Hypothalamic orexin neurons and the arousal switch
Orexin (also called hypocretin) is produced by a small cluster of neurons in the lateral hypothalamus. These neurons project widely and excite the brain's monoaminergic and cholinergic arousal centres, helping stabilise wakefulness and prevent inappropriate transitions into sleep. Loss of these neurons is the underlying cause of type 1 narcolepsy, which is characterised by excessive daytime sleepiness and cataplexy.
Because orexin sits at a control point of the sleep-wake system, it has become a target for drugs aiming to push the system in either direction.
Pushing the system awake or toward sleep
Modafinil promotes wakefulness, and part of its action is thought to involve increased activity in orexin-related arousal circuits, though its primary pharmacology centres on dopamine reuptake. Suvorexant works in the opposite direction as a dual orexin receptor antagonist, blocking orexin signalling to facilitate sleep onset in insomnia.
This is general educational information, not medical advice. Modafinil and orexin antagonists are prescription medicines with specific indications, contraindications, and interaction risks. Use only under a qualified clinician's supervision.