Sleep is affected by biological rhythms or periodic physiological changes. Biological rhythms are regular, periodic changes in a body’s functioning. There are three types of biological rhythms: Circadian rhythms: biological cycles that occur about every twenty-four hours, ultradian rhythms that occur more than once a day, and infradian rhythms that take longer than twenty hours
Biological Clocks
Endogenous rhythms exist because the body has biological clocks that keep time
- In humans, the suprachiasmatic nucleus (SCN) is the main biological clock that regulates circadian rhythms of sleep
- The SCN lies in the brain’s hypothalamus.
- When light stimulates receptors in the retina of the eye, the receptors send signals to the SCN which in turn sends the signal to the nearby pineal gland which secretes melatonin
Aging and Sleep
Sleep patterns change as people get older
Jet Lag
The fatigue and disorientation air travelers feel after a long flight
- People experience jet lag when the events in their environment are out of sync with their biological clocks
- Example: A traveler leaves New York City at eight in the morning and arrives in London about seven hours later. For her, it’s three in the afternoon, but because of the time change, in London it’s 8 in the evening. Her body, thinking it’s mid-afternoon, will be confused
REM Sleep
REM sleep is also called paradoxical sleep. During REM sleep, pulse rate and breathing become irregular, eyes move rapidly under closed lids, and muscles remain very relaxed.
- Genital arousal also happens during REM. People typically go through about four sleep cycles during one night of sleep.
The Function of Sleep
Researchers propose several theories to explain how sleep evolved to be a necessary behavior
- People conserve energy by sleeping periodically
- Sleep has a protective function, as it keeps people tucked away at night, safe from predators
- Restores body tissues that are depleted during daily activities
Sleep Deprivation
Different people need different amounts of sleep.
- Some people can function with fewer than six hours of sleep a night, while others can’t manage without at least nine hours
- Research shows that getting insufficient sleep can have negative effects on health, productivity, and performance
- Researchers have also studied the effects of insufficient REM sleep.
Sleep Disorders
Insomnia: a chronic problem with falling or staying asleep
- Narcolepsy: a tendency to fall asleep periodically during the day
- Sleep apnea: stop breathing many times during a night’s sleep, and wake up briefly to gasp for air
Sleep Research
Sleep research has provided a lot of information about what happens to the brain and body during sleep
Stage 1-4
In stage 1, the EEG shows mostly theta waves.
- Stage 2 lasts about twenty minutes and is characterized by short bursts of brain waves called sleep spindles. People in stage 3 and 4 sleep show slow breathing and pulse rates, have limp muscles, and are difficult to rouse. Sleepwalkers become physically active during stage 4.
