Sympathetic stimulation

Options

A. decreases blood pressure
B. increases heartbeat
C. decreases heartbeat
D. not related to heartbeat

Answer

To answer the question regarding sympathetic stimulation, we will break down the concepts related to the sympathetic nervous system and its effects on the heart and blood pressure.

### Step-by-Step Solution:

1. **Understanding Sympathetic Stimulation**:
- The sympathetic nervous system is part of the autonomic nervous system that prepares the body for 'fight or flight' responses. It is responsible for increasing heart rate and blood pressure during stressful situations.

2. **Role of Norepinephrine**:
- When the sympathetic nervous system is activated, it releases neurotransmitters, primarily norepinephrine (noradrenaline). This chemical plays a crucial role in the body's response to stress.

3. **Effects on Blood Vessels**:
- Norepinephrine acts as a vasoconstrictor, meaning it causes blood vessels to constrict (narrow). This constriction increases the resistance against which the heart must pump, leading to an increase in blood pressure.

4. **Effects on Heart Rate**:
- In addition to affecting blood vessels, norepinephrine also acts on the heart. It binds to beta-adrenergic receptors in the heart, which leads to an increase in heart rate (positive chronotropic effect) and increased force of contraction (positive inotropic effect).

5. **Conclusion**:
- Given the effects of sympathetic stimulation, the correct answer to the question is that sympathetic stimulation **increases heart rate**.

### Final Answer:
**Sympathetic stimulation increases heart rate.**

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