—neuronal /noor"euh nl, nyoor"-, noo rohn"l, nyoo-/, adj./noor"on, nyoor"-/, n.Cell Biol. a specialized, impulse-conducting cell that is the functional unit of the nervous system, consisting of the cell body and its processes, the axon and dendrites.[1880-85; < Gk neûron sinew, cord, nerve]
* * *or nerve cellAny of the cells of the nervous system.Sensory neurons relay information from sense organs, motor neurons carry impulses to muscles and glands, and interneurons transmit impulses between sensory and motor neurons. A typical neuron consists of dendrites (fibres that receive stimuli and conduct them inward), a cell body (a nucleated body that receives input from dendrites), and an axon (a fibre that relays the nerve impulse from the cell body outward to its terminals, the synaptic knobs). Both axons and dendrites may be referred to as nerve fibres. Impulses are conducted by neurotransmitter chemicals released by the axon's synaptic knobs across the synapses (junctions between neurons or between a neuron and an effector cell, such as a muscle cell) or, in some cases, pass directly from one neuron to the next. Most neurons are insulated by a myelin sheath formed by cells (Schwann cells) surrounding the axons. Bundles of fibres from neurons held together by connective tissue form nerves.
* * *▪ anatomyalso called nerve cellbasic cell of the nervous system in vertebrates and most invertebrates from the level of the cnidarians (cnidarian) (e.g., corals, jellyfish) upward. A typical neuron has a cell body containing a nucleus and two or more long fibres. Impulses are carried along one or more of these fibres, called dendrites, to the cell body; in higher nervous systems, only one fibre, the axon, carries the impulse away from the cell body. Bundles of fibres from neurons are held together by connective tissue and form nerves. Some nerves in large vertebrates are several feet long. A sensory neuron transmits impulses from a receptor, such as those in the eye (eye, human) or ear (ear, human), to a more central location in the nervous system, such as the spinal cord or brain. A motor neuron transmits impulses from a central area of the nervous system to an effector, such as a muscle.
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