neuron

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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.
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, 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

References in periodicals archive ?
There is abundant evidence that such age-associated alterations in cognition are related to decreased function of cholinergic neurons in the hippocampus and cortex [2-4].
Citation: "The Controlled Generation of Functional Basal Forebrain Cholinergic Neurons from Human Embryonic Stem Cells;" Christopher John Bissonnette, John A Kessler, et al.
Stability of numbers but not size of forebrain cholinergic neurons to 53 months.
Dr Elson said: This is the only study to date to characterise mitochondrial DNA errors in cholinergic neurons, a neuronal population that is highly vulnerable to cell death in Parkinsons disease patients.
The challenge of continued research is that cholinergic neurons remain difficult to study because they are intermingled with other types of neurons and are few in number compared to other types of neurons in the brain.
The second key challenge, he said, is the need for constant exposure to cholinergic neurons that comprise the nucleus basalis of Meynert (NBM) while avoiding exposure to untargeted neuronal populations.
Elderly patients are among the most affected population, in whom severe dementia, including Alzheimer's type, reduces the number of cholinergic neurons (15), possibly causing various types of sleep-wake disorders, including irregular SWC (16), difficulty in falling or staying asleep, or adhering to a consistent sleep/wake schedule (17).
The initial destruction was in an area called the medial septum, which connects to the hippocampus by GABA and cholinergic neurons.
Effects of two years of estrogen loss or replacement on nucleus basalis cholinergic neurons andcholinergic fibers to the dorsolateral prefrontal and inferior parietal cortex of monkeys.
The death of cholinergic neurons in the basalis nucleus of Meynert leads to a deficit in acetylcholine, a major transmitter believed to be involved with memory.
This vulnerability is associated with a significant decrease in cholinergic neurons or receptors in the aging brain, and an increase in the permeability of the blood-brain barrier, allowing for greater drug access to brain tissue.
Various studies have demonstrated that noradrenergic, serotonergic and cholinergic neurons of the LC fire quickly during wake, begin to slow with the onset of sleep and continue to slow as sleep deepens, then nearly stop firing during REM sleep.