The inner workings of the brain are quick, but really they have to be. Neurons need to be able to rapidly propagate information in their interior via electrical signals and they communicate with each other at special contact points known as the synapses. These chemical messenger substances (known as neurotransmitters) are stored in vesicles at the synapses. When a synapse becomes active, some of these vesicles fuse with the cell membrane and release their contents. To ensure that valuable time is not lost, synapses always have some readily releasable vesicles on standby.