What is Sleep?
Most people think that they can identify sleep just by looking at someone. If they show the obvious symptoms--immobility, closed eyes, no reaction to the environment--they are considered asleep. There is a lot more to it, however. Sleep is composed of REM sleep and non-REM sleep, both of which have their functions (although may not be clear).
Beginning Research
- Once thought to simply be a pause of most brain activity
- Sleepers are usually immobile and don’t react to their environment
- 1953: Nathaniel Kleitman and Eugene Aserinsky discovered that sleep regularly alternated in a cycle between REM (rapid eye movement) sleep and non-REM sleep (also known as quiet sleep).
- Led to belief that something active occurred during sleep
Non-REM Sleep
- Also known as "quiet sleep".
- Neurons in the brain stem reduce their activity greatly, while neurons in the cerebral cortex only reduce their activity by a small amount.
- Neurons in cortex fired synchronically
- Lower frequency rhythm than when awake
- Higher-voltage brain waves than waking
- Less energy is consumed when the brain is idle like this.
- Breathing and heart rate are stable
- Vivid dreams are rare
- Sleep-on neurons: a group of neurons at the base of the forebrain are most active during non-REM sleep. It isn't known how these are activated but some believe that it may be from heat, which is why we’re tired after a hot bath or w/e.
REM Sleep
- REM stands for Rapid Eye Movement, since the eyes move back and forth quickly.
- Most brain cells in forebrain and brain stem are active, sometimes as much as or more than in a waking state.
- Brain waves are of low voltage because neurons are behaving individually.
- Brain activity resembles wakeful activity.
- Brain consumes as much energy during REM as when awake.
- REM sleep-on cells in the brain stem help to start this state of REM sleep.
- Vivid dreams occur frequently since brain’s motor systems are activated, like when you're awake. Movement is prevented by the brain NOT releasing the neurotransmitters that would activate the muscles. The mechanisms that stop muscle movement do not work on the eyes, which is why the eyes move and twitch a lot.
- Heart rate and breathing are irregular, like when awake
- Body temperature is less regulated and drifts toward the temperature of the environment, like a reptile.
- Erections and clitoral enlargement present even if dream is not sexual.
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