Editing Autonomic nervous system


== '''Autonomic nervous system background''' ==

* Motor part controls     innervation of cardiac and smooth muscle and glands
* Pathway between spinal cord     and target organ is always interrupted by synapses in a ganglion - there     are thus preganglionic and postganglionic fibres
* Preganglionic SNS fibres are     in the lateral horn cells of T1-L2 segments of the spinal cord (the     thoracolumbar part of the autonomic nervous system, or 'thoracolumbar     outflow')
** Inhibitory to peristalsis,      vasomotor, motor to sphincters, and carry sensory fibres
* Preganglionic PNS fibres are     in certain cranial nerve nuclei and in lateral horn cells of sacral     segments of the spinal cord (the craniosacral part of the autonomic     nervous system, or 'craniosacral outflow')
* Postganglionic cells are in     peripheral nervous system ganglia
** Sympathetic cells are either      in the sympathetic trunk (collectively called paravertebral ganglia) or      in certain other ganglia (collectively called collateral ganglia - e.g.      coeliac ganglia)
** Postganglionic      parasympathetic cells are collectively called 'terminal ganglia', and are      usually within the walls of the target organ

== '''Sympathetic nervous system''' ==

=== '''Anatomy/function''' ===

** Sympathetic trunk runs from      base of skull to coccyx, alongside the vertebral column
*** Cervical: over transverse       processes
*** Thoracic: in front of the       heads of the ribs
*** Abdomen: anterolateral to       the lumbar bodies
*** Pelvis: medial to the       anterior sacral foramina
*** Terminates in the pelvis at       the ganglion impar
** Theoretically there is a      ganglion for each spinal nerve, but fusion occurs
*** Typically three cervical       ganglia, 11 thoracic ganglia, four lumbar and four sacral ganglia
** Each sympathetic trunk      ganglion has a collateral/visceral branch:
*** Cardiac branch in cervical       region, proceeding to cardiac plexus
*** Splanchnic nerves in       thorax, proceeding to coeliac ganglion
*** Lumbar splanchnic nerves       from the upper lumbar ganglia, proceeding to the inferior hypogastric       plexus
**** This divides to enter the        left and right inferior hypogastric plexuses
**** Joined by sacral        splanchnic nerves  from the        sacral ganglia (not to be confused with ''pelvic'' splanchnic nerves which        are parasympathetic)
** Each sympathetic visceral      plexus then receives contributions from parasympathetic visceral nerves,      so that mixed sympathetic-parasympathetic plexuses can be formed and      signals transmitted to target organs
*** Vagus to coeliac plexus
*** Pelvic splanchnics to       inferior hypogastric plexuses
** Branches are also given off      to local large blood vessels (e.g. cervical ganglia to carotid artery)
** Afferent sympathetic fibres      hitch along
** Options for preganglionic      cells reaching a sympathetic trunk ganglion:
*** Synapse with cell bodies in       a trunk ganglion - either the one they entered, or travel to another one
*** Leave the trunk ganglion       without synapsing, and either pass to a collateral ganglion or pass to       the adrenal medulla

=== '''Sympathetic     trunk/chain''' ===

==== '''Cervical      part''' ====

*** Pre-ganglionic fibres all       arise from upper thoracic outflow and ascend in the cervical sympathetic       trunk
*** Most outflow is from T1       level

==== '''Thoracic      part''' ====

*** Paired bundle of nerve       fibres
*** Course
**** Begins at T1 ganglion,        which is usually (80%) fused with the inferior cervical ganglion to        form the '''stellate ganglion''', which lies in front of and below the neck        of the first rib
**** The trunk then passes down        in front of the heads of the ribs, lying in front of all the        intercostal structures in the thorax (apart from the supreme        intercostal vein)
**** Exits from the thorax        beneath the medial arcuate ligament
*** Supply
**** Cardiac plexus -        sympathetic fibres from cervical and upper thoracic ganglia
**** Trachea and oesophagus        receive branches
**** There are usually 12        ganglia corresponding to each intercostal nerve, with each ganglion        giving off one grey and one white ramus to each intercostal nerve
**** Upper limb is mostly T2        and T3, but some T1, T4 and T5
**** Splanchnic nerves come        from the lower eight ganglia - see below
*** Removal of thoracic ganglia       4-12 bilaterally is theorised to remove pain fibres from the abdominal       viscera

==== '''Lumbar part''' ====

*** Comprises inputs from lower       thoracic ganglia and L1-L2 nerve roots
*** Left part along the left       margin of aorta, and right part behind IVC
*** The trunk passes down       across the pelvic brim to become the sacral part of the trunk
*** Just behind the medial       arcuate ligament, medial to psoas major
*** Lumbar splanchnic nerves       pass downwards and form the superior hypogastric plexus

