Tibialis posterior reflex – function, task & diseases


Tibialis posterior reflex

Of the Tibialis posterior reflex is a reflex of the tibialis posterior muscle (posterior tibial muscle), which is responsible for supination, the elevation of the inner margin of the foot. The reflex is triggered by a small hit with the reflex hammer directly above or below the inner ankle. The reflex arc is controlled by the tibial nerve, a major branch of the sciatic nerve. The failure of the reflex may indicate problems in the area of ​​the L5 vortex.

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What is the Tibialis Posterior Reflex??

The tibialis posterior reflex is a self-reflex that causes a lateral tipping of the sole of the foot inwards. The inner edge of the foot is pulled upwards and at the same time the outer edge of the foot moves downwards, a typical inward tilting movement (supination), which also develops in overstretching form when the foot is bent over.

Since it is a self-reflex triggered by the same organ where the stimulus arrives, the response times are extremely short. The nervous connection and control of the reflex runs only over one or a few dorsal root ganglia.

The tibialis posterior reflex is triggered by a small impact with the reflex hammer on the tendon of the posterior tibial muscle, the posterior tibial muscle, directly above or below the medial malleolus. The muscle reports the sudden stretching over afferent fibers of the tibial nerve into the spinal cord. The impulse is processed directly and causes the reflex-like contraction of the muscle via efferent motor fibers of the nerve.

The artificial triggering of the reflex serves mainly to prove the function of the nerve-crossing points in the area of ​​the L5 of the spinal column.

function & task

Since the processing of sensory perception of muscle stretching by the muscle spindles takes place directly in the spinal ganglion in the spinal cord and is answered with the appropriate contraction command, the reflex is extremely fast. The time from the release of the reflex to the incoming motor signal for muscle contraction is only about 30 to 50 milliseconds (ms). Prior processing in the motor centers of the central nervous system (CNS) would take significantly longer.

The short reflex arc from the triggering stimulus to the action serves to protect the muscle from overstretching. However, the reflex-triggering sensory message is not only sent to the spinal ganglion, but also parallel (collateral) to the antagonistic muscle. This ensures that it is inhibited and can not tighten at the same time.

The triggering impact with the reflex hammer on the tendon of the posterior tibial muscle, immediately above or below the ankle, results in only a slight but faster expansion of the entire muscle, so that virtually all muscle spindles require the rapid expansion of the muscle as a sensory message report the spinal ganglion. The spinal ganglion responds immediately and sends the contraction command to protect the muscle, without prior consultation with the CNS.

The advantage of the fast reaction time is the disadvantage that the reflex deliberately can not be influenced. The posterior tibial reflex also works after many quick repetitions. He does not wear off, like all other muscle stretching reflexes. It is therefore a congenital, unchangeable, unconditioned reflex.

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Diseases & complaints

Predestined for such mechanical nerve damage are the crossing points of the nerves on the spine in the area of ​​the intervertebral discs. A reduced muscle reflex may then provide a first suspicion of disc damage to a particular vertebra.

In the case of the tibialis posterior reflex, however, caution should be exercised, as the reflex may also occur in healthy people. T. only weak and not present in some people. Therefore, it is important to perform the reflex on both feet to make a comparison. Basically, muscle reflexes with unilateral weakening or amplification usually indicate a nerve damage. After a stroke, a paralyzed muscle can often be seen as having an increased muscle reflex. In rare cases, a clonus occurs after a stroke. It is a rhythmic twitching of the muscle after only a single stimulus. The contractions are apparently triggered by motor nerves coming from the CNS.

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Christina Cherry
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