Quantal neurotransmitter release

Quantal neurotransmitter release is release of neurotransmitter in discrete packets associated with individual synaptic vesicles. Packet count and postsynaptic packet response are different quantities; see the binomial distribution example under synaptic vesicle.

Synaptic release probability is the probability of release at a specified site during a specified opportunity, such as one presynaptic action potential. It depends on the site's state and conditions; it is not the probability that the receiving neuron fires. In the example under synaptic vesicle, $p$ refers to one available site, whereas $1-(1-p{)}^4$ refers to any of four independent sites releasing.