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A reflex is an involuntary, rapid and always similar reaction of an organism to a certain stimulus . Reflexes are mediated neuronally .

Reflexes can vary in complexity, innate or acquired , from a simple reflex arc to reflex circles of a "higher" type; in the latter case, learned, acquired, conditioned or conditioned reflexes are also used . Innate or unconditional reflexes represent biologically preformed modes of reaction. They are interpreted as an evolutionary adaptation to living conditions.

Reflexes enable living beings to live in a long-term constant environment: through an automatic, schematic or stereotypical reaction adjusted to such living conditions , which under constant circumstances is sufficient to live to sexual maturity and to produce offspring.

Properties of reflexes

Condition for the occurrence of reflexes is the ability of an organism , perceptions to do this automatically process and in just such a combination of sensory organs , nerves and muscles to specific stimuli to develop attractive adequate reactions ( irritability ) that enable it to independent living or to back up.

Genetically anchored and reflex responses are quasi evolutionarily "tested" responses; they only develop in living beings where they have proven to be effective for their own life with regard to long-term, constant living conditions . With innate reflexes, a living being has adaptive powers and survival skills that it does not have to learn first. Some reflexes that protect the body or individual organs from damage - such as the eyelid closing reflex - are therefore also referred to as protective reflexes .

Reflex forms

Behavioral biologists differentiate between the following types of reflexes:

  • Unconditional, unconditioned or innate reflexes : They are either fully developed when a living being is born or develop in the course of its development up to sexual maturity and the end of growth ( maturation ); It is typical for such biologically applied modes of reaction that each individual of a species shows identical reactions and reaction processes to similar stimulus constellations, which (can) only vary in the respective intensity such as speed or violence. One example is the blink reflex .
  • Conditional or conditioned reflexes : This is how reflexive modes of reaction are called that are not innate, but have been learned. They are also known as acquired reflexes . In this form of learning, visceral responses can also be conditioned; The Russian scientist Ivan Petrovich Pavlov (1849–1936) has made a particular contribution to researching this phenomenon . An example of this is his famous dog experiment : some dogs were always given a bell when they were served food. After a while, the dogs began to produce digestive secretions even if they only heard the sound of the bell. The originally neutral bell tone (because it was irrelevant for feeding) apparently assumed the same trigger function in the dogs as the food itself; In such cases, one also speaks of the fact that feeding and the sound of the bell have been associated , and this type of learning is called " classical conditioning ". As was shown in the behavioral learning research carried out mainly in the USA, all living beings capable of doing so can develop a myriad of modes of reaction through such associative learning; this knowledge has always been used in animal training in a targeted manner.
  • Self-reflexes are called reflexes in which the triggering stimulus and the reflex response take place in the same organ (usually muscle). An example of a self-reflex is the well-known knee or patellar tendon reflex , whichcan be triggeredwith a short blow just below the knee on the tendon of the relaxed quadriceps femoris muscle . The blow stimulates the stretch receptors in the muscle, the muscle spindles , anda contraction of the quadriceps muscle is achievedvia a reflex arc connected in the spinal cord, which leads to a brief stretching movement in the knee joint. The purpose of such muscular reflexes is to maintain or restore the respective posture by counter-regulation in the event of external impacts or sudden changes in position: For example, when a short step from behind into the hollow of the knee (sudden flexion and thus stretching of the quadriceps femoris muscle), the patellar tendon reflex can contribute to prevent a fall; It is similar with stumbling. In contrast to external reflexes, there is no habituation (weakening or absence of the reflex response in the event of repeated stimulation)with self-reflexes.
  • External reflexes : This is how reflexes are called when the organ that perceives the stimulus is not the organ that carries out the reflex response. One example is the corneal reflex : if the cornea of ​​the eye is irritated by a draft of air, the eyelid is reflexively closed. The irritation follows at a point which, due to the lack of muscles, cannot react itself; and the eyelid muscle, which is activated to protect the cornea, was not stimulated. In contrast to self- reflexes, external reflexes are habitable .
  • Coordinated reflex movements : One speaks of these when a more or less large group of muscles is activated in response to a stimulus (possibly including the activation of other organs such as glands or the heart and intestines and triggering other vegetative reactions). This includes, for example, the suckling reflex and the grasping reflex of the infant; these two reflexes can no longer be triggered after a while or can only be triggered again or again under pathological conditions. Above all, however, all emotional reactions (briefly referred to as feelings or expressions of emotions ) consist of highly coordinated reflex movements that come about as reflexes, but which, due to their complexity, can also be consciously influenced to a certain extent.
  • Early childhood or primitive reflexes : → Early childhood reflex .
  • Reflexesare muscle reflexes from the midbrain that control the assumption of the usual posture from an unusual body position. Ie a fallen animal stands up , a falling cat turns so that it lands in a standing position (see the cat's reflex ) . Often the head is brought into an upright position first, followed by the positioning of the rest of the body via the neck reflex . The righting reflexes , like the standing reflexes, are triggered by a posture and therefore belong to the static or statokinetic reflexes . See also: Statomotor activity

The term atavistic reflex does not come from behavioral research, but is used as a synonym for “primitive reflex” and is often used as a jargon-like term for reacting inappropriately to the situation - for example, by regression on behaviors that are culturally considered to be overcome or obsolete, and possibly also typical for children, etc. Ä.

See also


  • Ivan P. Pavlov (1927): Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex . In: Annals Of Neurosciences . tape 17 , no. 3 , 2010, p. 136-141 ( online ).

Web links

Wiktionary: Reflex  - explanations of meanings, word origins, synonyms, translations


  1. Magnus R. (1924) Stellreflexe . In: body position. Monographs from the entire field of the physiology of plants and animals. Page 195. Springer, Berlin, Heidelberg, 1924. DOI ; Print ISBN 978-3-662-23426-6 , online ISBN 978-3-662-25478-3
  2. ^ A. Bethe, Gv Bergmann, G. Embden, A. Ellinger: Handbook of normal and pathological physiology: Fifteenth Volume / First Half Correlatonen I / 1 , Springer-Verlag, 1930, page 41
  3. Compact lexicon of biology: Stellreflexe , In: