Final answer:
Synaptotagmin is the key protein that initiates neurotransmitter release by Ca2+ when it binds to the Ca2+ that enters the axon terminal, triggering vesicle fusion and neurotransmitter release. Other proteins such as SNAP, SNAREs, and Synapsin assist in various stages of vesicle docking, fusion, and regulation of neurotransmitter release.
Step-by-step explanation:
The process of neurotransmitter secretion involves several key synaptic proteins that work together to ensure that neurotransmitters are properly released into the synaptic cleft.
- SNAP: This protein helps in the pairing and fusion of vesicles with the membrane.
- SNAREs (synaptobrevin, syntaxin, SNAP-25): These proteins are essential for the docking and fusion of the neurotransmitter vesicles with the presynaptic membrane. They form a complex that brings the vesicle and membrane close enough to fuse.
- Synaptotagmin: This is the key protein in initiating transmitter release by Ca2+. When Ca2+ enters the axon terminal, it binds to synaptotagmin, triggering the fusion of vesicles with the presynaptic membrane and the subsequent release of neurotransmitters.
- Synapsin: It regulates neurotransmitter release by phosphorylation-dependent control of neurotransmitter vesicle availability.
When an action potential reaches the axon terminals, voltage-gated Ca2+ channels open, allowing Ca2+ to enter. The increase in intracellular Ca2+ concentration is the signal for the synaptic vesicles to fuse with the presynaptic membrane and release their neurotransmitter content into the synaptic cleft.