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144-621: Paralysis is most often caused by damage in the nervous system , especially the spinal cord . Other major causes are stroke , trauma with nerve injury , poliomyelitis , cerebral palsy , peripheral neuropathy , Parkinson's disease , ALS , botulism , spina bifida , multiple sclerosis , and Guillain–Barré syndrome . Temporary paralysis occurs during REM sleep , and dysregulation of this system can lead to episodes of waking paralysis . Drugs that interfere with nerve function , such as curare , can also cause paralysis. Pseudoparalysis ( pseudo- meaning "false, not genuine", from Greek ψεῦδος)

288-537: A connectome including its synapses. Every neuron and its cellular lineage has been recorded and most, if not all, of the neural connections are known. In this species, the nervous system is sexually dimorphic ; the nervous systems of the two sexes, males and female hermaphrodites , have different numbers of neurons and groups of neurons that perform sex-specific functions. In C. elegans , males have exactly 383 neurons, while hermaphrodites have exactly 302 neurons. Arthropods , such as insects and crustaceans , have

432-457: A nerve net , a diffuse network of isolated cells. In bilaterian animals, which make up the great majority of existing species, the nervous system has a common structure that originated early in the Ediacaran period, over 550 million years ago. The nervous system contains two main categories or types of cells: neurons and glial cells . The nervous system is defined by the presence of

576-399: A sensory input and ends with a motor output, passing through a sequence of neurons connected in series . This can be shown in the "withdrawal reflex" causing a hand to jerk back after a hot stove is touched. The circuit begins with sensory receptors in the skin that are activated by harmful levels of heat: a special type of molecular structure embedded in the membrane causes heat to change

720-408: A Mauthner cell are so powerful that a single action potential gives rise to a major behavioral response: within milliseconds the fish curves its body into a C-shape , then straightens, thereby propelling itself rapidly forward. Functionally this is a fast escape response, triggered most easily by a strong sound wave or pressure wave impinging on the lateral line organ of the fish. Mauthner cells are not

864-401: A capability for neurons to exchange signals with each other. Networks formed by interconnected groups of neurons are capable of a wide variety of functions, including feature detection, pattern generation and timing, and there are seen to be countless types of information processing possible. Warren McCulloch and Walter Pitts showed in 1943 that even artificial neural networks formed from

1008-400: A cell can send signals to other cells. One is by releasing chemicals called hormones into the internal circulation, so that they can diffuse to distant sites. In contrast to this "broadcast" mode of signaling, the nervous system provides "point-to-point" signals—neurons project their axons to specific target areas and make synaptic connections with specific target cells. Thus, neural signaling

1152-564: A central nervous system. In most jellyfish the nerve net is spread more or less evenly across the body; in comb jellies it is concentrated near the mouth. The nerve nets consist of sensory neurons, which pick up chemical, tactile, and visual signals; motor neurons, which can activate contractions of the body wall; and intermediate neurons, which detect patterns of activity in the sensory neurons and, in response, send signals to groups of motor neurons. In some cases groups of intermediate neurons are clustered into discrete ganglia . The development of

1296-423: A certain pattern. Most paralyses caused by nervous-system damage (e.g., spinal cord injuries ) are constant in nature; however, some forms of periodic paralysis , including sleep paralysis , are caused by other factors. Paralysis can occur in newborns due to a congenital defect known as spina bifida . Spina bifida causes one or more of the vertebrae to fail to form vertebral arches within the infant, which allows

1440-432: A chemically gated ion channel is activated, it forms a passage that allows specific types of ions to flow across the membrane. Depending on the type of ion, the effect on the target cell may be excitatory or inhibitory. When a second messenger system is activated, it starts a cascade of molecular interactions inside the target cell, which may ultimately produce a wide variety of complex effects, such as increasing or decreasing

1584-595: A child will be born with dwarfism. Dwarfism resulting from malnutrition or a hormonal abnormality may be treated with an appropriate diet or hormonal therapy. Growth hormone deficiency may be remedied via injections of human growth hormone (HGH) during early life. Genetic mutations of most forms of dwarfism caused by bone dysplasia cannot be altered yet, so therapeutic interventions are typically aimed at preventing or reducing pain or physical disability, increasing adult height, or mitigating psychosocial stresses and enhancing social adaptation. Forms of dwarfism associated with

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1728-402: A command neuron has, however, become controversial, because of studies showing that some neurons that initially appeared to fit the description were really only capable of evoking a response in a limited set of circumstances. At the most basic level, the function of the nervous system is to send signals from one cell to others, or from one part of the body to others. There are multiple ways that

1872-489: A common wormlike ancestor that appear as fossils beginning in the Ediacaran period, 550–600 million years ago. The fundamental bilaterian body form is a tube with a hollow gut cavity running from mouth to anus, and a nerve cord with an enlargement (a "ganglion") for each body segment, with an especially large ganglion at the front, called the "brain". Even mammals, including humans, show the segmented bilaterian body plan at

2016-478: A corresponding temporally structured stimulus, is called a central pattern generator . Internal pattern generation operates on a wide range of time scales, from milliseconds to hours or longer. One of the most important types of temporal pattern is circadian rhythmicity —that is, rhythmicity with a period of approximately 24 hours. All animals that have been studied show circadian fluctuations in neural activity, which control circadian alternations in behavior such as

2160-511: A divine manifestation, with records indicating that they were able to reach high positions in society at the time. The ancient Hindu text Bhagavat Purana devotes nine chapters to the adventures of Vamana , a dwarf avatar of Lord Vishnu. Depictions of dwarfism are also found in European paintings and many illustrations. Many European paintings (especially Spanish ) of the 16th–19th centuries depict dwarfs by themselves or with others. In

2304-556: A greatly simplified mathematical abstraction of a neuron are capable of universal computation . Historically, for many years the predominant view of the function of the nervous system was as a stimulus-response associator. In this conception, neural processing begins with stimuli that activate sensory neurons, producing signals that propagate through chains of connections in the spinal cord and brain, giving rise eventually to activation of motor neurons and thereby to muscle contraction, i.e., to overt responses. Descartes believed that all of

2448-487: A group of proteins that cluster together to form a structure resembling a postsynaptic density (the signal-receiving part of a synapse). However, the function of this structure is currently unclear. Although sponge cells do not show synaptic transmission, they do communicate with each other via calcium waves and other impulses, which mediate some simple actions such as whole-body contraction. Jellyfish , comb jellies , and related animals have diffuse nerve nets rather than

2592-449: A hierarchy of processing stages. At each stage, important information is extracted from the signal ensemble and unimportant information is discarded. By the end of the process, input signals representing "points of light" have been transformed into a neural representation of objects in the surrounding world and their properties. The most sophisticated sensory processing occurs inside the brain, but complex feature extraction also takes place in

