Final answer:
The three types of neurotransmitters are excitatory, inhibitory, and neuromodulatory, with respective roles in upregulating, downregulating, or modulating neuron activity.
Step-by-step explanation:
The three basic types of neurotransmitters are excitatory, inhibitory, and neuromodulatory. These categories describe the effect neurotransmitters have on the postsynaptic cell once they bind to their receptors. Excitatory neurotransmitters, like glutamate, increase the chance of an action potential in the postsynaptic neuron, while inhibitory neurotransmitters, such as GABA or serotonin, reduce this chance.
On the other hand, neuromodulatory neurotransmitters may influence a cell's response to other neurotransmitters or affect longer-term changes, such as gene transcription or metabolic processes within the neuron. This nuanced interaction plays a crucial role in the central nervous system (CNS), which comprises the brain and spinal cord, and is shielded not just physically by bones and meninges, but also chemically by the blood-brain barrier. Any imbalances or issues with these neurotransmitter systems can lead to mental and physical disorders, highlighting their profound impact on health and disease.