30 Innervation

STUDYAIMS

At the end of your study, you should be able to:

Describe the parasympathetic contribution to the autonomic innervation of abdominal viscera Describe the sympathetic contribution to the autonomic innervation of abdominal viscera Understand the organization of the autonomic plexuses of the abdomen

Describe the somatic innervation of the abdominal wall Know the branches of the lumbar plexus

Understand the principle of referred pain and describe common patterns of pain referral from the abdominal viscera

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GUIDE

Abdomen: Innervation

[Plate 297, Autonomic Nerves and Ganglia of Abdomen]

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[Plate 302, Autonomic Innervation of Large Intestine]

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[Plate 304, Autonomic Reflex Pathways: Schema]

Autonomic Nerves

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Parasympathetic nerves

Preganglionic fibres

Provided byvagus nerve and sacral splanchnic nerves

Synapse with postganglionic fibres in the walls of the relevant organs

Vagus nerve (CN X)

Give rise to anterior and posterior vagal trunks in thorax

Trunks enter abdomen at the esophageal hiatus

Anterior trunk (mainlyfrom the left vagus)

Enters anterior to the esophagus

Gives branches to the anterior surface of the stomach and to the liver

Posterior trunk (mainlyfrom the right vagus)

Enters posterior to the esophagus

Gives branches to the posterior surface of the stomach and celiac plexus

Fibers pass inferiorlyto root of superior mesenteric artery

Fibers contribute to perivascular plexuses

Accompanying celiac and superior mesenteric arteryand their branches

Extend as far as the arterial supply(two thirds of the way along the transverse colon)

Pelvic splanchnic nerves

From spinal cord levels S2-S4

Emerge through pelvic sacral foramina

Ascend from pelvis running in sigmoid mesocolon and peritoneum of posterior abdominal wall

Supplydistal one third of transverse colon, descending colon, sigmoid colon, and superior rectum

Postganglionic (postsynaptic) parasympathetic neurons found in enteric ganglia in wall of viscus Sympathetic nerves

Right and left sympathetic trunks

Enter behind the medial arcuate ligament of the diaphragm

Descend along psoas major, with right trunk behind inferior vena cava (IVC)

Lie on anterolateral sides of lumbar vertebrae

Receive white rami communicantes from, and send grayrami communicantes to, ventral rami of L1-L3 spinal nerves

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Postganglionic fibers in grayrami communicantes to corresponding ventral rami of spinal nerves distributed to the bodywall and lower limb

Give off three to four lumbar splanchnic nerves (presynaptic sympathetic fibers) mediallyto:

Intermesenteric plexus

Inferior mesenteric plexus

Superior hypogastric plexus

Postsynaptic fibers from these plexuses innerve nearbytarget organs.

Sympathetic (paravertebral) ganglia

Total of four abdominal sympathetic ganglia per trunk

Prevertebral sympathetic ganglia

Cell bodies of postsynaptic sympathetic neurons

Found in plexuses around roots of major branches of aorta Aortic plexuses

Network of parasympathetic and sympathetic nerves

Parasympathetic mainlyfrom posterior vagal trunk (see above)

Sympathetic fibers from thoracic and lumbar splanchnic nerves (Section 3: Thorax)

Contain prevertebral ganglia

Include:

Celiac plexus

Aorticorenal plexus

Renal plexus

Superior mesenteric plexus

Intermesenteric plexus

Inferior mesenteric plexus

Perivascular plexuses derived from the aortic plexuses

Visceral afferent fibers

Carrypain information

Travel with sympathetic fibers back to spinal cord

Referred pain

Information carried byvisceral afferent fibers

Fibers travel back to T5-L2/3 spinal cord levels via thoracic and lumbar splanchnic nerves

Clinical phenomenon of referred pain is visceral pain perceived as somatic pain over the dermatomes innervated bycutaneous nerves with fibers from those spinal cord levels:

Somatic Nerves

Thoracoabdominal nerves

Ventral primaryrami of T7-T11

Travel in the neurovascular plane between the internal oblique and transversus abdominis muscles

Innervate anterolateral abdominal wall, including parietal peritoneum Subcostal nerves

Ventral primaryrami of T12

Follow the inferior border of the 12th rib

Enter abdomen behind lateral arcuate ligaments

Cross quadratus lumborum muscles and pierces transversus abdominis muscles to enter neurovascular plane

Innervate anterolateral abdominal wall (including parietal peritoneum) Lumbar plexus

Iliohypogastric nerve (L1)

Divides into lateral and anterior cutaneous branches

Pierces internal and external oblique muscles

Supplies buttocks and suprapubic region

Ilioinguinal nerve (L1)

Travels in inguinal canal

Joins spermatic cord after piercing internal abdominal oblique (Note: does not enter inguinal canal through deep inguinal ring)

Provides cutaneous branches to skin of inguinal region

Genitofemoral nerve (L1,2)

Emerges from anterior surface of psoas major muscle

Genital branch enters deep inguinal ring to innervate the cremaster muscle

Femoral branch passes beneath inguinal ligament in vascular compartment to enter femoral triangle and provides

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cutaneous branches to anteromedial thigh Lateral femoral cutaneous nerve (L2,3)

Passes beneath or through inguinal ligament, medial to anterior superior iliac spine (ASIS)

Innervates anterolateral thigh Obturator nerve (L2-L4)

Emerges from medial border of psoas major muscle

Passes through pelvis

Exits via obturator canal

Supplies skin and adductor muscles of medial thigh Femoral nerve (L2-L4)

Emerges from lateral psoas major muscle

Innervates iliacus

Passes beneath inguinal ligament on surface of iliopsoas muscle in muscular compartment

Enters femoral triangle to innervate flexors of the hip/extensors of leg at knee, and skin of anterior thigh, medial aspect of leg and foot.

Lumbosacral trunk (L4,5)

Enters pelvis passing over ala of sacrum

Contributes to formation of sacral plexus with ventral rami of S1-S4 spinal nerves

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