Which of the following is a major type of neurotransmitter?

Neuropeptides are indeed a major type of neurotransmitter, playing a vital role in communication between neurons. They are small protein-like molecules that can influence a range of physiological processes, including pain perception, reward, food intake, learning, and memory. Neuropeptides are synthesized in neurons and can be released in response to various stimuli, modulating the activity of other neurotransmitters or altering the signaling pathways within the nervous system.

In contrast, carbohydrates are primarily utilized for energy and structural functions and do not serve as neurotransmitters. Hormones, while critical for signaling in various bodily functions, are distinct from neurotransmitters, which act primarily in the nervous system. Proteins, though fundamental to many cellular functions and structures, do not play the specific role of neurotransmitters either. Thus, neuropeptides stand out as a key category of neurotransmitters involved in neurotransmission and the modulation of nervous system activity.