This document describes the anatomical relationships of the nerves of the pelvis, with particular reference to the lumbar and sacral plexuses and their respective branches.
Anatomy notes - Shoulder, Posterior Scapular Region & Back
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Pelvic Nerves
Somatic Plexuses
Sacral and coccygeal plexuses
Situated on the posterolateral wall of the pelvic cavity and generally occur in the
plane between the muscles and blood vessels.
They are formed by the anterior rami of S1 to C0, with a significant contribution
from L4 and L5 that enter the plexus from the lumbar plexus.
The nerves of these plexuses contribute to the innervation of the lower limbs and
muscles of the pelvis and perineum. Cutaneous branches supply the skin over
the medial side of the foot, the posterior aspect of the lower limb and most of the
perineum.
The Sacral Plexus
Formed by the anterior rami of nerve roots S1 to S4, and the lumbosacral trunk
(L4 and L5). The plexus is formed in relation to the anterior surface of the
piriformis muscle, which is part of the posterior pelvic wall.
The Sacral contributions to the plexus pass out of the anterior sacral foramina
and course inferiorly and laterally on the pelvic wall.
The lumbosacral trunk, consisting of a branch of the anterior ramus of L4 and
the entire anterior ramus of L5 courses vertically into the pelvic cavity by passing
immediately anterior to the sacroiliac joints.
Pelvic Nerves 1
, Gray rami communicantes from ganglia of the sympathetic trunk connect with
each of the anterior rami and carry postganglionic sympathetic fibres destined
for the periphery to the somatic nerves.
Special visceral nerves - pelvic splanchnic nerves - originating from S2 to S4
deliver preganglionic parasympathetic fibres to the pelvic part of the prevertebral
plexus.
Each anterior ramus has ventral and dorsal divisions. These combine with
similar divisions from other nerve levels to produce terminal nerves. The anterior
ramus of S4 only features a ventral part.
Most of the nerves that originate in the sacral plexus leave the pelvic cavity by
passing through the greater sciatic foramen, inferior to the piriformis muscle to
enter the gluteal region of the thigh.
Major Nerves of the Sacral Plexus
Sciatic Nerve
The largest nerve of the body and carries contributions from L4 to S3.
It forms on the anterior surface of the piriformis muscle and leaves the pelvic
cavity through the greater sciatic foramen, inferior to piriformis.
Pelvic Nerves 2
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