reflex

—reflexly, adv. —reflexness, n.

adj., n. /ree"fleks/; v. /ri fleks"/, adj.

1. Physiol. noting or pertaining to an involuntary response to a stimulus, the nerve impulse from a receptor being transmitted inward to a nerve center that in turn transmits it outward to an effector.

2. occurring in reaction; responsive.

3. cast back; reflected, as light, color, etc.

4. bent or turned back.

5. designating a radio apparatus in which the same circuit or part performs two functions.

n.

6. Physiol.

a. Also called reflex act. movement caused by a reflex response.

b. Also called reflex action. the entire physiological process activating such movement.

7. any automatic, unthinking, often habitual behavior or response.

8. the reflection or image of an object, as exhibited by a mirror or the like.

9. a reproduction, as if in a mirror.

10. a copy; adaptation.

11. reflected light, color, etc.

12. Historical Ling. an element in a language, as a sound, that has developed from a corresponding element in an earlier form of the language: The (o) in "stone" is a reflex of Old English a.

13. a reflex radio receiver.

14. a reflex camera.

v.t.

15. to subject to a reflex process.

16. to bend, turn, or fold back.

17. to arrange in a reflex system.

[1500-10; < L reflexus bent back, ptp. of reflectere to REFLECT]

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In biology, an automatic and inborn response to a stimulus that involves a nerve impulse passing from a sensory nerve cell to a muscle or gland without reaching the level of consciousness.

Simple reflexes include sucking, swallowing, blinking, scratching, and the knee jerk. Most reflexes consist of complex patterns of many unconsciously coordinated muscular actions that form the basis of much instinctive behavior in animals. Examples include walking, standing, the cat's righting reflex, and basic sexual acts.

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▪ physiology

      in biology, an action consisting of comparatively simple segments of behaviour that usually occur as direct and immediate responses to particular stimuli uniquely correlated with them.

      Many reflexes of placental mammals appear to be innate. They are hereditary and are a common feature of the species and often of the genus. Reflexes include not only such simple acts as chewing, swallowing, blinking, the knee jerk, and the scratch reflex, but also stepping, standing, and mating. Built up into complex patterns of many coordinated muscular actions, reflexes form the basis of much instinctive (instinct) behaviour in animals.

      Humans also exhibit a variety of innate reflexes, which are involved with the adjustment of the musculature for optimum performance of the distance receptors (i.e., eye and ear), with the orientation of parts of the body in spatial relation to the head, and with the management of the complicated acts involved in ingesting food. Among the innate reflexes involving just the eyes (eye, human), for example, are: (1) paired shifting of the eyeballs, often combined with turning of the head, to perceive an object in the field of vision; (2) contraction of the intraocular muscles to adjust the focus of the retina for the viewing of near or far objects; (3) constriction of the pupil to reduce excessive illumination of the retina; and (4) blinking due to intense light or touching of the cornea.

      In its simplest form, a reflex is viewed as a function of an idealized mechanism called the reflex arc. The primary components of the reflex arc are the sensory-nerve cells (or receptors) that receive stimulation, in turn connecting to other nerve cells that activate muscle cells (or effectors), which perform the reflex action. In most cases, however, the basic physiological mechanism behind a reflex is more complicated than the reflex arc theory would suggest. Additional nerve cells capable of communicating with other parts of the body (beyond the receptor and effector) are present in reflex circuits. As a result of the integrative action of the nervous system in higher organisms, behaviour is more than the simple sum of their reflexes; it is a unitary whole that exhibits coordination between many individual reflexes and is characterized by flexibility and adaptability to circumstances. Many automatic, unconditioned reflexes can thus be modified by or adapted to new stimuli, making possible the conditioning of reflex responses. The experiments of the Russian physiologist Ivan Petrovich Pavlov (Pavlov, Ivan Petrovich), for example, showed that if an animal salivates at the sight of food while another stimulus, such as the sound of a bell, occurs simultaneously, the sound alone can induce salivation after several trials. The animal's behaviour is no longer limited by fixed, inherited reflex arcs but can be modified by experience and exposure to an unlimited number of stimuli.

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