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< HMA‎ | Pracs
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  • Model of cervical vertebra (know it's cervical vertebra because of bifid spinous process and foramen transversarium for vertebral arteries)
  • Spinal cord = white and grey matter. Grey matter = H shape = cell bodies
  • Anterior median fissure (for anterior spinal artery) on the ventral surface of the spinal cord
  • Root = attached to dorsal and ventral surfaces of spinal cord.
  • Dorsal (sensory) and ventral (motor) roots join (bundles of axons)
  • Dorsal root has dorsal root ganglion. Beyond DRG, dorsal and ventral roots merge, to form spinal nerve. Branches of this are the ventral ramus and dorsal ramus.
  • Dorsal root (sensor nerves) = unipolar neuron with cell body in DRG= information from:
    • Skin, muscles etc - of which we are aware
    • Viscera - of which we are unaware below a threshold (subconscious). This input has to be severe before it becomes conscious
  • Spinal nerve - dorsal and sensory neurons unite (mixed nerve)
  • Ventral horn --> ventral root (motor) = multipolar neuron = no ventral ganglion (soma in CNS)
  • Mixing (spinal nerve) = anatomically (not functionally) divided, unlike ventral and dorsal roots
    • Ventral ramus is supplying a lot more (esp in brachial and sacral plexus for limbs) as well as thoracic and abdominal walls
    • Dorsal ramus supplies paravertebral muscles and skin
  • Ventral root = lower motor neurons = somatic = voluntary = skeletal muscle
    • Also have axons on nerves for smooth muscle of internal organs/glands
    • Cell bodies located in the lateral horn/intermediolateral horn/sacral autonomic nucleus
  • We name segments of the spinal cord based on which hole the spinal nerve comes out of
  • T1-T2: has a lateral horn between ventral and dorsal horn
    • Lateral horn sends axons out via ventral roots
  • S2-S4: lateral horn called sacral autonomic nucleus (similar deal)
  • These two locations are the only places where this blob of cells occurs
  • These represent the cell bodies of the neurons of the ANS
  • Lower motor neurons (somatic) --> ventral root --> ventral ramus --> all the way to skeletal muscle
  • ANS neuron (autonomic) --> ventral root --> spinal nerve --> ventral ramus --> then innervates another nerve cell in the periphery at autonomic ganglion --> target organ (smooth muscle or gland)
  • Autonomic ganglion different to DRG (sensory ganglion) because it's a synapse
    • Therefore we have presynaptic/preganglionic neurons and postsynaptic/postganglionic neurons

Divisions of the ANS

Anatomical: origin of soma

  • Autonomic nerves = PS and S = pre and post ganglionic cells and ganglion
  • SNS: preganglionic cells are in T1-L1/L2/L3 --> extra bump (lateral horn)
    • Hence called 'thoracolumbar outflow'
  • PNS: preganglionic cell bodies = brainstem (autonomic nuclei)
    • Cell bodies send out axons and travel in cranial nerves (through holes in base of skull - NOT spinal nerves. They go through cranial foramen NOT spinal foramen). There are 12 cranial nerves (I - XII)
      • PNS fibres travel through III (oculomotor), VII (facial), IX (glossopharngeal), X (vagus) cranial nerves
  • S2-S4: sacral autonomic nucleus, also out via ventral roots to prevertebral ganglia
    • Craniosacral outflow (anatomical division)

Anatomical: preganglionic length and ganglion size/location

  • SNS:
    • axon of preganglionic neurons is short and ganglia are on either side of vertebrae (paravertebral ganglia; sympathetic chain). Then the postganglionic cell is very long
    • OR: prevertebral ganglia runs with aorta. These ganglia send nerves to target organ
    • Ganglia are large
  • PNS:
    • ganglia are located ON or NEAR target organ
    • preganglionic cells are very long (e.g. vagus nerve --> cardiac plexus or oesophageal plexus)
    • sacral region --> pelvic splanchnic nerves (comprised of preganglionic cells)
    • head and neck region -->
      • ciliary ganglion (from oculomotor nerve) --> lens muscles
      • ganglion in pterygopalatine fossa OR submandibular region (from facial nerve) --> lacrimal gland and submandibular salivary gland
      • ganglion near parotid (from glossopharyngeal nerve) --> parotid gland
      • visceral ganglia (from vagus nerve; wandering a long way from the cranium) --> viscera
    • Ganglia are small

Anatomical: postganglionic neuron length and neurotransmitter

  • PS short, S long
  • neurotransmitter = ACh (in S and NS)
  • transmitter released on target organ:
    • PS - ACh
    • S - NA or A
  • these two systems have opposite effects
  • the different neurotransmitters cause different functions (despite innervating the same thing)

