinates movement on the ipsilateral side of the body. |
Anatomy_Gray_2968 | Anatomy_Gray | Functionally, the cerebellar cortex can be divided into three areas. The vermis in the midline influences movements along the axis of the body, including the neck, trunk, abdomen, and pelvis (eFig. 9.66). Adjacent to the vermis, the intermediate zone controls muscles of the distal upper and lower limbs. The lateral zone participates in motor planning to coordinate sequential movements of the entire body. Input to these functional areas of cerebellar cortex come from the cerebral cortex, spinal cord, and brainstem by passing predominantly through the middle and inferior cerebellar peduncles. Fibers entering the cerebellum proceed as mossy fibers (from various regions) or climbing fibers (from olivary nucleus). Mossy fibers form excitatory synapses with dendrites of the granule cells, in the granule cell layer (eFig. 9.67). From here, the granule cells send axons to the molecular layer, where they bifurcate into parallel fibers that run longitudinally in the folia. The parallel fibers | Anatomy_Gray. Functionally, the cerebellar cortex can be divided into three areas. The vermis in the midline influences movements along the axis of the body, including the neck, trunk, abdomen, and pelvis (eFig. 9.66). Adjacent to the vermis, the intermediate zone controls muscles of the distal upper and lower limbs. The lateral zone participates in motor planning to coordinate sequential movements of the entire body. Input to these functional areas of cerebellar cortex come from the cerebral cortex, spinal cord, and brainstem by passing predominantly through the middle and inferior cerebellar peduncles. Fibers entering the cerebellum proceed as mossy fibers (from various regions) or climbing fibers (from olivary nucleus). Mossy fibers form excitatory synapses with dendrites of the granule cells, in the granule cell layer (eFig. 9.67). From here, the granule cells send axons to the molecular layer, where they bifurcate into parallel fibers that run longitudinally in the folia. The parallel fibers |
Anatomy_Gray_2969 | Anatomy_Gray | granule cell layer (eFig. 9.67). From here, the granule cells send axons to the molecular layer, where they bifurcate into parallel fibers that run longitudinally in the folia. The parallel fibers then synapse on Purkinje cells in the outermost Purkinje cell layer (eFig. 9.67). Climbing fibers project to the Purkinje cell layer and form powerful excitatory connections with the Purkinje cells. The Purkinje cells then project to the deep cerebellar nuclei (eFig. 9.67). | Anatomy_Gray. granule cell layer (eFig. 9.67). From here, the granule cells send axons to the molecular layer, where they bifurcate into parallel fibers that run longitudinally in the folia. The parallel fibers then synapse on Purkinje cells in the outermost Purkinje cell layer (eFig. 9.67). Climbing fibers project to the Purkinje cell layer and form powerful excitatory connections with the Purkinje cells. The Purkinje cells then project to the deep cerebellar nuclei (eFig. 9.67). |
Anatomy_Gray_2970 | Anatomy_Gray | As mentioned earlier, the cerebellum receives input from the cerebral cortex, brainstem, and spinal cord. Input from the cerebral cortex to the cerebellum is primarily involved in voluntary muscle control and coordination of movement. Axonal projections from the cerebral cortex destined for the cerebellum descend through the internal capsule and terminate on pontine nuclei (eFig. 9.68). The axons from the pontine nuclei then cross over as transverse fibers to enter the contralateral cerebellum through the middle cerebellar peduncle. | Anatomy_Gray. As mentioned earlier, the cerebellum receives input from the cerebral cortex, brainstem, and spinal cord. Input from the cerebral cortex to the cerebellum is primarily involved in voluntary muscle control and coordination of movement. Axonal projections from the cerebral cortex destined for the cerebellum descend through the internal capsule and terminate on pontine nuclei (eFig. 9.68). The axons from the pontine nuclei then cross over as transverse fibers to enter the contralateral cerebellum through the middle cerebellar peduncle. |
Anatomy_Gray_2971 | Anatomy_Gray | Input from the spinal cord to the cerebellum conveys information from muscles and joints to influence muscle tone and posture. The primary spinal cord pathways with connections to the cerebellum include the anterior or ventral spinocerebellar and the posterior or dorsal spinocerebellar tracts. These tracts originate from joint and cutaneous mechanoreceptors and ascend through the spinal cord to enter the ipsilateral cerebellum primarily through the inferior cerebellar peduncle (eFig. 9.69). A final source of cerebellar input arises from the vestibular nuclei and reticular formation in the brainstem. The connections are primarily involved in reflexive maintenance of balance. These nuclei send axonal projections to the ipsilateral cerebellum through the inferior cerebellar peduncle. | Anatomy_Gray. Input from the spinal cord to the cerebellum conveys information from muscles and joints to influence muscle tone and posture. The primary spinal cord pathways with connections to the cerebellum include the anterior or ventral spinocerebellar and the posterior or dorsal spinocerebellar tracts. These tracts originate from joint and cutaneous mechanoreceptors and ascend through the spinal cord to enter the ipsilateral cerebellum primarily through the inferior cerebellar peduncle (eFig. 9.69). A final source of cerebellar input arises from the vestibular nuclei and reticular formation in the brainstem. The connections are primarily involved in reflexive maintenance of balance. These nuclei send axonal projections to the ipsilateral cerebellum through the inferior cerebellar peduncle. |
