Nerves of the Abdomen Flashcards
What are major nerves of the anterolateral abdominal wall?
The thoracoabdominal, lateral cutaneous, subcostal, iliohypogastric, and ilioinguinal nerves
What are the thoracoadminal nerves?
Derived from T7-T11 and form the inferior intercostal nerves
What are the external oblique muscles innervated by?
Thoracoabdominal nerves (T7-T11) and subcostal nerve (T12).
What are the internal obliques innervated by?
Thoracoabdominal nerves (T7-T11), subcostal nerve (T12) and branches of the lumbar plexus.
What are the transversus abdominis muscles innervated by?
Thoracoabdominal nerves (T7-T11), subcostal nerve (T12) and branches of the lumbar plexus.
What is the rectus abdominis muscle innervated by?
Thoracoabdominal nerves (T7-T11).
Where do the thoracoabdominal nerves travel?
Pass between internal obliques and transversus abdominis to sheath of rectus abdominis
What is the pyramidalis muscle innervated by?
Subcostal nerve (T12)
What can sympathetic ganglia in the thorax also be referred to as?
Paravertebral (next to vertebral column)
What can sympathetic ganglia in the abdomen also be referred to as?
Prevertebral ganglia (sympathetic ganglia which lie between the paravertebral ganglia and the target organ)
Describe route of motor sympathetic fibres in abdomen
- Leave spinal cord via ventral rootlets
- Join with sensory fibres to form mixed spinal nerve
- Jump into sympathetic chain via white ramus communicans
- Pass through chain WITHOUT SYNAPSING
- Become abdominopelvic splanchnic nerves
- They then enter the prevertebral ganglia and synapse here
- Postsynaptic fibres pass into autonomic plexuses located primarily on the abdominal aorta and its branches (coeliac, SMA, IMA)
- Postganglionic then goes on to supply target organ
What are the 2 main types of abdominopelvic splanchnic nerves?
- Lower thoracic splanchnic nerves (greater, lesser and least)
- Lumbar splanchnic nerves
Describe lower thoracic splanchnic nerves
These three nerves (greater, lesser, and least) contain the most presynaptic sympathetic fibres. They pass through the diaphragm to send fibres to the celiac, aorticorenal, and superior mesenteric ganglia and plexuses.
Name the sympathetic supply of the abdomen
The sympathetic input comes from the thoracolumbar segments of the spinal cord (thorax and upper one or two lumbar segments)
- Greater, lesser and least splanchnic nerves
- Lumbar splanchnic nerves
Where is all autonomic supply of the abdomen via?
All via autonomic plexuses around coeliac trunk, SMA, IMA then follow blood vessels to target organ
What do preganglionic fibres of the sympathetic system release? What is effect of this?
ACh which is excitatory and stimulates ganglionic neurones
What do most postganglionic fibres of the sympathetic system release?
Noradrenaline at neuroeffector junction
What is difference between preganglionic sympathetic fibres in thorax and abdomen?
Thorax: can enter the sympathetic chain, ascend/ descend, synapase and course to their target organ but SYNAPSE IN CHAIN
Abdomen: fibres pass straight through the sympathetic chain and synapse nearer the target organ but DON’T SYNAPSE IN CHAIN
Describe lumbar splanchnic nerves
These nerves start at the abdominal sympathetic trunk and produce three or four lumbar splanchnic nerves that join the intermesenteric, inferior mesenteric, and superior hypogastric plexuses.
What forms the parasympathetic supply of the abdomen?
- Vagus nerve
2. Pelvic splanchnic nerves
Describe the vagal supply of the abdomen
The parasympathetic nerves include anterior and posterior vagal trunks that are the continuations of the left and right vagus nerves
Where do the vagal trunks enter the abdomen?
T10
Where do pelvic splanchnic nerves originate?
S2 - S4
What do pelvic splanchnic nerves innervate?
Hindgut and pelvic organs (parasympathetic innervation)
What are the abdominal autonomic plexuses?
Nerve networks (parasympathetic and sympathetic) that surround the three unpaired visceral arteries. Serve the abdominal and pelvic organs.
All interconnected.
Name the abdominal autonomic plexuses
- Aortic plexus
- Coeliac plexus
- Hepatic plexus
- Renal plexus
- Superior mesenteric plexus
- Inferior mesenteric plexus
- Intermesenteric plexus
- Superior hypogastric plexus
- Right and left inferior hypogastric plexus
Describe the coeliac plexus
Complex network of nerves in the abdomen, consists of paraaortic ganglia.
Located around the root of the celiac trunk, SMA and renal artery; has a parasympathetic root that contain fibres from the vagus nerves and the sympathetic roots are the greater and lesser splanchnic nerves.
Conveys postsynaptic output (sympathetic, parasympathetic and pain innervation) to abdominal viscera.
