Describe what happens at a synapse.

An action potential (electrical impulse) arrives at a synapse (a gap between two neurones) which causes calcium voltage-dependent gates to open in the presynaptic neurone. An influx of calcium ions triggers the movement of vesicles containing neurotransmitters towards the presynaptic membrane where they fuse with the membrane and release their contents into the synaptic cleft. These neurotransmitters diffuse across the synaptic cleft to bind with specific complementary receptors on the post-synaptic membrane which triggers the opening of sodium voltage-dependent channels in the post-synaptic neurone. An influx of sodium ions in the post-synaptic neurone produces a depolarization event and thus generates an action potential.