Sleep anatomy

Hypothalamus

Hypothalamus, a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal. 

Suprachiasmatic nucleus

Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm.  Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.  Most blind people maintain some ability to sense light and are able to modify their sleep/wake cycle.

Brain stem

• Brain stem, at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep.
• Brain stem includes structures called the pons, medulla, and midbrain. 
• Sleep-promoting cells within the hypothalamus and brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centers in the hypothalamus and brain stem. 
• Brain stem (esp pons and medulla) also plays a special role in REM sleep; it sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

Thalamus

• Thalamus acts as a relay for information from the senses to the cerebral cortex 
• During most stages of sleep, thalamus becomes quiet, letting you tune out the external world. 
• But during REM sleep, thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams.

Pineal gland

• Pineal gland, located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin,
• Melatonin helps put you to sleep once the lights go down.  People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day. 
• Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.

Basal forebrain

• It is near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system. 
• Release of adenosine (a chemical by-product of cellular energy consumption) from cells in the basal forebrain and probably other regions supports your sleep drive. 
• Caffeine counteracts sleepiness by blocking the actions of adenosine.

Amygdala

It is an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep.