Transmission of a nerve impulse to its target cell requires:...

Transmission of a nerve impulse to its target cell requires: a. endocytosis of neurotransmitters by excitatory presynaptic vesicles. b. thousands of molecules of neurotransmitter that had been stored in the postsynaptic cell to be released into the synaptic cleft. c. $\mathrm{Ca}^{2+}$ ions to diffuse through voltage-gated $\mathrm{Ca}^{2+}$ channels. d. a fall in Ca" in the cytoplasm to trigger a protein that causes the presynaptic vesicle to fuse with the plasma membrane. e. an action potential to open the Ca" gates so that Ca $^{2+}$ ions, in higher concentration outside the axon, can flow back into the cytoplasm of the neuron.

Transmission of a nerve impulse to its target cell requires:
a. endocytosis of neurotransmitters by excitatory presynaptic vesicles.
b. thousands of molecules of neurotransmitter that had been stored in the postsynaptic cell to be released into the synaptic cleft.
c. $\mathrm{Ca}^{2+}$ ions to diffuse through voltage-gated $\mathrm{Ca}^{2+}$ channels.
d. a fall in Ca" in the cytoplasm to trigger a protein that causes the presynaptic vesicle to fuse with the plasma membrane.
e. an action potential to open the Ca" gates so that Ca $^{2+}$ ions, in higher concentration outside the axon, can flow back into the cytoplasm of the neuron.

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Key Concepts

Action Potential

An action potential is a rapid change in electrical membrane potential that travels along a neuron. It serves as the trigger for a sequence of events that ultimately leads to the release of neurotransmitters at the synapse.

Voltage-Gated Calcium Channels

Voltage-gated calcium channels are specialized proteins in the presynaptic membrane that open in response to the depolarization caused by an action potential. Their opening allows calcium ions to enter the neuron, which is essential for initiating neurotransmitter release.

Calcium Ion Gradient

The concentration gradient of calcium ions—high outside the neuron and low inside—is critical because it drives the influx of calcium when the voltage-gated channels open. This influx is a key signal that prompts the synaptic vesicles to merge with the membrane.

Neurotransmitter Release via Exocytosis

The influx of calcium ions triggers the fusion of synaptic vesicles with the presynaptic plasma membrane, a process known as exocytosis. This fusion results in the release of neurotransmitters into the synaptic cleft, where they can then interact with receptors on the target cell.

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