Synaptic vesicles are :

Options

A. at the ends of dendrites and axons
B. at the ends of axons only
C. along the length of all long fibres
D. all of the above

Answer

### Step-by-Step Solution:

1. **Understanding Synaptic Vesicles**: Synaptic vesicles are small membrane-bound structures found in neurons. They contain neurotransmitters, which are chemicals that transmit signals across a synapse from one neuron to another.

2. **Location of Synaptic Vesicles**: These vesicles are specifically located at the axon terminals (also known as presynaptic terminals) of neurons. They are not found at the ends of dendrites or distributed along the length of the axon.

3. **Function of Synaptic Vesicles**: When an electrical signal (action potential) reaches the axon terminal, it triggers the influx of calcium ions. This increase in calcium concentration causes the synaptic vesicles to move towards the presynaptic membrane and fuse with it, leading to the release of neurotransmitters into the synaptic cleft.

4. **Neurotransmitter Release**: The neurotransmitters released from the synaptic vesicles then bind to specific receptors on the postsynaptic membrane, facilitating the transmission of the signal to the next neuron or target cell.

5. **Conclusion**: Therefore, synaptic vesicles are found only at the ends of the axon, and not at the ends of dendrites or along the length of the axon. Thus, the correct answer to the question is that synaptic vesicles are located at the ends of the axon.