Читать книгу Ridley's The Vulva - Группа авторов - Страница 94

This is entirely from the most caudal elements of both the sympathetic and parasympathetic systems.

 Sympathetic innervationThe sympathetic pathways are restricted to the region between the first thoracic and second lumbar levels of the spinal cord. The sympathetic innervation of the perineum is located therefore at L1 and L2. It reaches the perineum via postganglionic fibres, arising from the first two lumbar and all four sacral ganglia of the sympathetic trunks. These fibres are distributed with the corresponding segmental nerves. In addition, other sympathetic fibres from L1 and L2 leave the sympathetic trunk as the hypogastric nerves (lumbar splanchnic presacral nerves) and descend into the pelvis to be associated with autonomic pelvic plexuses, which are distributed with the blood vessels.

 Parasympathetic innervation

The parasympathetic pathways consist of cranial and caudal portions. The cranial portion is associated with four of the cranial nerves, whereas the caudal portion is associated with the second and third, or third and fourth, sacral segments of the spinal cord as the pelvic splanchnic nerves. These nerves together with the hypogastric sympathetic nerves form the autonomic pelvic plexuses.

The parasympathetic system does not participate in mediation of common sensations such as temperature and pain. The sensory components of the parasympathetic innervation of the perineum mediate the sensation of distension from the anal canal and vagina, while its motor component is responsible for the vascular engorgement of vaginal erectile tissue.

The cutaneous innervation of the perineum conveys all modalities of common sensation such as touch, pain, itch, and temperature, as well as complex sensations such as wetness. In addition, these cutaneous nerves carry postganglionic sympathetic nerves that provide motor innervation to sweat glands, pilomotor units, and blood vessels. These sacral spinal nerves also supply motor innervation to the muscles of the perineum. The anterior part of the perineum is supplied by two nerves that emerge from the superficial inguinal ring just above the body of the pubic bone. These are the ilioinguinal nerve (L1) and the genital branch (L2) of the genitofemoral nerve (L1 and L2). The lateral aspect of the perineum, more posteriorly, is supplied by the perineal branch (S1) of the posterior cutaneous nerve of the thigh (S1–S3). The remainder of the cutaneous innervation of the perineum is supplied by the pudendal nerve (S2–S4) and the perineal branch of the fourth sacral nerve, which also supplies the skin of the anal margin.