Anatomy_Gray_2972 | Anatomy_Gray | Output from the cerebellum originates from one of the four deep cerebellar nuclei. The largest collection of fibers leaving the cerebellum originates from the dentate nucleus. Axons from this nuclear complex project to the contralateral ventral nucleus of the thalamus after decussating in the superior cerebellar peduncle. From here, axons of the thalamic nuclei project to the motor cortex (eFig. 9.70). This pathway influences posture and movement. | Anatomy_Gray. Output from the cerebellum originates from one of the four deep cerebellar nuclei. The largest collection of fibers leaving the cerebellum originates from the dentate nucleus. Axons from this nuclear complex project to the contralateral ventral nucleus of the thalamus after decussating in the superior cerebellar peduncle. From here, axons of the thalamic nuclei project to the motor cortex (eFig. 9.70). This pathway influences posture and movement. |
Anatomy_Gray_2973 | Anatomy_Gray | The emboliform and globose nuclei, or interposed nuclei, have a similar course as the axons from the dentate, but with the addition of another synaptic target. Axons from the interposed nuclei decussate in the superior cerebellar peduncle to synapse on the contralateral ventral nucleus of the thalamus and the contralateral red nucleus in the midbrain (eFig. 9.70). Axons leaving the red nucleus descend to the inferior olivary nucleus in the medulla. The axonal projections from the interposed nuclei function in monitoring and correcting motor activity of the upper and lower extremities. | Anatomy_Gray. The emboliform and globose nuclei, or interposed nuclei, have a similar course as the axons from the dentate, but with the addition of another synaptic target. Axons from the interposed nuclei decussate in the superior cerebellar peduncle to synapse on the contralateral ventral nucleus of the thalamus and the contralateral red nucleus in the midbrain (eFig. 9.70). Axons leaving the red nucleus descend to the inferior olivary nucleus in the medulla. The axonal projections from the interposed nuclei function in monitoring and correcting motor activity of the upper and lower extremities. |
Anatomy_Gray_2974 | Anatomy_Gray | Axons from the fastigial nucleus project to the vestibular nuclei, reticular formation, contralateral ventral nucleus of the thalamus, and contralateral tectum. Vestibular axons pass through the inferior cerebellar peduncle to reach the ipsilateral vestibular nucleus and uncinate fasciculus to reach the contralateral vestibular nucleus (eFig. 9.70). Also going through the inferior cerebellar peduncle are axons heading to the reticular formation. Ascending in the superior cerebellar peduncles are axons that will synapse with the contralateral tectum and contralateral ventral nucleus of the thalamus. | Anatomy_Gray. Axons from the fastigial nucleus project to the vestibular nuclei, reticular formation, contralateral ventral nucleus of the thalamus, and contralateral tectum. Vestibular axons pass through the inferior cerebellar peduncle to reach the ipsilateral vestibular nucleus and uncinate fasciculus to reach the contralateral vestibular nucleus (eFig. 9.70). Also going through the inferior cerebellar peduncle are axons heading to the reticular formation. Ascending in the superior cerebellar peduncles are axons that will synapse with the contralateral tectum and contralateral ventral nucleus of the thalamus. |
Anatomy_Gray_2975 | Anatomy_Gray | The cerebellum is perfused by the vertebrobasilar system of arteries (eFig. 9.42). Before merging and forming the basilar artery, each vertebral artery gives rise to a PICA and posterior spinal artery and contributes to the formation of the anterior spinal artery (eFig. 9.71). The PICA perfuses the inferior portion of the cerebellum. At the level of the caudal pons, the AICA branches off the basilar artery and perfuses the anterior and lateral portion of the cerebellum, as well as the middle and inferior cerebellar peduncles (eFig. 9.71). Just before the midbrain, the superior cerebellar arteries branch off of the basilar artery and supply the superior cerebellar peduncles and superior portion of the cerebellar hemispheres (eFig. 9.71). Part VIII: Visual System | Anatomy_Gray. The cerebellum is perfused by the vertebrobasilar system of arteries (eFig. 9.42). Before merging and forming the basilar artery, each vertebral artery gives rise to a PICA and posterior spinal artery and contributes to the formation of the anterior spinal artery (eFig. 9.71). The PICA perfuses the inferior portion of the cerebellum. At the level of the caudal pons, the AICA branches off the basilar artery and perfuses the anterior and lateral portion of the cerebellum, as well as the middle and inferior cerebellar peduncles (eFig. 9.71). Just before the midbrain, the superior cerebellar arteries branch off of the basilar artery and supply the superior cerebellar peduncles and superior portion of the cerebellar hemispheres (eFig. 9.71). Part VIII: Visual System |
