What are the vesicle pools, and what happens when the ready one runs out? · Grey Matter

A terminal's vesicles fall into three functional groups: a readily releasable pool docked and primed at the active zone (about 1 to 2 % of the total), a recycling pool that refills it during normal activity (about 5 to 20 %), and a reserve pool holding most of the rest, mobilised only by intense stimulation.

What are the vesicle pools, and what happens when the ready one runs out?

A terminal's vesicles fall into three functional groups: a readily releasable pool docked and primed at the active zone (about 1 to 2 % of the total), a recycling pool that refills it during normal activity (about 5 to 20 %), and a reserve pool holding most of the rest, mobilised only by intense stimulation. During a fast train each spike spends some of the ready vesicles, and if refilling cannot keep up, later spikes release less, which is short-term depression. Recovery takes from hundreds of milliseconds to seconds, depending on how quickly vesicles are recycled and primed again. How large the ready pool is, and how fast it refills, sets how long a synapse can follow a high-frequency input.