Physiology Trace the neuronal activity initiated by striking

Physiology: Trace the neuronal activity initiated by striking the patellar tendon with a percussion hammer that leads to contraction of a muscle, particularly comparing monosynaptic vs. polysynaptic reflexes.

Solution

Patellar reflex is a simple stretch reflex (somatic reflex). Patellar reflex can be tested by knee jerk. The person is asked to sit on a bench with hanging legs freely and tap the patellar ligament just below the knee with the reflex hammer. This excites the muscle spindle of quadriceps that is innervated by femoral nerve. The fibular nerve innervate the biceps femoris and provides motor control (anterior region of the leg). It is an example of monosynaptic reflex.

A pair of muscles (flexor and extensor) act antagonistically to control the limb movement. The activation of one motor neuron simultaneously inhibits another neuron and this is mediated by the inter-neurons (so they synapse with both the types of muscles). The knee jerk reflex (patellar reflex) arises at the level of L₂ through L₄ of the spinal cord.