Anatomy_Gray_2976 | Anatomy_Gray | Part VIII: Visual System The visual system is a complex special sensory system that begins in the eyeball and has neuronal connections to the thalamus, brainstem, primary visual cortex, and association cortices. In addition to mediating visual perception, these connections are also involved in higher visual functions, such as determining spatial relationships between objects and structural features of objects. In this section we will explore the primary or geniculate visual pathway from the retina to the primary visual cortex. | Anatomy_Gray. Part VIII: Visual System The visual system is a complex special sensory system that begins in the eyeball and has neuronal connections to the thalamus, brainstem, primary visual cortex, and association cortices. In addition to mediating visual perception, these connections are also involved in higher visual functions, such as determining spatial relationships between objects and structural features of objects. In this section we will explore the primary or geniculate visual pathway from the retina to the primary visual cortex. |
Anatomy_Gray_2977 | Anatomy_Gray | Although the retinal layer of the eyeball is often considered the beginning of visual perception, the anterior structures of the eye play an important role in visual perception too. The anteriormost structure is the cornea and is the first layer through which light, the visual stimulus, enters the eye (eFig. 9.72). This transparent layer overlies the aqueous humor of the anterior chamber and the pupil, a small central aperture that controls how much light is admitted into the eye. After passing through the pupil light is refracted through the lens, which along with the ciliary body, separates the anterior portion of the eye from the posterior portion (eFig. 9.72). The lens is a clear biconvex structure that rounds in shape as the ciliary muscle contracts and relaxes the suspensory ligaments attached to the borders of the lens, a parasympathetically controlled process referred to as accommodation. | Anatomy_Gray. Although the retinal layer of the eyeball is often considered the beginning of visual perception, the anterior structures of the eye play an important role in visual perception too. The anteriormost structure is the cornea and is the first layer through which light, the visual stimulus, enters the eye (eFig. 9.72). This transparent layer overlies the aqueous humor of the anterior chamber and the pupil, a small central aperture that controls how much light is admitted into the eye. After passing through the pupil light is refracted through the lens, which along with the ciliary body, separates the anterior portion of the eye from the posterior portion (eFig. 9.72). The lens is a clear biconvex structure that rounds in shape as the ciliary muscle contracts and relaxes the suspensory ligaments attached to the borders of the lens, a parasympathetically controlled process referred to as accommodation. |
Anatomy_Gray_2978 | Anatomy_Gray | After the lens, light passes through the vitreous humor of the posterior chamber and is projected onto the layers of the retina (eFig. 9.73). The retina is composed of a non-neural layer and several layers of neural cells with synaptic connections. To reduce the amount of light reflected in the eye, the choroid layer lining the inner surface of the sclera (eFig. 9.72), along with the pigment epithelium layer (non-neural) of the retina, absorb and refract some of the light stimulus (eFig. 9.73). Interdigitating between the pigment epithelial cells, the photoreceptors transduce the light stimulus into an electrical signal in a process called phototransduction. Images formed on the retina are inverted in both vertical and lateral dimensions (eFig. 9.74). Because of this, the visual field is defined as having four quadrants: left/right and upper/lower. | Anatomy_Gray. After the lens, light passes through the vitreous humor of the posterior chamber and is projected onto the layers of the retina (eFig. 9.73). The retina is composed of a non-neural layer and several layers of neural cells with synaptic connections. To reduce the amount of light reflected in the eye, the choroid layer lining the inner surface of the sclera (eFig. 9.72), along with the pigment epithelium layer (non-neural) of the retina, absorb and refract some of the light stimulus (eFig. 9.73). Interdigitating between the pigment epithelial cells, the photoreceptors transduce the light stimulus into an electrical signal in a process called phototransduction. Images formed on the retina are inverted in both vertical and lateral dimensions (eFig. 9.74). Because of this, the visual field is defined as having four quadrants: left/right and upper/lower. |
Anatomy_Gray_2979 | Anatomy_Gray | Photoreceptors include rods, which are very sensitive to light and essential for vision in dimly lit conditions, and cones, which are responsible for color vision and high visual acuity. Although rods and cones are both distributed across the retina, rods outnumber cones by twentyfold and are concentrated in the periphery of the retina. Cones predominate near the macula and are the only photoreceptors present at the fovea (eFig. 9.72). The fovea represents the primary visual axis of the eye and is the location of maximal visual acuity. Despite their functional differences, both the rods and cones have an outer light-sensing segment, an inner segment, and a synaptic terminal. These synaptic terminals contact bipolar cells, the first-order neurons in the visual pathway (eFig. 9.73). Bipolar cells then synapse with ganglion cells, the second-order neurons in the visual pathway. Two other cell types present in the retina are horizontal and amacrine cells. These transversely oriented | Anatomy_Gray. Photoreceptors include rods, which are very sensitive to light and essential for vision in dimly lit conditions, and cones, which are responsible for color vision and high visual acuity. Although rods and cones are both distributed across the retina, rods outnumber cones by twentyfold and are concentrated in the periphery of the retina. Cones predominate near the macula and are the only photoreceptors present at the fovea (eFig. 9.72). The fovea represents the primary visual axis of the eye and is the location of maximal visual acuity. Despite their functional differences, both the rods and cones have an outer light-sensing segment, an inner segment, and a synaptic terminal. These synaptic terminals contact bipolar cells, the first-order neurons in the visual pathway (eFig. 9.73). Bipolar cells then synapse with ganglion cells, the second-order neurons in the visual pathway. Two other cell types present in the retina are horizontal and amacrine cells. These transversely oriented |
