If a doctor administers atropine IV,a muscarinic antagonist,followed by a high dose of ACh,you still see an increase in heart rate.Where is the ACh acting?

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Quizplus · Accepted Answer

Atropine blocks the binding of ACh to muscarinic receptors, which is the main receptor responsible for slowing down heart rate in the parasympathetic nervous system. By blocking this receptor, atropine allows the sympathetic nervous system to increase heart rate through the release of norepinephrine (NE). The high dose of ACh given after atropine administration would still bind to nicotinic receptors on the postganglionic sympathetic neurons, causing the release of NE to the heart and thereby increasing heart rate.

If a Doctor Administers Atropine IV,a Muscarinic Antagonist,followed by a High