Which one of the following is characteristic of the events occurring at an excitatory synapse?

Question

BlackTom AI · Accepted Answer

Binding of an excitatory neurotransmitter to postsynaptic ligand-gated cation channels allows sodium to flow into the postsynaptic neuron, producing a depolarizing excitatory postsynaptic potential (EPSP).

1. Relevant knowledge points and concepts
- Synaptic transmission sequence: presynaptic action potential → opening of voltage-gated Ca2+ channels → Ca2+ influx into presynaptic terminal → vesicle fusion and neurotransmitter release into the synaptic cleft → neurotransmitter binding to postsynaptic receptors.
- Excitatory synapses commonly use ligand-gated cation channels (e.g., AMPA-type glutamate receptors, nicotinic acetylcholine receptors) that are permeable to Na+ (and sometimes Ca2+), causing Na+ influx and membrane depolarization (EPSP).
- Inhibitory synapses typically open ligand-gated Cl− or K+ channels, causing hyperpolarization or shunting inhibition.

2. Step-by-step reasoning process
- An action potential arrives at the presynaptic terminal and opens voltage-gated Ca2+ channels.
- Ca2+ flows into the presynaptic terminal (influx), triggering synaptic vesicle fusion with the presynaptic membrane and exocytosis of neurotransmitter — vesicles do not physically cross the synaptic cleft.
- The released neurotransmitter diffuses across the cleft and binds to ligand-gated receptors on the postsynaptic membrane.
- At excitatory synapses, these ligand-gated receptors are cation channels that open and allow Na+ entry into the postsynaptic cell.
- Na+ influx depolarizes the postsynaptic membrane (EPSP), bringing it closer to action potential threshold.

3. Why the correct answer is correct
- The correct option states that ligand-gated sodium channels open to allow sodium entry into the postsynaptic neuron. This describes the canonical mechanism by which excitatory synapses produce EPSPs (e.g., glutamatergic AMPA receptors or nicotinic receptors).

4. Why other options are incorrect
- “Massive efflux of calcium from the presynaptic terminal”: incorrect because Ca2+ enters (influx), not exits, presynaptically to trigger release.
- “Synaptic vesicles diffuse across synaptic cleft and bind to the postsynaptic membrane”: incorrect because vesicles fuse with the presynaptic membrane and release neurotransmitter; they do not cross the cleft.
- “Ligand-gated potassium channels open to allow potassium out of the postsynaptic neuron”: opening K+ channels usually causes K+ efflux and hyperpolarization, producing inhibitory, not excitatory, effects.

Conclusion: The correct answer is “Ligand-gated sodium channels open to allow sodium entry into the postsynaptic neuron,” matching the provided answer.

Which one of the following is characteristic of the events occurring at an excitatory synapse?单项选择题

类似问题

Which one of the following statements about ligand-gated ion channels is CORRECT?

Nicotinic acetylcholine (Ach) receptors mediate synaptic transmission at the neuromuscular junction and are an example of .

Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium/potassium channel and opens it. This is an example of ________.

The membrane receptor on the dendrite that receives the neurotransmitter is a type of ______.

Ion channels located on the plasma membrane of a muscle, which open in response to binding of acetylcholine, are an example of a:

When a nerve cell is stimulated, it triggers the release of the neurotransmitter ligands. These then bind to the gated channel, allowing it to open. The flow of ions into the cell is what propagates the nerve signal. This describes a type of ______.

Using the analogy of an office key opening an office door to describe the action of chemical messengers on an ion channel, which of the following would be equivalent to inserting the correct key into the lock?

Ligand gated ion channels can be found:

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单