Reflex Arc

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reflex arc

[′rē‚fleks ‚ärk]
A chain of neurons composing the anatomical substrate or pathway of the unconditioned reflex.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Reflex Arc


a group of nerve structures involved in reflex action. The term “reflex arc,” or “nervous arc,” was introduced in 1850 by the British physician and physiologist M. Hall, who was describing the anatomic elements of a reflex.

A reflex arc includes (1) receptors, or nerve endings that respond to stimulation; (2) afferent (centripetal) nerve fibers, or the processes of receptor neurons that transmit impulses from sensory nerve endings to the central nervous system; (3) a nerve center, that is, neurons that sense excitation and transmit it to effector neurons through the appropriate synapses; (4) efferent (centrifugal) nerve fibers that transmit excitation from the central nervous system to the periphery; and (5) an effector organ whose activity changes as a result of a reflex.

The simplest two-neuron, or monosynaptic, reflex arc consists of receptor and effector neurons separated by a synapse. A multineuron, or polysynaptic, reflex arc consists of a receptor neuron, several internuncial neurons, and an effector neuron, all of which are separated by synapses. A reflex arc does not completely reflect the structure of a reflex because of the proven existence of reverse afference, that is, excitation that informs a nerve center about the condition of an effector organ.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Monosynaptic reflexes generated from adult injury and regenerated motoneurons and recorded in a peripheral nerve crush rat had a similar strength as in normal [20].
When a muscle is stretched, the earliest muscle contraction (e.g., 20 ms in biceps brachii) occurs due to the involuntary activation of monosynaptic reflexes. Following which, the voluntary muscle contraction of biceps occurs in 90-100 ms.
Monosynaptic reflexes: fiber axon synapses directly associated with medullary moto-neuron without interposition of intercalary neurons.