Explain a chemical synaptic transmission

Nerve impulses are transmitted along the axon by saltatory propagation. This is where the wave of depolarisation jumps across to small gaps known as nodes of ranvier, dramatically reducing the time taken for the action potential to reach the pre-synaptic knob. Once the action potential reaches the pre-synaptic knob, the rapid depolarisation causes voltage gated Ca ²⁺ ion channels to open, allowing calcium ions to flow down their concentration gradient into the pre-synaptic knob.

The introduction of Calcium ions causes vesicles containing the neurotransmitter Ach to fuse with the membrane of the pre synaptic knob, and exocytose their contents into the synaptic cleft. Once here, the Ach diffuses across the cleft until it reaches receptors on the post synaptic knob. The binding to these receptors then causes the opening of Sodium Ion channels on the post synapse membrane. Thus allowing sodium to flow into the axon, causing the threshold potential to be reached and carrying the action potential on.