The Autonomic Nervous System

• How is the nervous system classified?

  Here

  
• how many spinal nerves are there in total and how many are cervical, thoracic, lumbar, sacral and coccygeal?


  there are 31 pairs of spinal nerves:

  8 cervical

  12 thoracic

  5 lumbar

  5 sacral

  1 coccygeal

  
• Sympathetic nerves only arise from thoracic and lumbar spinal segments -> the system has thoracolumbar outflow

  parasympathetic nerves only arise from the brain stem and sacral spinal segments -> this system has craniosacral outflow

  Think of it as a sympathetic sandwich (the sympathetic nervous system is sandwiched between the parasympathetic)

  
• All ANS efferent pathways are comprised of two neurons that synapse in a ganglion. 

  There will always be: 

  A pre-synaptic/pre-ganglionic fibre. 

  A post-synaptic/post-ganglionic fibre.
• The Annoying Exception to synapses in the ANS:

  The adrenal medulla is innervated solely by preganglionic sympathetic neurons. 

  There is no post-ganglionic neuron

  There is no parasympathetic innervation

  Innervation of the adrenal glands causes a widespread sympathetic response via hormone release.
• Draw out a typical spinal nerve, the pathway it takes through that spinal cord level

  here

  
• Which horn is relevant to the sympathetic nervous system?

  lateral horn - which is only found in the thoracic, upper lumbar, and sacral regions, is the central component of the sympathetic division of the autonomic nervous system.
• Describe the pathway sympathetic efferents take

  1. pre-ganglionic sympathetic fibre originate in the lateral horn.
  2. travels through the ventral root, then the spinal nerve,  into the white ramus communicans
  3. This is ‘white’ as pre-ganglionic fibres are myelinated
  4. pre- and post-ganglionic neurons synapse in the sympathetic ganglion
  5. Post-ganglionic fibre exits the ganglion through the grey ramus communicans and travel to the target tissue.
  6. This is ‘grey’ as post-ganglionic fibres are unmyelinated.
• Draw the pathway that sympathetic efferents take

  Here

  
• the pathway of sympathetic efferents is analgous to a ‘broken washing machine’. Imagine the clothes come in white and come out grey

  here

  
• In some cases, fibres will travel up or down the sympathetic trunk to different vertebral levels before passing through the grey ramus communicans...

  
  

  the fact that action potentials can travel up and down levels in the sympathetic chain means there is diffuse response by sympathetic signalling.
• Sympathetic nervous system uses Ach, adrenaline and noradrenaline as its neurotransmitters. More commonly Ach and noradrenaline
• Draw how a sympathetic signal would change levels

  here

  
• which neurotransmitters are used in different synapses (sympathetic nervous system)?

  Within the sympathetic ganglion (between the pre- and post-ganglionic fibres), the neurotransmitter released is acetylcholine. 

  Post-ganglionic sympathetic fibres release noradrenaline as the neurotransmitter at their target tissue. 
• describe the pathway of a parasympathetic efferent?

  1. The efferent will run from the ventral horn
  2. Through the ventral root, 
  3. Into the spinal nerve, 
  4. Along the ventral/dorsal ramus,
  5. Where it will then synapse within a ganglion before it reaches the target tissue
  6. parasympathetic ganglia are found near to or within the lining of the target tissue
• describe the pathway of a parasympathetic efferent

  1. The efferent will run from the ventral horn
  2. Through the ventral root
  3. Into the spinal nerve
  4. Along the ventral/dorsal ramus where it will then synapse within a ganglion before it reaches the target tissue
  5. parasympathetic ganglia lie near or sometimes in the target organ

  
• Splanchnic nerves are autonomic fibres that target viscera.

  • They can be sympathetic or parasympathetic.
  • Sympathetic innervation to most viscera occurs via splanchnic nerves
  • Parasympathetic innervation to most viscera occurs via the vagus nerve.
• Splanchnic nerves

  • Splanchnic nerves target viscera.

  • They can be sympathetic or parasympathetic.

  • These synapse in prevertebral ganglia, that lie beside the blood vessels supplying the target organ.

  • Post-ganglionic fibres then ‘hitch a lift’ with these vessels.

  
• splanchnic nerves diagram! Draw this

  
• exceptions to the splanchnic nerves (innervation of viscera):

  The cardiac plexus:

  • Pre-ganglionic sympathetic fibres synapse in sympathetic chain at T1-4, as well as from the cervical ganglia

  The pulmonary plexus:

  • Pre-ganglionic sympathetic fibres synapse in the sympathetic chain at levels T1-4

  focus on the synapses on this diagram

  
• Parasympathetic cranial nerves

  • CN III – The Oculomotor Nerve

  • CN VII – The Facial Nerve

  • CN IX – The Glossopharyngeal Nerve

  • CN X – The Vagus Nerve

  Only Fancy Guests like Venison
• which 4 ganglia can parasympathetic cranial nerves synapse in?

