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Speer knew Germany was going to lose the war and deliberately extended its length, thus causing the deaths of millions of people in the death camps and on the battlefield who would have otherwise lived. Kitchen said, "There can be no doubt that Speer did indeed help to prolong the war longer than many thought possible, as a result of which millions were killed and Germany reduced to a pile of rubble". Architectural legacy Little remains of Speer's personal architectural works, other than the plans and photographs. No buildings designed by Speer during the Nazi era are extant in Berlin, other than the 4 entrance pavilions and underpasses leading to the Victory Column or Siegessule, and the Schwerbelastungskrper, a heavy loadbearing body built around 1941. The concrete cylinder, high, was used to measure ground subsidence as part of feasibility studies for a massive triumphal arch and other large structures proposed as part of Welthauptstadt Germania, Hitler's planned postwar renewal project for the city. Th
e cylinder is now a protected landmark and is open to the public. The tribune of the Zeppelinfeld stadium in Nuremberg, though partly demolished, can also be seen. During the war, the Speerdesigned Reich Chancellery was largely destroyed by air raids and in the Battle of Berlin. The exterior walls survived, but they were eventually dismantled by the Soviets. Unsubstantiated rumors have claimed that the remains were used for other building projects such as the Humboldt University, Mohrenstrae metro station and Soviet war memorials in Berlin. See also Speer Goes to Hollywood Downfall, 2004 German film where he was portrayed by actor Heino Ferch Legion Speer Transportflotte Speer Transportkorps Speer Hermann Giesler References Informational notes Citations Bibliography Printed sources Online sources Further reading Causey, Charles M. 2016. The Lion and the Lamb The True Holocaust Story of a Powerful Nazi Leader and a Dutch Resistance Wor
ker, External links Francisco Boix identifies Speer at Nuremberg 1905 births 1981 deaths 20thcentury German architects Articles containing video clips Deaths from cerebrovascular disease 20thcentury German male writers German people convicted of crimes against humanity Holocaust perpetrators Karlsruhe Institute of Technology alumni Members of the Reichstag of Nazi Germany Architects in the Nazi Party Nazi Germany ministers Nazi Party officials Neoclassical architects Officials of Nazi Germany People convicted by the International Military Tribunal in Nuremberg Politicians from Mannheim People from the Grand Duchy of Baden Recipients of the Knights Cross of the War Merit Cross Technical University of Berlin alumni Technical University of Munich alumni Architects from Mannheim Neurological disease deaths in England
The family Asteraceae , alternatively Compositae , consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae were first described in the year 1740. The number of species in Asteraceae is rivaled only by the Orchidaceae, and which is the larger family is unclear as the quantity of extant species in each family is unknown. Most species of Asteraceae are annual, biennial, or perennial herbaceous plants, but there are also shrubs, vines, and trees. The family has a widespread distribution, from subpolar to tropical regions in a wide variety of habitats. Most occur in hot desert and cold or hot semidesert climates, and they are found on every continent but Antarctica. The primary common characteristic is the existence of sometimes hundreds of tiny individual florets which are held together by protective involucres in flower heads, or more technically, capitula. The oldest known f
ossils are pollen grains from the Late Cretaceous Campanian to Maastrichtian of Antarctica, dated to c. 7666 million years myr. It is estimated that the crown group of Asteraceae evolved at least 85.9 myr Late Cretaceous, Santonian with a stem node age of 8889 myr Late Cretaceous, Coniacian. Asteraceae is an economically important family, providing food staples, garden plants, and herbal medicines. Species outside of their native ranges can be considered weedy or invasive. Description Members of the Asteraceae are mostly herbaceous plants, but some shrubs, vines, and trees such as Lachanodes arborea do exist. Asteraceae species are generally easy to distinguish from other plants because of their unique inflorescence and other shared characteristics, such as the joined anthers of the stamens. However, determining genera and species of some groups such as Hieracium is notoriously difficult see "damned yellow composite" for example. Roots Members of the family Asteraceae generally produce taproots, but someti
mes they possess fibrous root systems. Some species have underground stems in the form of caudices or rhizomes. These can be fleshy or woody depending on the species. Stems Stems are herbaceous, aerial, branched, and cylindrical with glandular hairs, generally erect, but can be prostrate to ascending. The stems can contain secretory canals with resin, or latex which is particularly common among the Cichorioideae. Leaves Leaves can be alternate, opposite, or whorled. They may be simple, but are often deeply lobed or otherwise incised, often conduplicate or revolute. The margins also can be entire or toothed. Resin or latex also can be present in the leaves. Inflorescences Nearly all Asteraceae bear their flowers in dense flower heads called capitula. They are surrounded by involucral bracts, and when viewed from a distance, each capitulum may appear to be a single flower. Enlarged outer peripheral flowers in the capitulum may resemble petals, and the involucral bracts may look like a calyx. Floral heads
In plants of the family Asteraceae, what appears to be a single flower is actually a cluster of much smaller flowers. The overall appearance of the cluster, as a single flower, functions in attracting pollinators in the same way as the structure of an individual flower in some other plant families. The older family name, Compositae, comes from the fact that what appears to be a single flower is actually a composite of smaller flowers. The "petals" or "sunrays" in a sunflower head are actually individual strapshaped flowers called ray flowers, and the "sun disk" is made of smaller circular shaped individual flowers called disc flowers. The word "aster" means "star" in Greek, referring to the appearance of some family members, as a "star" surrounded by "rays". The cluster of flowers that may appear to be a single flower, is called a head. The entire head may move tracking the sun, like a "smart" solar panel, which maximizes reflectivity of the whole unit and can thereby attract more pollinators. On the outsid
e the flower heads are small bracts that look like scales. These are called phyllaries, and together they form the involucre that protects the individual flowers in the head before they open. The individual heads have the smaller individual flowers arranged on a round or domelike structure called the receptacle. The flowers mature first at the outside, moving toward the center, with the youngest in the middle. The individual flowers in a head have 5 fused petals rarely 4, but instead of sepals, have threadlike, hairy, or bristly structures singularly called a pappus, plural pappi, which surround the fruit and can stick to animal fur or be lifted by wind, aiding in seed dispersal. The whitish fluffy head of a dandelion, commonly blown on by children, is made of pappi with tiny seeds attached at the ends. The pappi provide a parachute like structure to help the seed be carried away in the wind. A ray flower is a 3tipped 3lobed, strapshaped, individual flower in the head of some members of the family Asteracea
e. Sometimes a ray flower is 2tipped 2lobed. The corolla of the ray flower may have 2 tiny teeth opposite the 3lobed strap, or tongue, indicating evolution by fusion from an originally 5part corolla. Sometimes, the 32 arrangement is reversed, with 2 tips on the tongue, and 0 or 3 tiny teeth opposite the tongue. A ligulate flower is a 5tipped, strapshaped, individual flower in the heads of other members. A ligule is the strapshaped tongue of the corolla of either a ray flower or of a ligulate flower. A disk flower or disc flower is a radially symmetric i.e., with identical shaped petals arranged in circle around the center individual flower in the head, which is ringed by ray flowers when both are present. Sometimes ray flowers may be slightly off from radial symmetry, or weakly bilaterally symmetric, as in the case of desert pincushions Chaenactis fremontii. A radiate head has disc flowers surrounded by ray flowers. A ligulate head has all ligulate flowers. When a sunflower family flower head has only disc f
lowers that are sterile, male, or have both male and female parts, it is a discoid head. Disciform heads have only disc flowers, but may have two kinds male flowers and female flowers in one head, or may have different heads of two kinds all male, or all female. Pistillate heads have all female flowers. Staminate heads have all male flowers. Sometimes, but rarely, the head contains only a single flower, or has a single flowered pistillate female head, and a multiflowered male staminate male head. Floral structures The distinguishing characteristic of Asteraceae is their inflorescence, a type of specialised, composite flower head or pseudanthium, technically called a calathium or capitulum, that may look superficially like a single flower. The capitulum is a contracted raceme composed of numerous individual sessile flowers, called florets, all sharing the same receptacle. A set of bracts forms an involucre surrounding the base of the capitulum. These are called "phyllaries", or "involucral bracts". They ma
y simulate the sepals of the pseudanthium. These are mostly herbaceous but can also be brightly coloured e.g. Helichrysum or have a scarious dry and membranous texture. The phyllaries can be free or fused, and arranged in one to many rows, overlapping like the tiles of a roof imbricate or not this variation is important in identification of tribes and genera. Each floret may be subtended by a bract, called a "palea" or "receptacular bract". These bracts are often called "chaff". The presence or absence of these bracts, their distribution on the receptacle, and their size and shape are all important diagnostic characteristics for genera and tribes. The florets have five petals fused at the base to form a corolla tube and they may be either actinomorphic or zygomorphic. Disc florets are usually actinomorphic, with five petal lips on the rim of the corolla tube. The petal lips may be either very short, or long, in which case they form deeply lobed petals. The latter is the only kind of floret in the Carduoidea
e, while the first kind is more widespread. Ray florets are always highly zygomorphic and are characterised by the presence of a ligule, a strapshaped structure on the edge of the corolla tube consisting of fused petals. In the Asteroideae and other minor subfamilies these are usually borne only on florets at the circumference of the capitulum and have a 32 scheme above the fused corolla tube, three very long fused petals form the ligule, with the other two petals being inconspicuously small. The Cichorioideae has only ray florets, with a 50 scheme all five petals form the ligule. A 41 scheme is found in the Barnadesioideae. The tip of the ligule is often divided into teeth, each one representing a petal. Some marginal florets may have no petals at all filiform floret. The calyx of the florets may be absent, but when present is always modified into a pappus of two or more teeth, scales or bristles and this is often involved in the dispersion of the seeds. As with the bracts, the nature of the pappus is an
