AAMC FL Practice Exam

What triggers the release of neurotransmitters at the nerve terminal?

1. Action potential reaching the muscle fiber

2. Voltage dependent calcium channels opening

3. Inhibition of sodium channels

4. Reduction of extracellular calcium levels

The correct answer is: Voltage dependent calcium channels opening

The release of neurotransmitters at the nerve terminal is primarily triggered by the opening of voltage-dependent calcium channels. When an action potential travels down the axon and reaches the nerve terminal, it causes a depolarization of the membrane. This depolarization leads to the opening of these calcium channels, allowing calcium ions to flow into the neuron. The influx of calcium is crucial because it initiates a series of biochemical events that culminate in the fusion of neurotransmitter-containing vesicles with the presynaptic membrane. This fusion allows the neurotransmitters to be released into the synaptic cleft, where they can then bind to receptors on the postsynaptic cell, facilitating communication between neurons. In contrast, while the action potential is indeed a necessary precursor for this process, it is specifically the increase in intracellular calcium concentration that triggers the neurotransmitter release mechanism. The other options relate to processes that do not play a direct role in the neurotransmitter release mechanism at the nerve terminal.