=== '''Collateral     ganglia''' ===

** Midgut:
*** '''Coeliac       plexus'''
**** Wholly visceral - supplies        all abdominal organs including gonads
**** Lies around the origin of        coeliac trunk just above the pancreas
**** Contributing fibres
***** Greater and lesser         splanchnic nerves
***** Vagus
**** Mostly connects with        viscera via branches along the aortic vascular supply
*** '''Renal       ganglion''' -       relay for the least splanchnic nerve behind the renal artery
*** There are other       ganglia/plexuses along aorta from SMA to IMA, which I think are quite       variable and are just referred to as 'aorticorenal plexuses' in quite a       general way
** Hindgut: lumbar part of      sympathetic trunk
*** '''Superior       hypogastric plexus'''
**** A fenestrated network of        sympathetic fibres found just below the aortic bifurcation (L5)
**** Caudally fibres exit as        the hypogastric nerves, connecting to the inferior hypogastric        ('pelvic') plexus
*** '''Inferior       hypogastric plexus'''
**** SNS inflow from S3 and S4,        and sometimes S2
**** PNS inflow from S2-S4        (nervi erigentes)
**** Lies between parietal and        visceral layers of endopelvic fascia, lateral to lower third of rectum
**** Preservation is very        important during mobilisation of lateral ligaments of rectum - leads to        genitourinary dysfunction if damaged

=== '''Significant     collateral branches''' ===

** '''Thoracic      splanchnic nerves'''
*** Three splanchnic nerves       given off on each side by the sympathetic trunk
**** '''Greater        splanchnic:'''        arises from 5th-9th thoracic ganglia and slopes obliquely across the        vertebral bodies to exit through the crura of the diaphragm, mostly        passing to the coeliac ganglia with some fibres to the aorticorenal        ganglia
**** '''Lesser        splanchnic nerves:''' arise from 10th-11th ganglia, exit through diaphragm, bound        for coeliac ganglion and aorticorenal ganglia
**** '''Least        splanchnic nerves:''' arise from 12th ganglia, exit through diaphragm, bound for        aorticorenal ganglia
*** These provide SNS outflow       to abdominal viscera, and pain afferents
** '''Lumbar      splanchnic nerves'''
*** Arise from all lumbar       ganglia
*** Bound for coeliac, aortic       and superior hypogastric plexuses
** '''Hypogastric      nerves'''
*** Run from superior       hypogastric to inferior hypogastric plexus
*** 2-3mm in diameter, lying       about 1cm lateral to the midline and 2cm medial to the ureters
*** Lie between leaves of       endopelvic fascia
*** Adherent to posterolateral       mesorectum, connected with small unimportant rectal branches
*** Lie initially quite       superficially under peritoneum, eventually migrating further away from       the mesorectum to the pelvic sidewall and inferior hypogastric plexuses
*** Won't be seen if not       deliberately looked for and protected





== '''PNS''' ==

* Motor and secretomotor to the     gut and its glands
* Preganglionic fibres of     cranial origin have cell bodies intra-cranially
* Not all parts of the body     receive PNS supply - wholly visceral
* Adrenal glands and gonads do     not have PNS supply
* Anatomy of PNS outflow
** Foregut
*** Ciliary
*** Pterygopalatine
*** Submandibular
*** Otic
** Midgut: '''vagus''' 
*** Nucleus in dorsal motor       nucleus of the vagus
** Hindgut: pelvic splanchnic      nerves ('''nervi erigentes''')
*** Arise from cells in the       lateral grey horn of S2-S4
*** Also carry afferent fibres
*** Pierce the parietal layer       of endopelvic fascia and fuse with the sympathetic hypogastric nerves to       form the inferior hypogastric plexus
*** From there, run to pelvic       viscera and hindgut structures
*** Small rectal branches enter       the mesorectum, however most continue to genitourinary organs




== Sympathectomy ==

=== Cervical ===

** Dividing the sympathetic      chain between T1 and T2 causes nearly all the SNS inflow to upper limb to      be divided
** To achieve a complete      sympathectomy, the grey post-ganglionic rami passing from the stellate      ganglion to the brachial plexus can also be divided (in practice,      dividing just the T2 ganglion gives an adequate sympathectomy for      hyperhidrosis)
** This will also improve      flushing and hyperhidrosis of head and neck, but almost never causes a      Horner's syndrome
** Operative approaches: (see      separate topic under 'thoracic operations')
*** Percutaneous endoscopic -       chain is identified over the necks of second and third ribs and       diathermied at this point. Access via the third interspace in the       midaxillary and anterior axillary lines, with the patient in a       semi-sitting position to allow the lung to fall away
*** Trans-thoracic
*** Supra-clavicular

=== Lumbar ===

** Can be done for rest pain -      usually gives good denervation of foot
** Aim for L1-L2 level - avoid      interfering with L1 which is important for sexual function
** Approaches
*** Retroperitoneal
**** Follow the anterior        surface of psoas muscle medially onto the anterolateral aspect of the        vertebral bodies (ensure ureter is swept forward)
*** Anterior

[[Category:Anatomy]]