important diagnostic feature. There are usually five stamens. The filaments are fused to the corolla, while the anthers are generally connate syngenesious anthers, thus forming a sort of tube around the style theca. They commonly have basal andor apical appendages. Pollen is released inside the tube and is collected around the growing style, and then, as the style elongates, is pushed out of the tube ndelspritze. The pistil consists of two connate carpels. The style has two lobes. Stigmatic tissue may be located in the interior surface or form two lateral lines. The ovary is inferior and has only one ovule, with basal placentation. Fruits and seeds In members of the Asteraceae the fruit is achenelike, and is called a cypsela plural cypselae. Although there are two fused carpels, there is only one locule, and only one seed per fruit is formed. It may sometimes be winged or spiny because the pappus, which is derived from calyx tissue often remains on the fruit for example in dandelion. In some species, howe
ver, the pappus falls off for example in Helianthus. Cypsela morphology is often used to help determine plant relationships at the genus and species level. The mature seeds usually have little endosperm or none. Pollen The pollen of composites is typically echinolophate, a morphological term meaning "with elaborate systems of ridges and spines dispersed around and between the apertures." Metabolites In Asteraceae, the energy store is generally in the form of inulin rather than starch. They produce isochlorogenic acid, sesquiterpene lactones, pentacyclic triterpene alcohols, various alkaloids, acetylenes cyclic, aromatic, with vinyl end groups, tannins. They have terpenoid essential oils which never contain iridoids. Asteraceae produce secondary metabolites, such as flavonoids and terpenoids. Some of these molecules can inhibit protozoan parasites such as Plasmodium, Trypanosoma, Leishmania and parasitic intestinal worms, and thus have potential in medicine. Taxonomy History Compositae, the original nam
e for Asteraceae, were first described in 1740 by Dutch botanist Adriaan van Royen. Traditionally, two subfamilies were recognised Asteroideae or Tubuliflorae and Cichorioideae or Liguliflorae. The latter has been shown to be extensively paraphyletic, and has now been divided into 12 subfamilies, but the former still stands. The study of this family is known as synantherology. Phylogeny The phylogenetic tree presented below is based on Panero Funk 2002 updated in 2014, and now also includes the monotypic Famatinanthoideae. The diamond denotes a very poorly supported node 50 bootstrap support, the dot a poorly supported node 80. The family includes over 32,000 currently accepted species, in over 1,900 genera list in 13 subfamilies. The number of species in the family Asteraceae is rivaled only by Orchidaceae. Which is the larger family is unclear, because of the uncertainty about how many extant species each family includes. The four subfamilies Asteroideae, Cichorioideae, Carduoideae and Mutisioideae co
ntain 99 of the species diversity of the whole family approximately 70, 14, 11 and 3 respectively. Because of the morphological complexity exhibited by this family, agreeing on generic circumscriptions has often been difficult for taxonomists. As a result, several of these genera have required multiple revisions. Paleontology and evolutionary processes The oldest known fossils of members of Asteraceae are pollen grains from the Late Cretaceous of Antarctica, dated to 7666 myr Campanian to Maastrichtian and assigned to the extant genus Dasyphyllum. Barreda, et al. 2015 estimated that the crown group of Asteraceae evolved at least 85.9 myr Late Cretaceous, Santonian with a stem node age of 8889 myr Late Cretaceous, Coniacian. It is not known whether the precise cause of their great success was the development of the highly specialised capitulum, their ability to store energy as fructans mainly inulin, which is an advantage in relatively dry zones, or some combination of these and possibly other factors. Het
erocarpy, or the ability to produce different fruit morphs, has evolved and is common in Asteraceae. It allows seeds to be dispersed over varying distances and each is adapted to different environments, increasing chances of survival. Etymology and pronunciation The name Asteraceae comes to international scientific vocabulary from New Latin, from Aster, the type genus, aceae, a standardized suffix for plant family names in modern taxonomy. The genus name comes from the Classical Latin word , "star", which came from Ancient Greek , "star". It refers to the starlike form of the inflorescence. The original name Compositae is still valid under the International Code of Nomenclature for algae, fungi, and plants. It refers to the "composite" nature of the capitula, which consist of a few or many individual flowers. The vernacular name daisy, widely applied to members of this family, is derived from the Old English name of the daisy Bellis perennis , meaning "day's eye". This is because the petals open at d
awn and close at dusk. Distribution and habitat Asteraceae species have a widespread distribution, from subpolar to tropical regions in a wide variety of habitats. Most occur in hot desert and cold or hot semidesert climates, and they are found on every continent but Antarctica. They are especially numerous in tropical and subtropical regions notably Central America, eastern Brazil, the Mediterranean, the Levant, southern Africa, central Asia, and southwestern China. The largest proportion of the species occur in the arid and semiarid regions of subtropical and lower temperate latitudes. The Asteraceae family comprises 10 of all flowering plant species. Ecology Asteraceae are especially common in open and dry environments. Many members of Asteraceae are pollinated by insects, which explains their value in attracting beneficial insects, but anemophily is also present e.g. Ambrosia, Artemisia. There are many apomictic species in the family. Seeds are ordinarily dispersed intact with the fruiting body, the
cypsela. Anemochory wind dispersal is common, assisted by a hairy pappus. Epizoochory is another common method, in which the dispersal unit, a single cypsela e.g. Bidens or entire capitulum e.g. Arctium has hooks, spines or some structure to attach to the fur or plumage or even clothes, as in the photo of an animal just to fall off later far from its mother plant. Some members of Asteraceae are economically important as weeds. Notable in the United States are Senecio jacobaea ragwort, Senecio vulgaris groundsel, and Taraxacum dandelion. Some are invasive species in particular regions, often having been introduced by human agency. Examples include various tumbleweeds, Bidens, ragweeds, thistles, and dandelion. Dandelion was introduced into North America by European settlers who used the young leaves as a salad green. Uses Asteraceae is an economically important family, providing products such as cooking oils, leaf vegetables like lettuce, sunflower seeds, artichokes, sweetening agents, coffee substitutes
and herbal teas. Several genera are of horticultural importance, including pot marigold Calendula officinalis, Echinacea coneflowers, various daisies, fleabane, chrysanthemums, dahlias, zinnias, and heleniums. Asteraceae are important in herbal medicine, including Grindelia, yarrow, and many others. Commercially important plants in Asteraceae include the food crops Lactuca sativa lettuce, Cichorium chicory, Cynara scolymus globe artichoke, Helianthus annuus sunflower, Smallanthus sonchifolius yacn, Carthamus tinctorius safflower and Helianthus tuberosus Jerusalem artichoke. Plants are used as herbs and in herbal teas and other beverages. Chamomile, for example, comes from two different species the annual Matricaria chamomilla German chamomile and the perennial Chamaemelum nobile Roman chamomile. Calendula known as pot marigold is grown commercially for herbal teas and potpourri. Echinacea is used as a medicinal tea. The wormwood genus Artemisia includes absinthe A. absinthium and tarragon A. dracunculus. W
inter tarragon Tagetes lucida, is commonly grown and used as a tarragon substitute in climates where tarragon will not survive. Many members of the family are grown as ornamental plants for their flowers, and some are important ornamental crops for the cut flower industry. Some examples are Chrysanthemum, Gerbera, Calendula, Dendranthema, Argyranthemum, Dahlia, Tagetes, Zinnia, and many others. Many species of this family possess medicinal properties and are used as traditional antiparasitic medicine. Members of the family are also commonly featured in medical and phytochemical journals because the sesquiterpene lactone compounds contained within them are an important cause of allergic contact dermatitis. Allergy to these compounds is the leading cause of allergic contact dermatitis in florists in the US. Pollen from ragweed Ambrosia is among the main causes of socalled hay fever in the United States. Asteraceae are also used for some industrial purposes. French Marigold Tagetes patula is common in commer
cial poultry feeds and its oil is extracted for uses in cola and the cigarette industry. The genera Chrysanthemum, Pulicaria, Tagetes, and Tanacetum contain species with useful insecticidal properties. Parthenium argentatum guayule is a source of hypoallergenic latex. Several members of the family are copious nectar producers and are useful for evaluating pollinator populations during their bloom. Centaurea knapweed, Helianthus annuus domestic sunflower, and some species of Solidago goldenrod are major "honey plants" for beekeepers. Solidago produces relatively high protein pollen, which helps honey bees over winter. References Bibliography External links Asteraceae at the Angiosperm Phylogeny Website Compositae.org Compositae Working Group CWG and Global Compositae Database GCD Asterales families Extant Campanian first appearances
Apiaceae or Umbelliferae is a family of mostly aromatic flowering plants named after the type genus Apium and commonly known as the celery, carrot or parsley family, or simply as umbellifers. It is the 16thlargest family of flowering plants, with more than 3,700 species in 434 genera including such wellknown and economically important plants such as ajwain, angelica, anise, asafoetida, caraway, carrot, celery, chervil, coriander, cumin, dill, fennel, lovage, cow parsley, parsley, parsnip and sea holly, as well as silphium, a plant whose identity is unclear and which may be extinct. The family Apiaceae includes a significant number of phototoxic species, such as giant hogweed, and a smaller number of highly poisonous species, such as poison hemlock, water hemlock, spotted cowbane, fool's parsley, and various species of water dropwort. Description Most Apiaceae are annual, biennial or perennial herbs frequently with the leaves aggregated toward the base, though a minority are woody shrubs or small trees suc
h as Bupleurum fruticosum. Their leaves are of variable size and alternately arranged, or with the upper leaves becoming nearly opposite. The leaves may be petiolate or sessile. There are no stipules but the petioles are frequently sheathing and the leaves may be perfoliate. The leaf blade is usually dissected, ternate, or pinnatifid, but simple and entire in some genera, e.g. Bupleurum. Commonly, their leaves emit a marked smell when crushed, aromatic to foetid, but absent in some species. The defining characteristic of this family is the inflorescence, the flowers nearly always aggregated in terminal umbels, that may be simple or more commonly compound, often umbelliform cymes. The flowers are usually perfect hermaphroditic and actinomorphic, but there may be zygomorphic flowers at the edge of the umbel, as in carrot Daucus carota and coriander, with petals of unequal size, the ones pointing outward from the umbel larger than the ones pointing inward. Some are andromonoecious, polygamomonoecious, or even d
ioecious as in Acronema, with a distinct calyx and corolla, but the calyx is often highly reduced, to the point of being undetectable in many species, while the corolla can be white, yellow, pink or purple. The flowers are nearly perfectly pentamerous, with five petals and five stamens. There is often variation in the functionality of the stamens even within a single inflorescence. Some flowers are functionally staminate where a pistil may be present but has no ovules capable of being fertilized while others are functionally pistillate where stamens are present but their anthers do not produce viable pollen. Pollination of one flower by the pollen of a different flower of the same plant geitonogamy is common. The gynoecium consists of two carpels fused into a single, bicarpellate pistil with an inferior ovary. Stylopodia support two styles and secrete nectar, attracting pollinators like flies, mosquitoes, gnats, beetles, moths, and bees. The fruit is a schizocarp consisting of two fused carpels that separate
