Which of the following reflexes is primarily associated with the S1 nerve root?

The ankle reflex, also known as the Achilles reflex, is primarily associated with the S1 nerve root. This reflex helps assess the functioning of the spinal segments S1 and S2, which are part of the sacral plexus. When the Achilles tendon is tapped, it activates sensory receptors in the tendon, leading to a response that involves contraction of the gastrocnemius and soleus muscles, resulting in plantar flexion of the foot. The S1 nerve root is crucial for this action, making the ankle reflex a key indicator of the integrity of the S1 spinal segment.

In contrast, the patellar reflex is associated with the L2-L4 nerve roots, primarily involving the quadriceps muscle and the femoral nerve. The supinator reflex, also known as the brachioradialis reflex, relies on the C5-C6 nerve roots and tests the integrity of the radial nerve. Lastly, the biceps reflex is connected to the C5-C6 nerve roots as well and assesses the function of the musculocutaneous nerve. Each of these reflexes corresponds to different nerve roots, thus highlighting the importance of understanding which reflex correlates with specific spinal segments.