ANS of Abdomen Flashcards
Most abdominal viscera are innervated by both PS and SS with the exception of:
Adrenal medulla
The adrenal medulla is only innervated by:
SS
What is the effect of SS on the adrenal medulla?
It causes release of E and NE from adrenal medulla chromaffin cells into the system circulation. This E/NE release reinforces SS activities throughout the body and is a significant component of the stress syndrome
What do ANS fibers innervate in the abdomen?
Smooth muscle in the wall of the GI tract and blood vessels, as well as the GI glands - pancreas, liver etc
What do PS and SS regulate in the GI tract?
GI motility (peristalsis), secretions (both enzymatic and mucus) and blood flow which facilitates digestion
Describe the intrinsic control of activities in the GI tract:
Controlled by the ENTERIC PLEXUS within the GI wall (EP). PS and SS actions simply modify (agument/decrease) these activities. This is the brain-gut link
Describe the activities of 2 types of sensory (VA) fibers in the GI tract:
Course upstream either in the vagus nn or in SS nn. These fibers serve to regulate GI reflexes or for the transmission of pain, respectively.
Where is abdominal visceral pain referred to?
The body (soma) wall. Knowledge of referred pain from the abdomen is used to localize pathology involving the viscera
PS innervation to the upper GI goes to:
Stomach, spleen, pancreas, liver, duodenum
Describe PS innervation to the upper GI:
PS PREgangilionic fibers originate in the dorsal motor nucleus of X (mid medulla level) –> follow R and L Vagus nn into the ESOPHAGEAL PLEXUS –> enter the abdomen with the anterior and posterior vagal trunks –> pass thru the CELIAC PLEXUS –> follow blood vessels (mostly branches of celiac trunk) to the visceral wall where they terminate in PS terminal ganglia –> PS short POSTganglionic fibers
What do PS short postganglionic fibers innervate?
Smooth muscle and glands in the GI wall or in smooth muscle in blood vessels
What is the function of PS innervation of the Upper GI?
- Enhances peristalsis
- Causes relaxation of pyloric sphincter
- Increases GI secretions (enzymatic and mucus)
- Vasodilation for greater mobilization of absorbed foods into the portal circulation
What is found lateral to the celiac trunk?
R/L celiac ganglia which contains SS postganglionic neurons
PS postganglionics in the GI wall are part of what?
The GI enteric plexus and they ultimately innervate the visceral targets
PS innervation of the lower GI tract goes to:
Jejunum, ileum, cecum, ascending and transverse colon - as far as the left (splenic) colic flexure
PS origin and course of PREganglionics is the same as those for the Upper GI except that some of these PREganglionic PS fibers follow:
The superior mesenteric artery and its branches to the GI wall
What is the function of PS innervation to the lower GI tract:
- Enhances peristalsis
- Causes relaxation of pyloric sphincter
- Increases GI secretions (enzymatic and mucus)
- Vasodilation for greater mobilization of absorbed foods into the portal circulation
What receives innervation from the pelvic splanchnics?
Descending and sigmoid colons, as well as the rectum, receive PS PREganglionic fibers by way of the pelvic splanchnics
What forms the splanchnic nerves (found in the pelvic wall)?
Sacral segments (S2-4)
The origin of the PS PREganglionics are:
- Dorsal motor nucleus of X (jejunum, ileum, cecum, appendix, ascending and transverse colon)
- Sacral segments (S2-S4) - descending colon, sigmoid colon, rectum
What is the course of the thoracic splanchnic nerves?
Course through the thorax but innervate the abdomen. Lumbar splanchnics pass directly into the abdomen
Where do the SS PREganglionic cell bodies originate for the thoracic splanchnic nerves?
