Choose the pair that contains the two correct ways to cause an increase in the firing rate of pacemaker cells of the heart.
A) Stimulating the parasympathetic nerve to the heart; applying norepinephrine to pacemaker cells
B) Applying acetylcholine to pacemaker cells; stimulating the parasympathetic nerve to the heart
C) Damaging the sympathetic nerve to the heart; applying norepinephrine to pacemaker cells
D) Stimulating the sympathetic nerve to the heart; applying norepinephrine to pacemaker cells
E) Damaging the sympathetic nerve to the heart; applying acetylcholine to pacemaker cells

Question

Quizplus · Accepted Answer

The sympathetic nervous system activates pacemaker cells of the heart, which leads to an increase in the firing rate. Norepinephrine is the neurotransmitter that mediates this effect. Therefore, stimulating the sympathetic nerve to the heart and applying norepinephrine to pacemaker cells will both cause an increase in the firing rate, making choice D the correct pair. Choices A and B involve the parasympathetic nervous system, which slows down the firing rate of pacemaker cells, making them incorrect. Choices C and E involve contradictory actions and are therefore incorrect.

Choose the Pair That Contains the Two Correct Ways to Cause