Describe the process of synaptic neurotransmission

Neurotransmission is a mechanism of propagating an electrical signal between neurons via the movement of charged particles. It is initiated when the arrival of an action potential at the axon terminal triggers calcium entry via voltage-gated Ca channels. This causes neurotransmitter-containing vesicles to fuse with the pre-synaptic membrane, and release their contents into the cleft. The neurotransmitter molecules then bind to their respective receptors on the post-synaptic membrane, causing a respective influx of either positively- or negatively-charged ions - through, for instance, ligand-gated Na channels. This causes either a depolarisation or hyperpolarisation of the post-synaptic cell, leading either to an EPSP or IPSP which influences the likelihood of action potential generation.