What are small-molecule transmitters, and from what are they typically synthesized? Name and describe at least three different small-molecule transmitters.

Small-molecule transmitters are a type of neurotransmitter that are small in size and are synthesized within the nerve terminal. They are typically synthesized from simple building blocks such as amino acids, acetyl-CoA, and glucose.

Three different small-molecule transmitters include:

1. Acetylcholine: Acetylcholine is a small-molecule transmitter that is synthesized from the precursor molecule choline and acetyl-CoA. It is involved in the transmission of nerve impulses at synapses in the central nervous system and at neuromuscular junctions.

2. Dopamine: Dopamine is a small-molecule transmitter that is synthesized from the amino acid tyrosine. It plays a key role in the regulation of movement, motivation, and reward. Dysregulation of dopamine signaling has been implicated in various neurological and psychiatric disorders, such as Parkinson's disease and schizophrenia.

3. Serotonin: Serotonin is a small-molecule transmitter that is synthesized from the amino acid tryptophan. It is involved in the regulation of mood, appetite, and sleep. Imbalances in serotonin signaling have been linked to conditions such as depression and anxiety disorders.

Overall, small-molecule transmitters play crucial roles in the communication between nerve cells and are essential for the proper functioning of the nervous system.