Where does the time go between a spike reaching a terminal and the next cell responding? · Grey Matter

Most of it goes into opening the calcium channels and fusing the vesicle; crossing the 20 nm cleft takes only microseconds, and the receptors begin to open almost as soon as the transmitter lands.

Where does the time go between a spike reaching a terminal and the next cell responding?

Most of it goes into opening the calcium channels and fusing the vesicle; crossing the 20 nm cleft takes only microseconds, and the receptors begin to open almost as soon as the transmitter lands. At fast synapses in the rat cerebellum at body temperature, fusion lags calcium entry by about 60 microseconds and the postsynaptic current starts about 150 microseconds after the presynaptic spike begins. Textbooks give 0.5 to 1 ms for the synaptic delay, a figure from older and cooler preparations, and the postsynaptic potential then takes another millisecond or more to rise and reach the soma. The delay is short but it adds up: a signal that crosses five synapses has spent several milliseconds in transit at the synapses alone.