Interomediolateral cell column at T5-L2 spinal levels
Describe SS innervation through thoracic greater, lesser, and least splanchnic nerves:
SS PREgang cell bodies at T5-L2 –> fibers enter the SCG –> pass through ganglia without synapse and emerge from SCG –> form Greater (T5-9), lesser (T10-11), and least (T12) splanchnic nn. –> thoracic splanchnics terminate in the collateral ganglia (celiac, superior mesenteric, and aorticorenal) associated with the UPPER ABDOMINAL PLEXUS (serves to control upper GI)
Describe SS innervation through lumbar splanchnic nn:
SS pregangilionic fibers leaving L1-L3 SCG –> form 3 or 4 lumbar splanchnic nn –> these nerves terminate either in the inferior mesenteric ganglion or in scattered ganglia in the pelvic plexus
Those to the inferior mesenteric ganglion are associated with the LOWER ABDOMINAL PLEXUS (lower GI)
What is the function of SS innervation?
- Decreases GI motility (peristalsis)
- Decreases glandular secretion via Beta-2 NE receptors
- Enhances vasoconstriction via alpha-adrenergic receptors (Causes decreased blood flow) - important in the stress response when it is important to shift blood flow from the viscera to skeletal muscles
Upper plexus:
Celiac plexus
Lower plexus:
Fibers around descending aorta and inferior mesenteric artery
What is the upper abdominal plexus (aka celiac plexus)?
- Consists of PS PREganglionic fibers from the vagus nn
- PREganglionic SS fibers from the thoracic splanchinic nn
- Most collateral ganglia (celiac, superior mesenteric, and aorticorenal)
- POSTganglionic SS fibers
- VA fibers
What is the lower abdominal plexus (aka inferior mesenteric plexus)?
- Receives contributions from upper abdominal plexus
- Receives lumbar splanchnic nn
- Includes the inferior mesenteric ganglion
- Fibers from plexus continue as “subsidiary” plexuses over the inferior mesenteric a. (to lower GI) and gonadall aa (to testes and ovaries)
What is the enteric plexus?
It’s within the wall of the GI tract, from esophagus to rectum, a complex network of ANS nerve fibers and local neurons (both sensory and motor) serves to control the activities of the GI
EP, histologically, can be subdivided into:
A muscular plexus (Auerbach’s) and mucosal plexus (Meissner’s)
What is the function of EP?
It provides intrinsic regulation of GI function that is independent of the extrinsic SS and PS innervation. PS and SS actions simply modify those intrinsically generated by EP and integrate the CNS with the viscera
EP control of peristalsis is integrated by a local circuit formed by several neural types including:
- Burst
- Follower
- Mechanoreceptor which responds to stretch
- Inhibitory intrinsic
What is the effect of entrance of the bolus of food in the lumen?
It activates mechanoreceptors –> which facilitates inhibitory intrinsic –> to inhibit the follower neuron –> inhibition of the follower stops the drive of burst neuron to inhibit contractility of the smooth muscle cells –> this disinhibition causes smooth muscle cells to initiate contraction –> once they contract locally –> depolarizing current propagates thru adajecent smooth muscle cells via their gap junctions –> initiates the wave-like contraction (from proximal to distal) known as peristalsis
Visceral pain is always referred to:
The body wall (brain’s perception)
Pain originating from the thoracic and abdominal viscera follows:
SS nerves
Stomach pain (from carcinoma of stomach) follows:
THe LEFT Greater Splanchnic n
What is stomach pain referred to?
LEFT Epigastrium (T5-9)
Gallbladder pain (stones) follows:
The R Greater splanchnic n
What is gallbladder pain referred to?
RIGHT Epigastrium (T5-9). But if the bile spreads to the inferior surface of diaphragm, pain follows a different nerve
If bile spreads to the inferior surface of the diaphragm, pain follows:
The R Phrenic n. and is referred to the R shoulder (C3-5)
Appendix pain (appendicitis or inflammation) initially follows:
The Lesser splanchnic nn and is referred to the Umbilicus area (T10)
If inflammation gets worse, appendix pain follows:
The R lumbar splanchnic nn and the pain will be referred to the R lower quadrant
Kidney pain (stones) follows:
The Least splanchnic n
Where is kidney pain referred to?
The lower quadrant (Subcostal n, around T12)
