62 AUTONOMIC INNERVATION OF THE LIVER AND BILIARY TRACT

198



Regional Neuroscience



T5

T6



Right sympathetic trunk



Spinal sensory (dorsal root) ganglion

Left sympathetic trunk

Thoracic part of spinal cord



T7



Right greater thoracic

splanchnic nerve



T8



Posterior vagal trunk



Left greater splanchnic nerve

Anterior vagal trunk



T9



Common areas of

pancreatic pain



Celiac ganglia

Splenic artery



Celiac trunk



Superior

mesenteric

ganglion

Superior mesenteric artery and plexus



Sympathetic fibers

Presynaptic

Postsynaptic



Schema of intrinsic

nerve supply



Parasympathetic fibers

Presynaptic

Postsynaptic

Afferent fibers



9.63╇AUTONOMIC INNERVATION

OF THE PANCREAS

Secretion by the pancreas is under both neural and endocrine

control. Pancreatic exocrine glands and endocrine cells �(islets

of Langerhans) are innervated by parasympathetic subdiaphragmatic vagal nerve fibers via intramural ganglia and by

sympathetic nerve fibers derived from T5–T9 intermediolateral spinal cord gray via the celiac ganglion. Although only

a small anatomical component of the pancreas (1%), the

endocrine pancreas secretes several vital endocrine products, including glucagon (a fuel-mobilizing hormone); insulin (a fuel-storing hormone); somatostatin (a suppressor of



glucagons and insulin secretion); and pancreatic polypeptide

(an inhibitor of the secretion of enzymes and HCO3-, the bicarbonate ion, by the exocrine pancreas). ACh supplied by

the parasympathetic fibers stimulates insulin secretion by islet

cells, and norepinephrine secretion by the sympathetic fibers

(as well as epinephrine by the adrenal medulla) inhibits insulin secretion from the islet cells. ACh stimulates a variety

of hormones. Secretin acts on ductal cells of the pancreas to

stimulate secretion of fluid with a high HCO3- content. Cholecystokinin is secreted by I cells in response to fats in the

duodenum and upper jejunum and acts on aciner cells to

�stimulate the secretion of enzymes.



Peripheral Nervous System



199



Intermediolateral cell column

(lateral horn of gray matter)

T10



Medulla



Cortex



Abdominopelvic splanchnic

nerves (presynaptic fibers)



T11



Celiac, aorticorenal

and renal ganglia

T12



Postsynaptic

fibers supply

blood vessels



L1



Spinal cord



Sympathetic

trunk



Presynaptic fibers ramify

around cells of medulla



Suprarenal gland



9.64╇SCHEMATIC OF INNERVATION

OF THE ADRENAL GLAND

Sympathetic preganglionic nerve fibers from neurons in

the T10–L1 intermediolateral cell column pass through the

�sympathetic chain, travel in splanchnic nerves, and directly



innervate adrenal medullary chromaffin cells. These chromaffin cells are of neural crest origin and function as sympathetic

ganglion cells.



200



Regional Neuroscience



Preaortic

ganglia



CH2-CH-COOH

NH2



es



erv



Sympathetic

trunk



OH



h



nc



la

Sp



n

nic



Adrenal

cortex



Adrenal

medulla



CH2-CH2-NH2



OH



CH-CH2-NH

OH

CH3

OH

OH

Dopamine

Conversion

OH

stimulated

OH

by cortisol

CH-CH2-NH2

Epinephrine



T10

T11

T12

L1



++++



OH

Nor



+



epin



+



++++



eph



Epin



++



eph



rine



Cortisol



++++

+



Increased

cardiac

output



Basal

metabolic

rate

elevation



OH

Norepinephrine



rine

+++



+



Blood

pressure

elevation



Tyrosine



++++



Glucose



++++



Glycogen

Bronchial

dilation;

intestinal

inhibition

Kidney



Glycogenolysis;

