What is the trigger for neurotransmitter release from a synapse?

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The trigger for neurotransmitter release from a synapse involves a series of events that occur at the chemical synapse. Let me break it down for you:

Nerve Action Potential: When an action potential (a rapid change in voltage) propagates down the axon of a presynaptic neuron, it depolarizes the synaptic terminal.

Voltage-Gated Calcium Channels: The depolarization caused by the action potential opens voltage-gated Ca2+ channels in the presynaptic terminal, allowing calcium ions (Ca2+) to enter.

Exocytosis of Vesicles: The influx of calcium serves as the signal to trigger exocytosis of presynaptic vesicles. These vesicles contain neurotransmitters (such as acetylcholine, ACh).

Diffusion of Neurotransmitter: The released neurotransmitter (ACh) diffuses across the narrow synaptic cleft and binds to nicotinic ACh receptors on the postsynaptic cell membrane.

Postsynaptic Response: Binding of ACh to its receptors opens non-selective cation channels (allowing both K+ and Na+ ions to flow), leading to a local depolarization called the end-plate potential. If the depolarization reaches firing threshold, it triggers an action potential in the postsynaptic cell, which can lead to muscle contraction or other responses12.

In summary, the increase in internal Ca2+ is a crucial signal that initiates neurotransmitter release at chemical synapses. This process is conserved across all chemical synapses in the nervous system1. If you have any more questions or need further clarification, feel free to ask! 😊

Learn more

1

uw.pressbooks.pub

2

khanacademy.org

3

britannica.com

4

openbooks.lib.msu.edu

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