When an action potential comes down this pre-synaptic axon, when it reaches this point here, it sets off the process of these vesicles dumping their content into the synaptic cleft.

当动作电位到达轴突的突触前膜时,当到达这一点时 小泡就将其内含物,排放到突触间隙中去

耶鲁公开课 - 生物医学工程探索课程节选