2736-532: A hormonal cause, such as growth hormone deficiency , once called pituitary dwarfism . Achondroplasia is responsible for the majority of human dwarfism cases, followed by spondyloepiphyseal dysplasia and diastrophic dysplasia . The most recognizable and most common form of dwarfism in humans is achondroplasia, which accounts for 70% of dwarfism cases, and occurs in 4 to 15 out of 100,000 live births. It produces rhizomelic short limbs, increased spinal curvature, and distortion of skull growth. In achondroplasia

2880-497: A hundred known neurotransmitters, and many of them have multiple types of receptors. Many synapses use more than one neurotransmitter—a common arrangement is for a synapse to use one fast-acting small-molecule neurotransmitter such as glutamate or GABA , along with one or more peptide neurotransmitters that play slower-acting modulatory roles. Molecular neuroscientists generally divide receptors into two broad groups: chemically gated ion channels and second messenger systems . When

3024-482: A microscope. The author Michael Nikoletseas wrote: "It is difficult to believe that until approximately year 1900 it was not known that neurons are the basic units of the brain ( Santiago Ramón y Cajal ). Equally surprising is the fact that the concept of chemical transmission in the brain was not known until around 1930 ( Henry Hallett Dale and Otto Loewi ). We began to understand the basic electrical phenomenon that neurons use in order to communicate among themselves,

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3168-470: A nearly normal life expectancy. People with dwarfism can usually bear children, although there are additional risks to the mother and child depending upon the underlying condition. The most common and recognizable form of dwarfism in humans (comprising 70% of cases) is achondroplasia , a genetic disorder whereby the limbs are diminutive. Growth hormone deficiency is responsible for most other cases. There are many other less common causes. Treatment of

3312-414: A nervous system made up of a series of ganglia , connected by a ventral nerve cord made up of two parallel connectives running along the length of the belly . Typically, each body segment has one ganglion on each side, though some ganglia are fused to form the brain and other large ganglia. The head segment contains the brain, also known as the supraesophageal ganglion . In the insect nervous system ,

3456-551: A neuron, many types of neurons are capable, even in isolation, of generating rhythmic sequences of action potentials, or rhythmic alternations between high-rate bursting and quiescence. When neurons that are intrinsically rhythmic are connected to each other by excitatory or inhibitory synapses, the resulting networks are capable of a wide variety of dynamical behaviors, including attractor dynamics, periodicity, and even chaos . A network of neurons that uses its internal structure to generate temporally structured output, without requiring

3600-688: A number of organizations nationally and internationally. They are included in some events in the athletics at the Summer Paralympics . The Dwarf Athletic Association of America and the Dwarf Sports Association UK provide opportunities for dwarfs to compete nationally and internationally in the Americas and Europe, respectively. The World Dwarf Games (WDG) are a multi-sport event for athletes of short stature. The WDG have been held every four years since 1993 and are

3744-565: A protoplasmic protrusion that can extend to distant parts of the body and make thousands of synaptic contacts; axons typically extend throughout the body in bundles called nerves. Even in the nervous system of a single species such as humans, hundreds of different types of neurons exist, with a wide variety of morphologies and functions. These include sensory neurons that transmute physical stimuli such as light and sound into neural signals, and motor neurons that transmute neural signals into activation of muscles or glands; however in many species

3888-437: A small trunk, with average-sized limbs. Proportionate dwarfism is marked by a short torso with short limbs, thus leading to a height that is significantly below average. There may be long periods without any significant growth. Sexual development is often delayed or impaired into adulthood. This dwarfism type is caused by an endocrine disorder and not a skeletal dysplasia. Physical effects of malformed bones vary according to

4032-430: A special type of cell—the neuron (sometimes called "neurone" or "nerve cell"). Neurons can be distinguished from other cells in a number of ways, but their most fundamental property is that they communicate with other cells via synapses , which are membrane-to-membrane junctions containing molecular machinery that allows rapid transmission of signals, either electrical or chemical. Many types of neuron possess an axon ,

4176-507: A three-layered system of membranes, including a tough, leathery outer layer called the dura mater . The brain is also protected by the skull, and the spinal cord by the vertebrae . The peripheral nervous system (PNS) is a collective term for the nervous system structures that do not lie within the CNS. The large majority of the axon bundles called nerves are considered to belong to the PNS, even when

4320-410: A variant form of LTP that is conditioned on an extra input coming from a reward-signalling pathway that uses dopamine as neurotransmitter. All these forms of synaptic modifiability, taken collectively, give rise to neural plasticity , that is, to a capability for the nervous system to adapt itself to variations in the environment. The basic neuronal function of sending signals to other cells includes

4464-464: A wide range of professions. Individuals with dwarfism often face prejudice and stereotypes. Research by Klein (2019) has demonstrated that awareness of the stigmatization of this group can promote full participation in society. The research by Green and Pinter (2018) in the field of humor and social psychology can provide insights to reduce stereotypes and promote a more objective perception. In daily life, little people face numerous obstacles because

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4608-439: Is a common replacement of the term 'dwarfism', especially in a medical context. Short stature is clinically defined as a height within the lowest 2.3% of those in the general population. However, those with mild skeletal dysplasias may not be affected by dwarfism. In some cases of untreated hypochondroplasia , males grow up to 165 cm (5 feet 5 inches). Though that is short in a relative context, it does not fall into

4752-406: Is a deterioration of nerves in the spinal cord, starting in the posterior part of the cord. Affected dogs will become gradually weaker in the hind legs as nerves die off. Eventually, their hind legs become useless. They often also exhibit faecal and urinary incontinence. As the disease progresses, the paresis and paralysis gradually move forward. This disease also affects other large breeds of dogs. It

4896-407: Is a special type of identified neuron, defined as a neuron that is capable of driving a specific behavior individually. Such neurons appear most commonly in the fast escape systems of various species—the squid giant axon and squid giant synapse , used for pioneering experiments in neurophysiology because of their enormous size, both participate in the fast escape circuit of the squid. The concept of

5040-541: Is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system . Nerves that exit from the brain are called cranial nerves while those exiting from the spinal cord are called spinal nerves . The nervous system consists of nervous tissue which, at a cellular level, is defined by the presence of a special type of cell, called the neuron . Neurons have special structures that allow them to send signals rapidly and precisely to other cells. They send these signals in

5184-445: Is an abuse of terminology—it is the receptors that are excitatory and inhibitory, not the neurons—but it is commonly seen even in scholarly publications. One very important subset of synapses are capable of forming memory traces by means of long-lasting activity-dependent changes in synaptic strength. The best-known form of neural memory is a process called long-term potentiation (abbreviated LTP), which operates at synapses that use