at maturity into two mericarps, each containing a single seed. The fruits of many species are dispersed by wind but others such as those of Daucus spp., are covered in bristles, which may be hooked in sanicle Sanicula europaea and thus catch in the fur of animals. The seeds have an oily endosperm and often contain essential oils, containing aromatic compounds that are responsible for the flavour of commercially important umbelliferous seed such as anise, cumin and coriander. The shape and details of the ornamentation of the ripe fruits are important for identification to species level. Taxonomy Apiaceae was first described by John Lindley in 1836. The name is derived from the type genus Apium, which was originally used by Pliny the Elder circa 50 AD for a celerylike plant. The alternative name for the family, Umbelliferae, derives from the inflorescence being generally in the form of a compound umbel. The family was one of the first to be recognized as a distinct group in Jacques Daleschamps' 1586 Historia
generalis plantarum. With Robert Morison's 1672 Plantarum umbelliferarum distribution nova it became the first group of plants for which a systematic study was published. The family is solidly placed within the Apiales order in the APG III system. It is closely related to Araliaceae and the boundaries between these families remain unclear. Traditionally groups within the family have been delimited largely based on fruit morphology, and the results from this have not been congruent with the more recent molecular phylogenetic analyses. The subfamilial and tribal classification for the family is currently in a state of flux, with many of the groups being found to be grossly paraphyletic or polyphyletic. General According to the Angiosperm Phylogeny Website , 434 genera are in the family Apiaceae. Ecology The black swallowtail butterfly, Papilio polyxenes, uses the family Apiaceae for food and host plants for oviposition. The 22spot ladybird is also commonly found eating mildew on these shrubs. Uses Many
members of this family are cultivated for various purposes. Parsnip Pastinaca sativa, carrot Daucus carota and Hamburg parsley Petroselinum crispum produce tap roots that are large enough to be useful as food. Many species produce essential oils in their leaves or fruits and as a result are flavourful aromatic herbs. Examples are parsley Petroselinum crispum, coriander Coriandrum sativum, culantro, and dill Anethum graveolens. The seeds may be used in cuisine, as with coriander Coriandrum sativum, fennel Foeniculum vulgare, cumin Cuminum cyminum, and caraway Carum carvi. Other notable cultivated Apiaceae include chervil Anthriscus cerefolium, angelica Angelica spp., celery Apium graveolens, arracacha Arracacia xanthorrhiza, sea holly Eryngium spp., asafoetida Ferula asafoetida, galbanum Ferula gummosa, cicely Myrrhis odorata, anise Pimpinella anisum, lovage Levisticum officinale, and hacquetia Hacquetia epipactis. Cultivation Generally, all members of this family are best cultivated in the coolseason gard
en; indeed, they may not grow at all if the soils are too warm. Almost every widely cultivated plant of this group is a considered useful as a companion plant. One reason is because the tiny flowers clustered into umbels, are well suited for ladybugs, parasitic wasps, and predatory flies, which actually drink nectar when not reproducing. They then prey upon insect pests on nearby plants. Some of the members of this family considered "herbs" produce scents that are believed to ...mask the odours of nearby plants, thus making them harder for insect pests to find. Other uses The poisonous members of the Apiaceae have been used for a variety of purposes globally. The poisonous Oenanthe crocata has been used to stupefy fish, Cicuta douglasii has been used as an aid in suicides, and arrow poisons have been made from various other family species. Daucus carota has been used as coloring for butter. Dorema ammoniacum, Ferula galbaniflua, and Ferula moschata sumbul are sources of incense. The woody Azorella com
pacta Phil. has been used in South America for fuel. Toxicity Many species in the family Apiaceae produce phototoxic substances called furanocoumarins that sensitize human skin to sunlight. Contact with plant parts that contain furanocoumarins, followed by exposure to sunlight, may cause phytophotodermatitis, a serious skin inflammation. Phototoxic species include Ammi majus, Notobubon galbanum, the parsnip Pastinaca sativa and numerous species of the genus Heracleum, especially the giant hogweed Heracleum mantegazzianum. Of all the plant species that have been reported to induce phytophotodermatitis, approximately half belong to the family Apiaceae. The family Apiaceae also includes a smaller number of poisonous species, including poison hemlock, water hemlock, spotted cowbane, fool's parsley, and various species of water dropwort. Some members of the family Apiaceae, including carrot, celery, fennel, parsley and parsnip, contain polyynes, an unusual class of organic compounds that exhibit cytotoxic effe
cts. References Further reading Constance, L. 1971. "History of the classification of Umbelliferae Apiaceae." in Heywood, V. H. ed., The biology and chemistry of the Umbelliferae, 111. Academic Press, London. Cronquist, A. 1968. The Evolution and Classification of Flowering Plants. Boston Houghton Mifflin. French, D. H. 1971. "Ethnobotany of the Umbelliferae." in Heywood, V. H. ed., The biology and chemistry of the Umbelliferae, 385412. Academic Press, London. Hegnauer, R. 1971 "Chemical Patterns and Relationships of Umbelliferae." in Heywood, V. H. ed., The biology and chemistry of the Umbelliferae, 267277. Academic Press, London. Heywood, V. H. 1971. "Systematic survey of Old World Umbelliferae." in Heywood, V. H. ed., The biology and chemistry of the Umbelliferae, 3141. Academic Press, London. Judd, W. S. et al. 1999. Plant Systematics A Phylogenetic Approach. Sunderland, MA Sinauer Associates, Inc. Nieto Feliner, Gonzalo; Jury, Stephen Leonard Herrero Nieto, Alberto eds. Flora iberica.
Plantas vasculares de la Pennsula Ibrica e Islas Baleares. Vol. X. "AraliaceaeUmbelliferae" 2003 Madrid Real Jardn Botnico, CSIC in Spanish. External links Umbelliferae at The Families of Flowering Plants DELTA Apiaceae at Discover Life Umbellifer Resource Centre at the Royal Botanic Garden Edinburgh Umbellifer Information Server at Moscow State University Asterid families
An axon from Greek xn, axis, or nerve fiber or nerve fibre see spelling differences, is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons pseudounipolar neurons, such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. Nerve fibers are classed into three types group A nerve fibers, group B nerve fibers, and group C nerve fibers. Groups A and B are myelinated, and group C are unmyelinated. These groups include both sensory fibers and motor fibers. Ano
ther classification groups only the sensory fibers as Type I, Type II, Type III, and Type IV. An axon is one of two types of cytoplasmic protrusions from the cell body of a neuron; the other type is a dendrite. Axons are distinguished from dendrites by several features, including shape dendrites often taper while axons usually maintain a constant radius, length dendrites are restricted to a small region around the cell body while axons can be much longer, and function dendrites receive signals whereas axons transmit them. Some types of neurons have no axon and transmit signals from their dendrites. In some species, axons can emanate from dendrites known as axoncarrying dendrites. No neuron ever has more than one axon; however in invertebrates such as insects or leeches the axon sometimes consists of several regions that function more or less independently of each other. Axons are covered by a membrane known as an axolemma; the cytoplasm of an axon is called axoplasm. Most axons branch, in some cases very pr
ofusely. The end branches of an axon are called telodendria. The swollen end of a telodendron is known as the axon terminal which joins the dendron or cell body of another neuron forming a synaptic connection. Axons make contact with other cellsusually other neurons but sometimes muscle or gland cellsat junctions called synapses. In some circumstances, the axon of one neuron may form a synapse with the dendrites of the same neuron, resulting in an autapse. At a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Some synaptic junctions appear along the length of an axon as it extendsthese are called en passant "in passing" synapses and can be in the hundreds or even the thousands along one axon. Other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches taken together, can innervate multiple parts of the brain and generate thousan
ds of synaptic terminals. A bundle of axons make a nerve tract in the central nervous system, and a fascicle in the peripheral nervous system. In placental mammals the largest white matter tract in the brain is the corpus callosum, formed of some 200 million axons in the human brain. Anatomy Axons are the primary transmission lines of the nervous system, and as bundles they form nerves. Some axons can extend up to one meter or more while others extend as little as one millimeter. The longest axons in the human body are those of the sciatic nerve, which run from the base of the spinal cord to the big toe of each foot. The diameter of axons is also variable. Most individual axons are microscopic in diameter typically about one micrometer m across. The largest mammalian axons can reach a diameter of up to 20 m. The squid giant axon, which is specialized to conduct signals very rapidly, is close to 1 millimetre in diameter, the size of a small pencil lead. The numbers of axonal telodendria the branching structu
res at the end of the axon can also differ from one nerve fiber to the next. Axons in the central nervous system CNS typically show multiple telodendria, with many synaptic end points. In comparison, the cerebellar granule cell axon is characterized by a single Tshaped branch node from which two parallel fibers extend. Elaborate branching allows for the simultaneous transmission of messages to a large number of target neurons within a single region of the brain. There are two types of axons in the nervous system myelinated and unmyelinated axons. Myelin is a layer of a fatty insulating substance, which is formed by two types of glial cells Schwann cells and oligodendrocytes. In the peripheral nervous system Schwann cells form the myelin sheath of a myelinated axon. In the central nervous system oligodendrocytes form the insulating myelin. Along myelinated nerve fibers, gaps in the myelin sheath known as nodes of Ranvier occur at evenly spaced intervals. The myelination enables an especially rapid mode of ele
ctrical impulse propagation called saltatory conduction. The myelinated axons from the cortical neurons form the bulk of the neural tissue called white matter in the brain. The myelin gives the white appearance to the tissue in contrast to the grey matter of the cerebral cortex which contains the neuronal cell bodies. A similar arrangement is seen in the cerebellum. Bundles of myelinated axons make up the nerve tracts in the CNS. Where these tracts cross the midline of the brain to connect opposite regions they are called commissures. The largest of these is the corpus callosum that connects the two cerebral hemispheres, and this has around 20 million axons. The structure of a neuron is seen to consist of two separate functional regions, or compartments the cell body together with the dendrites as one region, and the axonal region as the other. Axonal region The axonal region or compartment, includes the axon hillock, the initial segment, the rest of the axon, and the axon telodendria, and axon terminals.
