Which nerve root is associated with the lateral foot and Achilles reflex?

Which nerve root is associated with the lateral foot and Achilles reflex?

• A. L5
• B. S1
• C. L4
• D. L2-3

Answer: (B)

The Achilles reflex and the sensation on the lateral foot are both governed by the S1 nerve root. The ankle (Achilles) reflex is mediated by the tibial nerve, which predominantly carries signals from S1. The lateral aspect of the foot is part of the S1 dermatome, supplied by the sural nerve. So S1 best accounts for both features. Other roots relate to different functions (for example, L5 with certain foot dorsiflexion/sensations, L4 with the patellar reflex, and L2-3 with hip/knee movements), which is why they don’t fit both findings as well.

The Achilles reflex and the sensation on the lateral foot are both governed by the S1 nerve root. The ankle (Achilles) reflex is mediated by the tibial nerve, which predominantly carries signals from S1. The lateral aspect of the foot is part of the S1 dermatome, supplied by the sural nerve. So S1 best accounts for both features. Other roots relate to different functions (for example, L5 with certain foot dorsiflexion/sensations, L4 with the patellar reflex, and L2-3 with hip/knee movements), which is why they don’t fit both findings as well.