Unidirectional transmission of a nerve impulse through nerve fibre is due to the fact that

Options

A. nerve fibre is insulated by a medullary sheath
B. sodium pump starts operating only at the cyton and then continues into the nerve fibre
C. neurotransmitters are released by dendrites and not by axon endings
D. neurotransmitters are released by the axon endings and not by dendrites.

Explanation

**Step-by-Step Solution:**

1. **Understanding Nerve Impulse Transmission:**
- Nerve impulses are electrical signals that travel along the nerve fibers (neurons). The direction of this transmission is crucial for proper communication within the nervous system.

2. **Direction of Transmission:**
- The transmission of nerve impulses is unidirectional, meaning it only travels in one direction—from the cell body (soma) to the nerve endings (axon terminals). This is important for maintaining the flow of information.

3. **Structure of a Neuron:**
- A typical neuron consists of dendrites, a cell body, an axon, and axon terminals. Dendrites receive signals, while the axon transmits the signals away from the cell body.

4. **Role of Synaptic Vesicles:**
- At the axon terminals, synaptic vesicles store neurotransmitters, which are chemicals that transmit signals across the synapse (the gap between neurons).

5. **Release of Neurotransmitters:**
- Neurotransmitters are released from the axon terminals and bind to receptors on the dendrites of the next neuron. This process initiates a new nerve impulse in the receiving neuron.

6. **Why Unidirectional Transmission Occurs:**
- The unidirectional nature of nerve impulse transmission is due to the fact that neurotransmitters are only released at the axon terminals and not at the dendrites. This ensures that the signal can only move from the axon of one neuron to the dendrites of another.

7. **Physical Limitations:**
- Additionally, the physical structure and length of neurons (which can be quite long) make it impractical for impulses to travel in the opposite direction. The design of neurons facilitates efficient signal transmission in one direction.

8. **Conclusion:**
- Therefore, the unidirectional transmission of nerve impulses through nerve fibers is primarily due to the release of neurotransmitters at the axon endings and not at the dendrites.

**Final Answer:**
The unidirectional transmission of a nerve impulse through nerve fibers is due to the fact that neurotransmitters are released by axon endings and not by dendrites.

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