Preganglionic fibre of parasympathetic nervous system secretes

Options

A. acetylcholine
B. adrenaline
C. aldosterone
D. both (1) and (2)

Answer

**Step-by-Step Solution:**

1. **Identify the Preganglionic Fibers of the Parasympathetic Nervous System:**
- The parasympathetic nervous system is one of the two divisions of the autonomic nervous system. It is responsible for the body's 'rest and digest' functions.

2. **Understand the Role of Neurotransmitters:**
- Neurotransmitters are chemicals that transmit signals across a synapse from one neuron to another 'target' neuron. In the context of the parasympathetic nervous system, the primary neurotransmitter involved is crucial for its function.

3. **Recognize the Chief Neurotransmitter:**
- The preganglionic fibers of the parasympathetic nervous system secrete **Acetylcholine**. This neurotransmitter plays a significant role in promoting the functions associated with the parasympathetic response, such as slowing the heart rate, increasing bodily secretions, and contracting smooth muscles.

4. **Evaluate Other Options:**
- **Adrenaline**: This is primarily associated with the sympathetic nervous system and is involved in the 'fight or flight' response, which increases heart rate. Therefore, it is not secreted by the preganglionic fibers of the parasympathetic nervous system.
- **Aldosterone**: This hormone is involved in regulating sodium and potassium levels in the body and does not play a role in the parasympathetic nervous system's neurotransmission.
- **Both First and Second**: Since only Acetylcholine is correct, this option is also incorrect.

5. **Conclusion:**
- The correct answer is that the preganglionic fibers of the parasympathetic nervous system secrete **Acetylcholine**.

**Final Answer:**
The preganglionic fibers of the parasympathetic nervous system secrete **Acetylcholine**.

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