Path of knee-jerk reflex arc is

Knee-jerk reflex (patellar reflex) is the sudden kicking movement of the lower leg in response to a sharp tap on the patellar tendon, which lies just below the kneecap. The sharp tap on the tendon slightly stretches the quadriceps muscle of the upper leg. This is detected by the muscle spindle (receptor) and the impulse is carried by afferent (sensory) neuron to the spinal cord through the dorsal root of the spinal nerve. This neuron synapses with the efferent (motor) neuron which leaves the spinal cord through the ventral root of the spinal cord and causes the contraction of the muscle. Knee-jerk reflex is a spinal reflex, and the response occurs without the impulse being carried to the brain.