Enumerate the major classes of neurotransmitter.

 Neurotransmitters can be categorized into several major classes based on their chemical structure and function. Here are the major classes of neurotransmitters:

1. Amino Acids

   • These are the most common neurotransmitters in the central nervous system.
   • Examples:
     • Glutamate (excitatory)
     • Gamma-Aminobutyric Acid (GABA) (inhibitory)
     • Glycine (inhibitory)

2. Monoamines

   • Derived from amino acids and regulate mood, arousal, and cognition.
   • Subclasses include:
     • Catecholamines (e.g., Dopamine, Norepinephrine, Epinephrine)
     • Indolamines (e.g., Serotonin, Melatonin)

3. Peptides (Neuropeptides)

   • Composed of short chains of amino acids.
   • Examples:
     • Endorphins (pain regulation)
     • Substance P (pain perception)
     • Oxytocin (social bonding)

4. Purines

   • Nucleotides that act as neurotransmitters.
   • Examples:
     • Adenosine
     • ATP (Adenosine triphosphate)

5. Acetylcholine (ACh)

   • Important in both the central and peripheral nervous systems.
   • Functions in muscle activation, attention, and memory.

6. Lipids

   • Act as signaling molecules, often involved in the modulation of neurotransmission.
   • Example:
     • Endocannabinoids (e.g., Anandamide)

7. Gases

   • These diffuse across cell membranes and modulate neurotransmission in an unconventional manner.
   • Examples:
     • Nitric oxide (NO)
     • Carbon monoxide (CO)

Each class of neurotransmitter plays a distinct role in regulating brain function and behavior.