Refer to the figure.

The figure shows an electron micrograph of a chemical synapse in the cerebral cortex. Which statement about this synapse is accurate?

Question

Refer to the figure.

The figure shows an electron micrograph of a chemical synapse in the cerebral cortex. Which statement about this synapse is accurate?

BlackTom AI · Accepted Answer

In chemical synapses, neurotransmitter-filled synaptic vesicles are clustered in the presynaptic terminal and are released by vesicle fusion at the presynaptic active zone.

1) Relevant concepts:
- Presynaptic terminal: the axon terminal that contains synaptic vesicles (small, membrane-bound spheres) with neurotransmitter.
- Active zone: the specialized region of the presynaptic membrane where vesicles dock and fuse in response to Ca2+ influx.
- Synaptic cleft: extracellular space between pre- and postsynaptic membranes where neurotransmitter is released.
- Postsynaptic density (PSD): an electron-dense specialization on the postsynaptic membrane rich in neurotransmitter receptors and scaffolding proteins.
- Gap junctions/connexons: form electrical synapses with direct cytoplasmic continuity; no vesicle-mediated release.

2) Step-by-step reasoning:
- The electron micrograph shows many small, round vesicles concentrated in the labeled presynaptic compartment — a hallmark of presynaptic terminals.
- At the membrane facing the cleft there is an active zone where vesicles dock and fuse; released neurotransmitter crosses the cleft and binds receptors concentrated in the postsynaptic density.
- The postsynaptic side lacks vesicle pools and instead shows the dense PSD structure, not vesicle fusion sites.

3) Intermediate observations (no numeric calculations needed):
- Presence of numerous vesicles on the presynaptic side and an electron-dense PSD on the postsynaptic side indicate classic chemical synaptic organization with vesicle fusion at the active zone.

4) Why the correct answer is correct:
- “Inside the presynaptic neuron are synaptic vesicles, which fuse with the membrane in the active zone” accurately describes vesicle location and the site of neurotransmitter release.

5) Why other options are incorrect:
- Choice A: vesicles are not inside the postsynaptic neuron and do not fuse at the PSD.
- Choice C: vesicles fuse at the presynaptic active zone, not at the postsynaptic density.
- Choice D: gap junctions/connexons indicate electrical synapses with no vesicles or synaptic cleft; the image shows a chemical synapse.
- Choice E: incorrect because a correct statement is present.

Conclusion: The correct statement is “Inside the presynaptic neuron are synaptic vesicles, which fuse with the membrane in the active zone,” which matches the provided answer.

Refer to the figure. The figure shows an electron micrograph of a chemical synapse in the cerebral cortex. Which statement about this synapse is accurate?单项选择题

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