neuron

neuron,

specialized cell in animals that, as a unit of the nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
..... Click the link for more information. , carries information by receiving and transmitting electrical impulses.

Neuron

(or nerve cell), the basic structural and functional unit of the nervous system.

A neuron receives signals that enter from receptors and other neurons and processes and transmits the signals in the form of nerve impulses to the effector nerve endings, which control the activities of the corresponding organs of response (muscles, gland cells, or other neurons). Neurons differentiate from neuroblasts, which arise in the neurula stage of embryonic development.

In the process of differentiation a neuron develops specialized structures to ensure the performance of the various neuronal functions. Branched outgrowths, or dendrites, are specialized to receive information; these structures have a receptive membrane and are sensitive to specific physiological stimuli. The excitatory and inhibitory processes that are localized in the receptive membrane accumulate and act on the stimulus region, the most excitable area of the surface membrane of the neuron; this serves as the origin for the spreading bioelectric potentials. The longest outgrowth, the axon (or axis cylinder), is covered by an electrically excitable conducting membrane that serves to transmit the potentials. Having reached the terminal sections of the axon, the nerve impulse excites the secretory membrane; as a result of this, a physiologically active substance, either a mediator substance (chemical transmitter) or a neurohormone, is secreted from the nerve endings.

In addition to structures associated with the performance of specific functions, a neuron has a nucleus (as do all living cells) that, together with the perinuclear cytoplasm, forms the cell body, or perikaryon. It is here that synthesis of macromolecules takes place. Some of these are transported along the axoplasm (the cytoplasm in the axon) to the nerve endings.

The structure, dimensions, and shape of neurons vary widely. Neurons of the cerebral cortex, cerebellum, and some other areas of the central nervous system have complex structures. Multipolar neurons are characteristic of the brain of vertebrates. In such neurons, several dendrites and one axon emerge from the cell-body; the initial section of the axon serves as the excitatory region. Numerous nerve endings from the outgrowths of other neurons converge on the cell body and dendrites of a multipolar neuron. The ganglia of invertebrates usually consist of unipolar neurons; the cell body only fulfills a trophic function and is connected with the axon at the axon hillock. It would appear that such a neuron does not necessarily have true dendrites, and reception of synaptic signals is effected by specialized areas on the surface of the axon. Neurons with two outgrowths are called bipolar; they occur most often as peripheral sensory neurons having one axon and one dendrite, which impinges on the cell surface.

Neurons are classified according to their position in a reflex arc: afferent, or sensory, neurons receive information from the external environment or from receptor cells; interneurons, or internuncial neurons, connect one neuron with another; efferent neurons transmit impulses to the organs of response (for example, motoneurons innervate muscles).

Neurons are also classified according to their chemical specificity, that is, according to the nature of the physiologically active substance that is secreted by the nerve endings of a given neuron. For example, a cholinergic neuron secretes acetylcholine and an adrenergic neuron secretes adrenaline. The number of neurons present in a nervous system determines the variety and complexity of functions that an organism can perform; for example, there are 10² neurons in the Rotatoria and more than 10¹⁰ in man.

REFERENCES

Eccles, G. Fiziologiia nervnykh kletok. Moscow, 1959. (Translated from English.)
Hyden, H. “Neiron.” (Translated from English.) In the collection Funktsional’naia morfologiia kletki. Moscow, 1963.
Mekhanizmy deiatel’nosti tsentral’nogo neirona. Moscow-Leningrad, 1966.
Nervnaia kletka: sb. st. Edited by N. V. Golikov. Leningrad, 1966.

D. A. SAKHAROV

neuron

[′nu̇‚rän] (neuroscience) A nerve cell, including the cell body, axon, and dendrites.

