Which nerve root does the Achilles reflex test?

The Achilles reflex primarily tests the S1 nerve root. This reflex is a deep tendon reflex that is elicited by tapping on the Achilles tendon, which is located at the back of the ankle. When stimulated, it causes contraction of the gastrocnemius and soleus muscles, resulting in plantarflexion of the foot.

The functional significance of the S1 nerve root is that it innervates the muscles involved in this reflex. Therefore, when assessing an individual's reflexes, the response from the Achilles tendon provides important information about the integrity and function of the S1 nerve root specifically, and by extension, the lower spinal cord segments associated with the S1 root.

Understanding this reflex and the specific nerve involvement can assist medical examiners in diagnosing potential neurological conditions or dysfunctions. While L5 and S2 are related to other lower limb functions and reflexes, the Achilles reflex is definitively linked to S1.