5328-570: Is an anatomical convention that a cluster of neurons in the brain or spinal cord is called a nucleus , whereas a cluster of neurons in the periphery is called a ganglion . There are, however, a few exceptions to this rule, notably including the part of the forebrain called the basal ganglia . Sponges have no cells connected to each other by synaptic junctions , that is, no neurons, and therefore no nervous system. They do, however, have homologs of many genes that play key roles in synaptic function. Recent studies have shown that sponge cells express

5472-514: Is called identified if it has properties that distinguish it from every other neuron in the same animal—properties such as location, neurotransmitter, gene expression pattern, and connectivity—and if every individual organism belonging to the same species has one and only one neuron with the same set of properties. In vertebrate nervous systems very few neurons are "identified" in this sense—in humans, there are believed to be none—but in simpler nervous systems, some or all neurons may be thus unique. In

5616-431: Is called presynaptic, and the cell that receives signals is called postsynaptic. Both the presynaptic and postsynaptic areas are full of molecular machinery that carries out the signalling process. The presynaptic area contains large numbers of tiny spherical vessels called synaptic vesicles , packed with neurotransmitter chemicals. When the presynaptic terminal is electrically stimulated, an array of molecules embedded in

5760-409: Is capable of a much higher level of specificity than hormonal signaling. It is also much faster: the fastest nerve signals travel at speeds that exceed 100 meters per second. At a more integrative level, the primary function of the nervous system is to control the body. It does this by extracting information from the environment using sensory receptors, sending signals that encode this information into

5904-816: Is depicted in many books, films, and TV series such as Willow , The Wild Wild West , The Man with the Golden Gun (and later parodied in Austin Powers ), Gulliver's Travels by Jonathan Swift , The Wizard of Oz , Willy Wonka & the Chocolate Factory , Bad Santa , A Son of the Circus , Little People, Big World , The Little Couple , A Song of Ice and Fire (and its TV adaptation Game of Thrones ), Seinfeld , The Orator , In Bruges , The Tin Drum by Günter Grass ,

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6048-496: Is no definitive cause of short stature. Dwarfism is often diagnosed in childhood on the basis of visible symptoms. A physical examination can usually suffice to diagnose certain types of dwarfism, but genetic testing and diagnostic imaging may be used to determine the exact condition. In a person's youth, growth charts that track height can be used to diagnose subtle forms of dwarfism that have no other striking physical characteristics. Short stature or stunted growth during youth

6192-423: Is not possible. The appropriate term for describing a person of particularly short stature (or with the genetic condition achondroplasia ) has developed euphemistically. The noun dwarf stems from Old English : dweorg , originally referring to a being from Germanic mythology —a dwarf —that dwells in mountains and in the earth, and is associated with wisdom, smithing, mining, and crafting. The etymology of

6336-469: Is only gray in preserved tissue, and is better described as pink or light brown in living tissue) contains a high proportion of cell bodies of neurons. White matter is composed mainly of myelinated axons, and takes its color from the myelin. White matter includes all of the nerves, and much of the interior of the brain and spinal cord. Gray matter is found in clusters of neurons in the brain and spinal cord, and in cortical layers that line their surfaces. There

6480-399: Is processed by the brain. In insects, many neurons have cell bodies that are positioned at the edge of the brain and are electrically passive—the cell bodies serve only to provide metabolic support and do not participate in signalling. A protoplasmic fiber runs from the cell body and branches profusely, with some parts transmitting signals and other parts receiving signals. Thus, most parts of

6624-421: Is referred to by the underlying diagnosed disorder. Disorders causing dwarfism are often classified by proportionality. Disproportionate dwarfism describes disorders that cause unusual proportions of the body parts, while proportionate dwarfism results in a generally uniform stunting of the body. Disorders that cause dwarfism may be classified according to one of hundreds of names, which are usually permutations of

6768-430: Is sometimes defined as an adult height of less than 147 centimetres (4 ft 10 in), regardless of sex; the average adult height among people with dwarfism is 120 centimetres (4 ft). Disproportionate dwarfism is characterized by either short limbs or a short torso. In cases of proportionate dwarfism , both the limbs and torso are unusually small. Intelligence is usually normal, and most people with it have

6912-464: Is suspected to be an autoimmune problem. Cats with a heart murmur may develop blood clots that travel through arteries. If a clot is large enough to block one or both femoral arteries, there may be hind leg paralysis because the major source of blood flow to the hind leg is blocked. Many snakes exhibit powerful neurotoxins that can cause non-permanent paralysis or death. Also, many trees contain neurotoxins. Nervous system In biology ,

7056-594: Is the tetrodotoxin of fish species such as Takifugu rubripes , the famously lethal pufferfish of Japanese fugu . This toxin works by binding to sodium channels in nerve cells, inhibiting the cells' proper function. A non-lethal dose of this toxin results in temporary paralysis. This toxin is also present in many other species ranging from toads to nemerteans . Paralysis can be seen in breeds of dogs that are chondrodysplastic . These dogs have short legs, and may also have short muzzles. Their intervertebral disc material can calcify and become more brittle. In such cases,

7200-431: Is the ability to extract biologically relevant information from combinations of sensory signals. In the visual system , for example, sensory receptors in the retina of the eye are only individually capable of detecting "points of light" in the outside world. Second-level visual neurons receive input from groups of primary receptors, higher-level neurons receive input from groups of second-level neurons, and so on, forming

7344-417: Is typically small (less than 5 cm [2 in]) and the cost high. The most effective means of increasing adult height by several inches is distraction osteogenesis , though availability is limited and the cost is high in terms of money, discomfort, and disruption of life. Most people with dwarfism do not choose this option, and it remains controversial. For other types of dwarfism, surgical treatment

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7488-413: Is usually what brings the condition to medical attention. Skeletal dysplasia is usually suspected because of obvious physical features (e.g., unusual configuration of face or shape of skull), because of an obviously affected parent, or because body measurements (arm span, upper to lower segment ratio) indicate disproportion. Bone X-rays are often key to diagnosing a specific skeletal dysplasia, but are not

7632-420: Is voluntary restriction or inhibition of motion because of pain, incoordination, orgasm, or other cause, and is not due to actual muscular paralysis. In an infant, it may be a symptom of congenital syphilis . Pseudoparalysis can be caused by extreme mental stresses, and is a common feature of mental disorders such as panic anxiety disorder . Paralysis can occur in localised or generalised forms, or it may follow

7776-661: The Talmud , it is said that the second born son of the Egyptian Pharaoh of the Bible was a dwarf. Recent scholarship has suggested that ancient Egyptians held dwarfs in high esteem. Several important mythological figures of the North American Wyandot nation are portrayed as dwarfs. As popular media has become more widespread, the number of works depicting dwarfs have increased dramatically. Dwarfism

7920-412: The brain or liver , sometimes severely enough to be more of an impairment than the unusual bone growth. Mental effects also vary according to the specific underlying syndrome. In most cases of skeletal dysplasia, such as achondroplasia, mental function is not impaired. However, there are syndromes which can affect the cranial structure and growth of the brain, severely impairing mental capacity. Unless

8064-410: The central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord . The PNS consists mainly of nerves , which are enclosed bundles of the long fibers, or axons , that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves (efferent), while those nerves that transmit information from

8208-568: The discrimination they may face. In addition to the medical aspect of the condition there are social aspects. For a person with dwarfism, height discrimination can lead to ridicule in childhood and discrimination in adulthood. In the United Kingdom, United States, Canada , Australia , and other English-speaking countries, labels that some people with dwarfism accept include dwarf (plural: dwarfs ), little person (LP), or person of short stature (see terminology ). Historically,

8352-409: The human brain , it is estimated that the total number of glia roughly equals the number of neurons, although the proportions vary in different brain areas. Among the most important functions of glial cells are to support neurons and hold them in place; to supply nutrients to neurons; to insulate neurons electrically; to destroy pathogens and remove dead neurons; and to provide guidance cues directing

8496-438: The insect brain have passive cell bodies arranged around the periphery, while the neural signal processing takes place in a tangle of protoplasmic fibers called neuropil , in the interior. The cephalic molluscs have two pairs of main nerve cords organized around a number of paired ganglia, the visceral cords serving the internal organs and the pedal ones serving the foot. Most pairs of corresponding ganglia on both sides of

8640-432: The mucopolysaccharidoses and other storage disorders . Hypogonadotropic hypogonadism may cause proportionate, yet temporary, dwarfism. NPR2 disproportionate dwarfism was discovered recently and is caused by a mutant gene. Serious chronic illnesses may produce dwarfism as a side effect. Harsh environmental conditions, such as malnutrition, may also produce dwarfism. These types of dwarfism are indirect consequences of

8784-470: The nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates, it consists of two main parts,

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8928-406: The primary somatosensory cortex and the inferior parietal cortex . The function of the mirror system is a subject of much speculation. Many researchers in cognitive neuroscience and cognitive psychology consider that this system provides the physiological mechanism for the perception/action coupling (see the common coding theory ). They argue that mirror neurons may be important for understanding

9072-407: The radially symmetric organisms ctenophores (comb jellies) and cnidarians (which include anemones , hydras , corals and jellyfish ) consist of a diffuse nerve net . All other animal species, with the exception of a few types of worm , have a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The size of

9216-480: The Old Indian dhvaras (a type of demonic being). The being may not have gained associations with small stature until a later period. The terms "little person", "LP" and "person of short stature" are the preferred terms of those with this disorder, and while many are uncomfortable with "dwarf" it remains a common term in some areas. However, the plural "dwarfs" as opposed to "dwarves" is generally preferred in

9360-668: The action potential, in the 1950s ( Alan Lloyd Hodgkin , Andrew Huxley and John Eccles ). It was in the 1960s that we became aware of how basic neuronal networks code stimuli and thus basic concepts are possible ( David H. Hubel and Torsten Wiesel ). The molecular revolution swept across US universities in the 1980s. It was in the 1990s that molecular mechanisms of behavioral phenomena became widely known ( Eric Richard Kandel )." A microscopic examination shows that nerves consist primarily of axons, along with different membranes that wrap around them and segregate them into fascicles . The neurons that give rise to nerves do not lie entirely within

9504-485: The actions of other people, and for learning new skills by imitation. Some researchers also speculate that mirror systems may simulate observed actions, and thus contribute to theory of mind skills, while others relate mirror neurons to language abilities. However, to date, no widely accepted neural or computational models have been put forward to describe how mirror neuron activity supports cognitive functions such as imitation. There are neuroscientists who caution that

9648-501: The axons of neurons to their targets. A very important type of glial cell ( oligodendrocytes in the central nervous system, and Schwann cells in the peripheral nervous system) generates layers of a fatty substance called myelin that wraps around axons and provides electrical insulation which allows them to transmit action potentials much more rapidly and efficiently. Recent findings indicate that glial cells, such as microglia and astrocytes, serve as important resident immune cells within

9792-415: The behavior of the other, as though the observer were itself acting. Such neurons have been directly observed in primate species. Birds have been shown to have imitative resonance behaviors and neurological evidence suggests the presence of some form of mirroring system. In humans, brain activity consistent with that of mirror neurons has been found in the premotor cortex , the supplementary motor area ,

9936-509: The behaviors of animals, and most of the behaviors of humans, could be explained in terms of stimulus-response circuits, although he also believed that higher cognitive functions such as language were not capable of being explained mechanistically. Charles Sherrington , in his influential 1906 book The Integrative Action of the Nervous System , developed the concept of stimulus-response mechanisms in much more detail, and behaviorism ,

10080-402: The best known identified neurons are the gigantic Mauthner cells of fish. Every fish has two Mauthner cells, in the bottom part of the brainstem, one on the left side and one on the right. Each Mauthner cell has an axon that crosses over, innervating neurons at the same brain level and then travelling down through the spinal cord, making numerous connections as it goes. The synapses generated by

10224-428: The body are linked by commissures (relatively large bundles of nerves). The ganglia above the gut are the cerebral, the pleural, and the visceral, which are located above the esophagus (gullet). The pedal ganglia, which control the foot, are below the esophagus and their commissure and connectives to the cerebral and pleural ganglia surround the esophagus in a circumesophageal nerve ring or nerve collar . A neuron

10368-410: The body to the CNS are called sensory nerves (afferent). The PNS is divided into two separate subsystems, the somatic and autonomic , nervous systems. The autonomic nervous system is further subdivided into the sympathetic , parasympathetic and enteric nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system

10512-427: The body's limbs are proportionately shorter than the trunk (abdominal area), with a larger head than average and characteristic facial features. Achondroplasia is an autosomal dominant disorder caused by the presence of an altered allele in the genome. If a pair of achondroplasia alleles are present, the result is fatal, usually perinatally. Achondroplasia is a mutation in the fibroblast growth factor receptor 3 . In

10656-417: The body, while all vertebrates have spinal cords that run along the dorsal midline. Worms are the simplest bilaterian animals, and reveal the basic structure of the bilaterian nervous system in the most straightforward way. As an example, earthworms have dual nerve cords running along the length of the body and merging at the tail and the mouth. These nerve cords are connected by transverse nerves like

