Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which action is controlled by the L4 spinal level?

1. Dorsiflexion

2. Hip extension

3. Knee flexion

4. Elbow extension

The correct answer is: Dorsiflexion

The L4 spinal level primarily contributes to the innervation of the muscles responsible for dorsiflexion of the ankle. Dorsiflexion is the movement that allows the foot to be raised upward towards the shin, which is primarily controlled by the tibialis anterior muscle, innervated by the deep peroneal nerve, which has roots from the L4 spinal segment. This level plays a crucial role in motor function and reflexes associated with the lower extremities, particularly the foot and ankle movements. In contrast, hip extension is mainly controlled by the spinal levels associated with the gluteus maximus muscle, which derives its innervation from the inferior gluteal nerve, originating from L5, S1, and S2. Knee flexion involves the hamstring muscles, innervated by branches from the sciatic nerve, which spans a higher range of spinal levels including L5 and S1. Elbow extension is governed by the radial nerve, which has its roots predominantly in C6, C7, and C8 spinal levels, illustrating that it is not controlled by the lumbar spine at all. Thus, identifying that dorsiflexion is associated specifically with the L4 level reflects a crucial understanding of spinal anatomy and its