Describe the hepatic plexus
Located around the hepatic artery and comes from the celiac plexus
Describe the renal plexus
Surround the renal arteries; formed by fibres from the celiac plexus, aortic plexus, and the least splanchnic nerve
Describe the superior mesenteric plexus
Surrounds the superior mesenteric artery; has three branches: the median branch comes from the celiac plexus, and the lateral branches come from the lesser and least splanchnic nerves
Describe the inferior mesenteric plexus
Surrounds the inferior mesenteric artery; has a medial root from the intermesenteric plexus and lateral roots from the lumbar ganglia of the sympathetic trunks
Describe the intermesenteric plexus
The part of the aortic plexus located between the superior and inferior mesenteric arteries; gives rise to the renal, testicular, ovarian, and uteric plexuses
Describe the superior hypogastric plexus
Located anterior to the bifurcation of the aorta; a continuation of the intermesenteric plexus
Describe the right and left inferior hypogastric plexus
Located on the sides of the rectum, uterine cervix, and the urinary bladder; formed by hypogastric nerves that come from the superior hypogastric plexus and receives parasympathetic fibres from the pelvic splanchnic nerves
What are the prevertebral ganglia of the abdomen associated with?
The three unpaired visceral arteries (CT, SMA, IMA)
What do prevertebral ganglia of the abdomen contain?
Synapse between pre-synaptic and post-synaptic sympathetic fibres
Describe how pain from appendix travels to CNS?
- Appendix becomes inflamed
- Sends afferent (sensory) fibres back to sympathetic chain
- Enters mixed spinal nerve via white ramus communicans
- Mixed nerve splits and afferent (sensory) info enters spinal cord via DORSAL root
What is the lumbar plexus?
A network of nerve fibres that supplies the skin and musculature of the lower limb. It is located in the lumbar region, forms part of the larger lumbosacral plexus
What is the lumbar plexus formed by?
Is formed by the union of the anterior rami of the first three lumbar nerves and a part of the fourth lumbar nerve (and contributions of subcostal nerve)
(Dorsal and ventral rootlets leave spinal cord, combine to form mixed nerve, mixed nerve then splits into anterior and posterior rami)
Where does the subcostal nerve run?
Between internal oblique and transversus abdominis
What does the subcostal nerve innervate?
Innervates the external oblique, internal oblique, transverse, rectus abdominis , and pyramidalis muscles.
What are major branches of lumbar plexus?
- Iliohypogastric nerve
- Ilioinguinal nerve
- Genitofemoral nerve
- Lateral femoral cutaneous nerve
- Obturator nerve
- Femoral nerve
Roots of iliohypogastric nerve?
L1 (contributions from T12)
Describe course of iliohypogastric nerve
Begins as common stalk that splits into iliohypogastric and ilioinguinal nerve
Emerges from the lateral border of the psoas muscle and runs in front of the quadratus lumborum.
Pierces the transverse abdominal muscle near the iliac crest to run between this muscle and the internal oblique muscle.
Pierces the internal oblique muscle and then continues medially deep to the external oblique muscle
Becomes superficial and supplies skin
What does iliohypogastric nerve innervate?
Motor - Internal oblique and transversus abdominis
Sensory - Skin above pubis, skin of gluteal region
Describe course of ilioinguinal nerve
Runs in front of quadratus lumborum, courses between internal and transversus abdominis towards anterior abdominal wall
After innervating muscles of anterior abdominal wall, it passes through inguinal canal and out the superficial ring (NOT THROUGH DEEP RING) to innervate some of skin around genital region
What does ilioinguinal nerve innervate?
Motor - innervates the internal oblique and transversus abdominis.
Sensory - Innervates the skin on the superior antero-medial thigh. Supplies some of skin of genital region
Roots of ilioinguinal nerve?
L1 (common stalk)
Roots of genitofemoral nerve?
L1, L2
Describe the course of the genitofemoral nerve (and genital branch)
Emerges on front of psoas muscle and descends on its anterior surface. After leaving the psoas major muscle, the genitofemoral nerve quickly divides into a genital branch, and a femoral branch.
Genital branch - enters inguinal canal through deep ring, passes out superficial ring
What does genital branch innervate?
Motor - innervates cremasteric muscle
Sensory - innervates the skin of the anterior scrotum (in males) or the skin over mons pubis and labia majora (in females)
What does femoral branch innervate?
Sensory - Skin on upper anterior thigh
Roots of lateral cutaneous nerve of the thigh?
L2, L3
What does the lateral cutaneous nerve of the thigh innervate?
Purely sensory function - innervates the anterior and lateral thigh down to the level of the knee.
Describe course of lateral cutaneous nerve
It enters the thigh at the lateral aspect of the inguinal ligament, where it provides cutaneous innervation to the skin there.
Roots of obturator nerve?
L2, L3, L4
Course of obturator nerve?
Descends along medial border of psoas muscle, runs forward on lateral wall of pelvis, enters thigh through obturator foramen
What does obturator nerve innervate?
