Sleep and Homeostasis Chapter

Homeostasis: Sleep and Health

Sleep and Health

How Sleep Homeostasis Helps to Maintain Human Health

This booklet is designed to answer questions about how the human body's cycle of sleep and wakefulness, and to explain a few ways that sleep contributes to overall health.

The Sleep System

Sleep is governed by internal changes in the body that work together to produce healthy patterns of sleep. Over the course of our waking hours, our homeostatic sleep drive strengthens. The level of brain activity is associated with our patterns of sleep and wakefulness. Sleep theory suggests that adenosine is produced when active and alert brain cells use energy. Sleep drive and adenosine increase in concert during wakefulness, and the level of adenosine in the brain dissipates as the sleep drive lessens and we enter a stage of wakefulness. How deeply we sleep or the length of time that we sleep varies according to the quality and quantity of sleep that we attained earlier in the day or night. While the sleep drive can be masked -- by consuming caffeine or striving to increase physical activity, for instance -- the only true way to reduce the sleep drive is by sleeping.

Our Internal Biological Clock

Our biological clock regulates many different daily cycles from a small set of neurons that are located deep within the brain. Our daily sleep / wake cycle is characterized by a relatively steady state of alertness for 16 hours of a typical day ("Division of Sleep Medicine," 2007). Our biological clock is highly synchronized to our sleep / wake cycle by a circadian alerting system. The chemical and hormonal alerting system grows stronger with every hour that we are awake, and simultaneously serves to oppose the sleep drive, which is also always present throughout the day ("Division of Sleep Medicine," 2007). When the alerting signal of the biological clock falls below a certain level, the load of the sleep drive overcomes the circadian alerting system and allows the brain to fall asleep ("Division of Sleep Medicine," 2007).

While You Were Sleeping

The first four hours or so after we fall asleep, our sleep drive is fairly strong, which makes it easy to stay asleep. But soon the internal clock begins to send signals to the parts of the brain that govern wakefulness (Saper, et al., 2005). The balance slowly tips and the sleeping person begins to move toward a wakeful state. In this way, the synchronized sleep drive and the circadian system interact to provide consolidated periods when we are asleep and when we are awake.

At some point in the middle of the afternoon, the alerting signal diminishes for an hour or two. But the sleep drive continues to strengthen during this time, so people become sleepy or less alert (Saper, et al., 2005). It is not just serendipity that many cultures have adapted to this brief lull in alertness by instituting siestas or daily mid-afternoon naps. As evening falls and bedtime approaches, the alerting…