Given that impulses from parasympathetic nerves decrease heart rate, and that the neurotransmitter for parasympathetic postganglionic fibers is acetylcholine (ACh), predict how the following chemicals might affect heart rate. A) Pilocarpine, a drug that simulates the action of ACh, will increase heart rate. B) Pilocarpine, a drug that simulates the action of ACh, will decrease heart rate. C) Atropine, a drug that blocks the action of ACh, will decrease heart rate. D) Pilocarpine, a drug that simulates the action of ACh, will increase heart rate; and atropine, a drug that blocks the action of ACh, will decrease heart rate.

The correct option is B (Pilocarpine, a drug that simulates the action of ACh, will decrease heart rate).

Explanation:

Heart rate which is the speed at which the contraction of the heart is measured per minute can increase in certain instances like stress, excitement and exercise. This temporal acceleration of the heart rate is reduced through the parasympathetic nervous system which releases the neurotransmitter, acetylcholine( ACh). This neurotransmitter binds to M2 muscarinic receptors at the cardiac muscle cells causing the heart rate to decrease.

Pilocarpine is a muscarinic acetylcholine receptor agonist which stimulates the action of ACh and will bring about the decrease of heart rate when administered.

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