ABSTRACT
A nerve impulse propagating into a bouton causes a large influx of Ca2+ ions (Fig. 7 A). The input of 4 ci+ ions activates via calmodulin a synaptic vesicle and may cause it momentarily to open a channel (Fig. 7C) through the contacting presynaptic membrane, as indicated by the curved arrow in Fig. 4, so that its total transmitter content is liberated into the synaptic cleft in a process called exocytosis.
