Reflexes - self-reflex and extraneous reflex

Fast reaction through self-reflex

A self-reflex is characterized by the fact that the stimulus site and the responding organ are identical. Most of our own reflexes are protective muscle stretching reflexes in which short muscle stretching - caused, for example, by a reflex hammer or a sudden buckling of the knee joint - leads to a contraction and thus twitching of the affected muscle. Thus, the patellar tendon reflex (PSR) prevents the knee from collapsing suddenly, as the thigh muscle reflexively pushes the lower leg forward and brings us back into balance.

Switching takes place in the spinal cord

With the muscle reflexes, the function of many spinal nerves can be checked, as the nerve excitation from the stimulus site reaches the spinal cord and is directly returned. Since the spinal cord is only a switch, these reflexes are called monosynaptic, they are usually after the muscle or tendon, which is tested: important muscle reflexes are next to the PSR on the leg of the Achilles tendon and adductor reflex, on the arm of biceps and triceps reflex and on the jaw the masseter reflex.

In addition, there are many others that provide detailed neurological examination to determine whether there is damage to individual nerve tracts (individual reflexes absent) or whether there is a general nervous dysfunction (no or increased reflexes present).

Reaction to detours due to extraneous reflex

In the more complex polysynaptic extraneous reflex, the stimulus leads to a nervous switch in the spinal cord and the nerve excitation is switched over to other organs, which then react to the stimulus.

In clinical practice, the pupil reflex is checked, especially in suspected brain damage, which leads to a narrowing of the pupil when light enters the eye (optic nerve is irritated) (pupil fibers react). Since the reaction of the pupils in the brain is coupled with each other, usually both pupils contract, even if only one eye is exposed to the light. With massive brain damage and brain death, this reflex is no longer present.

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