10800-476: The brain is anatomically divided into the protocerebrum , deutocerebrum , and tritocerebrum . Immediately behind the brain is the subesophageal ganglion , which is composed of three pairs of fused ganglia. It controls the mouthparts , the salivary glands and certain muscles . Many arthropods have well-developed sensory organs, including compound eyes for vision and antennae for olfaction and pheromone sensation. The sensory information from these organs

10944-565: The brain is directly affected by the underlying disorder, there is little to no chance of mental impairment that can be attributed to dwarfism. The psycho-social limitations of society may be more disabling than the physical symptoms, especially in childhood and adolescence, but people with dwarfism vary greatly in the degree to which social participation and emotional health are affected. Dwarfism can result from many medical conditions, each with its own separate symptoms and causes. Extreme shortness in humans with proportional body parts usually has

11088-430: The brain to the spinal cord that are capable of enhancing or inhibiting the reflex. Although the simplest reflexes may be mediated by circuits lying entirely within the spinal cord, more complex responses rely on signal processing in the brain. For example, when an object in the periphery of the visual field moves, and a person looks toward it many stages of signal processing are initiated. The initial sensory response, in

11232-403: The brain. One target is a set of spinal interneurons that project to motor neurons controlling the arm muscles. The interneurons excite the motor neurons, and if the excitation is strong enough, some of the motor neurons generate action potentials, which travel down their axons to the point where they make excitatory synaptic contacts with muscle cells. The excitatory signals induce contraction of

11376-420: The cell bodies of the neurons to which they belong reside within the brain or spinal cord. The PNS is divided into somatic and visceral parts. The somatic part consists of the nerves that innervate the skin, joints, and muscles. The cell bodies of somatic sensory neurons lie in dorsal root ganglia of the spinal cord. The visceral part, also known as the autonomic nervous system, contains neurons that innervate

11520-436: The central nervous system, processing the information to determine an appropriate response, and sending output signals to muscles or glands to activate the response. The evolution of a complex nervous system has made it possible for various animal species to have advanced perception abilities such as vision, complex social interactions, rapid coordination of organ systems, and integrated processing of concurrent signals. In humans,

11664-409: The central nervous system. The nervous system of vertebrates (including humans) is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is the major division, and consists of the brain and the spinal cord . The spinal canal contains the spinal cord, while the cranial cavity contains the brain. The CNS is enclosed and protected by the meninges ,

11808-444: The chance of recovery declines rapidly, since with continued pressure, the spinal cord tissue deteriorates and dies. Another type of paralysis is caused by a fibrocartilaginous embolism. This is a microscopic piece of disc material that breaks off and becomes lodged in a spinal artery. Nerves served by the artery will die when deprived of blood. The German Shepherd Dog is especially prone to developing degenerative myelopathy . This

11952-424: The claims being made for the role of mirror neurons are not supported by adequate research. In vertebrates, landmarks of embryonic neural development include the birth and differentiation of neurons from stem cell precursors, the migration of immature neurons from their birthplaces in the embryo to their final positions, outgrowth of axons from neurons and guidance of the motile growth cone through

12096-437: The condition depends on the underlying cause. Those with genetic disorders such as osteochondrodysplasia can sometimes be treated with surgery or physical therapy. Hormone disorders can also be treated with growth hormone therapy before the child's growth plates fuse. Individual accommodations such as specialized furniture, are often used by people with dwarfism. Many support groups provide services to aid individuals and

12240-649: The context of achondroplasia, this mutation causes FGFR3 to become constitutively active, inhibiting bone growth. Growth hormone deficiency (GHD) is a medical condition in which the body produces insufficient growth hormone . Growth hormone, also called somatotropin, is a polypeptide hormone which stimulates growth and cell reproduction. If this hormone is lacking, stunted or even halted growth may become apparent. Children with this disorder may grow slowly and puberty may be delayed by several years or indefinitely. Growth hormone deficiency has no single definite cause. It can be caused by mutations of specific genes, damage to

12384-460: The decrease in muscle contraction. In invertebrates, this clearly indicates that, e.g., Microbracon (wasp genus) venom causes paralysis of the neuromuscular system by acting at a presynaptic site. Philanthus venom inhibits both the fast and slow neuromuscular system at identical concentrations. It causes a decrease in the frequency of the miniature potentials without affecting their amplitude significantly. In some species of wasp , to complete

12528-435: The disc may rupture, with disc material ending up in the spinal canal, or rupturing more laterally to press on spinal nerves. A minor rupture may only result in paresis , but a major rupture can cause enough damage to cut off circulation. If no signs of pain can be elicited, surgery should be performed within 24 hours of the incident, to remove the disc material and relieve pressure on the spinal cord . After 24 hours,

12672-414: The effects of the condition, but lack of proportion may be permanent. Pain and disability may be ameliorated by physical therapy, braces or other orthotic devices, or by surgical procedures. The only simple interventions that increase perceived adult height are dress enhancements, such as shoe lifts or hairstyle. Growth hormone is rarely used for shortness caused by bone dysplasias, since the height benefit

12816-408: The electrical field across the membrane. If the change in electrical potential is large enough to pass the given threshold, it evokes an action potential, which is transmitted along the axon of the receptor cell, into the spinal cord. There the axon makes excitatory synaptic contacts with other cells, some of which project (send axonal output) to the same region of the spinal cord, others projecting into

12960-408: The embryo towards postsynaptic partners, the generation of synapses between these axons and their postsynaptic partners, and finally the lifelong changes in synapses which are thought to underlie learning and memory. All bilaterian animals at an early stage of development form a gastrula , which is polarized, with one end called the animal pole and the other the vegetal pole . The gastrula has

13104-420: The endocrine system may be treated using hormonal therapy . If the cause is prepubescent hyposecretion of growth hormone, supplemental growth hormone may correct the abnormality. If the receptor for growth hormone is itself affected, the condition may prove harder to treat. Hypothyroidism is another possible cause of dwarfism that can be treated through hormonal therapy. Injections of thyroid hormone can mitigate

13248-425: The environment is tailored to average-sized individuals. Some little people can only use ATMs, kitchens, toilets, and sinks with aids. Low stools and step stools play a special role, as they can be used in various ways to bridge the height difference. Stools are also useful as footrests while sitting, as the legs of short people dangle in the air when sitting on an average chair, which can be painful and uncomfortable in

