How does a nerve ending work?

The action potential has been propagated along the axon of the neuron causing the depolarisation of the membrane. When this action potential reaches the end of the neuron, or the synapse, it also depolarises the membrane. This depolarisation causes voltage-gated calcium ion channels to open. The calcium ions then diffuse down their concentration gradient and into the synapse through these voltage gated channels. The presence of Ca^2+ ions causes vesicles filled with a chemical called a neurotransmitter to move toward the pre-synaptic membrane. These vesicles fuse with the membrane causing the release of the neurotransmitter into the synaptic cleft, which is the tiny gap between the two neurons. The neurotransmitter then diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane. This binding causes an action potential in the neuron, and this is propagated along the neuron. Importantly, the neurotransmitter is broken down by enzymes at the post-synaptic membrane to prevent continuous nerve impulses and to maintain a concentration gradient for the diffusion of more neurotransmitter during the next impulse.