Question

By whose action is the heartbeat accelerated?

• A. cranial nerves and adrenaline
• B. cranial nerves and acetylcholine
• C. sympathetic nerves and epinephrine
• D. sympathetic nerves and acetylcholine

Answer 1

Answer: (C)

The heartbeat is extrinsically controlled by external neural signals from the brain. The centre of heartbeat regulation in the brain is the medulla oblongata. The neural signals carried by the nerves of the autonomous nervous system (ANS) heavily influence the heart rate and cardiac output of the heart. The sympathetic nerves increase the heart rate, strength of ventricular contraction and, in turn, the cardiac output. The parasympathetic nerves show just the opposite action (decreases heartbeat, speed of conduction and cardiac output).
The parasympathetic nerves travel through the tenth cranial nerve (X) called vagus nerve. The vagus nerve secretes acetylcholine which reduces the heartbeat.
Adrenaline (epinephrine) and noradrenaline (norepinephrine) are excitatory hormones, produced by the adrenal medulla, that are catecholamines in nature. These medullary hormones are secreted during emergency situations like a fight or flight. The rush of these hormones through the body increases the heart rate and, in turn, the cardiac output.