13392-568: The exact number of those affected unknown. Prognosis is largely on a case-by-case basis depending on the severity, and life expectancy may not be impacted unless there are respiratory complications. Other causes of dwarfism are spondyloepiphyseal dysplasia congenita , diastrophic dysplasia , pseudoachondroplasia , hypochondroplasia , Noonan syndrome , primordial dwarfism , Cockayne syndrome , Kniest dysplasia , Turner syndrome , osteogenesis imperfecta (OI), and hypothyroidism . Severe shortness with skeletal distortion also occurs in several of

13536-427: The extreme ranges of the growth charts. Disproportionate dwarfism is characterized by shortened limbs or a shortened torso. In achondroplasia one has an average-sized trunk with short limbs and a larger forehead. Facial features are often affected and individual body parts may have problems associated with them. Spinal stenosis , ear infection , and hydrocephalus are common. In case of spinal dysostosis , one has

13680-428: The following roots: Examples include achondroplasia and chondrodystrophy . Many types of dwarfism are currently impossible to prevent because they are genetically caused. Genetic conditions that cause dwarfism may be identified with genetic testing , by screening for the specific variations that result in the condition. However, due to the number of causes of dwarfism, it may be impossible to determine definitively if

13824-503: The form of electrochemical impulses traveling along thin fibers called axons , which can be directly transmitted to neighboring cells through electrical synapses or cause chemicals called neurotransmitters to be released at chemical synapses . A cell that receives a synaptic signal from a neuron may be excited , inhibited , or otherwise modulated . The connections between neurons can form neural pathways , neural circuits , and larger networks that generate an organism's perception of

13968-422: The form of electrochemical waves called action potentials , which produce cell-to-cell signals at points where axon terminals make synaptic contact with other cells. Synapses may be electrical or chemical. Electrical synapses make direct electrical connections between neurons, but chemical synapses are much more common, and much more diverse in function. At a chemical synapse, the cell that sends signals

14112-403: The generally unhealthy or malnourished condition of the individual, and not of any specific disease. The dwarfism often takes the form of simple short stature, without any deformities, thus leading to proportionate dwarfism. In societies where poor nutrition is widespread, the average height of the population may be reduced below its genetic potential by the lack of proper nutrition. Sometimes there

14256-472: The great majority of neurons participate in the formation of centralized structures (the brain and ganglia) and they receive all of their input from other neurons and send their output to other neurons. Glial cells (named from the Greek for "glue") are non-neuronal cells that provide support and nutrition , maintain homeostasis , form myelin , and participate in signal transmission in the nervous system. In

14400-464: The internal organs, blood vessels, and glands. The autonomic nervous system itself consists of two parts: the sympathetic nervous system and the parasympathetic nervous system . Some authors also include sensory neurons whose cell bodies lie in the periphery (for senses such as hearing) as part of the PNS; others, however, omit them. The vertebrate nervous system can also be divided into areas called gray matter and white matter . Gray matter (which

14544-587: The involvement of dwarf athletes. " Midget wrestling " had its heyday in the 1950s–'70s, when wrestlers such as Little Beaver , Lord Littlebrook , and Fuzzy Cupid toured North America, and Sky Low Low was the first holder of the National Wrestling Alliance 's World Midget Championship . In the next couple of decades, more wrestlers became prominent in North America including foreign wrestlers like Japan 's Little Tokyo . Although

14688-734: The level of the nervous system. The spinal cord contains a series of segmental ganglia, each giving rise to motor and sensory nerves that innervate a portion of the body surface and underlying musculature. On the limbs, the layout of the innervation pattern is complex, but on the trunk it gives rise to a series of narrow bands. The top three segments belong to the brain, giving rise to the forebrain, midbrain, and hindbrain. Bilaterians can be divided, based on events that occur very early in embryonic development, into two groups ( superphyla ) called protostomes and deuterostomes . Deuterostomes include vertebrates as well as echinoderms , hemichordates (mainly acorn worms), and Xenoturbellidans . Protostomes,

14832-720: The long run and may hinder fine motor skills during work. To be mobile, some individuals use customized scooters or bicycles, as it can be problematic, depending on the type of short stature, to walk longer distances. With specially adapted vehicles, most individuals of short stature can drive without further hindrances. Generally, pedal extensions and an individually adjusted seat at the correct height are required. Some little people are tall enough to drive without pedal extensions. Usually, patients with skeletal dysplasia with limited mobility can receive allowances or grants for vehicle assistance through governmental help or rehabilitation providers. Dwarfs have support and compete in sport by

14976-402: The lower limbs before the upper limbs. It can be associated with: Ascending paralysis contrasts with descending paralysis , which occurs in conditions such as botulism . Many animal species use paralyzing toxins to capture prey, evade predation, or both. In stimulated muscles, the decrease in frequency of the miniature potentials runs parallel to the decrease in postsynaptic potential, and to

15120-411: The lungs. Symptoms starting at birth may be mild or can be fatal. There are recognizable features in individuals with this genetic disorder. Some are short stature, narrow chest, "facial features such as a prominent forehead, underdevelopment of the upper jaw, cheekbones and eye sockets (midface hypoplasia), and a squared-off jaw." It is considered a more severe skeletal dysplasia, but is very rare, with

15264-589: The medical context, possibly because the plural "dwarves" was popularized by author J. R. R. Tolkien , describing a race of characters in his The Lord of the Rings books resembling Norse dwarfs . " Midget ", whose etymology indicates a "tiny biting insect", came into prominence in the mid-19th century after Harriet Beecher Stowe used it in her novels Sunny Memories of Foreign Lands and Oldtown Folks where she described children and an extremely short man, respectively. Later some people of short stature considered

15408-485: The membrane are activated, and cause the contents of the vesicles to be released into the narrow space between the presynaptic and postsynaptic membranes, called the synaptic cleft . The neurotransmitter then binds to receptors embedded in the postsynaptic membrane, causing them to enter an activated state. Depending on the type of receptor, the resulting effect on the postsynaptic cell may be excitatory, inhibitory, or modulatory in more complex ways. For example, release of

15552-414: The more diverse group, include arthropods , molluscs , and numerous phyla of "worms". There is a basic difference between the two groups in the placement of the nervous system within the body: protostomes possess a nerve cord on the ventral (usually bottom) side of the body, whereas in deuterostomes the nerve cord is on the dorsal (usually top) side. In fact, numerous aspects of the body are inverted between

15696-410: The muscle cells, which causes the joint angles in the arm to change, pulling the arm away. In reality, this straightforward schema is subject to numerous complications. Although for the simplest reflexes there are short neural paths from sensory neuron to motor neuron, there are also other nearby neurons that participate in the circuit and modulate the response. Furthermore, there are projections from

