How does neurotransmission across a synapse occur?

Neurotransmission, put simply, is how your brain controls your body. It occurs by the passage of action potentials (electrical signals) across a synapse between two or more neurons. Neurons don't touch each other, but contact between it and thousands of other neurons is made using neurotransmitters. 

When an action potential reaches the axon terminal, neurotransmitters stored in vesicles in the terminal buttons of axons are released into the synaptic cleft. In the cleft, the neurotransmitters bind with corresponding receptors of post-synaptic neurons and lead to a configurational change in the neuron, allowing positively charged particles to enter the neuron. This begins another action potential in the dendrite of the neuron. 

After neurotransmission, the neurons are released into the synapse where they are either reabsorbed or deactivated by enzymes.

If, in case, the neurotransmitter is blocked or replaced, the physiological state is affected, leading to a change in mood, cognition and behaviour.