Describe what happens at a chemical synapse

As the action potenial reaches the synaptic terminal depolarisation causes voltage-gated Ca²⁺ channels to open. The opening of these ion channels causes an influx of Ca²⁺ ions because of the high concentration gradient which is maintained across the cell membrane. Ca²⁺ in the synpatic terminal causes vesicles containing neurotransmitter molecules to move towards the membrane, and neurotransmitters to be released into the cleft by exocytosis. The neurotransmitter molecules diffuse across the cleft and bind to complementary receptors on the post-synaptic cell. The binding of neurotransmitters causes ion channels associated with the receptors to open, allowing the influx of ions. If sufficient ions enter the post-synaptic cell, an action potential will be generated.