Part 2 of a 6-Part Series

Sleep is essential for our bodies to function.  It is during sleep that the body removes toxins, and our cells divide, grow, and repair. Without sleep our brains cannot create new neurons, make connections between neurons, and lay down memories. Sleep affects every tissue and system of the body and is crucial to brain function.

Sleep and arousal are dependent upon circadian rhythm. Circadian rhythm is the cycle of day and night, light and dark, and changing season resulting from the earth’s rotation. Deep within the brain are several structures that are responsible for falling asleep and waking.  Light and darkness are the triggers that begin a series of events that bring on sleep and help us to awaken. 

In addition to being tuned into environmental circadian rhythm, we also have our personal circadian rhythm and our personal internal clock, our chronotype. Whether you are a morning bird or a night owl is actually a genetic trait.

Morning people wake naturally, often not needing an alarm. They love mornings, enjoy breakfast, feel less fatigue during the day, and go to bed early. They often find it difficult staying up for late night parties and outings.  Night people frequently have difficulty waking and usually need that alarm, often hitting the snooze button. They like to stay up late and sleep in. Getting up and going in the morning takes them a while.  They make great night shift workers because it fits right in with their natural rhythm.

Our sleep/arousal cycle is controlled by several structures located deep within the brain. The hypothalamus, a peanut-sized structure deep within the brain is our internal master clock. The hypothalamus regulates our sleep/arousal patterns, body temperature, hormone release from the pituitary gland, hunger and thirst, sexual behavior and reproduction, and even moods and behavior. 

Inside the hypothalamus is a cluster of thousands of nerve cells that receive information about light exposure directly from the retina of our eyes. The brain stem, a structure at the base of the brain that is the beginning of the spinal cord, communicates with the hypothalamus to control transitions between sleep and arousal.

Both the brain stem and the hypothalamus have sleep-promoting cells which produce a chemical called GABA in response to decreasing light and approaching darkness to help us fall asleep. GABA inhibits our level of arousal.

When darkness approaches, the light-sensitive cells within the hypothalamus communicate with pineal gland, a tiny, pea-shaped structure located deep within the brain. The pineal gland then releases melatonin, which increases sleepiness and helps us fall asleep.

Once we are asleep, we experience several stages of brain activity, known as the sleep cycle. In addition to the hypothalamus and the brain stem, several other structures of the brain are involved with the regulation of our sleep cycles and are active during sleep.

Check back shortly to read part 3 of my series on sleep. I will discuss the stages of sleep and the parts of the brain involved. So, stay tuned!