What is the enteric NS?
'Brain of the gut', consisting of more than 100m intrinsic neurones that extend most of the GIT
How is the ENS arranged?
In ganglionated plexuses with interconnecting bundles of unmyelinated nerve fibres
What does the ENS allow the GIT to do?
Perform basic reflex functions of secretion, absorption, mixing and gut movements without the influence of CNS or ANS
How does the CNS communicate with the ENS?
Via para/sympathetic nerves with intrinsic neurones of ENS to bring about modulation GIT functions
Where do axons of intrinsic neurones of ENS project to?
Sympathetic ganglia, pancreas, gall bladder, trachea, spinal cord and brain stem
What is the general plan of the GIT? FITB
Where is the ENS distributed?
Intrinsic network of neurones is in the tissues of the gut wall from oesophagus to anus
Where does the ANS innervate?
It has 2 divisions which innervate organs of abdomen and pelvis
Where does the ANS arise from?
Different anatomical regions of CNS -> sympathetic arising from spinal cord segments T1-L2 and the parasympathetic system arising from cranial nerves III, VII, IX and X and spinal cord segments S2-4
What is the function of the efferent autonomic nerves in the abdomen?
Motor to smooth muscle and secretomotor to glands
What is the function of the afferent autonomic nerves in the abdomen?
Sympathetic: pain Parasympathetic: specific functional sensation (stretch)
What are the sympathetic nerves to the abdomen? FITB
At what spinal level does the greater splanchnic nerve emerge?
At what spinal level does the Lesser splanchnic nerve emerge?
At what spinal level does the least splanchnic nerve emerge?
Where does the parasympathetic supply come from in the organs of the abdomen and pelvis?
Vagus nerve (CNX) and sacral outflow (S2-4)
How are the sympathetic autonomic nerves to peripheral vessels and skin distributed?
Sympathetic nerves run with somatic nerves to the same region
How are the autonomic nerves to organs lacking somatic innervation distributed?
Most nerves run with arteries to same organs, with few cases where autonomic nerves run seperately
What is a nerve plexus?
Interconnecting network of nerves
How are the autonomic nerves to the abdomen routed?
Via plexuses surrounding the aorta and its branches
Where do the sympathetic nerves synapse?
At the ganglia associated with these plexuses
How are plexuses and ganglia named?
According to associated blood vessels
What are the 9 main plexuses/ganglia in the abdomen?
Anterior vagal trunk, superior mesenteric ganglion, coeliac trunk and ganglion, renal plexus and ganglion, inferior mesenteric ganglion, sympathetic trunk and ganglion, superior hypogastric plexus and inferior hypogastric plexus
Where are the 9 important plexuses/ganglia located? FITB
Which nerve plexuses and ganglia surround the aorta and where do they innervate?
Why is referred pain caused?
The cerebral cortex of the brain hasn't got a sensory map for visceral organs and diaphragm, so can't localise the pain from these, hence the pain is referred
Where is the pain from visceral organs referred to?
Regions of skin supplied by nerves with the same segmental supply (dermatomes)
What is a dermatome?
An area of skin supplied by a single spinal nerve (i.e. single segment of the spinal cord)
How do dermatomes prevent complete anaesthesia in a region?
Adjacent dermatomes overlap so that on the trunk at least 3 spinal nerves would have to be blocked to produce a region of complete anaesthesia
What does the dermatomal map of the body look like?