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parasympathetics

parasympathetics

Cholinergic effects of muscarinic receptors:

Muscarinic M1 receptor actions:

  • CNS:
    • ? motion sickness; Parkinsonian tremor & extrapyr.;
    • ? memory function; EEG inc. voltage & freq. alpha-rhythm;
      • ⇒ cortical arousal;
    • produce slow excitatory post-syn. potentials → modulatory effect:
    • symp.ganglia;
    • post-gang. neurons of myenteric plexus;
    • postganglionic intramural neurons → inc. gastric secret.
    • presynaptic nerve terminals of autonomic neurons (some are M2):
      • ⇒ decr. transmitter release incl. NA & ACh;
      • ⇒ decr. symp. stimulation of heart, etc;

Muscarinic M2 receptors:

  • heart:
    • hyperpol. & decr. rate spontaneous depol. at SA node
      • ⇒ delay attainment of threshold level → decr.HR;
    • decr. AV conduction → may cause CHB in XS;
    • inc. funct. refract. period AV node → decr. vent.resp. to AF
    • decr. contract.(esp. atrial); decr. duration of AP;
    • decr. effective refractory period;
    • if disease or arrhythmia → partial depol. then ⇒ inc. cond. velocity in atrial muscle
      • ⇒ exac. AF/flutter from ectopic focus;
    • decr. automaticity of Purkinje fibres;
    • inc. threshold for VF;
    • decr. myocardial response to catecholamines;
  • vascular:
    • vasodilatation;

Muscarinic M3 receptors:

  • secretion
    • inc.: nose/mouth/pharynx/bronchi (incl. salivary & lacrimal), gastric; exocrine sweat glands;
  • sm.muscle:
    • pupil constriction; accomodation; bronchoconstriction;
    • inc. GIT tone, motility; relax GIT sphincters;
      • ⇒ N, belching, vomit, cramps, defecation;
    • inc. urinary & biliary systems tone & contractions;
      • ⇒ inc. detrussor tone but decr. trigone tone;
parasympathetics.txt · Last modified: 2009/11/13 00:45 (external edit)