Knee jerk

Knee jerk or patellar reflex is a type of reflex that is elicited when the patellar tendon is tapped. The knee jerk reflex is a simple neural circuit involving only two neurons: a sensory neuron and a motor neuron. It is a classic example of a monosynaptic reflex.

Anatomy

The patellar tendon is connected to the quadriceps femoris muscle, the large muscle group at the front of the thigh. When the tendon is tapped, it stretches the muscle, which triggers a signal in the sensory neuron. This signal travels to the spinal cord, where it synapses directly with a motor neuron. The motor neuron sends a signal back to the quadriceps, causing it to contract and the knee to jerk.

Function

The knee jerk reflex is a protective mechanism that helps to maintain balance and posture. It is also used in medical examinations to assess the health of the nervous system. A lack of reflex can indicate damage to the peripheral nerves or the spinal cord, while an exaggerated reflex can suggest damage to certain parts of the brain.

Clinical significance

In neurology, the knee jerk reflex is used as a diagnostic tool. It can help to localize lesions in the nervous system, and can also provide information about the integrity of the motor neurons. In conditions such as multiple sclerosis, stroke, and spinal cord injury, the reflex may be altered or absent.

See also

• Reflexes
• Neurological examination
• Monosynaptic reflex
• Spinal cord