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Anatomy, physiology and pharmacology of the autonomic supply of

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					Anatomy, physiology and
  pharmacology of the
autonomic supply of the
         heart
     The Medulla control centre
• The medulla is the primary site in the brain for regulating
  sympathetic and parasympathetic (vagal) outflow to the
  heart and blood vessels.
• The nucleus tractus solitarius of the medulla
  receives sensory input from different baroreceptors and
  chemoreceptors in the circulation.
• The medulla also receives information from other brain
  regions (e.g., hypothalamus). The hypothalamus and
  higher centres modify the activity of the medullary
  centres and are particularly important in stimulating
  cardiovascular responses to emotion and stress (e.g.,
  exercise, thermal stress).
The flow of Autonomic cardiac Qi
   SNS innervation of the heart
• Preganglionic neurons of the sympathetic
  division of the heart originate in the spinal
  cord and emerge in the spinal nerves at
  the levels of T-1 through to T-5, then
  leave the sympathetic chain as post
  ganglionic neurons travelling to the
  cardiac plexus.
  SNS innervation of the heart
• Sympathetic efferents are more diffuse
  their parasympathetic counterparts,
  being present throughout the atria
  (especially in the SA node, but also the AV
  node) and ventricles, including the
  conduction system of the heart.
  Sympathetic nerve endings release Nor-
  adrenaline.
   SNS innervation of the heart
Obviously, the SNS is stimulated in flight, fight and
  fright, but cardiac function is also altered by SNS
  affects on neural activation. When you’re awake:
• HR increases (positive chronotropy)
• Force of contraction increases (positive
  inotropy)
• AV nodal conduction velocity increases -
  increased PR interval (positive dromotropy)
• Increased rate of myocyte relaxation
  (positive lusitropy)
PNS innervation of the heart
   PNS innervation of the heart
• Supplied by the right (primarily innervates the SA
  node) and left vagus (left vagus innervates the AV
  node) nerves (CN X) which provide cervical cardiac
  nerves to the cardiac plexus.
• Unlike the sympathetic innervation, which must first
  synapse within chain ganglia to supply the heart with
  postsynaptic (postganglionic) fibres, the
  parasympathetic fibres synapse at ganglia located
  directly on the heart and short postsynaptic fibres
  then supply the target organ.
• Atrial muscle is more innervated by vagal efferents
  than the ventricular myocardium
   PNS innervation of the heart
ACh released by vagus nerve binds to M2
  muscarinic receptors producing:
• negative chronotropy
• Negative dromotropy
• negative inotropy
• Negative lusitropy
in the atria (the negative inotropic and lusitropic
  effects of vagal stimulation are relatively weak in
  the ventricles – since not much PNS
  representation there).
Balance of Qi
      Messing with autonomic
            receptors
• Β-blockers (especially type 1 selective) will
  antagonise β-adrenoceptors leading to slower
  HR, negative inotropy, longer PR intervals etc (eg.
  Metoprolol, Atenolol, Bisoprolol etc)  Used in
  treatment of Angina, HTN, Heart failure, acute MI,
  arrhythmias etc.
• Muscarinic anticholinergics (eg. Atropine) will
  antagonise the muscarinic receptors responsible
  for parasympathetic stimulation of the heart leading
  to the brakes being removed from the heart,
  resulting in an increase in HR, shorter PR interval
  etc  used in severe bradycardia and conduction
  block.
           Something quirky
The autonomic nerve presynaptic terminals also
  possess adrenergic and cholinergic receptors
  that function to regulate the release of
  Noradrenaline:
• Prejunctional α2-adrenoceptors inhibit
  Noradrenaline release
• Prejunctional β2-adrenoceptors facilitate
  noradrenaline release
• Prejunctional M2 receptors inhibit noradrenalin
  release, which is one mechanism by which vagal
  stimulation overrides sympathetic stimulation in
  the heart.

				
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posted:10/13/2012
language:English
pages:13
Jun Wang Jun Wang Dr
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