neuron

artificial neural network

neuron

[noor´on] a highly specialized cell of the nervous system, having two characteristic properties: irritability (ability to be stimulated) and conductivity (ability to conduct impulses). They are composed of a cell body (called also neurosome or perikaryon), containing the nucleus and its surrounding cytoplasm, and one or more processes (fibers" >nerve fibers) extending from the body. Called also nerve cell. adj., adj neuro´nal.
The nerve fibers are actually extensions of the cytoplasm surrounding the nucleus of the neuron. A nerve cell may have only one such slender fiber extending from its body, in which case it is classified as unipolar. A neuron having two processes is bipolar, and one with three or more processes is multipolar. Most neurons are multipolar; this type is widely distributed throughout the central nervous system and autonomic ganglia. The multipolar neurons have a single process called an axon and several branched extensions called dendrites. The dendrites receive stimuli from other nerves or from a receptor organ, such as the skin or ear, and transmit them through the neuron to the axon. The axon conducts the impulses to the dendrite of another neuron or to an effector organ that is thereby stimulated to action. Many processes are covered with a layer of lipid material called the sheath" >myelin sheath. Peripheral nerve fibers have a thin outer covering called neurilemma.Types of Neurons. Neurons that receive stimuli from the outside environment and transmit them toward the brain are called afferent or sensory neurons. Those that carry impulses in the opposite direction, away from the brain and other nerve centers to muscles, are called efferent neurons, motor neurons, or motoneurons. Another type, the interneuron, found in the brain and spinal cord, conducts impulses from afferent to efferent neurons.Synapses. The point at which an impulse is transmitted from one neuron to another is called a synapse. The transmission is chemical in nature; that is, there is no direct contact between the axon of one neuron and the dendrites of another. The cholinergic nerves (parasympathetic nervous system) liberate at their axon endings a substance called acetylcholine, which acts as a stimulant to the dendrites of adjacent neurons. In a similar manner, the adrenergic nerves (sympathetic nervous system) liberate epinephrine" >epinephrine or related substances. The synapse may involve one neuron in chemical contact with many adjacent neurons, or it may involve the axon terminals of one neuron and the dendrites of a succeeding neuron in a nerve pathway. There are many different patterns of synapses.Receptor End-Organs. The dendrites of the sensory neurons are designed to receive stimuli from various parts of the body. These dendrites are called receptor end-organs and are of three general types: exteroceptors, interoceptors, and proprioceptors. The exteroceptors are located near the external surface of the body, receive impulses from the skin, and transmit information about the senses of touch, heat, cold, and other factors in the external environment. The interoceptors are located in the internal organs and receive information from the viscera, e.g., pressure, tension, and pain. The proprioceptors are found in muscles, tendons, and joints and transmit “muscle sense,” by which one is aware of the position of one's body in space.Neurons and Effectors. The axons of motor neurons form synapses with skeletal fibers to produce motion. These junctions are called motor end-plates or myoneural junctions. The axon of a motor neuron divides just before it enters the muscle fibers and forms synapses near the nuclei of muscle fibers. These motor neurons are called somatic efferent neurons. Visceral efferent neurons form synapses with smooth muscle, cardiac muscle, and glands.

Upper and lower motor neurons. From Damjanov, 2000.Golgi n's 1. (type I): pyramidal cells with long axons, which leave the gray matter of the central nervous system, traverse the white matter, and terminate in the periphery.2. (type II): stellate neurons with short axons in the cerebral and cerebellar cortices and in the retina.motor neuron motoneuron.postganglionic n's neurons whose cell bodies lie in the autonomic ganglia and whose purpose is to relay impulses beyond the ganglia.preganglionic n's neurons whose cell bodies lie in the central nervous system and whose efferent fibers terminate in the autonomic ganglia.

neu·ron

(nū'ron), The morphologic and functional unit of the nervous system, consisting of the nerve cell body, the dendrites, and the axon. Synonym(s): nerve cell, neurocyte, neurone [G. neuron, a nerve]

neuron

(no͝or′ŏn′, nyo͝or′-)n.1. Any of the impulse-conducting cells that constitute the brain, spinal column, and nerves in vertebrates, consisting of a nucleated cell body with one or more dendrites and a single axon.2. A similar impulse-conducting cell in invertebrates. In both senses also called nerve cell.

neu′ro·nal (no͝or′ə-nəl, nyo͝or′-, no͝o-rōn′l, nyo͝o-), neu·ron′ic adj.neu′ro·nal·ly adv.

neu·ron

(nūr'on) [TA] The morphologic and functional unit of the nervous system, consisting of the nerve cell body with its dendrites and axon.
Synonym(s): neurocyte, neurone. [G. neuron, a nerve]

neuron

(noo'ron?) [Gr. neuron, nerve, sinew]

NEURON STRUCTUREA nerve cell, the structural and functional unit of the nervous system. A neuron consists of a cell body (perikaryon) and its processes, an axon and one or more dendrites. Neurons function in the initiation and conduction of impulses. They transmit impulses to other neurons or cells by releasing neurotransmitters at synapses. Alternatively, a neuron may release neurohormones into the bloodstream. Synonym: nerve cell See: illustrationneuronal (noor''on-al), adjective

afferent neuron

A neuron that conducts sensory impulses toward the brain or spinal cord. Synonym: sensory neuron

association neuron

Interneuron.

