Which nerve is responsible for innervating the external urethral sphincter?

The pudendal nerve is responsible for innervating the external urethral sphincter, which is a critical component in the control of micturition (urination). This nerve, originating from the sacral plexus (specifically S2 to S4), supplies motor innervation to the external urethral sphincter, enabling conscious control over the release of urine.

Additionally, the pudendal nerve provides sensory innervation to areas around the perineum, facilitating both protective reflexes and sensory feedback related to bladder fullness. Its role is crucial in maintaining urinary continence and facilitating voluntary urination.

In contrast, the vagus nerve primarily innervates structures in the thoracic and abdominal cavities and is involved in parasympathetic control of visceral organs, but it does not have a role in the innervation of the external urethral sphincter. The femoral nerve mainly supplies the anterior compartment of the thigh and is involved in hip flexion and knee extension, while the obturator nerve is responsible for innervating the adductor muscles of the thigh. Neither the femoral nor the obturator nerves are involved in the control of the external urethral sphincter.