The Achilles tendon reflex tests nerve roots at which level?

The Achilles tendon reflex tests nerve roots at which level?

• A. L5 to S1 nerve roots assessed via plantarflexion response.
• B. L4 to L5 nerve roots via dorsiflexion response.
• C. S1 to S2 nerve roots via plantarflexion.
• D. L3 to L4 nerve roots via knee extension.

Answer: (A)

The Achilles tendon reflex mainly tests the sacral nerve roots S1 (and to a lesser extent S2) through plantarflexion. When the tendon is tapped, the stretch of the gastrocnemius-soleus complex activates muscle spindle fibers, sending signals via the tibial nerve to the spinal cord at the S1–S2 levels. The reflex arc then elicits a motor response back to the plantarflexor muscles, producing downward movement of the foot. That plantarflexion response points to the S1–S2 nerve roots as the key level tested. Knee extension is a different reflex (L3–L4), and dorsiflexion tests involve other pathways, not the Achilles reflex. So the most accurate description is plantarflexion indicating S1–S2 nerve roots.

The Achilles tendon reflex mainly tests the sacral nerve roots S1 (and to a lesser extent S2) through plantarflexion. When the tendon is tapped, the stretch of the gastrocnemius-soleus complex activates muscle spindle fibers, sending signals via the tibial nerve to the spinal cord at the S1–S2 levels. The reflex arc then elicits a motor response back to the plantarflexor muscles, producing downward movement of the foot. That plantarflexion response points to the S1–S2 nerve roots as the key level tested.

Knee extension is a different reflex (L3–L4), and dorsiflexion tests involve other pathways, not the Achilles reflex. So the most accurate description is plantarflexion indicating S1–S2 nerve roots.