A synapse is the fluid filled gap between the presynaptic neuron and postsynaptic neuron. 1) An electrical impulse travels along an axon of the presynaptic neuron. 2) When the impulse reaches the nerve-ending, it releases chemical messengers called neurotransmitters. 3) These chemicals diffuse across the synapse and bind with specific receptor molecules on the membrane of the next neuron. 4) This stimulates the second neuron to transmit the electrical impulse.