15840-426: The nerves themselves—their cell bodies reside within the brain, spinal cord , or peripheral ganglia . All animals more advanced than sponges have nervous systems. However, even sponges , unicellular animals, and non-animals such as slime molds have cell-to-cell signalling mechanisms that are precursors to those of neurons. In radially symmetric animals such as the jellyfish and hydra, the nervous system consists of

15984-403: The nervous system and looks for interventions that can prevent or treat them. In the peripheral nervous system, the most common problem is the failure of nerve conduction, which can be due to different causes including diabetic neuropathy and demyelinating disorders such as multiple sclerosis and amyotrophic lateral sclerosis . Neuroscience is the field of science that focuses on the study of

16128-402: The nervous system as well as many peripheral organs, but in mammals, all of these "tissue clocks" are kept in synchrony by signals that emanate from a master timekeeper in a tiny part of the brain called the suprachiasmatic nucleus . A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors"

16272-496: The nervous system in radiata is relatively unstructured. Unlike bilaterians , radiata only have two primordial cell layers, endoderm and ectoderm . Neurons are generated from a special set of ectodermal precursor cells, which also serve as precursors for every other ectodermal cell type. The vast majority of existing animals are bilaterians , meaning animals with left and right sides that are approximate mirror images of each other. All bilateria are thought to have descended from

16416-536: The nervous system ranges from a few hundred cells in the simplest worms, to around 300 billion cells in African elephants . The central nervous system functions to send signals from one cell to others, or from one part of the body to others and to receive feedback. Malfunction of the nervous system can occur as a result of genetic defects, physical damage due to trauma or toxicity, infection, or simply senescence . The medical specialty of neurology studies disorders of

16560-435: The nervous system. The nervous system derives its name from nerves, which are cylindrical bundles of fibers (the axons of neurons ), that emanate from the brain and spinal cord , and branch repeatedly to innervate every part of the body. Nerves are large enough to have been recognized by the ancient Egyptians, Greeks, and Romans, but their internal structure was not understood until it became possible to examine them using

16704-486: The neurotransmitter acetylcholine at a synaptic contact between a motor neuron and a muscle cell induces rapid contraction of the muscle cell. The entire synaptic transmission process takes only a fraction of a millisecond, although the effects on the postsynaptic cell may last much longer (even indefinitely, in cases where the synaptic signal leads to the formation of a memory trace ). There are literally hundreds of different types of synapses. In fact, there are over

16848-454: The neurotransmitter glutamate acting on a special type of receptor known as the NMDA receptor . The NMDA receptor has an "associative" property: if the two cells involved in the synapse are both activated at approximately the same time, a channel opens that permits calcium to flow into the target cell. The calcium entry initiates a second messenger cascade that ultimately leads to an increase in

16992-474: The number of glutamate receptors in the target cell, thereby increasing the effective strength of the synapse. This change in strength can last for weeks or longer. Since the discovery of LTP in 1973, many other types of synaptic memory traces have been found, involving increases or decreases in synaptic strength that are induced by varying conditions, and last for variable periods of time. The reward system , that reinforces desired behaviour for example, depends on

17136-438: The only identified neurons in fish—there are about 20 more types, including pairs of "Mauthner cell analogs" in each spinal segmental nucleus. Although a Mauthner cell is capable of bringing about an escape response individually, in the context of ordinary behavior other types of cells usually contribute to shaping the amplitude and direction of the response. Mauthner cells have been described as command neurons . A command neuron

17280-453: The pituitary gland, Turner's syndrome , poor nutrition, or even stress (leading to psychogenic dwarfism ). Laron syndrome (growth hormone insensitivity) is another cause. Those with growth hormone issues tend to be proportionate. Metatropic means "changing form" and refers to this form of skeletal dysplasia as there is an abnormality in the growth plates. Skeletal changes continue over time and may need surgical intervention to help protect

17424-428: The possibilities for generating intricate temporal patterns become far more extensive. A modern conception views the function of the nervous system partly in terms of stimulus-response chains, and partly in terms of intrinsically generated activity patterns—both types of activity interact with each other to generate the full repertoire of behavior. The simplest type of neural circuit is a reflex arc , which begins with

17568-783: The receptors that it activates. Because different targets can (and frequently do) use different types of receptors, it is possible for a neuron to have excitatory effects on one set of target cells, inhibitory effects on others, and complex modulatory effects on others still. Nevertheless, it happens that the two most widely used neurotransmitters, glutamate and GABA , each have largely consistent effects. Glutamate has several widely occurring types of receptors, but all of them are excitatory or modulatory. Similarly, GABA has several widely occurring receptor types, but all of them are inhibitory. Because of this consistency, glutamatergic cells are frequently referred to as "excitatory neurons", and GABAergic cells as "inhibitory neurons". Strictly speaking, this

17712-416: The reproductive cycle, the female wasp paralyses a prey item such as a grasshopper and places it in her nest. In the species Philanthus gibbosus , the paralysed insect (most often a bee species) is coated in a thick layer of pollen. The adult P. gibbosus then lays eggs in the paralysed insect, which is devoured by the larvae when they hatch. A well-known example of a vertebrate-produced paralyzing toxin

17856-646: The retina of the eye, and the final motor response, in the oculomotor nuclei of the brainstem , are not all that different from those in a simple reflex, but the intermediate stages are completely different. Instead of a one or two step chain of processing, the visual signals pass through perhaps a dozen stages of integration, involving the thalamus , cerebral cortex , basal ganglia , superior colliculus , cerebellum , and several brainstem nuclei. These areas perform signal-processing functions that include feature detection , perceptual analysis, memory recall , decision-making , and motor planning . Feature detection

18000-510: The roundworm C. elegans , whose nervous system is the most thoroughly described of any animal's, every neuron in the body is uniquely identifiable, with the same location and the same connections in every individual worm. One notable consequence of this fact is that the form of the C. elegans nervous system is completely specified by the genome, with no experience-dependent plasticity. The brains of many molluscs and insects also contain substantial numbers of identified neurons. In vertebrates,

18144-399: The rungs of a ladder. These transverse nerves help coordinate the two sides of the animal. Two ganglia at the head (the " nerve ring ") end function similar to a simple brain . Photoreceptors on the animal's eyespots provide sensory information on light and dark. The nervous system of one very small roundworm, the nematode Caenorhabditis elegans , has been completely mapped out in

18288-713: The school of thought that dominated psychology through the middle of the 20th century, attempted to explain every aspect of human behavior in stimulus-response terms. However, experimental studies of electrophysiology , beginning in the early 20th century and reaching high productivity by the 1940s, showed that the nervous system contains many mechanisms for maintaining cell excitability and generating patterns of activity intrinsically, without requiring an external stimulus. Neurons were found to be capable of producing regular sequences of action potentials, or sequences of bursts, even in complete isolation. When intrinsically active neurons are connected to each other in complex circuits,

