Heartbeat is accelerated by

Options

A. (a) cranial nerves and adrenaline
B. (b) cranial nerves and acetylcholine
C. (c) sympathetic nerves and epinephrine
D. (d) sympathetic nerves and acetylcholine

Answer

To determine what accelerates the heartbeat, we can follow these steps:

1. **Understanding Heartbeat Control**: The heartbeat is primarily controlled by two systems: the nervous system and hormones. It is important to note that the heartbeat is an involuntary action, meaning it is not consciously controlled.

2. **Role of the Autonomic Nervous System (ANS)**: The autonomic nervous system (ANS) plays a crucial role in regulating the heartbeat. Within the ANS, there are two branches: the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system is responsible for accelerating the heartbeat.

3. **Sympathetic Nervous System Activation**: When the body is under stress or in a "fight or flight" situation, the sympathetic nervous system is activated. This activation leads to the release of hormones that affect heart function.

4. **Hormonal Influence**: One of the key hormones released during sympathetic activation is epinephrine (also known as adrenaline). This hormone is secreted by the adrenal medulla into the bloodstream.

5. **Mechanism of Action**: Once in the bloodstream, epinephrine binds to specific receptors in the heart called beta-adrenergic receptors. This binding stimulates the sinoatrial (SA) node, which is the natural pacemaker of the heart, leading to an increase in heart rate.

6. **Conclusion**: Therefore, the factors that accelerate the heartbeat are the sympathetic nerves and the hormone epinephrine. Based on the options provided, the correct answer is the one that includes both sympathetic nerves and epinephrine.

**Final Answer**: The heartbeat is accelerated by sympathetic nerves and epinephrine.

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