Question

Once the axon terminal/bouton membrane becomes depolarized, what are the detailed steps that trigger neurotransmitter release and what is the role of calcium?

Answer 1

Steps of release of neurotransmitters:-

• Calcium is a key ion involved in the release of chemical transmitter substances.
• The depolarization of the presynaptic terminal leads to an increase in Ca2+ permeability.
• The Ca2+ channels are normally closed, but if there is a depolarization of the membrane (caused by a presynaptic action potential), the channel opens and the opening of the channel allows calcium influx.
• The opening of the Ca2+ channel allows for calcium to flow down its concentration gradient from the outside to the inside of the synaptic terminal.
• This influx leads to an increase in the concentration of the Ca2+ in the presynaptic terminal, which by interacting with proteins associated with synaptic vesicles leads to the release of the chemical transmitter (neurotransmitter) substance.

Calcium is a vital element in the process of neurotransmitter release. When Ca2+ channels are blocked, neurotransmitter release is inhibited.

Ca2+ ions facilitate the binding of the transmitter substance with receptor molecules in the post-synaptic membrane.