Patellar tendon reflex

The patellar tendon reflex (also hamstring reflex , knee phenomenon , patellar reflex or quadriceps stretch reflex ) is a monosynaptic (connected via only one synapse ) reflex from the group of self-reflexes .

Tripping

The reflex can be triggered by a light tap on the patellar tendon below the kneecap. This is the tendon of the four-headed thigh muscle (quadriceps femoris muscle). As a reflex response, contraction of the quadriceps leads to an extension of the knee joint .

physiology

Stretch receptors (so-called muscle spindles ) in the quadriceps register the stretch and report it to the spinal cord . Contrary to popular belief, the Golgi tendon organs are not involved in the patellar tendon reflex. They are also stretched by the blow on the patellar tendon, but the Golgi tendon organs only serve to regulate muscle tension. In humans, the sensitive neurons ( afferents ) move to the lumbar segments L2-L4, in domestic animals to L3-L6. There the excitation is switched to the motor neurons ( efferents ) via a synapse . These neurons traverse the lumbar plexus and back to the muscle in the femoral nerve , where a contraction of the quadriceps femoris is triggered.

So that the reflex of the antagonist (counteracting muscle) is not triggered at the same time , here the hamstrings ( Musculus biceps femoris , also called hamstring), an inhibiting mechanism works: The axon , which conducts the triggering information into the spinal cord, is branched, it points so there is a divergence. One branch runs to motor neurons that innervate the quadriceps femoris muscle, and another via a synapse that is linked to an inhibitory neuron that controls the biceps femoris. The action potential that comes from the leg extension (quadriceps femoris) suppresses that of the hamstring ( biceps femoris muscle ) at the same time .

Medical importance

A lack of the reflex indicates damage to the respective spinal cord segments or the femoral nerve .

This article is about a health issue. It is not used for self-diagnosis and does not replace a diagnosis by a doctor. Please note the information on health issues !