In: Anatomy and Physiology
Describe the events that take place when the action potential spreads throughout the axon terminal leading up to the release of neurotransmitters into the synaptic cleft.
When a nerve is stimulated (like mechanically or by some other stimulus) then sodium channel open. This causes influx of sodium inside neuron and lead to rise in membrane potential (it rises from resting membrane potential of about - 70 mV to a more positive value). When threshold potential (about - 55 mV) is reached then voltage gated sodium channel open and there is rapid influx of sodium. This gives riser to action potential. In myelinated neuron the action potential travel by saltatory conductance . It means that action potential is generated at Node of Raniver because voltage gated sodium channel are present there. When action potential reaches axon terminal then it lead to opening of voltage gated calcium channel. This lead to influx of calcium inside. The calcium binds to synaptic vesicles that contain neurotransmitters like acetyl choline. Binding of calcium causes these vesicles to fide with presynaptic membrane (a process called as docking). This lead to release of neurotransmitters in synaptic cleft. The neurotransmitters then act on postsynaptic neuron or other tissue.