What synapses are and how impulses travel across them

A synapse is a gap between neourons, signals go in only one direction so there is a pre-synaptic neuron and a post-synaptic neuron. The signal originates near the cell body of the pre-synaptic neuron. It travels via action potential down the axon to what is called the  terminal button , which forms one part of the synapse. The terminal button contains neurotransmitters stored in vesicles. When the signal reaches the end of the axon, these vesicles fuse with the cell membrane and the neurotransmitters are dumped outside of the cell a  process called exocytosis into the synapse.