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What is the sympathetic nerve supply of the abdomen?
- Greater, lesser and least splanchnic nerves
- Lumbar splanchnic nerves
What does the somatic NS control?
External actions of skin and muscle
What does the autonomic NS control?
Internal activities of organs and glands
What is the spinal cord divided into?
31 segments which each segment giving rise to a pair of spinal nerves
- 8 pairs of cervical
- 12 pairs of thoracic
- 5 pairs of lumbar
- 5 pairs of sacral
- 1 pair of coccygeal
What is the dorsal horn of the spinal cord concerned with?
Receiving sensory information (afferent sensory fibres arrive)
What is the ventral horn of the spinal cord concerned with?
Sending motor information (efferent motor fibres leave)
When these efferent and afferent fibres come together, what does it make up?
A mixed spinal nerve –> enclosed by sheath
What are thoracic spinal nerves called?
Intercostal nerves supplying intercostal muscles, pleura, skin etc
What do intercostal muscles continue into the abdomen as?
Thoracoabdominal nerves suppling anterolateral muscles, peritoneum etc
Are intercostal/thoracoabdominal nerves somatic or autonomic?
Somatic nerves (e.g. consciously contract biceps or abdominal muscles)
Describe the autonomic sympathetic supply of the abdomen
- Greater, lesser and least splanchnic nerves
- Lumbar splanchnic nerves
N.B. splanchnic nerves generally refer to sympathetic nerves (one exception)
Where do greater, lesser and least splanchnic nerves begin?
Within thorax and then pierce diaphragm (emerge from the thoracic sympathetic chain)
What do the greater, lesser and least splanchnic nerves supply?
Foregut and midgut
What do the lumbar splanchnic nerves supply?
Hindgut
Describe the autonomic parasympathetic supply of the abdomen
- Vagus nerve (pierces diaphragm along with oesophagus)
- Pelvic splanchnic nerves (exception to sympathetic splanchnic)
What does the vagus nerve supply?
Foregut and midgut (all the way to the distal 1/3 of the TC)
What do pelvic splanchnic nerves supply?
Hindgut and pelvic organs
What are the only splanchnic nerves that are parasympathetic?
Pelvic splanchnic nerves
What do these autonomic nerve fibres form?
Autonomic plexuses –> around coeliac trunk, SMA, IMA then follow blood vessels to target organ
What do these autonomic nerve fibres form?
Autonomic plexuses –> around coeliac trunk, SMA, IMA then follow blood vessels to target organ
What happens if that sympathetic information needs to get to the body wall (e.g. for a sweat gland)?
It can re-enter the spinal nerve via the grey ramus communicans –> enter into the somatic spinal nerve
What happens if that sympathetic information needs to get to the body wall (e.g. for a sweat gland)?
It can re-enter the spinal nerve via the grey ramus communicans
Where does the sympathetic nervous system emerge?
From the spinal cord at the thoracic and lumbar segments (T1 down to around L2)
Where are preganglionic neurones of the sympathetic nervous system located?
In the lateral horns of spinal segments T1-L2
When preganglionic fibres leave the spinal cord and enter into the sympathetic chain, what happens?
They synapse (at the point of entry or could ascend or descend within chain)
Postganglionic then make way towards target organs via a plexus (braid of nerves)
Where are sympathetic ganglia located?
Near the spinal cord
What do preganglionic sympathetic fibres release?
ACh which is excitatory and stimulates ganglionic neurones
Within the abdomen, how is the sympathetic nerve supply different regarding synapsing?
Sympathetic fibres leave spinal cord, enter chain and pass straight through (without synapsing)
They course around the blood vessels of the GI tract (coeliac trunk, SMA, IMA) and it is here where they synapse
Within the abdomen, how is the sympathetic nerve supply different regarding synapsing?
Sympathetic fibres leave spinal cord, enter chain and pass straight through (without synapsing)
They course around the blood vessels of the GI tract (coeliac trunk, SMA, IMA) and it is here where they synapse
Where do synapses of sympathetic fibres occur in the abdomen?
Near the blood vessels of the GI tract
Where do synapses of sympathetic fibres occur in the abdomen?
Near the blood vessels of the GI tract
Describe route of motor efferent sympathetic nerves in the thorax
• Motor efferent fibres leave the spinal cord via the ventral root that then contribute to the mixed spinal nerve
• Sympathetic so then jump into sympathetic chain via the white ramus communicans
o Then synapses and postganglionic fibre go towards target organ
o Or, ascends or descends before it synapses then head out to target organ
• If fibre needs to make its way to body wall, it jumps back into spinal nerve via the grey ramus communicans which then heads to body wall
What are sympathetic ganglia in the thorax also referred to as?
Paravertebral (as next to vertebral column)
Describe route of motor efferent sympathetic nerves in the abdomen
• Motor efferent fibres leave spinal cord via the ventral root the contribute to mixed spinal nerve
• Jump into sympathetic chain via white ramus communicans
o Passes straight through chain (without synapsing) towards blood vessels (coeliac, SMA, IMA) and synapses there
o Postganglionic fibre then goes on to supply target organs
What are sympathetic ganglia in the abdomen also referred to as?
Prevertebral ganglia
What sensory route does pain (e.g. ischaemia) take?
Afferent fibres for pain use the sympathetic system to go back to the CNS
What sensory route does general sensation from the organs (e.g. how full the stomach is) take?
The parasympathetic system
Describe route during appendicitis
- Appendix becomes inflamed
- Sends afferent fibres back to the sympathetic chain
- Enters mixed spinal nerve via white ramus communicans
- Mixed nerve splits and afferent information enters spinal cord via dorsal root