Anatomy_Gray_2980 | Anatomy_Gray | cells then synapse with ganglion cells, the second-order neurons in the visual pathway. Two other cell types present in the retina are horizontal and amacrine cells. These transversely oriented interneurons moderate the excitation level of bipolar and ganglion cells. | Anatomy_Gray. cells then synapse with ganglion cells, the second-order neurons in the visual pathway. Two other cell types present in the retina are horizontal and amacrine cells. These transversely oriented interneurons moderate the excitation level of bipolar and ganglion cells. |
Anatomy_Gray_2981 | Anatomy_Gray | Axons from the ganglion cells coalesce at the optic disc, which is absent of photoreceptors and thus creates a blind spot in the visual field. As they leave the optic disc they form the optic nerve, acquire a myelin sheath provided by oligodendrocytes, and are invested by the cranial meninges (eFig. 9.72). These morphological features derived during embryonic development, define the optic nerve as a component of the CNS. Anterior to the infundibular stalk, the optic nerves converge at the optic chiasm. Within the chiasm, axons from the nasal portion of the retina decussate and enter into the contralateral optic tract (eFig. 9.75). Conversely, axons from the temporal portion of the retina stay ipsilateral to enter the ipsilateral optic tract (eFig. 9.75). | Anatomy_Gray. Axons from the ganglion cells coalesce at the optic disc, which is absent of photoreceptors and thus creates a blind spot in the visual field. As they leave the optic disc they form the optic nerve, acquire a myelin sheath provided by oligodendrocytes, and are invested by the cranial meninges (eFig. 9.72). These morphological features derived during embryonic development, define the optic nerve as a component of the CNS. Anterior to the infundibular stalk, the optic nerves converge at the optic chiasm. Within the chiasm, axons from the nasal portion of the retina decussate and enter into the contralateral optic tract (eFig. 9.75). Conversely, axons from the temporal portion of the retina stay ipsilateral to enter the ipsilateral optic tract (eFig. 9.75). |
Anatomy_Gray_2982 | Anatomy_Gray | Continuing posteriorly, the optic tracts course around the midbrain to enter the lateral geniculate nucleus of the thalamus (eFig. 9.75). At this level, a small portion of the fibers from the optic tract travel to the pretectal area and superior colliculus to mediate the pupillary light reflex. Axons leaving the lateral geniculate nucleus form the optic radiations, which continue on to the primary visual cortex in the occipital lobe (eFig. 9.76). Fibers traveling in the lower portion of the optic radiations terminate on the lower half of the primary visual cortex, whereas fibers in the upper portion terminate on the upper half of the cortex (eFig. 9.76). A full review of how the visual field is represented throughout the visual pathway can be reviewed in eFig. 9.77. | Anatomy_Gray. Continuing posteriorly, the optic tracts course around the midbrain to enter the lateral geniculate nucleus of the thalamus (eFig. 9.75). At this level, a small portion of the fibers from the optic tract travel to the pretectal area and superior colliculus to mediate the pupillary light reflex. Axons leaving the lateral geniculate nucleus form the optic radiations, which continue on to the primary visual cortex in the occipital lobe (eFig. 9.76). Fibers traveling in the lower portion of the optic radiations terminate on the lower half of the primary visual cortex, whereas fibers in the upper portion terminate on the upper half of the cortex (eFig. 9.76). A full review of how the visual field is represented throughout the visual pathway can be reviewed in eFig. 9.77. |
Anatomy_Gray_2983 | Anatomy_Gray | As mentioned previously, images formed on the retina are inverted in both vertical and lateral dimensions. In addition, the fibers from the nasal portion of the hemiretina decussate at the optic chiasm. Because of this, the optic tracts, thalamus, optic radiations, and primary visual cortex receive information relating only to the contralateral half of the visual field. Knowledge of how the visual field is represented throughout the visual pathway is essential for identifying the location of lesions in patients with visual field deficits. Examples of lesions in the five major structures of the visual pathway (optic nerve, optic chiasm, optic tract, optic radiations, primary visual cortex) and their associated visual field deficits are represented in eFig. 9.78. Part IX: Auditory and | Anatomy_Gray. As mentioned previously, images formed on the retina are inverted in both vertical and lateral dimensions. In addition, the fibers from the nasal portion of the hemiretina decussate at the optic chiasm. Because of this, the optic tracts, thalamus, optic radiations, and primary visual cortex receive information relating only to the contralateral half of the visual field. Knowledge of how the visual field is represented throughout the visual pathway is essential for identifying the location of lesions in patients with visual field deficits. Examples of lesions in the five major structures of the visual pathway (optic nerve, optic chiasm, optic tract, optic radiations, primary visual cortex) and their associated visual field deficits are represented in eFig. 9.78. Part IX: Auditory and |
