sleepSilvia’s Corner is written by Silvia Hafliger, MD, assistant professor of psychiatry. In her posts, Dr. Hafliger will discuss a wide range of mental health topics and provide useful information to patients and their families.

The Mystery of Sleep  — Part 2

Brain Rhythm

Every process in the body has its own rhythm, including body temperature, the release of hormones and sleep. Sleep and wakefulness are regulated by the master clock in our brain, known as the anterior hypothalamus. It is located in the brain stem, where there is a cluster of cell bodies called Suprachiasmic nucleus. These pacemaker cells are influenced by light, temperature, social cues and food. They not only control day and night time but also regulate our immune system, cell signaling and hunger. There are additional cells in the brain stem that operate similar to a light switch. Cells in the Tuberomammillary bodies act like an “on switch,” promoting alertness and wakefulness by releasing a neuropeptide called histamine. The awake state is also regulated by orexin, another neuropeptide. Cells in the ventral pre-optic nucleus act like an “off switch,” promoting sleep by releasing GABA, an inhibitory neurotransmitter. The sleep state is further regulated by melatonin.

Neurotransmitters involved in sleep and wakefulness

Below is a list of some important chemicals involved in sleep and alertness.

  • Adenosine promotes sleep. It is a byproduct of cell energy metabolism that builds up as the day progresses. Caffeine blocks adenosine from binding to purine receptor, causing us to be less sleepy.
  • Histamine promotes wakefulness.
  • Acetylcholine promotes REM sleep.
  • Dopamine/norepinephrine promotes arousal.
  • Melatonin promotes sleep. It is produced by the pineal gland in response to a decrease in light. Melatonin levels start rising around 6 p.m. and peak around midnight.
  • Orexin promotes wakefulness. Patients who suffer from narcolepsy or excessive day time sleepiness are shown to lack cells producing orexin.

Read The Mystery of Sleep — Part 1 here.