Question

What is the correct order for the events of neurotransmitter release from the synaptic terminal?

1) 1) Extracellular Ca₂⁺ enters terminal and binds to sensor protein in the cytoplasm
2) 2) Exocytosis of neurotransmitter into synaptic cleft
3) 3) Action potential reaches axon terminal
4) 4) Ca₂⁺-protein complex stimulates fusion of the docked synaptic vesicle with the plasma membrane
5) 5) Voltage-gated Ca₂⁺ channels open

Answer 1

The correct sequence for neurotransmitter release at the synaptic terminal starts with the arrival of an action potential, followed by the opening of Ca²⁺ channels, association of Ca²⁺ with sensor proteins, vesicle fusion, and eventually exocytosis of the neurotransmitter.

Step-by-step explanation:

The correct order for the events of neurotransmitter release from the synaptic terminal is as follows:

1. Action potential reaches axon terminal.
2. Voltage-gated Ca²⁺ channels open.
3. Extracellular Ca²⁺ enters terminal and binds to sensor protein in the cytoplasm.
4. Ca²⁺-protein complex stimulates fusion of the docked synaptic vesicle with the plasma membrane.
5. Exocytosis of neurotransmitter into synaptic cleft.

When an action potential reaches the axon terminal, it depolarizes the membrane, prompting voltage-gated sodium (Na⁺) and then calcium (Ca²⁺) channels to open. The influx of Ca²⁺ ions results in a cascade that causes synaptic vesicles to merge with the presynaptic membrane, resulting in the release of neurotransmitters into the synaptic cleft through exocytosis, where they can bind to receptors on the postsynaptic neuron, initiating a new sequence of events.