Ask A Scientist

What happens when a human falls asleep? Does the body and mind just shut down?

Asked by: Matt Borne
School: Maine-Endwell Middle School
Grade: 6
Teacher: Kevin Wagstaff
Hobbies/Interests: Playing basketball, baseball, manhunt and singing
Career Interest: Sports announcer

Answer from Siva P. Adusumilli

Research Assistant and PhD Candidate, Binghamton University

Title: Research Assistant and PhD Candidate, Binghamton University
Department: Electrical Engineering, Center for Autonomous Solar Energy
Research areas: Thin films, semiconductors, nano materials and solar cells

It is amazing to know what happens while humans do their most loved thing . . . sleep! Sleep is as important as food and water and it is also considered to be one of the many life-sustaining elements. We spend about one-third of our lives asleep and human bodies need sleep for a healthy lifestyle. Until the mid-20th century, most people thought of sleep as a passive part of their daily lives, but thanks to research, we now better understand the tremendously active role it plays in our emotional and physical well being.

During sleep, organs do not shut down, but it is during this time that the body undergoes growth, repair and detoxification. This is how babies become kids and kids become adults. Sleep usually coincides with the release of growth hormones in children and young adults. Cells from the human body increase production of proteins during deep sleep. Proteins are the building blocks needed for cell growth and for the repair of damage caused from stress and physical wounds.

Sleep consists of five stages and these stages repeat in a cycle. 

During stage 1, muscle activity slows and we slowly drift in and out of a light sleep.

In stage 2, our brain waves become slower with occasional rapid waves called sleep spindles. In this phase, eye movement ceases, body temperature starts to decrease and heart rate begins to slow.

In stage 3, the brain produces slow moving delta waves, high amplitude brain waves that are associated with deep sleep. In this stage, the body begins the restoration phase. Blood flow to muscles increases, as does the release of hormones that stimulate cell growth.

In stage 4, you will find yourself in a deep sleep, while the body continues to heal itself. In this phase, the brain exclusively produces delta waves. And, because most of the high level functions of the brain (like speech) are not used, more blood is diverted to other parts of the body.

During stages 3 and 4, we enter into deep sleep, where there are no eye or muscle movements. People awakened during this deep sleep stage do not adjust immediately and feel very shaky and disoriented, as there is zero muscle activity and takes a while their senses and muscle functions to return. 

In stage 5 or Rapid Eye Movement (REM), the final stage, dreaming and breathing become rapid and irregular. The eyes begin moving quickly in different directions and limbs become temporarily paralyzed. At this point, blood flow rises sharply to several brain areas related to memory processing and emotional experience.

Overall, a complete cycle of all five stages takes 90 to 100 minutes, on average. The first sleep cycle contains short REM and long deep sleep time. As time progresses, REM sleep increases in length with reduced deep sleep which makes us ready to wake up when hit by sunlight.



Last Updated: 9/18/13