It also includes the myelin sheath. The Nissl bodies that produce the neuronal proteins are absent in the axonal region. Proteins needed for the growth of the axon, and the removal of waste materials, need a framework for transport. This axonal transport is provided for in the axoplasm by arrangements of microtubules and intermediate filaments known as neurofilaments. Axon hillock The axon hillock is the area formed from the cell body of the neuron as it extends to become the axon. It precedes the initial segment. The received action potentials that are summed in the neuron are transmitted to the axon hillock for the generation of an action potential from the initial segment. Axonal initial segment The axonal initial segment AIS is a structurally and functionally separate microdomain of the axon. One function of the initial segment is to separate the main part of an axon from the rest of the neuron; another function is to help initiate action potentials. Both of these functions support neuron cell polarit
y, in which dendrites and, in some cases the soma of a neuron receive input signals at the basal region, and at the apical region the neuron's axon provides output signals. The axon initial segment is unmyelinated and contains a specialized complex of proteins. It is between approximately 20 and 60 m in length and functions as the site of action potential initiation. Both the position on the axon and the length of the AIS can change showing a degree of plasticity that can finetune the neuronal output. A longer AIS is associated with a greater excitability. Plasticity is also seen in the ability of the AIS to change its distribution and to maintain the activity of neural circuitry at a constant level. The AIS is highly specialized for the fast conduction of nerve impulses. This is achieved by a high concentration of voltagegated sodium channels in the initial segment where the action potential is initiated. The ion channels are accompanied by a high number of cell adhesion molecules and scaffolding proteins
that anchor them to the cytoskeleton. Interactions with ankyrin G are important as it is the major organizer in the AIS. Axonal transport The axoplasm is the equivalent of cytoplasm in the cell. Microtubules form in the axoplasm at the axon hillock. They are arranged along the length of the axon, in overlapping sections, and all point in the same direction towards the axon terminals. This is noted by the positive endings of the microtubules. This overlapping arrangement provides the routes for the transport of different materials from the cell body. Studies on the axoplasm has shown the movement of numerous vesicles of all sizes to be seen along cytoskeletal filaments the microtubules, and neurofilaments, in both directions between the axon and its terminals and the cell body. Outgoing anterograde transport from the cell body along the axon, carries mitochondria and membrane proteins needed for growth to the axon terminal. Ingoing retrograde transport carries cell waste materials from the axon terminal t
o the cell body. Outgoing and ingoing tracks use different sets of motor proteins. Outgoing transport is provided by kinesin, and ingoing return traffic is provided by dynein. Dynein is minusend directed. There are many forms of kinesin and dynein motor proteins, and each is thought to carry a different cargo. The studies on transport in the axon led to the naming of kinesin. Myelination In the nervous system, axons may be myelinated, or unmyelinated. This is the provision of an insulating layer, called a myelin sheath. The myelin membrane is unique in its relatively high lipid to protein ratio. In the peripheral nervous system axons are myelinated by glial cells known as Schwann cells. In the central nervous system the myelin sheath is provided by another type of glial cell, the oligodendrocyte. Schwann cells myelinate a single axon. An oligodendrocyte can myelinate up to 50 axons. The composition of myelin is different in the two types. In the CNS the major myelin protein is proteolipid protein, and i
n the PNS it is myelin basic protein. Nodes of Ranvier Nodes of Ranvier also known as myelin sheath gaps are short unmyelinated segments of a myelinated axon, which are found periodically interspersed between segments of the myelin sheath. Therefore, at the point of the node of Ranvier, the axon is reduced in diameter. These nodes are areas where action potentials can be generated. In saltatory conduction, electrical currents produced at each node of Ranvier are conducted with little attenuation to the next node in line, where they remain strong enough to generate another action potential. Thus in a myelinated axon, action potentials effectively "jump" from node to node, bypassing the myelinated stretches in between, resulting in a propagation speed much faster than even the fastest unmyelinated axon can sustain. Axon terminals An axon can divide into many branches called telodendria Greekend of tree. At the end of each telodendron is an axon terminal also called a synaptic bouton, or terminal bouton. Axon
terminals contain synaptic vesicles that store the neurotransmitter for release at the synapse. This makes multiple synaptic connections with other neurons possible. Sometimes the axon of a neuron may synapse onto dendrites of the same neuron, when it is known as an autapse. Action potentials Most axons carry signals in the form of action potentials, which are discrete electrochemical impulses that travel rapidly along an axon, starting at the cell body and terminating at points where the axon makes synaptic contact with target cells. The defining characteristic of an action potential is that it is "allornothing" every action potential that an axon generates has essentially the same size and shape. This allornothing characteristic allows action potentials to be transmitted from one end of a long axon to the other without any reduction in size. There are, however, some types of neurons with short axons that carry graded electrochemical signals, of variable amplitude. When an action potential reaches a pre
synaptic terminal, it activates the synaptic transmission process. The first step is rapid opening of calcium ion channels in the membrane of the axon, allowing calcium ions to flow inward across the membrane. The resulting increase in intracellular calcium concentration causes synaptic vesicles tiny containers enclosed by a lipid membrane filled with a neurotransmitter chemical to fuse with the axon's membrane and empty their contents into the extracellular space. The neurotransmitter is released from the presynaptic nerve through exocytosis. The neurotransmitter chemical then diffuses across to receptors located on the membrane of the target cell. The neurotransmitter binds to these receptors and activates them. Depending on the type of receptors that are activated, the effect on the target cell can be to excite the target cell, inhibit it, or alter its metabolism in some way. This entire sequence of events often takes place in less than a thousandth of a second. Afterward, inside the presynaptic terminal,
a new set of vesicles is moved into position next to the membrane, ready to be released when the next action potential arrives. The action potential is the final electrical step in the integration of synaptic messages at the scale of the neuron. Extracellular recordings of action potential propagation in axons has been demonstrated in freely moving animals. While extracellular somatic action potentials have been used to study cellular activity in freely moving animals such as place cells, axonal activity in both white and gray matter can also be recorded. Extracellular recordings of axon action potential propagation is distinct from somatic action potentials in three ways 1. The signal has a shorter peaktrough duration 150s than of pyramidal cells 500s or interneurons 250s. 2. The voltage change is triphasic. 3. Activity recorded on a tetrode is seen on only one of the four recording wires. In recordings from freely moving rats, axonal signals have been isolated in white matter tracts including the alveus an
d the corpus callosum as well hippocampal gray matter. In fact, the generation of action potentials in vivo is sequential in nature, and these sequential spikes constitute the digital codes in the neurons. Although previous studies indicate an axonal origin of a single spike evoked by shortterm pulses, physiological signals in vivo trigger the initiation of sequential spikes at the cell bodies of the neurons. In addition to propagating action potentials to axonal terminals, the axon is able to amplify the action potentials, which makes sure a secure propagation of sequential action potentials toward the axonal terminal. In terms of molecular mechanisms, voltagegated sodium channels in the axons possess lower threshold and shorter refractory period in response to shortterm pulses. Development and growth Development The development of the axon to its target, is one of the six major stages in the overall development of the nervous system. Studies done on cultured hippocampal neurons suggest that neurons init
ially produce multiple neurites that are equivalent, yet only one of these neurites is destined to become the axon. It is unclear whether axon specification precedes axon elongation or vice versa, although recent evidence points to the latter. If an axon that is not fully developed is cut, the polarity can change and other neurites can potentially become the axon. This alteration of polarity only occurs when the axon is cut at least 10 m shorter than the other neurites. After the incision is made, the longest neurite will become the future axon and all the other neurites, including the original axon, will turn into dendrites. Imposing an external force on a neurite, causing it to elongate, will make it become an axon. Nonetheless, axonal development is achieved through a complex interplay between extracellular signaling, intracellular signaling and cytoskeletal dynamics. Extracellular signaling The extracellular signals that propagate through the extracellular matrix surrounding neurons play a prominent role
in axonal development. These signaling molecules include proteins, neurotrophic factors, and extracellular matrix and adhesion molecules. Netrin also known as UNC6 a secreted protein, functions in axon formation. When the UNC5 netrin receptor is mutated, several neurites are irregularly projected out of neurons and finally a single axon is extended anteriorly. The neurotrophic factors nerve growth factor NGF, brainderived neurotrophic factor BDNF and neurotrophin3 NTF3 are also involved in axon development and bind to Trk receptors. The gangliosideconverting enzyme plasma membrane ganglioside sialidase PMGS, which is involved in the activation of TrkA at the tip of neutrites, is required for the elongation of axons. PMGS asymmetrically distributes to the tip of the neurite that is destined to become the future axon. Intracellular signaling During axonal development, the activity of PI3K is increased at the tip of destined axon. Disrupting the activity of PI3K inhibits axonal development. Activation of PI
3K results in the production of phosphatidylinositol 3,4,5trisphosphate PtdIns which can cause significant elongation of a neurite, converting it into an axon. As such, the overexpression of phosphatases that dephosphorylate PtdIns leads into the failure of polarization. Cytoskeletal dynamics The neurite with the lowest actin filament content will become the axon. PGMS concentration and factin content are inversely correlated; when PGMS becomes enriched at the tip of a neurite, its factin content is substantially decreased. In addition, exposure to actindepolimerizing drugs and toxin B which inactivates Rhosignaling causes the formation of multiple axons. Consequently, the interruption of the actin network in a growth cone will promote its neurite to become the axon. Growth Growing axons move through their environment via the growth cone, which is at the tip of the axon. The growth cone has a broad sheetlike extension called a lamellipodium which contain protrusions called filopodia. The filopodia are the
