The Dynamics of Sleep
Sleep affects our physical and mental health in many ways.
Our Brain and Sleep
Nerve-signaling chemicals called neurotransmitters control whether we are asleep or awake by acting on different groups of nerve cells (neurons) in the brain.
Your brain is very active during sleep. Neurons in the brainstem that connects the brain to the spinal cord produce serotonin and norepinephrine neurotransmitters that keep parts of our brain active while we are awake.
A chemical called adenosine builds up in our blood while we are awake, causing drowsiness. This chemical gradually breaks down while we sleep.
Neurons at the base of the brain begin signaling when we fall asleep. These neurons switch off the neurons that keep us awake.
How Sleep Works
While sleeping you pass through five phases: Sleep stages 1, 2, 3, 4, and REM (rapid eye movement). These stages cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1.
Stages 1 and 2
During stage 1 you drift in and out of sleep and awaken easily. You may experience sudden muscle contractions and a falling sensation when awakening.
When you enter stage 2 sleep your eye movements stop. Your brainwaves slow, with occasional bursts of rapid waves called sleep spindles.
Stage 3 and 4 Deep Sleep
In stage 3 extremely slow delta brainwaves begin to appear, and no eye movement or muscle activity occur. By stage 4 your brain produces delta waves almost exclusively.
It is very difficult to wake someone during stage 3 and 4 deep sleep. People awakened during deep sleep often feel groggy and disoriented for several minutes upon waking.
When you enter REM (Rapid Eye Movement) sleep your eyes move around rapidly and your arm and leg muscles are temporarily paralyzed. Your breathing becomes more rapid, your heart rate increases, your blood pressure rises, and males have penile erections.
If your REM sleep is disrupted one night, your body will not follow the normal sleep cycle progression the next time you doze off. You may slip directly into REM sleep and go through extended periods of REM until you "catch up" on this stage of sleep.
We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM, and the remaining 30 percent in other stages. Infants spend about half of their sleep time in REM sleep.
Sleep, Caffeine and Drugs
Sleep and wakefulness are influenced by different brain neurotransmitter signals, so foods and medicine that change the balance of these signals affect whether we feel alert or drowsy and how well we sleep.
Caffeinated drinks such as tea and coffee, and drugs such as diet pills and decongestants, stimulate the brain and can cause insomnia. Many antidepressants suppress REM sleep.
Heavy smokers often have reduced REM sleep because they tend to wake up after 3 or 4 hours of sleep due to nicotine withdrawal. And although alcohol can help people fall into light sleep, it also prevents deeper, more restorative stages of sleep.
by Dr Jill Ammon-Wexler
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