associative neuron

A neuron that mediates impulses between a sensory and a motor neuron.

bipolar neuron

1. A neuron that bears two processes. 2. A neuron of the retina that receives impulses from the rods and cones and transmits them to a ganglion neuron. See: retina for illus.

central neuron

A neuron confined entirely to the central nervous system.

commissural neuron

A neuron whose axon crosses to the opposite side of the brain or spinal cord.

efferent neuron

A neuron whose axon carries motor impulses away from the brain or spinal cord.

gamma motor neuron

A small nerve originating in the anterior horns of the spinal cord that transmits impulses through type A gamma fibers to intrafusal fibers of the muscle spindle for muscle control.

ganglion neuron

A neuron of the retina that receives impulses from bipolar neurons. Axons of ganglion neurons converge at the optic disk to form the optic nerve. See: retina for illus.

internuncial neuron

Interneuron.

lower motor neuron

A peripheral motor neuron that originates in the ventral horns of the gray matter of the spinal cord and terminates in skeletal muscles. Lesions of these neurons produce flaccid paralysis of the muscles they innervate. Synonym: lower motoneuron

mirror neuron

Any of a group of neurons that become active both when an animal moves in a certain way and when the animal observes others performing the same action. Learning by simulation or imitation is thought to be a function of the system of mirror neurons in the brain.

motor neuron

A neuron that carries impulses from the central nervous system either to muscle tissue to stimulate contraction or to glandular tissue to stimulate secretion.

multipolar neuron

A neuron with one axon and many dendrites.

peripheral neuron

A neuron whose process constitutes a part of the peripheral nervous system (cranial, spinal, or autonomic nerves).

peripheral motor neuron

A motor neuron that transmits impulses to skeletal muscle. Synonym: peripheral motoneuron

postganglionic neuron

A neuron of the autonomic nervous system whose cell body lies in an autonomic ganglion and whose axon terminates in a visceral effector (smooth or cardiac muscle or glands).

preganglionic neuron

A neuron of the autonomic nervous system whose cell body lies in the central nervous system and whose axon terminates in a peripheral ganglion, synapsing with postganglionic neurons.

sensory neuron

Afferent neuron.

serotonergic neuron

A nerve cell that uses serotonin as its neurotransmitter.

unipolar neuron

A neuron whose cell body bears one process.

upper motor neuron

A motor neuron (actually an interneuron) found completely within the central nervous system that synapses with or regulates the actions of lower motor neurons in the spinal cord and cranial nerves. Lesions of these neurons produce spastic paralysis in the muscles they innervate. Synonym: upper motoneuron

Neuron

The cells within the body which make up the nervous system, specifically those along which information travels.Mentioned in: Coma, Pain

neuron

Structural unit of the nervous system consisting of the nerve cell body and its various processes, the dendrites, the axon and the ending (also called bouton, end foot or axon terminal). There are many types of neurons within the nervous system; some transmit afferent nerve impulses to the brain (e.g. those carrying information from the photoreceptors to the visual cortex), or to the spinal cord (e.g. those carrying information from the receptors in the skin to the spinal cord). They are called sensory neurons. Others transmit efferent motor nerve impulses to a muscle (e.g. those carrying information from the Edinger-Westphal nucleus to the sphincter pupillae and ciliary muscles). These are called motor neurons. Other neurons carry nerve impulses from one neuron to another (internuncial neurons). Note: also spelt neurone. See action potential; synapse.

neu·ron

(nūr'on) [TA] Morphologic and functional unit of nervous system, consisting of nerve cell body, dendrites, and the axons.
Synonym(s): neurone. [G. neuron, a nerve]

neuron

neu·ron

neu•ron

neu·ron

neuron

neuron

neuron,

Neuron

REFERENCES

neuron

neuron

neuron

neuron

neu·ron

neuron

neu·ron

neuron

afferent neuron

association neuron

associative neuron

bipolar neuron

central neuron

commissural neuron

efferent neuron

gamma motor neuron

ganglion neuron

internuncial neuron

lower motor neuron

mirror neuron

motor neuron

multipolar neuron

peripheral neuron

peripheral motor neuron

postganglionic neuron

preganglionic neuron

sensory neuron

serotonergic neuron

unipolar neuron

upper motor neuron

Neuron

neuron

neu·ron

NEURON

neuron

Synonyms for neuron

noun a cell that is specialized to conduct nerve impulses

Synonyms

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