All of the following is/are true regarding muscarinic action except:
Correct Answer: Cardiac muscarinic receptors are predominantly M 3 type
Description: Ans: D (Cardia,.) Cardiac muscuranic receptors are predominantly M 2 type & mediate vagal bradycardia- KDT 7!h/niJ DICYCLOMINE Katzung 12th/l 18,126; KDT 7th/l117 It is an antagonist of M 1 & M3(smooth muscle)- Katzung Short tl/2 but action lasts up to 6 hr It has direct smooth muscle relaxant action in addition to weak anticholinergic Indication are- Morning sickness, motion sickness, dysmenorrhoea, irritable bowel syndrome MUSCARINIC ACTIONS KDT 7th/W3 Heart "At the A-V node & His-Purkinje fibres refractory period(RP) is increased & conduction is slowed; PR interval increases & partial to complete A-V block may be produced" Eye "Contraction of circular muscle of iris- miosis" "Contraction of ciliary muscle-spasm of accommodation, increased outflow facility, reduction in intraocular tension especially in glaucomatous patients)" Smooth muscle "Peristalsis in the ureter is increased. The detrusor muscle contracts while the bladder trigone & sphincter relaxes voiding of bladder" Glands 'Secretion from all parasympathetically innervated glands is increased via M3 & some M2 receptors: sweating, salivation, lacrimation, increased tracheobronchial & gastric secretion" Tab(KDT7th/101): Characteristics of important subtypes of muscarinic receptor M1 M2 M3 Location & Function served Autonomic ganglia: Depolarisation(late EPSP) Gastric glands: Histamine release, acid secretions CMS: Learning, memory' motor functions SA node: Hyperpolarisation, irate of impulse generations AV node: Velocity of conduction Atrium: Shortening of APD, contractility Ventricle: contractility Cholinergic nerve ending: Ach release CNS: Tremor, analgesia Visceral smooth muscle: contraction Visceral smooth muscle: contraction Iris: Constriction of pupil Ciliary' muscle: contraction Exocrine glands: secretion Vascular endothelium: the release of NO - vasodilation Agonists Antagonists Qxotremorine Pirenzepine, telenzepine Methacholine Tripitramme Bethanechol Darifenacin
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