All parts of the brain › Sleep

What part of the brain controls sleep?

No single part. The hypothalamus holds both the body’s master clock, the suprachiasmatic nucleus, which sets the daily timing of sleep, and a switch: a group of neurons in its ventrolateral preoptic nucleus that quiets the brain’s arousal centres to bring on sleep. The pineal gland releases melatonin at night on the clock’s signal. Arousal systems in the brainstem and the thalamus keep the cortex awake, and circuits in the pons switch on REM (dreaming) sleep. [1][2][3][4]

The 3D brain needs JavaScript. The list of parts still says what each one does for sleep.

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All 5 parts are lit together. Drag to turn, pinch or scroll to zoom, tap a part on the brain or a name in the list to focus it; .

Sleep: 5 parts lit

Hypothalamus, pineal gland, pons, thalamus and brainstem. Tap one to see where it is and what it does.

The parts and their roles

Holds the suprachiasmatic nucleus, the master circadian clock that receives light signals straight from the retina, and the ventrolateral preoptic nucleus, whose GABA and galanin neurons inhibit the arousal centres during sleep; orexin neurons in its lateral part help keep you awake. [1][2][5] Where is the hypothalamus?
Makes melatonin from serotonin and releases it in darkness, under control of the suprachiasmatic nucleus; melatonin levels rise in the evening and signal night to the rest of the body. [3][6] Where is the pineal gland?
Neurons in the pons and the nearby midbrain switch on REM sleep, and pontine circuits send signals down to the spinal cord that relax the body’s muscles during it (REM atonia); its locus coeruleus, a noradrenaline-making arousal nucleus, falls almost silent in REM. [7][8] Where is the pons?
Relays sensory signals to the cortex and becomes less responsive to them in deep sleep; its reticular nucleus generates the sleep spindles, short 11–16 Hz bursts that mark stage 2 non-REM sleep on an EEG. [9][10] Where is the thalamus?
Houses most of the ascending reticular activating system, the network of nuclei (noradrenaline, serotonin, acetylcholine and others) whose projections to the thalamus and cortex keep the brain awake and alert. [4][11] Where is the brainstem?

How they work together

Light reaches the clock directly: special retinal ganglion cells containing the pigment melanopsin send signals along the retinohypothalamic tract to the suprachiasmatic nucleus, which is how daylight resets the body’s roughly 24-hour rhythm. [12][1]
The clock reaches the pineal gland by a long detour: suprachiasmatic nucleus → paraventricular nucleus of the hypothalamus → the spinal cord → the superior cervical ganglion in the neck → back up to the pineal gland, which is why light at night lowers melatonin. [3][6]
The sleep switch works like a flip-flop: the ventrolateral preoptic nucleus and the arousal centres inhibit each other, so whichever side is stronger shuts the other off and the change between waking and sleep is quick rather than gradual; orexin neurons steady the switch. [2]
When you sleep is set by two processes together: sleep pressure that builds the longer you are awake (linked to adenosine), and the circadian timing from the suprachiasmatic nucleus. A night runs in cycles of non-REM and REM sleep of about 90 minutes each. [13][14][15]
Honest limit: the hypothalamic nuclei that do this work are each a few millimetres across and have no separate piece on this model, so the whole hypothalamus lights; the locus coeruleus, the raphe nuclei and the basal forebrain, which also take part, are lit only as part of the pons and brainstem or not at all, and the flip-flop switch is a model built largely on animal studies. [2][16]

Sources

Facts describe anatomy and normal function only. A part lit here takes part in sleep; it does not do it alone, and it does other jobs too. The 3D model is the adult male BodyParts3D brain (credits and licence); on it the brainstem includes the midbrain, pons and medulla, so lighting the brainstem lights all three.