Quantal neurotransmitter release

Quantal neurotransmitter release is the process by which neurons communicate by releasing neurotransmitters in discrete, measurable units known as quanta. Each quantum represents the contents of a single synaptic vesicle, which fuses with the presynaptic membrane to release neurotransmitters into the synaptic cleft. This process is tightly regulated by calcium ion signaling and specialized SNARE protein complexes that enable vesicle docking and fusion. Following release, synaptic vesicles are recycled through multiple pathways to maintain synaptic function. Disruptions in this mechanism are linked to neurological disorders such as autism spectrum disorder, Alzheimer's disease, and myasthenia gravis.

Neurotransmitters are released into the synapse in small packages called quanta, which are stored inside structures called synaptic vesicles. One quantum generates a miniature end plate potential (MEPP) which is the smallest amount of stimulation that one neuron can send to another neuron. Quantal release is the mechanism by which most traditional endogenous neurotransmitters are transmitted throughout the body. The aggregate sum of many MEPPs is an end plate potential (EPP). A normal end plate potential usually causes the postsynaptic neuron to reach its threshold of excitation and elicit an action potential. Electrical synapses do not use quantal neurotransmitter release and instead use gap junctions between neurons to send current flows between neurons. The goal of any synapse is to produce either an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic potential (IPSP), which generate or repress the expression, respectively, of an action potential in the postsynaptic neuron. It is estimated that an action potential will trigger the release of approximately 20% of an axon terminal's neurotransmitter load.