The lumbar spinal nerves (L1–L5) pass from the spinal cord through the IV foramina inferior to the corresponding vertebrae, where they divide into posterior and anterior rami. Each ramus contains sensory and motor fibers. The posterior rami pass posteriorly to supply the muscles of the back and overlying skin, whereas the anterior rami pass laterally and inferiorly, to supply the skin and muscles of the inferiormost trunk and lower limb
LUMBAR PLEXUS
The anterior rami of the upper four lumbar nerves form the lumbar plexus ) in the psoas muscle The anterior rami give off gray rami communicantes to the sympathetic trunk, and the upper two give receive white rami communicantes from the sympathetic trunk. The branches of the plexus emerge from the lateral and medial borders of the muscle and from its anterior surface
The iliohypogastric nerve, ilioinguinal nerve, lateral cutaneous nerve of the thigh, and femoral nerve emerge from the lateral border of the psoas, in that order from above downward.
The iliohypogastric and ilioinguinal nerves (L1) cross the quadratus lumborum muscle and enter the lateral and anterior abdominal wall
The lateral cutaneous nerve of the thigh crosses the iliac fossa in front of the iliacus muscle and enters the thigh behind the lateral end of the inguinal ligament.
The femoral nerve (L2 to 4) is the largest branch of the lumbar plexus. It runs downward and laterally between the psoas and the iliacus muscles and enters the thigh behind the inguinal ligament and lateral to the femoral vessels and the femoral sheath. In the abdomen, it supplies the iliacus muscle.
The obturator nerve and the fourth lumbar root of the lumbosacral trunk emerge from the medial border of the psoas at the brim of the pelvis.
The obturator nerve (L2 to 4) crosses the pelvic brim in front of the sacroiliac joint and behind the common iliac vessels. It leaves the pelvis by passing through the obturator foramen into the thigh.
The fourth lumbar root of the lumbosacral trunk takes part in the formation of the sacral plexus .It descends anterior to the ala of the sacrum and joins the first sacral nerve.
The genitofemoral nerve (L1 and 2) emerges on the anterior surface of the psoas. It runs downward in front of the muscle and divides into a genital branch, which enters the spermatic cord and supplies the cremaster muscle, and a femoral branch, which supplies a small area of the skin of the thigh.
CREMASTERIC REFLEX
in which stimulation of the skin of the thigh in the male results in reflex contraction of the cremaster muscle and the drawing upward of the testis within the scrotum.
SYMPATHETIC INNERVATION
The sympathetic part of the autonomic innervation of the abdominal viscera consists of the following:
Abdominopelvic splanchnic nerves from the thoracic and abdominal sympathetic trunks.
Prevertebral sympathetic ganglia.
Abdominal aortic plexus and its extensions, the peri-arterial plexuses
Abdominopelvic splanchnic nerves
Lower thoracic splanchnic nerves (greater, lesser, and least): from the thoracic part of the sympathetic trunks.
The greater splanchnic nerve (from the sympathetic trunk at T5 through T9 or T10 vertebral levels),
lesser splanchnic nerve (from T10 and T11 levels), and
least splanchnic nerve (from the T12 level)
Lumbar splanchnic nerves: from the lumbar part of the sympathetic trunks.
Prevertebral sympathetic ganglia
The cell bodies of postsynaptic sympathetic neurons constitute the major prevertebral ganglia that cluster around the roots of the major branches of the abdominal aorta: the celiac, aorticorenal, superior mesenteric, and inferior mesenteric ganglia.
With the exception of the innervation of the suprarenal medulla, the synapse between presynaptic and postsynaptic sympathetic neurons occurs in the prevertebral ganglia
.Postsynaptic sympathetic nerve fibers pass from the prevertebral ganglia to the abdominal viscera by means of the peri-arterial plexuses associated with the branches of the abdominal aorta.
Sympathetic innervation in the abdomen, as elsewhere, is primarily involved in producing vasoconstriction. With regard to the gastrointestinal tract, it acts to inhibit (slow down or stop) peristalsis.
.Postsynaptic sympathetic nerve fibers pass from the prevertebral ganglia to the abdominal viscera by means of the peri-arterial plexuses associated with the branches of the abdominal aorta.
Sympathetic innervation in the abdomen, as elsewhere, is primarily involved in producing vasoconstriction. With regard to the gastrointestinal tract, it acts to inhibit (slow down or stop) peristalsis.
PARASYMPATHETIC INNERVATION
Anterior and posterior vagal trunks.
Pelvic splanchnic nerves.
Abdominal (para-aortic) autonomic plexuses and their extensions, the periarterial plexuses.
Intrinsic (enteric) parasympathetic ganglia, components of intrinsic enteric plexuses of the enteric nervous system.
The vagus nerves supply parasympathetic fibers to the digestive tract from the esophagus through the transverse colon.
Pelvic splanchnic nerves supply the descending and sigmoid colon and rectum.
Parasympathetic stimulation promotes peristalsis and secretion (although much of the latter is usually hormonally regulated).
Sensory innervation:
Visceral afferent fibers follow the autonomic fibers retrograde to sensory ganglia.
Afferent fibers conveying pain sensation from abdominal viscera proximal to the middle of the sigmoid colon run with the sympathetic fibers to the thoracolumbar spinal sensory ganglia; all other visceral afferent fibers run with the parasympathetic fibers.
Thus, visceral afferent fibers conveying reflex information from the gut proximal to the middle of the sigmoid colon pass to vagal sensory ganglia;
fibers conveying both pain and reflex information from the gut distal to the middle of the sigmoid colon pass to spinal sensory ganglia S2–S4
