Discuss neural communication. (Include how signals travel throughout the body, how neurotransmitters work, excitatory and inhibitory messages and how some drugs can affect those messages.)
This would be much more appropriate in the Science Question Site. When neurotransmitters cross the synapses they can be picked up by receptors. Once a receptor is activated, the response could be excitatory in nature which means it will be more likely that an action will occur. Or the response could be inhibitory which means it is less likely that an action will occur. One spawns an action and one suppresses an action. A science teacher on the question board could explain it much better.