hyperglycemia



CNS

excitability

+++



Free fatty acids

Lipolysis



+++



Urinary excretion of metabolites



9.65╇INNERVATION OF THE ADRENAL GLAND

The adrenal medullary chromaffin cells act as modified

sympathetic ganglion cells, which are innervated by preganglionic sympathetic nerve fibers from T10 to L1 intermediolateral cells of the spinal cord. An adrenal portal system

conveys blood directly from the adrenal cortex to the adrenal

medulla. Cortisol, derived from action of the hypothalamo-

pituitary-adrenal axis, bathes the chromaffin cells in very high

concentrations, inducing the enzyme phenylethanolamineN-methyl-transferase, which is responsible for the synthesis

of epinephrine. Approximately 70% to 80% of the adrenal

medullary output of catecholamines is epinephrine; the



�

remaining

output is norepinephrine. Both epinephrine and

norepinephrine can be taken up into sympathetic postganglionic noradrenergic nerve terminals at any site throughout the body by the high-affinity uptake carrier and can be

subsequently released. A sympathetic arousal response that

�generates the secretion of epinephrine from the adrenal medulla will therefore provide altered catecholamine content

(higher epinephrine) because of high-affinity uptake in nerve

terminals throughout the body; subsequent release of this

epinephrine modifies the usual sympathetic balance of alpha

versus beta receptor stimulation on target organs for a brief

period.



Peripheral Nervous System



201



2nd lumbar sympathetic trunk ganglion

Intermesenteric (abdominal aortic) plexus

Gray and white rami communicantes



Inferior mesenteric ganglion



L2



Lumbar splanchnic nerves

Right sympathetic trunk

and its 3rd lumbar ganglion

L3



Inferior mesenteric artery and plexus



Gray rami communicantes

Superior hypogastric

plexus (presacral nerve)

L4



Superior rectal artery and plexus



Right and left hypogastric nerves



Nerves from inferior hypogastric

plexuses to sigmoid

and descending colon



1st sacral sympathetic trunk ganglion



Right ureter and ureteral plexus



Gray rami communicantes

L5



Seminal vesicle

Sacral part of sympathetic trunk



S1



Sacral plexus



Ductus deferens



S2

S3

S4

S5



Pelvic splanchnic nerves

(sacral parasympathetic outflow)

Pudendal nerve



Vesical plexus

Inferior rectal plexus

Prostatic plexus

Cavernous plexus



Right inferior hypogastric (pelvic) plexus



9.66╇ AUTONOMIC PELVIC NERVES AND GANGLIA

Sympathetic nerve fibers supply the pelvis through the sympathetic trunk ganglia and the superior hypogastric plexus.

These fibers travel along visceral and vascular nerves to the

colon, ureters, and great vessels, such as the inferior mesenteric and common iliac vessels. Parasympathetic nerve fibers

arise from the S2–S4 intermediate gray of the spinal cord and

travel via the pelvic splanchnic nerves to distribute with the

branches of the inferior hypogastric plexus. The parasympathetic ganglia are intramural, in or adjacent to the wall of the

organ innervated.



Dorsal nerve of penis



CLINICAL POINT

The pelvic nerves and ganglia contain both sympathetic and parasympathetic components. The sympathetic trunk ganglia and superior hypogastric plexus distribute sympathetic nerve fibers to pelvic viscera, and S2–S4

intermediate gray neurons send pelvic splanchnic nerves via the inferior

hypogastric plexuses to end in intramural ganglia that supply the pelvic

viscera. Of particular functional importance is the autonomic �distribution

to the bladder and reproductive organs. �Lesions in these pelvic autonomic

nerves can occur with diabetes, demyelinating diseases, and mass lesions.

Damage to pelvic parasympathetic nerves can produce a flaccid bladder

with overflow incontinence and can cause erectile impotence in males. It

should be noted that both parasympathetic and sympathetic autonomic

nerves play roles in sexual function. Parasympathetic nerves are essential for proper erectile function, and sympathetic nerves play a role in

ejaculation and may also contribute to erectile function; beta-�adrenergic

�blockers sometimes have the side effect of erectile impotence.