13. Various effects of drugs on synapses: DRUG ACTION EFFECT Mimic a neurotransmitter Switch on a synapse Stimulate the release of a neurotransmitter Switch on a synapse Open a neuroreceptor channel Switch on a synapse Block a neuroreceptor channel Switch off a synapse Inhibit the breakdown enzyme Switch on a synapse Inhibit the Na + K + ATPase pump Stop action potentials Block the Na + or K + channels Stop action potentials