Question

If the sympathetic nerve to the heart is cut- off, the heartbeat will
A. Increase
B. Decrease
C. Remain the same
D. Stop

Answer 1

The sympathetic nervous system deals with the body's rapid involuntary response to dangerous or stressful situations.

Complete answer:
The sympathetic nervous system is a division of the nervous system that functions to produce localised adjustments such as sweating in response to an increase in temperature and reflex adjustments of the cardiovascular system. Let us analyse all the given options to find out the correct answer.

Option a: Sympathetic nerves supplying the heart are not needed to start the contractions, however, it can bring about an increase or decrease in the rate of contractions when necessary. It releases hormones such as catecholamines - epinephrine and norepinephrine to accelerate the heart rate in stressful conditions. Therefore, this is an incorrect option.
Option b: Sympathetic nerves supplying the heart are not needed to start the contractions, however, it can bring about an increase or decrease in the rate of contractions when necessary. It releases hormones such as catecholamines - epinephrine and norepinephrine to accelerate the heart rate in stressful conditions. Therefore, this is an incorrect option.
Option c: The tissue of the heart is said to be myogenic, i.e., it does not need electrical impulses from a nerve to make it contract. When the cardiac muscle is supplied with oxygen and nutrients, it continues to contract at a steady pace. Stimulation by the sympathetic nervous system causes an elevation in intracellular calcium and thus an increase in contraction of both the atria and ventricles. Sympathetic nerves supplying the heart are not needed to start the contractions, however, it can bring about an increase or decrease in the rate of contractions when necessary. Therefore, this is the correct option.
Option d: Sympathetic nerves supplying the heart are not needed to start the contractions, however, it can bring about an increase or decrease in the rate of contractions when necessary. So, if the sympathetic nerve to the heart is cut- off, the heartbeat will not stop. Therefore, this is an incorrect option.

Hence the correct answer is option ‘c’.

Note: It is to be noted that the medulla is the primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels.