An<unk>  is a synapse in which an action potential in the presynaptic cell increases the probability of an action potential occurring in the postsynaptic cell (see also: EPSP)).
At an<unk> , the neurotransmitter opens  sodium (Na+) channels, a slight depolarization of the receiving neuron occurs because of the movement of the positively charged sodium ions into the cell.
Excitatory synapse
Chemical synapse
Cell junction
Blood-brain barrier
Sensory receptor
Endocannabinoid system
Postganglionic fibers
Commissural fibers