MSD Manual

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Reflex Arc: A No-Brainer
Reflex Arc: A No-Brainer
Reflex Arc: A No-Brainer

A reflex arc is the pathway that a nerve reflex, such as the knee jerk reflex, follows.

  • 1. A tap on the knee stimulates sensory receptors, generating a nerve signal.

  • 2. The signal travels along a nerve to the spinal cord.

  • 3. In the spinal cord, the signal is transmitted from the sensory nerve to a motor nerve.

  • 4. The motor nerve sends the signal back to a muscle in the thigh.

  • 5. The muscle contracts, causing the lower leg to jerk upward. The entire reflex occurs without involving the brain.