Which neurotransmitter acts as both a neurotransmitter and a neuromodulator?

Norepinephrine is notable for its dual role as both a neurotransmitter and a neuromodulator. As a neurotransmitter, it is directly involved in the transmission of signals between neurons, particularly in the sympathetic nervous system where it plays a crucial role in the fight-or-flight response. This allows it to influence various physiological responses, such as increased heart rate and heightened alertness.

Furthermore, norepinephrine functions as a neuromodulator, meaning it can influence a wide array of neuronal activities more broadly than just signal transmission. It modulates the overall excitability of neurons and can affect mood, attention, and arousal levels by altering the strength and efficacy of synaptic communication within neural circuits. This property sets it apart from other neurotransmitters listed, which primarily fulfill one of these roles without the same degree of modulation.

Considering the context of neurotransmission and how different chemicals operate in the nervous system, norepinephrine’s capability to serve both functions underscores its importance in various cognitive and physiological processes.