Question

Discuss about knee-jerk reflex.

Answer 1

Hint: The knee-jerk reflex or the patellar reflex is a reflex in which the knee jerks when there is a sudden tap on it. It is a type of involuntary action. It is used to assess the various medical conditions and nervous tissues.

Complete step by step answer: The knee-jerk reflex is also referred to as the Patellar reflex. It is a stretch reflex. It tests the second, third, and fourth lumbar segments of the spinal cord. It is caused by striking the knee-tendon or the patella region. When the knee-tendon or the patella region is struck then it produces a signal wave that travels back to the spinal cord. This signal then synapses without the interneurons to the spinal cord. From this region then, an alpha motor neuron conducts an impulse. This impulse is efferent in nature. It is conducted back to the quadriceps muscles. These muscles then trigger contraction. This contraction is coordinated along with the flexor hamstring muscles which is antagonistic in nature. It makes the leg jerk or kick. This whole process is known as the knee-jerk reflex.

Note: The knee-jerk reflex is used as a test to assess the nervous tissues of the second to fourth lumbar segments of the spinal cord. When the hammer is tapped once, then the leg normally gets extended and comes to the rest. If this reflex has a decreased magnitude or if it is absent then it is known as Westphal’s sign, and it indicates a problem in the body. It is absent and diminished in the sleep or the lower motor neuron lesions. On the other hand, if the leg shows multiple oscillations then it is a sign of cerebellar diseases. Exaggerated oscillations indicate hyperthyroidism, nervousness, and anxiety.