What are the two main categories of neurotransmitters based on size?

What are the two main categories of neurotransmitters based on size?

• A. Neuropeptides and small-molecule transmitters.
• B. Large proteins and peptides.
• C. Amino acids and lipids.
• D. Gases and lipids.

Answer: (A)

The main idea is the size-based split of neurotransmitters into small-molecule transmitters and neuropeptides. Small-molecule transmitters are tiny chemicals like acetylcholine, GABA, glutamate, glycine, and biogenic amines. They’re made right at the nerve terminal, packed into small vesicles, and released quickly in response to an action potential to produce fast, precise postsynaptic effects that are cleared rapidly by reuptake or enzymes. Neuropeptides are larger peptide chains that are synthesized in the neuron's soma, processed and packaged into dense-core vesicles, and transported down the axon for release. They typically require higher-frequency activity and produce slower, longer-lasting modulatory effects on receptors, often GPCRs, shaping network activity rather than driving the immediate ionotropic response. That size-based distinction—neuropeptides versus small-molecule transmitters—is why these two groups are the correct pairing. The other options mix different kinds of signaling molecules (proteins, lipids, gases) that don’t form the standard size-based binary used to categorize neurotransmitters.

The main idea is the size-based split of neurotransmitters into small-molecule transmitters and neuropeptides. Small-molecule transmitters are tiny chemicals like acetylcholine, GABA, glutamate, glycine, and biogenic amines. They’re made right at the nerve terminal, packed into small vesicles, and released quickly in response to an action potential to produce fast, precise postsynaptic effects that are cleared rapidly by reuptake or enzymes.

Neuropeptides are larger peptide chains that are synthesized in the neuron's soma, processed and packaged into dense-core vesicles, and transported down the axon for release. They typically require higher-frequency activity and produce slower, longer-lasting modulatory effects on receptors, often GPCRs, shaping network activity rather than driving the immediate ionotropic response.

That size-based distinction—neuropeptides versus small-molecule transmitters—is why these two groups are the correct pairing. The other options mix different kinds of signaling molecules (proteins, lipids, gases) that don’t form the standard size-based binary used to categorize neurotransmitters.