  • The ciliary ganglion

  • The otic ganglion

  • The pterygopalatine ganglion

  • The submandibular ganglion
• which 4 ganglia can parasympathetic cranial nerves synapse in?


  • The ciliary ganglion

  • The otic ganglion

  • The pterygopalatine ganglion

  • The submandibular ganglion

  
• The oculomotor nerve

  • Pre-ganglionic parasympathetic fibres arise from the Edinger-Westphal Nucleus of the midbrain

  • The oculomotor nucleus gives rise to all other fibres in the nerve

  • Pre-ganglionic parasympathetic fibres of CNIII synapse in the ciliary ganglion.

  Post-ganglionic fibres target:

  • The ciliary muscles.

  • The sphincter pupillae.

  
• The Facial nerve

  • Pre-ganglionic parasympathetic fibres arise from the Salivatory-Lacrimal (Superior Salivatory) Nucleus of the pons

  • The facial nucleus gives rise to all other fibres in the nerve

  CNVII parasympathetic fibres can synapse in either:

  • The pterygopalatine ganglion - Post-ganglionic pterygopalatine fibres target the lacrimal glands

  • The submandibular ganglion - Post-ganglionic submandibular fibres target the sublingual and submandibular glands

  
• The glossopharyngeal nerve

  • Pre-ganglionic parasympathetic fibres arise from the Salivatory-Lacrimal (inferior Salivatory) Nucleus of the medulla.

  • The nucleus ambiguus gives rise to other fibres in the nerve. (alot of nerves come through NA)

  • Pre-ganglionic parasympathetic fibres of CNIX synapse in the otic ganglion.

  • Post-ganglionic fibres target the parotid gland

  
• summary of parasympathetic nerves of head and neck (not vagus included)

  
• what does the vagus nerve supply (parasympathetic)? up to midgut

  • smooth muscle of the trachea, bronchi and gastro-intestinal tract
  • regulates heart rhythm (cardiac branches slow HR)
  • bronchial branches constrict the bronchi
  • esophageal branches control involuntary muscles in the esophagus, stomach, gallbladder, pancreas, and small intestine, stimulating peristalsis and gastrointestinal secretions
• The vagus nerve

  • Pre-ganglionic parasympathetic fibres arise from the Dorsal Vagal Motor Nucleus of the medulla.
  • The nucleus ambiguus gives rise to other fibres in the nerve.
  • Vaga- wanderer
  • CNX post-ganglionic fibres target the thoracic and abdominal viscera (up to where? the midgut).

  This means that this nerve is responsible for the majority of thoracic and abdominal parasympathetic innervation.

  
• Horner’s syndrome

  Sympathetic nerves reach the eye by travelling along the internal carotid and ophthalmic arteries. Any lesion along this pathway can result in Horner’s.

  Symptoms of Horner’s include:

  Miosis – A permanently constricted pupil

  Ptosis – Eyelid drooping

  Anhydrosis – An inability to sweat

  Enophthalmos – A sunken appearance to the eye

  
• Oculomotor nerve palsy

  • often mistaken for Horner's syndrome (and vice versa) as both result in paralysis of the upper eyelid/ptosis.

  Levator palpebrae superioris is a skeletal muscle.

  • This is innervated by somatic fibres of CNIII (ONP).

  The superior tarsal muscle (Muller’s muscle) is a smooth muscle.

  • This is under sympathetic control (HS).

  One under conscious and one under autonomic control
• list/compare the symptoms for Horner's Syndrome and Oculomotor Nerve Palsy

  note that ONP affects parasympathetic nerve

  
• visceral afferents can be reflexive or nociceptive
• reflexive visceral afferents - These fibres do not reach our consciousness – they can project to the spinal cord, brainstem or hypothalamus.
• nociceptive afferents - These signals do reach our consciousness but are poorly localised. Generalised pain.

  This is because visceral afferents are less densely packed than somatic afferents.
• The pathway of a visceral afferent:

  • The afferent neuron will run from the receptor -> along the ventral/dorsal ramus -> into the spinal nerve -> through the dorsal root -> And into the spinal cord, where it will then synapse in the dorsal horn of grey matter.
  • Visceral afferents will often ‘hitch a lift’ with other nerves -> anatomical feature allowing for referred pain; where the pain is felt corresponds with which nerves the afferents are travelling with

  
• The pelvic pain line

  • Pain from the viscera above or in contact with the inferior layer of the peritoneum is carried with splanchnic nerves (T10 – L1)

  • Pain from sub-peritoneal structures is carried with the pelvic splanchnic nerve (S2 – 4)

  •Pain emanating from above the PPL will be referred to the dermatomes supplied by T10 – L1.

  •Pain emanating from below the PPL will be referred to the dermatomes supplied by S2 – 4.