Pelvic Nerves: MRCOG Part 1 questions and key facts

The pudendal nerve (S2-S4) is the primary nerve supplying the muscles of the perineum, including the external urethral sphincter. The external urethral sphincter is a skeletal muscle that allows for voluntary control over micturition. Therefore, the pudendal nerve is essential for maintaining urinary continence.

Pelvic splanchnic nerves (S2-S4) carry parasympathetic fibres that innervate the detrusor muscle of the bladder, promoting bladder contraction and urination. They do not directly innervate the external urethral sphincter.

Hypogastric nerves carry sympathetic fibres that are involved in bladder filling and storage, primarily affecting the internal urethral sphincter (smooth muscle). They play a less significant role in the voluntary control offered by the external sphincter.

The sacral splanchnic nerves contribute to the sympathetic innervation of the pelvic organs, but they do not innervate the external urethral sphincter.

The vagus nerve primarily innervates thoracic and abdominal viscera and does not extend to the pelvic region.

Sacrospinous colpopexy is a surgical procedure used to treat pelvic organ prolapse, specifically vaginal vault prolapse. The procedure involves attaching the vaginal apex to the sacrospinous ligament, a strong ligament that runs from the ischial spine to the lateral aspect of the sacrum and coccyx. This provides support to the vaginal vault and helps restore normal pelvic anatomy.

The pudendal nerve is a major nerve in the pelvic region that originates from the sacral plexus (S2-S4 nerve roots). It courses posterior to the sacrospinous ligament, in close proximity to the ischial spine. This anatomical relationship makes the pudendal nerve vulnerable to injury during sacrospinous colpopexy, particularly if sutures are placed too deeply or too close to the ischial spine.

The sciatic nerve is another important nerve in this region, but it lies more laterally and inferiorly, further away from the surgical site. Therefore, it's less likely to be injured during this procedure.

The femoral, obturator, and superior gluteal nerves are located outside the immediate vicinity of the sacrospinous ligament and are not at significant risk during this surgery.

The cervix, like other visceral organs, has a dual nerve supply from both the sympathetic and parasympathetic nervous systems. However, the primary pathway for transmitting pain sensation from the cervix is through the pelvic splanchnic nerves. These nerves carry parasympathetic fibres originating from the S2-S4 spinal cord segments.

During procedures like cervical dilation or in conditions causing cervical inflammation, pain signals are generated. These signals travel along afferent fibres that accompany the parasympathetic efferent fibres within the pelvic splanchnic nerves. The signals then ascend through the spinal cord to reach higher brain centres, where they are perceived as pain.

The vagus nerves are not involved in transmitting pain from the cervix. The vagus nerve primarily innervates thoracic and abdominal viscera, but its role in pelvic innervation is minimal.

Pudendal nerves are somatic nerves and involved in voluntary control of the perineum and not pain from the cervix. Ilioinguinal and genitofemoral nerves supply the skin of the groin and genitalia but not pain from the cervix.