Removal of transmitter is important. The system has to be reset. Transmitters open ligand gated channels on the post synaptic membrane. Ions flow through the open channel and change the post synaptic potential. Post synaptic potentials are graded.
Synapses are also the site of action of many mind altering drugs.
Depression linked to low levels of seretonin. Dopamine thought to be involved in schizophrenia and Parkinson's disease . Amphetamines increases norephinephrine in the brain. Nicotine mimics the effects of acetylcholine. Prozac inhibits the reabsorption of serotonin.