In general, action potentials that reach the synaptic knobs cause a neurotransmitter to be released into the synaptic cleft.
一般来说,动作电位到达突触节会导致神经递质释放到突触间隙。
A cleft in someone's chin is a line down the middle of it.
(下巴上的)裂纹
If someone has a cleft chin, they have a cleft in their chin.
(下巴)裂的