<prompt> All of the following isare true regarding muscarinic action except:MiosisDetrusor muscle contractionDicyclomine is an antimuscarinic drug used for smooth muscle relaxationCardiac muscarinic receptors are predominantly M 3 type  <response>: Ans: D Cardia,. Cardiac muscuranic receptors are predominantly M 2 type mediate vagal bradycardia- KDT 7!hniJ DICYCLOMINE Katzung 12thl 18,126; KDT 7thl117 It is an antagonist of M 1 M3smooth muscle- Katzung Short tl2 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 7thW3 Heart At the A-V node His-Purkinje fibres refractory periodRP 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 TabKDT7th101: Characteristics of important subtypes of muscarinic receptor M1 M2 M3 Location Function served Autonomic ganglia: Depolarisationlate 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 