mechanism by which the entire process adheres to surfaces and explores the surrounding environment. Actin plays a major role in the mobility of this system. Environments with high levels of cell adhesion molecules CAMs create an ideal environment for axonal growth. This seems to provide a "sticky" surface for axons to grow along. Examples of CAM's specific to neural systems include NCAM, TAG1an axonal glycoproteinand MAG, all of which are part of the immunoglobulin superfamily. Another set of molecules called extracellular matrixadhesion molecules also provide a sticky substrate for axons to grow along. Examples of these molecules include laminin, fibronectin, tenascin, and perlecan. Some of these are surface bound to cells and thus act as short range attractants or repellents. Others are difusible ligands and thus can have long range effects. Cells called guidepost cells assist in the guidance of neuronal axon growth. These cells that help axon guidance, are typically other neurons that are sometimes immat
ure. When the axon has completed its growth at its connection to the target, the diameter of the axon can increase by up to five times, depending on the speed of conduction required. It has also been discovered through research that if the axons of a neuron were damaged, as long as the soma the cell body of a neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells. This is also referred to as neuroregeneration. NogoA is a type of neurite outgrowth inhibitory component that is present in the central nervous system myelin membranes found in an axon. It has a crucial role in restricting axonal regeneration in adult mammalian central nervous system. In recent studies, if NogoA is blocked and neutralized, it is possible to induce longdistance axonal regeneration which leads to enhancement of functional recovery in rats and mouse spinal cord. This has yet to be done on humans. A recent study has also found that macrophages activated throu
gh a specific inflammatory pathway activated by the Dectin1 receptor are capable of promoting axon recovery, also however causing neurotoxicity in the neuron. Length regulation Axons vary largely in length from a few micrometers up to meters in some animals. This emphasizes that there must be a cellular length regulation mechanism allowing the neurons both to sense the length of their axons and to control their growth accordingly. It was discovered that motor proteins play an important role in regulating the length of axons. Based on this observation, researchers developed an explicit model for axonal growth describing how motor proteins could affect the axon length on the molecular level. These studies suggest that motor proteins carry signaling molecules from the soma to the growth cone and vice versa whose concentration oscillates in time with a lengthdependent frequency. Classification The axons of neurons in the human peripheral nervous system can be classified based on their physical features and sig
nal conduction properties. Axons were known to have different thicknesses from 0.1 to 20 m and these differences were thought to relate to the speed at which an action potential could travel along the axon its conductance velocity. Erlanger and Gasser proved this hypothesis, and identified several types of nerve fiber, establishing a relationship between the diameter of an axon and its nerve conduction velocity. They published their findings in 1941 giving the first classification of axons. Axons are classified in two systems. The first one introduced by Erlanger and Gasser, grouped the fibers into three main groups using the letters A, B, and C. These groups, group A, group B, and group C include both the sensory fibers afferents and the motor fibres efferents. The first group A, was subdivided into alpha, beta, gamma, and delta fibers A, A, A, and A. The motor neurons of the different motor fibers, were the lower motor neurons alpha motor neuron, beta motor neuron, and gamma motor neuron having the A, A
, and A nerve fibers respectively. Later findings by other researchers identified two groups of Aa fibers that were sensory fibers. These were then introduced into a system that only included sensory fibers though some of these were mixed nerves and were also motor fibers. This system refers to the sensory groups as Types and uses Roman numerals Type Ia, Type Ib, Type II, Type III, and Type IV. Lower motor neurons have two kind of fibers Different sensory receptors innervate different types of nerve fibers. Proprioceptors are innervated by type Ia, Ib and II sensory fibers, mechanoreceptors by type II and III sensory fibers and nociceptors and thermoreceptors by type III and IV sensory fibers. Autonomic The autonomic nervous system has two kinds of peripheral fibers Clinical significance In order of degree of severity, injury to a nerve can be described as neurapraxia, axonotmesis, or neurotmesis. Concussion is considered a mild form of diffuse axonal injury. Axonal injury can also cause central chromat
olysis. The dysfunction of axons in the nervous system is one of the major causes of many inherited neurological disorders that affect both peripheral and central neurons. When an axon is crushed, an active process of axonal degeneration takes place at the part of the axon furthest from the cell body. This degeneration takes place quickly following the injury, with the part of the axon being sealed off at the membranes and broken down by macrophages. This is known as Wallerian degeneration. Dying back of an axon can also take place in many neurodegenerative diseases, particularly when axonal transport is impaired, this is known as Wallerianlike degeneration. Studies suggest that the degeneration happens as a result of the axonal protein NMNAT2, being prevented from reaching all of the axon. Demyelination of axons causes the multitude of neurological symptoms found in the disease multiple sclerosis. Dysmyelination is the abnormal formation of the myelin sheath. This is implicated in several leukodystrophie
s, and also in schizophrenia. A severe traumatic brain injury can result in widespread lesions to nerve tracts damaging the axons in a condition known as diffuse axonal injury. This can lead to a persistent vegetative state. It has been shown in studies on the rat that axonal damage from a single mild traumatic brain injury, can leave a susceptibility to further damage, after repeated mild traumatic brain injuries. A nerve guidance conduit is an artificial means of guiding axon growth to enable neuroregeneration, and is one of the many treatments used for different kinds of nerve injury. History German anatomist Otto Friedrich Karl Deiters is generally credited with the discovery of the axon by distinguishing it from the dendrites. Swiss Rdolf Albert von Klliker and German Robert Remak were the first to identify and characterize the axon initial segment. Klliker named the axon in 1896. LouisAntoine Ranvier was the first to describe the gaps or nodes found on axons and for this contribution these axonal fea
tures are now commonly referred to as the nodes of Ranvier. Santiago Ramn y Cajal, a Spanish anatomist, proposed that axons were the output components of neurons, describing their functionality. Joseph Erlanger and Herbert Gasser earlier developed the classification system for peripheral nerve fibers, based on axonal conduction velocity, myelination, fiber size etc. Alan Hodgkin and Andrew Huxley also employed the squid giant axon 1939 and by 1952 they had obtained a full quantitative description of the ionic basis of the action potential, leading to the formulation of the HodgkinHuxley model. Hodgkin and Huxley were awarded jointly the Nobel Prize for this work in 1963. The formulae detailing axonal conductance were extended to vertebrates in the FrankenhaeuserHuxley equations. The understanding of the biochemical basis for action potential propagation has advanced further, and includes many details about individual ion channels. Other animals The axons in invertebrates have been extensively studied. The lo
ngfin inshore squid, often used as a model organism has the longest known axon. The giant squid has the largest axon known. Its size ranges from a half typically to one millimetre in diameter and is used in the control of its jet propulsion system. The fastest recorded conduction speed of 210 ms, is found in the ensheathed axons of some pelagic Penaeid shrimps and the usual range is between 90 and 200 ms cf 100120 ms for the fastest myelinated vertebrate axon. In other cases as seen in rat studies an axon originates from a dendrite; such axons are said to have "dendritic origin". Some axons with dendritic origin similarly have a "proximal" initial segment that starts directly at the axon origin, while others have a "distal" initial segment, discernibly separated from the axon origin. In many species some of the neurons have axons that emanate from the dendrite and not from the cell body, and these are known as axoncarrying dendrites. In many cases, an axon originates at an axon hillock on the soma; such axon
s are said to have "somatic origin". Some axons with somatic origin have a "proximal" initial segment adjacent the axon hillock, while others have a "distal" initial segment, separated from the soma by an extended axon hillock. See also Electrophysiology Ganglionic eminence Giant axonal neuropathy Neuronal tracing Pioneer axon References External links "Slide 3 Spinal cord" Neurohistology
The ancient Aramaic alphabet was adapted by Arameans from the Phoenician alphabet and became a distinct script by the 8th century BC. It was used to write the Aramaic language and had displaced the PaleoHebrew alphabet, itself a derivative of the Phoenician alphabet, for the writing of Hebrew. The letters all represent consonants, some of which are also used as matres lectionis to indicate long vowels. The Aramaic alphabet is historically significant since virtually all modern Middle Eastern writing systems can be traced back to it as well as numerous nonChinese writing systems of Central and East Asia. That is primarily from the widespread usage of the Aramaic language as both a lingua franca and the official language of the NeoAssyrian and NeoBabylonian Empires, and their successor, the Achaemenid Empire. Among the scripts in modern use, the Hebrew alphabet bears the closest relation to the Imperial Aramaic script of the 5th century BC, with an identical letter inventory and, for the most part, nearly iden
tical letter shapes. The Aramaic alphabet was an ancestor to the Nabataean alphabet and the later Arabic alphabet. Writing systems like the Aramaic one that indicate consonants but do not indicate most vowels other than by means of matres lectionis or added diacritical signs, have been called abjads by Peter T. Daniels to distinguish them from alphabets, such as the Greek alphabet, which represent vowels more systematically. The term was coined to avoid the notion that a writing system that represents sounds must be either a syllabary or an alphabet, which would imply that a system like Aramaic must be either a syllabary as argued by Ignace Gelb or an incomplete or deficient alphabet as most other writers have said. Rather, it is a different type. Origins The earliest inscriptions in the Aramaic language use the Phoenician alphabet. Over time, the alphabet developed into the form shown below. Aramaic gradually became the lingua franca throughout the Middle East, with the script at first complementing and t