(Motor - Innervates the muscles: obturator externus, pectineus, adductor longus, adductor brevis, adductor magnus, gracilis)
Sensory - Skin of medial thigh
Roots of femoral nerve?
L2, L3, L4
What are thoracic splanchnic nerves?
Splanchnic nerves that arise from the sympathetic trunk in the thorax and travel inferiorly to provide sympathetic innervation to the abdomen.
What do thoracic splanchnic nerves contain?
Preganglionic sympathetic fibres and general visceral afferent fibres
Are thoracic splanchnic nerves sympathetic or parasympathetic in function?
Sympathetic
Are lumbar splanchnic nerves sympathetic or parasympathetic in function?
Sympathetic
Are sacral splanchnic nerves sympathetic or parasympathetic in function?
Sympathetic
Are pelvic splanchnic nerves sympathetic or parasympathetic in function?
Parasympathetic
What are the 3 main thoracic splanchnic nerves?
Greater, lesser, least
Where do lumbar splanchnic nerves arise from?
Sympathetic trunk at L1-L4
Where do presynaptic parasympathetic fibres usually synapse?
In the wall of the organ that they innervate
Describe parasympathetic effect in abdomen
It increases gland secretion and promotes peristalsis and digestion
Describe sympathetic effect in abdomen
Inhibits peristalsis, constricts blood vessels and redirects blood to skeletal muscles.
What are the only splanchnic nerves that are parasympathetic?
Pelvic
Where do the greater thoracic splanchnic nerves primarily synapse?
In coeliac and superior mesenteric ganglia
Some presynaptic fibres pass directly into the suprarenal medulla, to synapse there.
Are prevertebral ganglia sympathetic or parasympathetic?
Sympathetic ganglia, so no parasympathetics would synapse there
Describe components of coeliac plexus
Receive presynaptic sympathetic fibres from the greater thoracic splanchnic nerves (and lumbar splanchnic nerves). Most fibres synapse here and the postsynaptic fibres flow out along the celiac trunk and branches.
The coeliac plexus also receive presynaptic parasympathetic fibres from the celiac branch of the posterior vagal trunk. These fibres will NOT synapse in the coeliac ganglia, which are sympathetic ganglia. These parasympathetic fibres merely pass through the celiac ganglia and plexus to reach the organ walls, where they synapse.
Some fibres from the celiac ganglia, both sympathetic and parasympathetic, pass down on the surface of the aorta to reach the adjacent superior mesenteric ganglion and plexus.
How is pain detected in the abdomen?
Via general visceral afferent (GVA) fibres that conduct sensory impulses (usually pain or reflex) from the internal organs, glands, and blood vessels to the CNS
What are GVA fibres?
Afferent fibres that aren’t classed as parasympathetic or sympathetic
In the abdomen, what do GVA fibres (pain sensation) pass alongside?
Usually accompany sympathetic efferent (motor) fibres to the posterior root of spinal cord segments
Describe the pathway of GVA fibres
- Signal begins at sensory receptor in organ and travels in afferent fibre alongside sympathetic efferent fibre
- Signal travels up to ganglion where sympathetic efferent fibre synapses
- Signal continues back along splanchnic nerve into sympathetic chain
- (Move into ventral ramus) via white ramus communicans and then into mixed spinal nerve
- GVA pathway splits and enters spinal cord via dorsal root (sympathetic efferent enters via ventral root)
- Cell body of visceral afferent nerve located here
where the cell body of the visceral afferent nerve is located.
What is the exception to this route of GVA fibres in abdomen?
The nerves that innervate distal 1/2 of sigmoid colon and rectum
Describe pathway of GVA fibres that innervate distal 1/2 of sigmoid colon and rectum
These afferent fibres follow the path of parasympathetic efferent fibres back to the vertebral column
The afferent fibres enter the S2-S4 sensory (dorsal root) ganglia followed by the spinal cord
How is pain from the abdominal viscera referred?
Pain from the visceral peritoneum is referred to areas of skin (dermatomes) which are supplied by the same sensory ganglia and spinal cord segments as the nerve fibres innervating the viscera.
Is pain from the viscera well or poorly localised?
Poorly localised
What vertebral levels does pain from the foregut pass to?
Where is pain from foregut referred to?
T6-T9
Epigastric region
What are the structures of the foregut?
Oesophagus, stomach, pancreas, liver, gallbladder and the duodenum (proximal to the entrance of the common bile duct).
What are the structures of the midgut?
Duodenum (distal to the entrance of the common bile duct) to the junction of the proximal two thirds of the transverse colon with the distal third.
What are the structures of the hindgut?
Distal one third of the transverse colon to the upper part of the anal canal.
What vertebral level does pain from the midgut pass to?
Where is pain from midgut referred to?
T8-T12
Umbilical region
What vertebral level does pain from the hindgut pass to?
Where is pain from hindgut referred to?
T12-L2
Pubic region of abdomen