18432-400: The sensitivity of the cell to stimuli, or even altering gene transcription . According to a rule called Dale's principle , which has only a few known exceptions, a neuron releases the same neurotransmitters at all of its synapses. This does not mean, though, that a neuron exerts the same effect on all of its targets, because the effect of a synapse depends not on the neurotransmitter, but on

18576-459: The shape of a disk with three layers of cells, an inner layer called the endoderm , which gives rise to the lining of most internal organs, a middle layer called the mesoderm , which gives rise to the bones and muscles, and an outer layer called the ectoderm , which gives rise to the skin and nervous system. Chondrodysplastic Dwarfism is a condition of people and animals marked by unusually small size or short stature. In humans, it

18720-507: The short-lived reality show The Littlest Groom , and the films The Station Agent and Zero . The Animal Planet TV series Pit Boss features dwarf actor Shorty Rossi and his talent agency, "Shortywood Productions", which Rossi uses to provide funding for his pit bull rescue operation, "Shorty's Rescue". Rossi's three full-time employees, featured in the series, are little people and aspiring actors. In September 2014, Creative Business House along with Donnons Leur Une Chance, created

18864-531: The sleep-wake cycle. Experimental studies dating from the 1990s have shown that circadian rhythms are generated by a "genetic clock" consisting of a special set of genes whose expression level rises and falls over the course of the day. Animals as diverse as insects and vertebrates share a similar genetic clock system. The circadian clock is influenced by light but continues to operate even when light levels are held constant and no other external time-of-day cues are available. The clock genes are expressed in many parts of

19008-446: The sole diagnostic tool. Most children with suspected skeletal dysplasias are referred to a genetics clinic for diagnostic confirmation and genetic counseling . Since about the year 2000, genetic tests for some of the specific disorders have become available. During an initial medical evaluation of shortness, the absence of disproportion and other clues listed above usually indicates causes other than bone dysplasias. In men and women,

19152-399: The sole requirement for being considered a dwarf is having an adult height under 147 cm (4 ft 10 in) and it is almost always sub-classified with respect to the underlying condition that is the cause of the short stature. Dwarfism is usually caused by a genetic variant; achondroplasia is caused by a mutation on chromosome 4 . If dwarfism is caused by a medical disorder, the person

19296-498: The sophistication of the nervous system makes it possible to have language, abstract representation of concepts, transmission of culture, and many other features of human society that would not exist without the human brain. Most neurons send signals via their axons , although some types are capable of dendrite-to-dendrite communication. (In fact, the types of neurons called amacrine cells have no axons, and communicate only via their dendrites.) Neural signals propagate along an axon in

19440-432: The specific disease. Many involve joint pain caused by abnormal bone alignment, or from nerve compression. Early degenerative joint disease, exaggerated lordosis or scoliosis , and constriction of spinal cord or nerve roots can cause pain and disability. Reduced thoracic size can restrict lung growth and reduce pulmonary function. Some forms of dwarfism are associated with disordered function of other organs, such as

19584-399: The spinal cord and in peripheral sensory organs such as the retina. Although stimulus-response mechanisms are the easiest to understand, the nervous system is also capable of controlling the body in ways that do not require an external stimulus, by means of internally generated rhythms of activity. Because of the variety of voltage-sensitive ion channels that can be embedded in the membrane of

19728-522: The spinal cord to protrude from the rest of the spine. In extreme cases, this can cause spinal cord function inferior to the missing vertebral arches to cease. This cessation of spinal cord function can result in paralysis of lower extremities. Documented cases of paralysis of the anal sphincter in newborns have been observed when spina bifida has gone untreated. While life-threatening, many cases of spina bifida can be corrected surgically if operated on within 72 hours of birth. Ascending paralysis presents in

19872-513: The term midget was used to describe dwarfs (primarily proportionate); however, some now consider this term offensive. A defining characteristic of dwarfism is an adult height less than 2.3% of the CDC standard growth charts . There is a wide range of physical characteristics. Variations in individuals are identified by diagnosing and monitoring the underlying disorders. There may not be any complications outside adapting to their size. Short stature

20016-632: The term is seen by some as pejorative, many past and current midget wrestlers including Hornswoggle said they take pride in the term due to its history in the industry and its marketability. In art, literature, and movies, dwarfs are rarely depicted as ordinary people who are very short but rather as a species apart. Novelists , artists , and moviemakers may attach special moral or aesthetic significance to their "apartness" or misshapenness. Artistic representations of dwarfism are found on Greek vases and other ancient artifacts, including ancient Egyptian art in which dwarfs are likely to have been seen as

20160-419: The two groups, including the expression patterns of several genes that show dorsal-to-ventral gradients. Most anatomists now consider that the bodies of protostomes and deuterostomes are "flipped over" with respect to each other, a hypothesis that was first proposed by Geoffroy Saint-Hilaire for insects in comparison to vertebrates. Thus insects, for example, have nerve cords that run along the ventral midline of

20304-626: The word dwarf is contested, and scholars have proposed varying theories about the origins of the being, including that dwarfs may have originated as nature spirits or as beings associated with death, or as a mixture of concepts. Competing etymologies include a basis in the Indo-European root * dheur- (meaning ' damage ' ), the Indo-European root * dhreugh (whence modern Dutch droom ' dream ' and bedrog ' deception ' ), and comparisons have been made with

20448-527: The word to be offensive because it was the descriptive term applied to P. T. Barnum 's dwarfs used for public amusement during the freak show era. It is also not considered accurate as it is not a medical term or diagnosis, though it is sometimes used as a slang term to describe those who are particularly short, whether or not they have dwarfism. Individuals with dwarfism are capable of actively participating in various aspects of society. They have access to education, sports, and can pursue careers, engaging in

20592-674: The world and determine its behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide structural and metabolic support. Many of the cells and vasculature channels within the nervous system make up the neurovascular unit , which regulates cerebral blood flow in order to rapidly satisfy the high energy demands of activated neurons. Nervous systems are found in most multicellular animals , but vary greatly in complexity. The only multicellular animals that have no nervous system at all are sponges , placozoans , and mesozoans , which have very simple body plans. The nervous systems of

20736-469: The world's largest sporting event exclusively for athletes with dwarfism. The Dwarf Sports Association UK organizes between 5 and 20 events per month for athletes with restricted growth conditions in the UK. For instance, swimming and bicycling are often recommended for people with skeletal dysplasias, since those activities put minimal pressure on the spine. Since its early days, professional wrestling has had

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