Anatomy_Gray_2984 | Anatomy_Gray | Part IX: Auditory and Cranial nerve VIII, the vestibulocochlear nerve, conveys sensory information from the vestibular and auditory organs of the inner ear to the pontomedullary junction of the brainstem. Although these sensory modalities are conveyed to the brainstem by a common nerve bundle, each of these sensory functions has different central pathways. In this section we will first review the central auditory pathways and then the vestibular pathways. | Anatomy_Gray. Part IX: Auditory and Cranial nerve VIII, the vestibulocochlear nerve, conveys sensory information from the vestibular and auditory organs of the inner ear to the pontomedullary junction of the brainstem. Although these sensory modalities are conveyed to the brainstem by a common nerve bundle, each of these sensory functions has different central pathways. In this section we will first review the central auditory pathways and then the vestibular pathways. |
Anatomy_Gray_2985 | Anatomy_Gray | Sound waves, the auditory stimulus, are directed toward the external acoustic meatus by the pinna of the outer ear and through the ear canal to the tympanic membrane (eFig. 9.79). Vibration of the tympanic membrane, induced by the incoming sound waves, is transmitted to the three ossicle bones (malleus, incus, and stapes) of the middle ear. These bones amplify sound waves so they can be converted to pressure waves at the oval window of the fluid-filled cochlea. To prevent damage from loud or high-decibel sounds, movements of the malleus and stapes are reduced by the tensor tympani and stapedius muscles. | Anatomy_Gray. Sound waves, the auditory stimulus, are directed toward the external acoustic meatus by the pinna of the outer ear and through the ear canal to the tympanic membrane (eFig. 9.79). Vibration of the tympanic membrane, induced by the incoming sound waves, is transmitted to the three ossicle bones (malleus, incus, and stapes) of the middle ear. These bones amplify sound waves so they can be converted to pressure waves at the oval window of the fluid-filled cochlea. To prevent damage from loud or high-decibel sounds, movements of the malleus and stapes are reduced by the tensor tympani and stapedius muscles. |
Anatomy_Gray_2986 | Anatomy_Gray | In the cochlea, sound waves are converted into an electrical signal at the organ of Corti. The organ of Corti rests upon the basilar membrane in the scala media, which is filled with endolymph (eFig. 9.80). In addition to contributing to the formation of the scala media with the vestibular membrane, the basilar membrane separates the cochlea into the scala vestibuli and scala tympani, which are filled with perilymph and are continuous with one another at the helicotrema (eFig. 9.80). | Anatomy_Gray. In the cochlea, sound waves are converted into an electrical signal at the organ of Corti. The organ of Corti rests upon the basilar membrane in the scala media, which is filled with endolymph (eFig. 9.80). In addition to contributing to the formation of the scala media with the vestibular membrane, the basilar membrane separates the cochlea into the scala vestibuli and scala tympani, which are filled with perilymph and are continuous with one another at the helicotrema (eFig. 9.80). |
Anatomy_Gray_2987 | Anatomy_Gray | As the sound waves move through the perilymph they displace the basilar membrane, which causes deflection of the hair cells in the organ of Corti (eFig. 9.81A). These sensory receptors synapse with sensory neurons, which have cell bodies in spiral ganglion located within the modiolus of the cochlea (eFig. 9.80). Axons leaving the modiolus form the cochlear nerve near the base of the cochlea. The cochlear nerve then passes through the internal acoustic meatus and subarachnoid space to enter the pontomedullary junction at the cerebellopontine angle. | Anatomy_Gray. As the sound waves move through the perilymph they displace the basilar membrane, which causes deflection of the hair cells in the organ of Corti (eFig. 9.81A). These sensory receptors synapse with sensory neurons, which have cell bodies in spiral ganglion located within the modiolus of the cochlea (eFig. 9.80). Axons leaving the modiolus form the cochlear nerve near the base of the cochlea. The cochlear nerve then passes through the internal acoustic meatus and subarachnoid space to enter the pontomedullary junction at the cerebellopontine angle. |