hen displacing Assyrian cuneiform, as the predominant writing system. Achaemenid Empire The First Persian Empire Around 500 BC, following the Achaemenid conquest of Mesopotamia under Darius I, Old Aramaic was adopted by the Persians as the "vehicle for written communication between the different regions of the vast Persian empire with its different peoples and languages. The use of a single official language, which modern scholarship has dubbed as Official Aramaic, Imperial Aramaic or Achaemenid Aramaic, can be assumed to have greatly contributed to the astonishing success of the Achaemenid Persians in holding their farflung empire together for as long as they did." Imperial Aramaic was highly standardised; its orthography was based more on historical roots than any spoken dialect and was inevitably influenced by Old Persian. The Aramaic glyph forms of the period are often divided into two main styles, the "lapidary" form, usually inscribed on hard surfaces like stone monuments, and a cursive form whose l
apidary form tended to be more conservative by remaining more visually similar to Phoenician and early Aramaic. Both were in use through the Achaemenid Persian period, but the cursive form steadily gained ground over the lapidary, which had largely disappeared by the 3rd century BC. For centuries after the fall of the Achaemenid Empire in 331 BC, Imperial Aramaic, or something near enough to it to be recognisable, would remain an influence on the various native Iranian languages. The Aramaic script would survive as the essential characteristics of the Iranian Pahlavi writing system. 30 Aramaic documents from Bactria have been recently discovered, an analysis of which was published in November 2006. The texts, which were rendered on leather, reflect the use of Aramaic in the 4th century BC in the Persian Achaemenid administration of Bactria and Sogdiana. The widespread usage of Achaemenid Aramaic in the Middle East led to the gradual adoption of the Aramaic alphabet for writing Hebrew. Formerly, Hebrew had
been written using an alphabet closer in form to that of Phoenician, the PaleoHebrew alphabet. Aramaicderived scripts Since the evolution of the Aramaic alphabet out of the Phoenician one was a gradual process, the division of the world's alphabets into the ones derived from the Phoenician one directly and the ones derived from Phoenician via Aramaic is somewhat artificial. In general, the alphabets of the Mediterranean region Anatolia, Greece, Italy are classified as Phoenicianderived, adapted from around the 8th century BC, and those of the East the Levant, Persia, Central Asia and India are considered Aramaicderived, adapted from around the 6th century BC from the Imperial Aramaic script of the Achaemenid Empire. After the fall of the Achaemenid Empire, the unity of the Imperial Aramaic script was lost, diversifying into a number of descendant cursives. The Hebrew and Nabataean alphabets, as they stood by the Roman era, were little changed in style from the Imperial Aramaic alphabet. Ibn Khaldun 133214
06 alleges that not only the old Nabataean writing was influenced by the "Syrian script" i.e. Aramaic, but also the old Chaldean script. A cursive Hebrew variant developed from the early centuries AD, but it remained restricted to the status of a variant used alongside the noncursive. By contrast, the cursive developed out of the Nabataean alphabet in the same period soon became the standard for writing Arabic, evolving into the Arabic alphabet as it stood by the time of the early spread of Islam. The development of cursive versions of Aramaic also led to the creation of the Syriac, Palmyrene and Mandaic alphabets, which formed the basis of the historical scripts of Central Asia, such as the Sogdian and Mongolian alphabets. The Old Turkic script is generally considered to have its ultimate origins in Aramaic, in particular via the Pahlavi or Sogdian alphabets, as suggested by V. Thomsen, or possibly via Kharosthi cf., Issyk inscription. Brahmi script was also possibly derived or inspired by Aramaic. Brahm
ic family of scripts includes Devanagari. Languages using the alphabet Today, Biblical Aramaic, Jewish NeoAramaic dialects and the Aramaic language of the Talmud are written in the modernHebrew alphabet distinguished from the Old Hebrew script. In classical Jewish literature, the name given to the modernHebrew script was "Ashurit" the ancient Assyrian script, a script now known widely as the Aramaic script. It is believed that during the period of Assyrian dominion that Aramaic script and language received official status. Syriac and Christian NeoAramaic dialects are today written in the Syriac alphabet, which script has superseded the more ancient Assyrian script and now bears its name. Mandaic is written in the Mandaic alphabet. The nearidentical nature of the Aramaic and the classical Hebrew alphabets caused Aramaic text to be typeset mostly in the standard Hebrew script in scholarly literature. Maaloula In Maaloula, one of few surviving communities in which a Western Aramaic dialect is still spoken, an
Aramaic institute was established in 2007 by Damascus University that teaches courses to keep the language alive. The institute's activities were suspended in 2010 amidst fears that the square Aramaic alphabet used in the program too closely resembled the square script of the Hebrew alphabet and all the signs with the square Aramaic script were taken down. The program stated that they would instead use the more distinct Syriac alphabet, although use of the Aramaic alphabet has continued to some degree. Al Jazeera Arabic also broadcast a program about Western NeoAramaic and the villages in which it is spoken with the square script still in use. Letters Matres lectionis In Aramaic writing, Waw and Yodh serve a double function. Originally, they represented only the consonants w and y, but they were later adopted to indicate the long vowels and respectively as well often also and respectively. In the latter role, they are known as or "mothers of reading". lap, likewise, has some of the characteristics o
f a because in initial positions, it indicates a glottal stop followed by a vowel, but otherwise, it often also stands for the long vowels or . Among Jews, the influence of Hebrew often led to the use of H instead, at the end of a word. The practice of using certain letters to hold vowel values spread to Aramaicderived writing systems, such as in Arabic and Hebrew, which still follow the practice. Unicode The Imperial Aramaic alphabet was added to the Unicode Standard in October 2009, with the release of version 5.2. The Unicode block for Imperial Aramaic is U10840U1085F The Syriac Aramaic alphabet was added to the Unicode Standard in September 1999, with the release of version 3.0. The Syriac Abbreviation a type of overline can be represented with a special control character called the Syriac Abbreviation Mark U070F. The Unicode block for Syriac Aramaic is U0700U074F See also Syriac alphabet References Sources Byrne, Ryan. "Middle Aramaic Scripts". Encyclopaedia of Language and Linguistics. Elsev
ier. 2006 Daniels, Peter T., et al. eds. The World's Writing Systems. Oxford. 1996 Coulmas, Florian. The Writing Systems of the World. Blackwell Publishers Ltd, Oxford. 1989 Rudder, Joshua. Learn to Write Aramaic A StepbyStep Approach to the Historical Modern Scripts. n.p. CreateSpace Independent Publishing Platform, 2011. 220 pp. . Includes a wide variety of Aramaic scripts. Ancient Hebrew and Aramaic on Coins, reading and transliterating ProtoHebrew, online edition Judaea Coin Archive. External links Comparison of Aramaic to related alphabets Omniglot entry 8thcentury BC establishments Obsolete writing systems Persian scripts Righttoleft writing systems
"American shot" or "cowboy shot" is a translation of a phrase from French film criticism, plan amricain, and refers to a mediumlong "knee" film shot of a group of characters, who are arranged so that all are visible to the camera. The usual arrangement is for the actors to stand in an irregular line from one side of the screen to the other, with the actors at the end coming forward a little and standing more in profile than the others. The purpose of the composition is to allow complex dialogue scenes to be played out without changes in camera position. In some literature, this is simply referred to as a 34 shot. One of the other main reasons why French critics called it "American shot" was its frequent use in western genre. This was because a shot that started at knee level would reveal the weapon of a cowboy, usually holstered at his waist. It is actually the closest the camera can get to an actor while keeping both his face and his holstered gun in frame. The French critics thought it was characteristic
of American films of the 1930s or 1940s; however, it was mostly characteristic of cheaper American movies, such as Charlie Chan mysteries where people collected in front of a fireplace or at the foot of the stairs in order to explain what happened a few minutes ago. Howard Hawks legitimized this style in his films, allowing characters to act, even when not talking, when most of the audience would not be paying attention. It became his trademark style. References Cinematography
Acute disseminated encephalomyelitis ADEM, or acute demyelinating encephalomyelitis, is a rare autoimmune disease marked by a sudden, widespread attack of inflammation in the brain and spinal cord. As well as causing the brain and spinal cord to become inflamed, ADEM also attacks the nerves of the central nervous system and damages their myelin insulation, which, as a result, destroys the white matter. It is often triggered by a viral infection or very rarely vaccinations. ADEM's symptoms resemble the symptoms of multiple sclerosis MS, so the disease itself is sorted into the classification of the multiple sclerosis borderline diseases. However, ADEM has several features that distinguish it from MS. Unlike MS, ADEM occurs usually in children and is marked with rapid fever, although adolescents and adults can get the disease too. ADEM consists of a single flareup whereas MS is marked with several flareups or relapses, over a long period of time. Relapses following ADEM are reported in up to a quarter of patie
nts, but the majority of these 'multiphasic' presentations following ADEM likely represent MS. ADEM is also distinguished by a loss of consciousness, coma and death, which is very rare in MS, except in severe cases. It affects about 8 per 1,000,000 people per year. Although it occurs in all ages, most reported cases are in children and adolescents, with the average age around 5 to 8 years old. The disease affects males and females almost equally. ADEM shows seasonal variation with higher incidence in winter and spring months which may coincide with higher viral infections during these months. The mortality rate may be as high as 5; however, full recovery is seen in 50 to 75 of cases with increase in survival rates up to 70 to 90 with figures including minor residual disability as well. The average time to recover from ADEM flareups is one to six months. ADEM produces multiple inflammatory lesions in the brain and spinal cord, particularly in the white matter. Usually these are found in the subcortical and c
entral white matter and cortical graywhite junction of both cerebral hemispheres, cerebellum, brainstem, and spinal cord, but periventricular white matter and gray matter of the cortex, thalami and basal ganglia may also be involved. When a person has more than one demyelinating episode of ADEM, the disease is then called recurrent disseminated encephalomyelitis or multiphasic disseminated encephalomyelitis MDEM. Also, a fulminant course in adults has been described. Signs and symptoms ADEM has an abrupt onset and a monophasic course. Symptoms usually begin 13 weeks after infection. Major symptoms include fever, headache, nausea and vomiting, confusion, vision impairment, drowsiness, seizures and coma. Although initially the symptoms are usually mild, they worsen rapidly over the course of hours to days, with the average time to maximum severity being about four and a half days. Additional symptoms include hemiparesis, paraparesis, and cranial nerve palsies. ADEM in COVID19 Neurological symptoms were the
