The patellar reflex, also known as the knee-jerk reflex, is a simple, involuntary response that occurs when the patellar tendon is tapped. This action stretches the tendon and the connected quadriceps muscle, triggering sensory neurons that send signals to the spinal cord. The spinal cord then sends a quick signal back to the quadriceps, causing the muscle to contract and the leg to kick forward. This reflex is a type of monosynaptic reflex, meaning it involves only one synapse between the sensory and motor neurons. It is commonly tested in medical examinations to assess the integrity of the neurological system and the functioning of the L2-L4 spinal nerves.