Anatomy_Gray_2988 | Anatomy_Gray | The first-order axons entering the brainstem from the cochlea terminate ipsilaterally on the dorsal and ventral cochlear nuclei. From here, second-order axons have several synaptic targets. Second-order axons forming the ascending auditory pathway ascend to the pons and project bilaterally on the superior olivary nucleus (eFig. 9.82). These bilateral projections are important for auditory acuity and localizing the origin of a sound. From here, fibers continue to ascend as the lateral lemniscus and terminate in the inferior colliculus of the midbrain. Axons leaving the inferior colliculus then have a synaptic relay in the medial geniculate nucleus of the thalamus before reaching the final synaptic target: the primary auditory cortex (superior temporal gyrus) of the temporal lobe (eFig. 9.82). Throughout this pathway, from the basilar membrane to the primary auditory cortex, auditory stimuli are tonotopically represented. This is analogous to the somatotopic map previously discussed in | Anatomy_Gray. The first-order axons entering the brainstem from the cochlea terminate ipsilaterally on the dorsal and ventral cochlear nuclei. From here, second-order axons have several synaptic targets. Second-order axons forming the ascending auditory pathway ascend to the pons and project bilaterally on the superior olivary nucleus (eFig. 9.82). These bilateral projections are important for auditory acuity and localizing the origin of a sound. From here, fibers continue to ascend as the lateral lemniscus and terminate in the inferior colliculus of the midbrain. Axons leaving the inferior colliculus then have a synaptic relay in the medial geniculate nucleus of the thalamus before reaching the final synaptic target: the primary auditory cortex (superior temporal gyrus) of the temporal lobe (eFig. 9.82). Throughout this pathway, from the basilar membrane to the primary auditory cortex, auditory stimuli are tonotopically represented. This is analogous to the somatotopic map previously discussed in |
Anatomy_Gray_2989 | Anatomy_Gray | Throughout this pathway, from the basilar membrane to the primary auditory cortex, auditory stimuli are tonotopically represented. This is analogous to the somatotopic map previously discussed in the section on somatosensory systems pathways. | Anatomy_Gray. Throughout this pathway, from the basilar membrane to the primary auditory cortex, auditory stimuli are tonotopically represented. This is analogous to the somatotopic map previously discussed in the section on somatosensory systems pathways. |
Anatomy_Gray_2990 | Anatomy_Gray | In addition to the ascending auditory pathway, the superior olivary nucleus receives descending input from the primary auditory cortex as a form of feedback (eFig. 9.82). The superior olivary nucleus then sends descending olivocochlear fibers to the organ of Corti, which has an inhibitory function on the hair cells to prevent damage from harmfully loud sounds. It is also believed that the superior olivary nucleus has connections with the motor nuclei of the trigeminal and facial nerve to mediate reflexive contraction of the tensor tympani and stapedius muscles in response to loud sounds. | Anatomy_Gray. In addition to the ascending auditory pathway, the superior olivary nucleus receives descending input from the primary auditory cortex as a form of feedback (eFig. 9.82). The superior olivary nucleus then sends descending olivocochlear fibers to the organ of Corti, which has an inhibitory function on the hair cells to prevent damage from harmfully loud sounds. It is also believed that the superior olivary nucleus has connections with the motor nuclei of the trigeminal and facial nerve to mediate reflexive contraction of the tensor tympani and stapedius muscles in response to loud sounds. |
Anatomy_Gray_2991 | Anatomy_Gray | The vestibular nerve transmits afferent or sensory information regarding movement and position of the head from the vestibular organs, which include semicircular ducts, utricle, and saccule. Like the cochlear apparatus, each of these vestibular organs is located within a membranous (ductal) portion of the vestibular apparatus, which is surrounded by a bony (canal) portion (eFig. 9.83). The cell bodies for these sensory receptors are located in the vestibular (Scarpa’s) ganglion within the internal acoustic meatus (eFig. 9.83). The vestibular nerve then passes through the internal acoustic meatus and subarachnoid space to enter the pontomedullary junction at the cerebellopontine angle. | Anatomy_Gray. The vestibular nerve transmits afferent or sensory information regarding movement and position of the head from the vestibular organs, which include semicircular ducts, utricle, and saccule. Like the cochlear apparatus, each of these vestibular organs is located within a membranous (ductal) portion of the vestibular apparatus, which is surrounded by a bony (canal) portion (eFig. 9.83). The cell bodies for these sensory receptors are located in the vestibular (Scarpa’s) ganglion within the internal acoustic meatus (eFig. 9.83). The vestibular nerve then passes through the internal acoustic meatus and subarachnoid space to enter the pontomedullary junction at the cerebellopontine angle. |
Anatomy_Gray_2992 | Anatomy_Gray | The central processes of the vestibular axons predominantly terminate in the four vestibular nuclei (superior, inferior, medial, and lateral), which are located in the rostral medulla and caudal pons (eFig. 9.40). Axons leaving the vestibular nuclei have several ascending and descending synaptic targets. These pathways connect with visual motor, descending motor, and cerebellar pathways to coordinate movement and maintain posture and balance (eFig. 9.84). | Anatomy_Gray. The central processes of the vestibular axons predominantly terminate in the four vestibular nuclei (superior, inferior, medial, and lateral), which are located in the rostral medulla and caudal pons (eFig. 9.40). Axons leaving the vestibular nuclei have several ascending and descending synaptic targets. These pathways connect with visual motor, descending motor, and cerebellar pathways to coordinate movement and maintain posture and balance (eFig. 9.84). |
