Learning Modules - Medical Gross Anatomy
Autonomics of the Pelvis - Page 11 of 12

     
Autonomic Innervation of the Uterus: The uterovaginal plexus of the female stems from the intermediate part of the inferior hypogastric plexus. Its branches innervate the uterus, uterine tube, cervix and upper vagina. Sympathetic innervation originates in segments of the lower thoracic spinal cord and passes through lumbar splanchnics and the inferior mesenteric/hypogastric series of plexuses and finally to the uterovaginal plexus. Parasympathetic innervation originates in the S2 through S4 spinal cord segments and passes through pelvic splanchnics to the inferior hypogastric plexus and then into the uterovaginal plexus. (Remember that the pudendal nerve (S2-S4) does not carry parasympathetic fibers.) Visceral afferent fibers originating in the fundus and body of the uterus travel retrograde with sympathetics along the hypogastric nerves and superior hypogastric plexus to reach the lower thoracic segments of the spinal cord. Afferent fibers of the upper vagina and cervix travel back along the pelvic splanchnics (S2-S4) and on the pudendal nerve.

Clinical Sidenote: There are several ways in which pain is regionally managed during childbirth.

  1. A spinal block, in which anaesthetic agent placed into the L3/L4 subarachnoid space numbs everything inferior to the waist. In this case a mother would not be conscious of anything below her waist and would need to rely on electronic monitoring of uterine contractions to help deliver the baby.
  2. Pudendal nerve block involves direct administration of anaesthetic agent into the nerve as it exits the greater sciatic foramen. This type of anaesthetic provides a nerve block over the S2 through S4 dermatomes only, which includes the perineum and the lower one-fourth of the vagina. It does not block pain felt from the body or fundus of the uterus because those afferent fibers travel retrograde along sympathetics heading to the thoracic region. By not numbing these regions, a mother can still feel contractions and play an active role in labor.
  3. A caudal epidural block can be administered via an in-dwelling catheter into the sacral canal. Within the sacral canal, the agent bathes the sacral nerve roots, which reach the cervix, upper vagina and form the pudendal nerve.

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