The Achilles reflex is associated with which spinal nerve?

The Achilles reflex, also known as the posterior tibial reflex, is primarily associated with the S1 spinal nerve root. The reflex is tested by tapping the Achilles tendon while the patient’s foot is in a relaxed position, which should cause plantarflexion of the foot. This reflex is an important indicator of the function of the S1 nerve roots and the integrity of the associated pathways in the peripheral nervous system.

The S1 nerve root specifically innervates muscles involved in ankle and foot movement, making it crucial for performing actions that require plantarflexion. When assessing the Achilles reflex, healthcare providers can evaluate both the neural pathways and the state of the muscle function that are connected to the S1 nerve root.

In contrast, spinal nerve roots such as L4, L5, and C7 are not involved in the Achilles reflex, as they correspond to different muscle groups and reflex actions. For instance, L4 and L5 are more associated with knee extension and dorsiflexion of the foot, while C7 is related to upper extremity reflexes like triceps reflex. Thus, the focus on the S1 nerve root in the context of the Achilles reflex is what makes it the correct choice in this question.