What are the events that lead to synaptic transmission between two neurons?

There are three compartments to consider- the presynaptic neuron, the synaptic cleft and the postsynaptic neuron. In a classical excitatory synapse: 1. An action potential arrives at the presynaptic neuron, depolarising the presynaptic membrane 2. Voltage-gated Calcium channels open, leading to Calcium ion influx 3. Vesicles (membrane-bound packages of neurotransmitter such as Acetylcholine) migrate and fuse to the presynaptic membrane 4. Neurotransmitter is released into the synaptic cleft via exocytosis 5. Neurotransmitter binds to specific neurotransmitter receptors on the postsynaptic membrane. Excess neurotransmitter is broken down by enzymes in the synaptic cleft (eg Acetylcholinesterase). 6. After neurotransmitter binds to postsynaptic neurotransmitter receptors, Sodium channels in the postsynaptic membrane open leading to Sodium ion influx 7. If there is sufficient Sodium ion influx, an action potential will be initiated in the postsynaptic neuron and carried forward. In this way, electrical energy in the presynaptic neuron is converted to chemical energy for neurotransmission to occur in the synaptic cleft. Following this, chemical energy is converted into electrical energy in the postsynaptic neuron. This type of neurotransmission enables unidirectonal transfer of information, and facilitates summation of signals both temporally and spatially.