Anatomy_Gray_2993 | Anatomy_Gray | Axons ascending after leaving the vestibular nuclei form the medial longitudinal fasciculus to reach the oculomotor, trochlear, and abducent nuclei (eFig. 9.85). These connections coordinate movement of the head and eyes so that visual fixation on an object can be maintained. Other axons ascending from the vestibular nuclei project to the cerebral cortex after a synaptic relay in the ventral posterior nucleus of the thalamus (eFig. 9.84B). This connection assists in consciously orienting oneself in space. In addition to these connections, axons leaving the vestibular nuclei pass through the inferior cerebellar peduncle to reach the cerebellum and modulate equilibrium (eFig. 9.84B). | Anatomy_Gray. Axons ascending after leaving the vestibular nuclei form the medial longitudinal fasciculus to reach the oculomotor, trochlear, and abducent nuclei (eFig. 9.85). These connections coordinate movement of the head and eyes so that visual fixation on an object can be maintained. Other axons ascending from the vestibular nuclei project to the cerebral cortex after a synaptic relay in the ventral posterior nucleus of the thalamus (eFig. 9.84B). This connection assists in consciously orienting oneself in space. In addition to these connections, axons leaving the vestibular nuclei pass through the inferior cerebellar peduncle to reach the cerebellum and modulate equilibrium (eFig. 9.84B). |
Anatomy_Gray_2994 | Anatomy_Gray | Axons descending after leaving the vestibular nuclei form the medial and lateral vestibulospinal tracts ipsilaterally (eFig. 9.84B). As mentioned in the previous section on medial motor systems in the spinal cord, the axons in these pathways synapse on interneurons within the anterior horn gray matter to influence spinal motor neuron activity and maintain posture and balance. Part X: Hypothalamus The hypothalamus is a neuroendocrine organ that regulates physiological processes for survival such as consumption of fluid and food, temperature control, the sleep–wake cycle, growth, and reproduction. As a result of this vast array of functions, the nuclei of the hypothalamus make connections with several other neural and endocrine structures in the body (eFig. 9.86). In this section we will explore the nuclei of the hypothalamus and their main connections. | Anatomy_Gray. Axons descending after leaving the vestibular nuclei form the medial and lateral vestibulospinal tracts ipsilaterally (eFig. 9.84B). As mentioned in the previous section on medial motor systems in the spinal cord, the axons in these pathways synapse on interneurons within the anterior horn gray matter to influence spinal motor neuron activity and maintain posture and balance. Part X: Hypothalamus The hypothalamus is a neuroendocrine organ that regulates physiological processes for survival such as consumption of fluid and food, temperature control, the sleep–wake cycle, growth, and reproduction. As a result of this vast array of functions, the nuclei of the hypothalamus make connections with several other neural and endocrine structures in the body (eFig. 9.86). In this section we will explore the nuclei of the hypothalamus and their main connections. |
Anatomy_Gray_2995 | Anatomy_Gray | Located in the ventralmost aspect of the diencephalon, the hypothalamus is bounded by the lamina terminalis anteriorly, the hypothalamic sulcus superiorly, and the tegmentum of the midbrain posteriorly (eFig. 9.87). Laterally the hypothalamus is bordered by the substantia innominata rostrally and the posterior limb of the internal capsule caudally. It forms the floor in addition to the lower portion of the lateral walls in the third ventricle. When viewing the external surface of the ventral brain, the area containing the hypothalamus is circumscribed by the optic chiasm, optic tract, crus cerebri, and caudal edge of the mammillary bodies (eFig. 9.88). | Anatomy_Gray. Located in the ventralmost aspect of the diencephalon, the hypothalamus is bounded by the lamina terminalis anteriorly, the hypothalamic sulcus superiorly, and the tegmentum of the midbrain posteriorly (eFig. 9.87). Laterally the hypothalamus is bordered by the substantia innominata rostrally and the posterior limb of the internal capsule caudally. It forms the floor in addition to the lower portion of the lateral walls in the third ventricle. When viewing the external surface of the ventral brain, the area containing the hypothalamus is circumscribed by the optic chiasm, optic tract, crus cerebri, and caudal edge of the mammillary bodies (eFig. 9.88). |
Anatomy_Gray_2996 | Anatomy_Gray | Continuous with the hypothalamus inferiorly is the pituitary gland. These two structures are connected by the infundibulum and hypophysial stalk just caudal to the optic chiasm (eFig. 9.87). The intimate relationship of the hypothalamus to the portal circulation of the pituitary gland allows the hypothalamus to be an efficient regulator of hormone synthesis and release. Releasing and inhibiting factors synthesized by the hypothalamus pass through these portal vessels via the tuberoinfundibular tract (eFig. 9.89) to reach the anterior pituitary (adenohypophysis) and control release of hormones produced by the anterior pituitary such as adrenocorticotropic hormone, luteinizing hormone, follicle-stimulating hormone, thyroid-stimulating hormone, growth hormone, and prolactin (eFig. 9.90). | Anatomy_Gray. Continuous with the hypothalamus inferiorly is the pituitary gland. These two structures are connected by the infundibulum and hypophysial stalk just caudal to the optic chiasm (eFig. 9.87). The intimate relationship of the hypothalamus to the portal circulation of the pituitary gland allows the hypothalamus to be an efficient regulator of hormone synthesis and release. Releasing and inhibiting factors synthesized by the hypothalamus pass through these portal vessels via the tuberoinfundibular tract (eFig. 9.89) to reach the anterior pituitary (adenohypophysis) and control release of hormones produced by the anterior pituitary such as adrenocorticotropic hormone, luteinizing hormone, follicle-stimulating hormone, thyroid-stimulating hormone, growth hormone, and prolactin (eFig. 9.90). |