main presentation of COVID19, which did not correlate with the severity of respiratory symptoms. The high incidence of ADEM with hemorrhage is striking. Brain inflammation is likely caused by an immune response to the disease rather than neurotropism. CSF analysis was not indicative of an infectious process, neurological impairment was not present in the acute phase of the infection, and neuroimaging findings were not typical of classical toxic and metabolic disorders. The finding of bilateral periventricular relatively asymmetrical lesions allied with deep white matter involvement, that may also be present in cortical graywhite matter junction, thalami, basal ganglia, cerebellum, and brainstem suggests an acute demyelination process. Additionally, hemorrhagic white matter lesions, clusters of macrophages related to axonal injury and ADEMlike appearance were also found in subcortical white matter. Causes Since the discovery of the antiMOG specificity against multiple sclerosis diagnosis it is considered that
ADEM is one of the possible clinical causes of antiMOG associated encephalomyelitis About how the antiMOG antibodies appear in the patients serum there are several theories A preceding antigenic challenge can be identified in approximately twothirds of people. Some viral infections thought to induce ADEM include influenza virus, dengue, enterovirus, measles, mumps, rubella, varicella zoster, EpsteinBarr virus, cytomegalovirus, herpes simplex virus, hepatitis A, coxsackievirus and COVID19. Bacterial infections include Mycoplasma pneumoniae, Borrelia burgdorferi, Leptospira, and betahemolytic Streptococci. Exposure to vaccines The only vaccine proven related to ADEM is the Semple form of the rabies vaccine, but hepatitis B, pertussis, diphtheria, measles, mumps, rubella, pneumococcus, varicella, influenza, Japanese encephalitis, and polio vaccines have all been implicated. The majority of the studies that correlate vaccination with ADEM onset use small samples or case studies. Large scale epidemiological st
udies e.g., of MMR vaccine or smallpox vaccine do not show increased risk of ADEM following vaccination. An upper bound for the risk of ADEM from measles vaccination, if it exists, can be estimated to be 10 per million, which is far lower than the risk of developing ADEM from an actual measles infection, which is about 1 per 1,000 cases. For a rubella infection, the risk is 1 per 5,000 cases. Some early vaccines, later shown to have been contaminated with host animal CNS tissue, had ADEM incident rates as high as 1 in 600. In rare cases, ADEM seems to follow from organ transplantation. Diagnosis ADEM term has been inconsistently used at different times. Currently, the commonly accepted international standard for the clinical case definition is the one published by the International Pediatric MS Study Group, revision 2007. Given that the definition is clinical, it is currently unknown if all the cases with ADEM are positive for antiMOG autoantibody, but in any case, it seems strongly related to ADEM diagno
sis. Differential diagnosis Multiple sclerosis While ADEM and MS both involve autoimmune demyelination, they differ in many clinical, genetic, imaging, and histopathological aspects. Some authors consider MS and its borderline forms to constitute a spectrum, differing only in chronicity, severity, and clinical course, while others consider them discretely different diseases. Typically, ADEM appears in children following an antigenic challenge and remains monophasic. Nevertheless, ADEM does occur in adults, and can also be clinically multiphasic. Problems for differential diagnosis increase due to the lack of agreement for a definition of multiple sclerosis. If MS were defined just by the separation in time and space of the demyelinating lesions as McDonald did, it would not be enough to make a difference, as some cases of ADEM satisfy these conditions. Therefore, some authors propose to establish the separation line in the shape of the lesions around the veins, being therefore "perivenous vs. confluent de
myelination". The pathology of ADEM is very similar to that of MS with some differences. The pathological hallmark of ADEM is perivenular inflammation with limited "sleeves of demyelination". Nevertheless, MSlike plaques confluent demyelination can appear Plaques in the white matter in MS are sharply delineated, while the glial scar in ADEM is smooth. Axons are better preserved in ADEM lesions. Inflammation in ADEM is widely disseminated and illdefined, and finally, lesions are strictly perivenous, while in MS they are disposed around veins, but not so sharply. Nevertheless, the cooccurrence of perivenous and confluent demyelination in some individuals suggests pathogenic overlap between acute disseminated encephalomyelitis and multiple sclerosis and misclassification even with biopsy or even postmortem ADEM in adults can progress to MS Multiphasic disseminated encephalomyelitis When the person has more than one demyelinating episode of ADEM, the disease is then called recurrent disseminated encephalomy
elitis or multiphasic disseminated encephalomyelitis MDEM. It has been found that antiMOG autoantibodies are related to this kind of ADEM Another variant of ADEM in adults has been described, also related to antiMOG autoantibodies, has been named fulminant disseminated encephalomyelitis, and it has been reported to be clinically ADEM, but showing MSlike lesions on autopsy. It has been classified inside the antiMOG associated inflammatory demyelinating diseases. Acute hemorrhagic leukoencephalitis Acute hemorrhagic leukoencephalitis AHL, or AHLE, acute hemorrhagic encephalomyelitis AHEM, acute necrotizing hemorrhagic leukoencephalitis ANHLE, WestonHurst syndrome, or Hurst's disease, is a hyperacute and frequently fatal form of ADEM. AHL is relatively rare less than 100 cases have been reported in the medical literature , it is seen in about 2 of ADEM cases, and is characterized by necrotizing vasculitis of venules and hemorrhage, and edema. Death is common in the first week and overall mortality is about 7
0, but increasing evidence points to favorable outcomes after aggressive treatment with corticosteroids, immunoglobulins, cyclophosphamide, and plasma exchange. About 70 of survivors show residual neurological deficits, but some survivors have shown surprisingly little deficit considering the magnitude of the white matter affected. This disease has been occasionally associated with ulcerative colitis and Crohn's disease, malaria, sepsis associated with immune complex deposition, methanol poisoning, and other underlying conditions. Also anecdotal association with MS has been reported Laboratory studies that support diagnosis of AHL are peripheral leukocytosis, cerebrospinal fluid CSF pleocytosis associated with normal glucose and increased protein. On magnetic resonance imaging MRI, lesions of AHL typically show extensive T2weighted and fluidattenuated inversion recovery FLAIR white matter hyperintensities with areas of hemorrhages, significant edema, and mass effect. Treatment No controlled clinical trials
have been conducted on ADEM treatment, but aggressive treatment aimed at rapidly reducing inflammation of the CNS is standard. The widely accepted firstline treatment is high doses of intravenous corticosteroids, such as methylprednisolone or dexamethasone, followed by 36 weeks of gradually lower oral doses of prednisolone. Patients treated with methylprednisolone have shown better outcomes than those treated with dexamethasone. Oral tapers of less than three weeks duration show a higher chance of relapsing, and tend to show poorer outcomes. Other antiinflammatory and immunosuppressive therapies have been reported to show beneficial effect, such as plasmapheresis, high doses of intravenous immunoglobulin IVIg, mitoxantrone and cyclophosphamide. These are considered alternative therapies, used when corticosteroids cannot be used or fail to show an effect. There is some evidence to suggest that patients may respond to a combination of methylprednisolone and immunoglobulins if they fail to respond to either se
parately In a study of 16 children with ADEM, 10 recovered completely after highdose methylprednisolone, one severe case that failed to respond to steroids recovered completely after IV Ig; the five most severe cases with ADAM and severe peripheral neuropathy were treated with combined highdose methylprednisolone and immunoglobulin, two remained paraplegic, one had motor and cognitive handicaps, and two recovered. A recent review of IVIg treatment of ADEM of which the previous study formed the bulk of the cases found that 70 of children showed complete recovery after treatment with IVIg, or IVIg plus corticosteroids. A study of IVIg treatment in adults with ADEM showed that IVIg seems more effective in treating sensory and motor disturbances, while steroids seem more effective in treating impairments of cognition, consciousness and rigor. This same study found one subject, a 71yearold man who had not responded to steroids, that responded to an IVIg treatment 58 days after disease onset. Prognosis Full reco
very is seen in 50 to 70 of cases, ranging to 70 to 90 recovery with some minor residual disability typically assessed using measures such as mRS or EDSS, average time to recover is one to six months. The mortality rate may be as high as 510. Poorer outcomes are associated with unresponsiveness to steroid therapy, unusually severe neurological symptoms, or sudden onset. Children tend to have more favorable outcomes than adults, and cases presenting without fevers tend to have poorer outcomes. The latter effect may be due to either protective effects of fever, or that diagnosis and treatment is sought more rapidly when fever is present. ADEM can progress to MS. It will be considered MS if some lesions appear in different times and brain areas Motor deficits Residual motor deficits are estimated to remain in about 8 to 30 of cases, the range in severity from mild clumsiness to ataxia and hemiparesis. Neurocognitive Patients with demyelinating illnesses, such as MS, have shown cognitive deficits even when the
re is minimal physical disability. Research suggests that similar effects are seen after ADEM, but that the deficits are less severe than those seen in MS. A study of six children with ADEM mean age at presentation 7.7 years were tested for a range of neurocognitive tests after an average of 3.5 years of recovery. All six children performed in the normal range on most tests, including verbal IQ and performance IQ, but performed at least one standard deviation below age norms in at least one cognitive domain, such as complex attention one child, shortterm memory one child and internalizing behaviouraffect two children. Group means for each cognitive domain were all within one standard deviation of age norms, demonstrating that, as a group, they were normal. These deficits were less severe than those seen in similar aged children with a diagnosis of MS. Another study compared nineteen children with a history of ADEM, of which 10 were five years of age or younger at the time average age 3.8 years old, tested an
average of 3.9 years later and nine were older mean age 7.7y at time of ADEM, tested an average of 2.2 years later to nineteen matched controls. Scores on IQ tests and educational achievement were lower for the young onset ADEM group average IQ 90 compared to the late onset average IQ 100 and control groups average IQ 106, while the late onset ADEM children scored lower on verbal processing speed. Again, all groups means were within one standard deviation of the controls, meaning that while effects were statistically reliable, the children were as a whole, still within the normal range. There were also more behavioural problems in the early onset group, although there is some suggestion that this may be due, at least in part, to the stress of hospitalization at a young age. Research The relationship between ADEM and antiMOG associated encephalomyelitis is currently under research. A new entity called MOGDEM has been proposed. About animal models, the main animal model for MS, experimental autoimmune encep
