Visceral Innervation And Development Of The Kidneys/Gonads

Question 1

Describe the parasympathetic and sympathetic innervation of the visceral abdominal organs.

(Simply where the cell bodies are)

Answer 1

Parasympathetic: increases gut motility and secretion

Preganglionic: brainstorm (vagus nerve)
Sacral spinal cord segments (S2-S4) Pelvic splanchnic nerves

Postganglionic cell body is in the terminal ganglia.

Sympathetic: vasoconstriction, decreases gut motility

Preganglionic: Lateral horn of spinal nerves T5-L2

Postganglionic cell body is in the PREVERTEBRAL ganglia.

Myenteric Plexus (auerbach):
-cell body is located between the longitudinal and circular muscle layers  

Sympathetic: relaxes muscle tone, decreases peristalsis

Parasympathetic: increases peristalsis

Submucosal plexus (Meissner's) 
-cell body is located under the circular 

Sympathetic: modulates fluid transport

Parasympathetic: increases secretion (secretomoter)

Question 2

Describe what occurs in hirschsprung’s disease

Answer 2

There is a mutation in the Ret gene which causes failure of the neural crest to reach the enteric plexuses (intrinsic regulation)

So segments of the bowel (usually the rectalsigmoid region) is lacking intrinsic innervation, that results in overriding extrinsic signals which causes that region to be constricted.

That also causes the proximal portion to dilate (aganglionic megacolon)

Question 3

Describe the general pathway sympathetic distribution to the abdomen viscera

Answer 3

Cell body in the lateral horn of L5 to L2, axon enters the ventral ramus > enters the white communicans > goes into the paravertebral ganglion > enters a splanchnic nerve > prevertebral ganglion > blood vessels to the organs

Question 4

Describe the distribution of sympathetic innervation of the abdominal viscera.
(Which splanchnic nerve, preganglion location, preverebral ganglion, the embryonic region of the gut tube)

Answer 4

Preganglionic cell body: T5-T9
Splanchnic: greater thoracic splanchnics
Prevertebral: celiac
Embryonic region: foregut

T10-T11
Lesser thoracic splanchnic
Superior mesenteric
Midgut

T12
Least thoracic splanchnic
Aorticorenal/superior mesenteric
Midgut

L1-L2
Lumbar splanchnics
Inferior mesenteric
Hindgut

Question 5

Describe the parasympathetic innervation of abdominal viscera

Location of cell bodies

Pathway

Answer 5

Cell body location: brainstem
Preganglionic: vagus/vagal trunks
Postganglionic: enteric plexus
Embryonic region: foregut/midgut

S2-S4
Pelvic splanchnic nerve
Enteric plexus
Hindgut

Foregut:

1. Stomach: Preganglions are in the anterior and posterior vagal trunks (there are originally two vagus nerves and also rotation), synapse directly on postganglionic neurons in enteric ganglion
2. Rest of foregut: The axons PASS but do NOT SYNAPSE in the celiac plexus and are distributed on branches to organ wall/enteric plexus

Midgut:
Vagal trunks > pass through superior mesenteric ganglia > distributed on branches of superior mesenteric artery> synapse on enteric plexus

Hindgut: S2-S4, go through pelvic splanchnic nerves > distributed on branches of inferior mesenteric > synapse in enteric plexus

Question 6

Describe the sympathetic and parasympathetic afferent paths.

Example foregut

Answer 6

Travels back on artery >celiac ganglion> greater thoracic splanchnic nerve > paravertebral ganglia > white ramus communicans > ventral ramus > synapse at dorsal horn between levels T5-L2

Parasympathetic
In this case very similar to sympathetic

artery > celiac ganglion > vagal nerve > branstem

Question 7

Describe visceral, referred and parietal pain.

Answer 7

Visceral pain - is dull, poorly localized, perceived in the midline and tells you foregut (epigastric), midgut (umbillical), hindgut (suprapubic region), dermatomes correspond to where sympathetic and somatic converge on the spinal cord.
Foregut T5-T9
Midgut -T10-T11
Superpubic L1

Referred pain: As stimulus intensifies, the pain becomes referred and that lateralizes pain and becomes more intense
Gallbladder pain (T7) would be localized subcostal and on the right side 

Parietal pain: is somatic sensory nerves and occurs from noxious stimulus to the parietal peritonium.
More intense and more precise pain.
A good sign is aggravation by movements and coughing
Stimulus goes right into ventral ramus and then into dorsal horn

Question 8

What are the functions of the sympathetic and parasympathetic pathways in the GI system and which afferents run through them?

Answer 8

Sympathetic - increase vasoconstriction, decrease secretion and motility
-pain and pressure afferents follow sympathetic pathways (distension)

Parasympathetic - increases motility and secretion
-reflex afferents follow parasympathetic pathways