The ankle jerk (Achilles tendon reflex) tests which segmental level and peripheral nerve?

• A S1 via the tibial nerve ✓
• B L5 via the tibial nerve
• C L4 via the deep peroneal nerve
• D S2 via the common peroneal nerve

Explanation

The Achilles tap stretches the calf muscles, chiefly gastrocnemius and soleus, whose afferent and efferent limbs run in the tibial nerve; the reflex centre is S1. By contrast the knee jerk is L3, L4 through the femoral nerve. L5 has no single tendon reflex of its own, which is why L5 radiculopathy weakens dorsiflexion without abolishing any jerk. This makes the ankle jerk the key bedside test for S1 integrity.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.