Neurotransmitters diffuse across a :

Options

A. chemical synapse
B. myelin sheath
C. channel protein
D. both (a) and (b)

Explanation

**Step-by-Step Solution:**

1. **Understanding Neurotransmitters**: Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another.

2. **Identifying the Synaptic Gap**: When a nerve impulse reaches the end of an axon, neurotransmitters are released into the synaptic gap, which is the small space between the axon terminal of one neuron and the receptor sites on the next neuron.

3. **Options Analysis**: The question provides four options:
- A) Chemical synapse
- B) Bilayer sheet
- C) Channel protein
- D) Both A and B

4. **Correct Answer Identification**: The neurotransmitters diffuse across the synaptic gap specifically in a chemical synapse. Therefore, the correct answer is:
- A) Chemical synapse

5. **Eliminating Incorrect Options**:
- B) Bilayer sheet refers to the structure of cell membranes, not a pathway for neurotransmitter diffusion.
- C) Channel protein is involved in the movement of ions across membranes but does not directly relate to the diffusion of neurotransmitters across a synapse.
- D) Both A and B is incorrect because only option A is relevant.

6. **Final Conclusion**: The neurotransmitters diffuse across a chemical synapse.

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