What are some reasons that synaptic transmissions might not work correctly?
Here are three: low amounts of neurotransmitters, recreational drugs, proteins called plaque that can interfere with synaptic transmission.
At times, the cells in the brain that produce neurotransmitter chemicals may not be working right and fail to produce adequate amounts. Recreational drugs can interfere with neurotransmitter receptor sites in the next synapse. Plaque is a kind of protein chemical that forms in Alzheimer patient's brains and results in memory loss. See pic.