Knee-jerk reflex

Knee-jerk reflex (also known as the patellar reflex) is a type of reflex that is elicited by a sharp tap on the patellar tendon, which lies just below the knee. The reflex is caused by the stretch reflex mechanism to prevent the muscle from stretching too far.

Mechanism

The knee-jerk reflex is a monosynaptic reflex that involves a single synapse in the spinal cord. When the patellar tendon is tapped, the quadriceps muscle is stretched, which stimulates the muscle spindles. These sensory receptors send a signal to the spinal cord, which in turn sends a signal back to the quadriceps muscle, causing it to contract and the lower leg to kick forward.

Clinical significance

The knee-jerk reflex is used in neurological examinations to test the function of the nervous system. An absent or decreased knee-jerk reflex may indicate damage to the peripheral nerves, spinal cord, or muscle disease. An exaggerated knee-jerk reflex may indicate damage to the brain or spinal cord.

See also

• Reflexes
• Monosynaptic reflex
• Neurological examination

References

Knee-jerk reflex Resources
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