Prac questions

Things to identify

  • Ganglia, postganglionic nerves of S and PS
  • Coeliac, aorticorenal, SM ganglion, IM ganglion = all on branches of aorta
  • Vagus nerve = parasympathetic fibres + recurrent laryngeal fibres (motor)
    • Just like how ventral roots have S and motor
    • Plexuses on oesophagus, thoracic viscera, abdominal viscera
    • Pulmonary (ant/inf tracheal bifurcation) and cardiac (ant/post thoracic aorta) plexuses are mixed S and PS
    • pelvic splanchnic = preganglionic PS neurons for pelvic organs
  • thoracolumbar region schematic (SNS) (note that the origin of the fibres of the SNS in the ventral root is the lateral horn of the grey matter)

Gray799.svg

Question 1

  • Ventral roots = motor efferents
  • Dorsal roots = sensory afferents
  • Autonomic ganglion = junction/synapse between dendrivte of preganglionic nerve and soma of postganglionic nerve.

Question 2

  • Difference in colour = preganglionic neuron is myelinated; postganglionic neuron is unmyelinated
  • Myelin sheath = Schwann cell attached to axon in development, wraps around s oyou have plasma membrane wrapped around containing myelin protein and fat of lipid bilayer
    • Unmyelinated = have wrapping cells (to prevent short circuit), but not wrapping (therefore grey)
  • No sympathetic fibres arise from these vertebral levels (but come down sympathetic chain to innervate ganglia at those levels)
    • Therefore no white rami communicantes at these levels

Question 3

  • Cervico-thoracic ganglion (stellate) in root of neck (thoracic inlet)
    • =top ganglion
    • =axons running through and also terminating in ganglion
    • =near apex of lung (vulnerable to Pancoast's tumour)
    • tumour damages axons of cervicothoracic ganglion
      • dilator pupillae muscle
      • SMC in upper eyelid and under eye
      • sweat glands in face
      • blood vessels in face
  • PS and S both innervate all these structures. If you lose S, then PS is unregulated
  • constrictor pupillae is unregulated --> constriction (unilateral) (=miosis)
  • superior tarsal muscle in upper eyelid --> droops (unilateral) --> ptosis
  • enopthalmus --> when smooth muscle below eye droops, eye sinks down/falls
  • anhydrosis --> one side doesn't sweat
  • vasodilation (flushing)
  • Horner's syndrome is the term for this group of symptoms (due to Pancoast's tumour)

Question 8

  • S - fight/flight
  • PS - rest/digest
  • PS of heart and lungs = vagus
  • S of heart and lungs = stellate ganglion (heart) + T1-T4 thoracic ganglia (lungs)
  • Inferior cervical ganglion (the top sympathetic ganglion that has a white ramus communicans) and the first thoracic ganglion are often fused = cervicothoracic ganglion (stellate ganglion)
  • Heart: vagus + cervical ganglion form meshwork = cardiac plexuses (superficial - in front of ascending aorta, and deep - behind a. aorta)
  • Lungs: vagus + T1-T4 ganglia --> pulmonary plexuses (anterior - in front of tracheal bifurcation, and posterior - behind it)
    • anterior pulmonary plexus and deep cardiac plexus are often mixed because the tracheal bifurcation is just behind ascending aorta, so they're nearby

Functional considerations

Lung:

  • PS - bronchoconstriction and increase glandular secretions (more fluid in air spaces)
  • S - bronchodilation (muscle relax, airway wide), decreased secretions of glands (mcuoserous, preventing drying)

Heart:

  • S - increased HR, increased force of contraction, decreased nodal delay (time difference between SA node and AV node firing decreases) --> decreased PR interval
  • PS - decreased nodal delay, decreased heart rate, decreased force of contraction
  • One vagus - the other one makes up for it
  • Even if you take both away, no big deal (RHR goes from 60 bpm (vagal tone) to 80 bmp (no vagal tone, intrinsic SA firing))

Random notes

  • Nucleus = collection of cell bodies forming clumps of grey matter
  • PS: vagal trunks and oesophageal plexus pass through diaphragm, to contribute to the coeliac, SM, IM plexuses (merging with S fibres)
  • vagus:
    • recurrent laryngeal nerve
    • pulmonary plexus
    • cardiac plexus
    • oesophageal plexus
    • contribs to SM, C, IM plexus, supply down to Lt colic flexure
      • below here, PS supply is via pelvic splanchnic nerves (come off ventral ramus, see diagram above)
  • sacral splanchnic n's from S chain (sacral S ganglion to pelvic organs)
    • cf pelvic splanchnic n's from PNS

Images