Explain the process of synaptic transmission

The synapse is the junction between two neurons. When an action potential reaches the synaptic knob of a neuron, voltage-gate calcium channels are opened, causing an influx of positively charged calcium ions into the cell. This causes vesicles containing neurotransmitters, such as acetylcholine, to move towards the pre-synaptic membrane. When the vesicle reaches the membrane, the contents are expelled into the synaptic cleft by exocytosis. Neurotransmitters diffuse across the space, down its concentration gradient, until it reaches the post-synaptic membrane, where it binds to appropriate neuroreceptors. Binding to neuroreceptors causes depolarisation in the post-syanaptic neuron as voltage-gated sodium channels are opened, and positively charged sodium ions move into the cell. When enough neurotransmitters bind to neuroreceptors, the post-synaptic membrane passes the threshold level of depolarisation and an action potential is created and the impulse is transmitted.