halomyelitis EAE is also an animal model for ADEM. Being an acute monophasic illness, EAE is far more similar to ADEM than MS. See also Optic neuritis Transverse myelitis Victoria Arlen References External links Information for parents about Acute disseminated encephalomyelitis Multiple sclerosis Autoimmune diseases Central nervous system disorders Enterovirusassociated diseases Measles
Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum. Ataxia can be limited to one side of the body, which is referred to as hemiataxia. Several possible causes exist for these patterns of neurological dysfunction. Dystaxia is a mild degree of ataxia. Friedreich's ataxia has gait abnormality as the most commonly presented symptom. The word is from Greek a negative prefix order "lack of order". Types Cerebellar The term cerebellar ataxia is used to indicate ataxia due to dysfunction of the cerebellum. The cerebellum is responsible for integrating a significant amount of neural information that is used to coordinate smoothly ongoing movements and to participate in motor planning. Although ataxia is not present with all cerebellar lesions
, many conditions affecting the cerebellum do produce ataxia. People with cerebellar ataxia may have trouble regulating the force, range, direction, velocity, and rhythm of muscle contractions. This results in a characteristic type of irregular, uncoordinated movement that can manifest itself in many possible ways, such as asthenia, asynergy, delayed reaction time, and dyschronometria. Individuals with cerebellar ataxia could also display instability of gait, difficulty with eye movements, dysarthria, dysphagia, hypotonia, dysmetria, and dysdiadochokinesia. These deficits can vary depending on which cerebellar structures have been damaged, and whether the lesion is bi or unilateral. People with cerebellar ataxia may initially present with poor balance, which could be demonstrated as an inability to stand on one leg or perform tandem gait. As the condition progresses, walking is characterized by a widened base and high stepping, as well as staggering and lurching from side to side. Turning is also problematic
and could result in falls. As cerebellar ataxia becomes severe, great assistance and effort are needed to stand and walk. Dysarthria, an impairment with articulation, may also be present and is characterized by "scanning" speech that consists of slower rate, irregular rhythm, and variable volume. Also, slurring of speech, tremor of the voice, and ataxic respiration may occur. Cerebellar ataxia could result with incoordination of movement, particularly in the extremities. Overshooting or hypermetria occurs with fingertonose testing and heel to shin testing; thus, dysmetria is evident. Impairments with alternating movements dysdiadochokinesia, as well as dysrhythmia, may also be displayed. Tremor of the head and trunk titubation may be seen in individuals with cerebellar ataxia. Dysmetria is thought to be caused by a deficit in the control of interaction torques in multijoint motion. Interaction torques are created at an associated joint when the primary joint is moved. For example, if a movement required rea
ching to touch a target in front of the body, flexion at the shoulder would create a torque at the elbow, while extension of the elbow would create a torque at the wrist. These torques increase as the speed of movement increases and must be compensated and adjusted for to create coordinated movement. This may, therefore, explain decreased coordination at higher movement velocities and accelerations. Dysfunction of the vestibulocerebellum flocculonodular lobe impairs balance and the control of eye movements. This presents itself with postural instability, in which the person tends to separate hisher feet upon standing, to gain a wider base and to avoid titubation bodily oscillations tending to be forwardbackward ones. The instability is, therefore, worsened when standing with the feet together, regardless of whether the eyes are open or closed. This is a negative Romberg's test, or more accurately, it denotes the individual's inability to carry out the test, because the individual feels unstable even with ope
n eyes. Dysfunction of the spinocerebellum vermis and associated areas near the midline presents itself with a widebased "drunken sailor" gait called truncal ataxia, characterised by uncertain starts and stops, lateral deviations, and unequal steps. As a result of this gait impairment, falling is a concern in patients with ataxia. Studies examining falls in this population show that 7493 of patients have fallen at least once in the past year and up to 60 admit to fear of falling. 'Dysfunction of the cerebrocerebellum' lateral hemispheres presents as disturbances in carrying out voluntary, planned movements by the extremities called appendicular ataxia. These include Intention tremor coarse trembling, accentuated over the execution of voluntary movements, possibly involving the head and eyes, as well as the limbs and torso Peculiar writing abnormalities large, unequal letters, irregular underlining A peculiar pattern of dysarthria slurred speech, sometimes characterised by explosive variations in voice int
ensity despite a regular rhythm Inability to perform rapidly alternating movements, known as dysdiadochokinesia, occurs, and could involve rapidly switching from pronation to supination of the forearm. Movements become more irregular with increases of speed. Inability to judge distances or ranges of movement happens. This dysmetria is often seen as undershooting, hypometria, or overshooting, hypermetria, the required distance or range to reach a target. This is sometimes seen when a patient is asked to reach out and touch someone's finger or touch his or her own nose. The rebound phenomenon, also known as the loss of the check reflex, is also sometimes seen in patients with cerebellar ataxia, for example, when patients are flexing their elbows isometrically against a resistance. When the resistance is suddenly removed without warning, the patients' arms may swing up and even strike themselves. With an intact check reflex, the patients check and activate the opposing triceps to slow and stop the movement. Pat
ients may exhibit a constellation of subtle to overt cognitive symptoms, which are gathered under the terminology of Schmahmann's syndrome. Sensory The term sensory ataxia is used to indicate ataxia due to loss of proprioception, the loss of sensitivity to the positions of joint and body parts. This is generally caused by dysfunction of the dorsal columns of the spinal cord, because they carry proprioceptive information up to the brain. In some cases, the cause of sensory ataxia may instead be dysfunction of the various parts of the brain that receive positional information, including the cerebellum, thalamus, and parietal lobes. Sensory ataxia presents itself with an unsteady "stomping" gait with heavy heel strikes, as well as a postural instability that is usually worsened when the lack of proprioceptive input cannot be compensated for by visual input, such as in poorly lit environments. Physicians can find evidence of sensory ataxia during physical examination by having patients stand with their feet t
ogether and eyes shut. In affected patients, this will cause the instability to worsen markedly, producing wide oscillations and possibly a fall; this is called a positive Romberg's test. Worsening of the fingerpointing test with the eyes closed is another feature of sensory ataxia. Also, when patients are standing with arms and hands extended toward the physician, if the eyes are closed, the patients' fingers tend to "fall down" and then be restored to the horizontal extended position by sudden muscular contractions the "ataxic hand". Vestibular The term vestibular ataxia is used to indicate ataxia due to dysfunction of the vestibular system, which in acute and unilateral cases is associated with prominent vertigo, nausea, and vomiting. In slowonset, chronic bilateral cases of vestibular dysfunction, these characteristic manifestations may be absent, and dysequilibrium may be the sole presentation. Causes The three types of ataxia have overlapping causes, so can either coexist or occur in isolation. Cere
bellar ataxia can have many causes despite normal neuroimaging. Focal lesions Any type of focal lesion of the central nervous system such as stroke, brain tumor, multiple sclerosis, inflammatory such as sarcoidosis, and "chronic lymphocytyc inflammation with pontine perivascular enhancement responsive to steroids syndrome" CLIPPERS will cause the type of ataxia corresponding to the site of the lesion cerebellar if in the cerebellum; sensory if in the dorsal spinal cord...to include cord compression by thickened ligamentum flavum or stenosis of the boney spinal canal...and rarely in the thalamus or parietal lobe; or vestibular if in the vestibular system including the vestibular areas of the cerebral cortex. Exogenous substances metabolic ataxia Exogenous substances that cause ataxia mainly do so because they have a depressant effect on central nervous system function. The most common example is ethanol alcohol, which is capable of causing reversible cerebellar and vestibular ataxia. Chronic intake of etha
nol causes atrophy of the cerebellum by oxidative and endoplasmic reticulum stresses induced by thiamine deficiency. Other examples include various prescription drugs e.g. most antiepileptic drugs have cerebellar ataxia as a possible adverse effect, Lithium level over 1.5mEqL, synthetic cannabinoid HU211 ingestion and various other medical and recreational drugs e.g. ketamine, PCP or dextromethorphan, all of which are NMDA receptor antagonists that produce a dissociative state at high doses. A further class of pharmaceuticals which can cause short term ataxia, especially in high doses, are benzodiazepines. Exposure to high levels of methylmercury, through consumption of fish with high mercury concentrations, is also a known cause of ataxia and other neurological disorders. Radiation poisoning Ataxia can be induced as a result of severe acute radiation poisoning with an absorbed dose of more than 30 grays. Vitamin B12 deficiency Vitamin B12 deficiency may cause, among several neurological abnormalities, o
verlapping cerebellar and sensory ataxia. Hypothyroidism Symptoms of neurological dysfunction may be the presenting feature in some patients with hypothyroidism. These include reversible cerebellar ataxia, dementia, peripheral neuropathy, psychosis and coma. Most of the neurological complications improve completely after thyroid hormone replacement therapy. Causes of isolated sensory ataxia Peripheral neuropathies may cause generalised or localised sensory ataxia e.g. a limb only depending on the extent of the neuropathic involvement. Spinal disorders of various types may cause sensory ataxia from the lesioned level below, when they involve the dorsal columns. Nonhereditary cerebellar degeneration Nonhereditary causes of cerebellar degeneration include chronic alcohol use disorder, head injury, paraneoplastic and nonparaneoplastic autoimmune ataxia, high altitude cerebral oedema, coeliac disease, normal pressure hydrocephalus and infectious or postinfectious cerebellitis. Hereditary ataxias Ataxia may
depend on hereditary disorders consisting of degeneration of the cerebellum or of the spine; most cases feature both to some extent, and therefore present with overlapping cerebellar and sensory ataxia, even though one is often more evident than the other. Hereditary disorders causing ataxia include autosomal dominant ones such as spinocerebellar ataxia, episodic ataxia, and dentatorubropallidoluysian atrophy, as well as autosomal recessive disorders such as Friedreich's ataxia sensory and cerebellar, with the former predominating and Niemann Pick disease, ataxiatelangiectasia sensory and cerebellar, with the latter predominating, and abetalipoproteinaemia. An example of Xlinked ataxic condition is the rare fragile Xassociated tremorataxia syndrome or FXTAS. ArnoldChiari malformation congenital ataxia ArnoldChiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla through the foramen magnum, sometimes causing hydrocephalus as a resu

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