Visceral pain Flashcards
What is the enteric nervous system
ENS is considered as the “brain of the gut”
ENS consists of more than 100 million (400 – 600 million in humans) intrinsic neurones that extend most of the length of the GI tract
What is the enteric nervous system arranged into
ENS is arranged in ganglionated plexuses with interconnecting bundles of unmyelinated nerve fibres
ganglion- cell body of neurones- plexus- unmyelinated nerve fibres that connect ganglia or supply organs
What are the functions of the enteric nervous system
ENS enables the GI tract to perform its basic reflex functions of secretion, absorption, mixing and gut movements without the influence of the central nervous system (CNS) or autonomic nervous system (ANS)
However, the CNS via the sympathetic and parasympathetic nerves communicate with the intrinsic neurones of the ENS and bring about modulation GI tract functions
Axons of the intrinsic neurones of ENS also project to sympathetic ganglia, the pancreas, gall bladder, trachea, spinal cord and brain stem.
Describe the myenteric plexus
Myenteric plexus (of Auerbach) Found in the muscularis of the gut wall Controls longitudinal and circular muscle in peristalsis and contractions
Describe the submucosal plexus
Submucosal plexus (of Meissner) works with secretory glands and smooth muscle wall (muscularis mucosae)- controls contraction and relaxation of the inner lining of the gut wall
Describe the distribution of the enteric nervous system
The intrinsic network of neurons of the ENS is situated in the tissues of the gut wall from oesophagus to anus
What is meant by the autonomic nervous system
The structure of the ANS is different from that of the somatic NS (e.g. ganglia, myelination, neuro-transmitters)
2 divisions of the ANS, sympathetic and parasympathetic, innervate organs of the abdomen & pelvis
Describe the ANS
They arise from different anatomical regions of the CNS
The sympathetic nervous system arises from spinal cord segments T1-L2
The parasympathetic system arises from cranial nerves III, VII, IX, X (oculomotor, facial, glossopharyngeal & vagus) in the brain stem, and spinal cord segments S2-4
Summarise the functions of the ANS supply to the abdomen
Efferent nerves: motor to smooth muscle secretomotor to glands Afferent nerves: Sympathetic: pain Parasympathetic: specific functional sensation, e.g. stretch
Outline the sympathetic innervation of the abdomen and pelvis
Preganglionic sympathetic fibres may pass through the sympathetic trunk and paravertebral ganglia without synapsing, together with similar fibres from other levels form splanchnic nerves (greater, lesser, least, lumbar and sacral), which pass into the abdomen and pelvic regions.
These preganglionic fibres are derived from T5-L2
The splanchnic nerves generally connect with sympathetic ganglia around the roots of major arteries that branch from the abdominal aorta
These ganglia are part of a large prevertebral plexus that also has input from the parasympathetic nervous system
Postganglionic fibres are distributed in extensions from the plexus, predominately along arteries, to viscera in the abdomen and pelvis
Describe the greater splanchnic nerves
Arise from t5-T9 paravertebral galglia
Pre-ganglionic
Travel to coeliac ganglion in the abdomen (part of the prevertebral plexus)
Describe the lesser splanchnic nerves
Arise from T10-T11 paravertebral ganglia- travel to aorticorenal ganglia
Describe the least splanchnic nerve
T12
Travels to renal plexus
Describe the lumber splanchnic nerves
2-4 lumbar splanchnic nerves which pass from the lumbar part of the sympathetic trunk and enter the prevertebral plexus.
Describe the sacral splanchnic nerves
Pass from sacral part of the sympathetic trunk
Enter inferior hypogastric plexus, which is an extension of the prevertebral plexus into the pelvis
What happens in the sacral region
Preganglionic PSNs fibres form special visceral nerves (the pelvic splanchnic nerves)- which originate from the anterior rami of S2-S4 and enter pelvic extensions of the prevertebral plexus formed in the abdominal aorta
In organs of the G.I system, the preganglionic fibres synapse directly on neurons in the ganglia of the enteric nervous system
THERE ARE NO POSTGANGLIONIC PSNS MOTOR NEURON IN THE PATHWAY.
Summarise the parasympathetic supply
From vagus and sacral outflow
Describe the parasympathetic innervation of the vagus nerve
Provide parasympathetic innervation to the foregut and midgut (everything until distal one third of transverse colon)
These branches contain preganglionic parasympathetic fibres and visceral afferent fibres, which are distributed with the other components of the prevertebral plexus along the branches of the abdominal aorta.
Describe the pelvic splanchnic nerves
Carry parasympathetic preganglionic fibres from the S2-S4 anterior rami
Enter inferior hypogastric plexus of the pelvis
Some fibres move upwards into the inferior mesenteric part of the prevertebral plexus
Once there, these fibres are distributed with branches of the inferior mesenteric artery and provide parasympathetic innervation of the hindgut.
Summarise the distribution of the autonomic nerves
To peripheral vessels and skin
(sympathetic only):
Sympathetic nerves run with somatic nerves to the same region
To organs (viscera) lacking somatic innervation: most nerves run with the arteries to the same organs there are a few cases where autonomic nerves run separately
Describe sympathetic innervation of skin and blood vessels
Follow the somatic nerves to the periphery (glands, smooth muscle)
Describe sympathetic innervation of the viscera
Sympathetic nerves run with the arteries
Summarise autonomic plexuses and ganglia
The autonomic nerves to the abdomen are routed via plexuses* surrounding the aorta and its branches.
Sympathetic nerves synapse at ganglia associated with these plexuses.
Plexuses and ganglia are named according to the associated blood vessels (e.g. coeliac plexus and ganglia, renal plexus and ganglia).
What is meant by a plexus
*Plexus = interconnecting network of nerves (or vessels)
