Q25. Label the parts of a chemical synapse below and briefly describe what happens in the presynaptic and postsynaptic cells.

Background

Topic: Chemical Synapses in the Nervous System

This question is testing your understanding of the structure and function of a chemical synapse, which is the junction between two neurons where neurotransmitters are released to transmit signals.

Key Terms and Concepts:

• Presynaptic cell: The neuron sending the signal.

• Postsynaptic cell: The neuron (or muscle/gland cell) receiving the signal.

• Synaptic vesicles: Membrane-bound sacs in the presynaptic terminal containing neurotransmitters.

• Neurotransmitter: Chemical messenger released into the synaptic cleft.

• Synaptic cleft: The small gap between the presynaptic and postsynaptic membranes.

• Receptors: Proteins on the postsynaptic membrane that bind neurotransmitters.

Step-by-Step Guidance

1. Identify the main structures in the diagram: the presynaptic terminal (axon terminal), synaptic vesicles, synaptic cleft, and postsynaptic membrane.

2. Recall that when an action potential reaches the presynaptic terminal, it triggers the opening of voltage-gated calcium channels, allowing Ca2+ to enter the cell.

3. The influx of Ca2+ causes synaptic vesicles to move toward and fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft by exocytosis.

4. Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane, leading to a response in the postsynaptic cell (such as opening ion channels).

5. To complete the answer, label each part in the diagram and briefly describe the sequence of events in both the presynaptic and postsynaptic cells.

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