Although the heart does not require the nervous system to initiate contraction events:
A) it is sympathetically innervated via cardiac nerve fibers.
B) it is parasympathetically innervated by vagus nerve fibers.
C) it is innervated by the phrenic nerve.
D) it is innervated by the sympathetic division of the autonomic nervous system only.
E) both (a) and (b) above.

Question

Quizplus · Accepted Answer

Although the heart can initiate contraction events on its own through specialized cardiac muscle cells called pacemaker cells, it is still innervated by the autonomic nervous system. The sympathetic division of the autonomic nervous system innervates the heart via cardiac nerve fibers and increases the heart rate and force of contraction during times of stress or physical activity. The parasympathetic division innervates the heart via vagus nerve fibers and has the opposite effect, slowing down the heart rate and reducing the force of contraction during times of rest or relaxation. Therefore, both options (a) and (b) are correct. Option (c) is incorrect since the phrenic nerve is responsible for innervating the diaphragm muscle that is involved in breathing. Option (d) is incorrect since the heart is also innervated by the parasympathetic division.

Although the Heart Does Not Require the Nervous System to Initiate