When calcium ions (\(\mathrm{Ca^{2+}}\)) enter the synaptic terminal, which of the following events is triggered?

• A. Voltage-gated sodium channels close.
• B. The postsynaptic neuron immediately generates an action potential.
• C. Vesicles containing neurotransmitters fuse with the presynaptic membrane.
• D. Neurotransmitters are degraded in the synaptic cleft.

Answer: (C)

Verified step by step guidance

1. Understand the role of calcium ions (\(\mathrm{Ca^{2+}}\)) in the synaptic terminal. Calcium ions are critical for neurotransmitter release in the nervous system. When an action potential reaches the synaptic terminal, voltage-gated calcium channels open, allowing \(\mathrm{Ca^{2+}}\) to enter the cell.
2. Recognize that the influx of \(\mathrm{Ca^{2+}}\) triggers the fusion of vesicles containing neurotransmitters with the presynaptic membrane. This process is known as exocytosis, where neurotransmitters are released into the synaptic cleft.
3. Eliminate incorrect options: Voltage-gated sodium channels closing is unrelated to calcium ion entry. Sodium channels are involved in the propagation of the action potential, not neurotransmitter release.
4. Clarify why the postsynaptic neuron does not immediately generate an action potential. The neurotransmitters released into the synaptic cleft must first bind to receptors on the postsynaptic membrane, which may or may not lead to an action potential depending on the type of neurotransmitter and receptor interaction.
5. Explain why neurotransmitters are not degraded immediately upon release. Degradation or reuptake of neurotransmitters occurs after they have performed their function of transmitting the signal to the postsynaptic neuron.