Patellar reflex

The patellar tendon reflex (also knee -jerk, knee jerk, Patellareflex or Quadricepsdehnungsreflex ) is a monosynaptic ( via only one synapse interconnected ) reflex from the group of reflexes.

Release

The reflex can be triggered by a light tap on the patellar tendon below the kneecap. It is the tendon of insertion of four thigh muscle ( quadriceps femoris). As a reflex response occurs by contraction of the quadriceps in a stretching of the knee joint.

Physiology

Stretch receptors (so-called muscle spindles ) register the strain in the quadriceps and report them to the spinal cord. Contrary to the general opinion of the Golgi tendon organs are not involved in the patellar tendon. Although they are also stretched by the blow on the patellar tendon, but the Golgi tendon organs are for the regulation of muscle tone. When people pull the sensitive neurons ( afferents ) to the lumbar segments L2 -L4, in domestic animals to L3 - L6. There, the excitation is switched on each synapse on the motor neurons ( efferent ). These neurons through the lumbar plexus and femoral nerve back to the muscle where contraction of the quadriceps femoris muscle is triggered.

Thus, in this reflex is not also the reflex of the antagonist ( opposing muscle) is triggered, here the hamstrings ( biceps femoris, and hamstrings ), and in effect a mechanism of inhibition: The axon, which conducts the triggering information into the spinal cord is branched, it has thus, a divergence. Here a road runs to motor neurons that innervate the quadriceps femoris and another via a synapse that is associated with an inhibitory neuron that controls the biceps femoris. The action potential coming from the leg extension ( quadriceps femoris), so while suppressing that of Beinbeugers ( biceps femoris).

Medical importance

An absence of the reflex suggests damage to the local spinal cord segments or the femoral nerve.

• Proprioceptive reflex