Anatomy_Gray_2997 | Anatomy_Gray | A second connection exists between the hypothalamus and pituitary through nerve fibers, which originate in the supraoptic region and paraventricular nuclei of the medial hypothalamus and extend through the hypothalamohypophyseal tract to the posterior lobe of the pituitary for release into the circulatory system (eFig. 9.89). Internally, the hypothalamus is composed of many small nuclei, which are divided by a parasagittal plane into a medial and lateral zone. Landmarks for this dividing point are the columns of the fornix and the mammillothalamic tract as they reside within this sagittal plane (eFig. 9.91). The hypothalamus is also divided by coronal planes into a preoptic area and periventricular zone. Note that the periventricular zone is not to be confused with the paraventricular nucleus, which is a thin region of cell bodies lying medial to the medial zone. | Anatomy_Gray. A second connection exists between the hypothalamus and pituitary through nerve fibers, which originate in the supraoptic region and paraventricular nuclei of the medial hypothalamus and extend through the hypothalamohypophyseal tract to the posterior lobe of the pituitary for release into the circulatory system (eFig. 9.89). Internally, the hypothalamus is composed of many small nuclei, which are divided by a parasagittal plane into a medial and lateral zone. Landmarks for this dividing point are the columns of the fornix and the mammillothalamic tract as they reside within this sagittal plane (eFig. 9.91). The hypothalamus is also divided by coronal planes into a preoptic area and periventricular zone. Note that the periventricular zone is not to be confused with the paraventricular nucleus, which is a thin region of cell bodies lying medial to the medial zone. |
Anatomy_Gray_2998 | Anatomy_Gray | Within the lateral zone of the hypothalamus is a large bundle of axons forming the medial forebrain bundle (MFB) (eFig. 9.90). Theses fibers interconnect the hypothalamus with the septal nuclei rostrally and nuclear complexes within the brainstem. Axons arising from the large lateral nucleus in this zone enter the MFB and function in promoting feeding behavior. The other and smaller nuclear group in this zone is the tuberal group. Axons from the tuberal nuclei make connections with the anterior pituitary through the tuberoinfundibular tract to regulate release of hormones in the hypophysial portal system and to the cerebellum to regulate motor activity (eFig. 9.89). | Anatomy_Gray. Within the lateral zone of the hypothalamus is a large bundle of axons forming the medial forebrain bundle (MFB) (eFig. 9.90). Theses fibers interconnect the hypothalamus with the septal nuclei rostrally and nuclear complexes within the brainstem. Axons arising from the large lateral nucleus in this zone enter the MFB and function in promoting feeding behavior. The other and smaller nuclear group in this zone is the tuberal group. Axons from the tuberal nuclei make connections with the anterior pituitary through the tuberoinfundibular tract to regulate release of hormones in the hypophysial portal system and to the cerebellum to regulate motor activity (eFig. 9.89). |
Anatomy_Gray_2999 | Anatomy_Gray | The medial zone is divided into three regions: supraoptic, tuberal, and mammillary. There are four nuclei in the supraoptic region, which play a role in thermoregulation, osmoregulation, and the sleep–wake cycle. The supraoptic and paraventricular nuclei in this region synthesize antidiuretic hormone or vasopressin, which stimulates water uptake and oxytocin for stimulation of uterine contractions and lactation in the mammary glands. Axons from these nuclei are conveyed by the hypothalamohypophyseal tract to the posterior pituitary for release into the circulatory system (eFig. 9.89). A third nuclear group in this region is the suprachiasmatic nucleus. This nucleus receives input directly from the retina to influence circadian rhythms, which contribute to the light–dark cycle. The anterior nucleus is the final group and functions predominantly in regulating body temperature. | Anatomy_Gray. The medial zone is divided into three regions: supraoptic, tuberal, and mammillary. There are four nuclei in the supraoptic region, which play a role in thermoregulation, osmoregulation, and the sleep–wake cycle. The supraoptic and paraventricular nuclei in this region synthesize antidiuretic hormone or vasopressin, which stimulates water uptake and oxytocin for stimulation of uterine contractions and lactation in the mammary glands. Axons from these nuclei are conveyed by the hypothalamohypophyseal tract to the posterior pituitary for release into the circulatory system (eFig. 9.89). A third nuclear group in this region is the suprachiasmatic nucleus. This nucleus receives input directly from the retina to influence circadian rhythms, which contribute to the light–dark cycle. The anterior nucleus is the final group and functions predominantly in regulating body temperature. |
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