Which neurotransmitter affects sleep? Select all that apply. One, some, or all responses may be…

➤ Why does histamine cause wakefulness and drowsiness when blocked?
Histamine neurons in the tuberomammillary nucleus fire during wakefulness and promote cortical activation and alertness. Blocking H1 histamine receptors with first‑generation antihistamines causes sedation and drowsiness. Histamine thus helps maintain daytime wakefulness and opposes sleep‑promoting systems like GABA.