Illustration of a junction, or synapse, between two nerve cells (neurons). As the electrical signal reaches the presynaptic end (top) of a neuron it triggers the release of neurotransmitters (bottom) across the gap, or synaptic cleft, between the two cells. The neurotransmitters bind to receptors on the postsynaptic membrane (blue), changing the membrane's excitability and triggering an electrical impulse.