Professional and Linguistic Assessments Board (PLAB) Practice Exam

What movement is primarily controlled by the S1 spinal level?

1. Dorsiflexion

2. Hip flexion

3. Plantar flexion

4. Extension of the knee

The correct answer is: Plantar flexion

The movement primarily controlled by the S1 spinal level is plantar flexion. At the S1 level, the primary nerve involved is the tibial nerve, which innervates muscles such as the gastrocnemius and soleus. These muscles are crucial for the movement of plantar flexion, which involves pointing the toes and pushing off the ground when walking or running. Plantar flexion is vital for various activities that require the foot to push down and propel the body forward. The S1 level's contribution to this movement highlights its role in the lower extremity's functional mechanics, particularly in activities such as jumping, walking on tiptoes, and propulsion. In contrast, the other movements listed involve different spinal levels and nerve innervations. For example, dorsiflexion is primarily controlled by the L4-L5 levels and involves muscles that lift the toes upward. Hip flexion is governed by the lumbar plexus, particularly L2 and L3, while the extension of the knee is primarily associated with the L2-L4 level, engaging the quadriceps muscle group. Thus, the specific role of the S1 spinal level in controlling plantar flexion is critical for understanding lower limb functionality and movement.