What Do You Know About Sleep?

1) Sleep is essential for survival. True ____ False ____

TRUE. Studies performed using laboratory rats show that these animals will normally live for two to three years, but that rats deprived of REM sleep survive an average of only five months. Rats deprived of all sleep survive only about three weeks. ³² In humans, extreme sleep deprivation can cause an apparent state of paranoia and hallucinations in otherwise healthy individuals. However, despite identifying several physiological changes that occur in the brain and body during sleep, scientists still do not fully understand the functions of sleep. All animals, birds and reptiles sleep. Sleep may also occur among lower life forms, such as fish and invertebrates, but it is hard to know because EEG patterns are not comparable to those of vertebrates.

2) When you sleep, your body and brain activities are at rest. True ____ False ____

FALSE. Sleep is a highly organized sequence of events that follows a regular, cyclic program each night. It is an active process (not a passive one) that is required to sustain life.

3) During an average night’s sleep, about four hours are spent dreaming. True ____ False ____

FALSE. Two hours are spent dreaming during the average night’s sleep, mostly during REM sleep (although dreaming occurs during nonREM sleep and at the onset of sleep as well). The significance of dreaming to one’s health and the meaning of dreams remain mysteries.

4) During REM Sleep, (the Rapid Eye Movement stage…

A. Brain activity increases in the motor and sensory areas
B. Heart rate increases
C. There is greater chance for apnea
D. All of the above
E. None of the above

D. All of the above. Both brain and heart rate increase. There may also be brief episodes of apnea, and the airway resistance is also increased.

5) Sleep is a time for release of many of the body’s hormones. True ____ False ____

TRUE. For example, scientists believe that the release of growth hormone is related in part to repair processes that occur during sleep. Follicle stimulating hormoneand luteinizing hormone, which are involved in maturational and reproductive processes, are among the hormones released during sleep. In fact, the sleep-dependent release of luteinizing hormone is thought to be the event that initiates puberty. Other hormones, such as thyroid-stimulating hormone, are released prior to sleep.

6) Which of the organ systems are linked to the sleep cycle?

A) Endocrine system.
B) Renal system.
C) Alimentary activity.
D) All of the above.

Answer: D

Endocrine system . Sleep is one of the events that modify the timing of secretion for certain hormones.

Renal system . Kidney filtration, plasma flow, and the excretion of sodium, chloride, potassium, and calcium all are reduced during both NREM and REM sleep. These changes cause urine to be more concentrated during sleep.

Alimentary activity . In a person with normal digestive function, gastric acid secretion is reduced during sleep. In those with an active ulcer, gastric acid secretion is actually increased and swallowing occurs less frequently.

7) Sleep is a process that is controlled by the full brain. True ____ False ____

FALSE . Specific regions of the brain initiate and control sleep. The basal forebrain, including the hypothalamus, is an important region for controlling NREM sleep and may be the region keeping track of how long we have been awake and how large our sleep debt is. The brainstem region known as the pons is critical for initiating REM sleep.

8) Sleep patterns change during an individual’s life. True ____ False ____

TRUE. In fact, age affects sleep more than any other natural factor. Newborns sleep an average of 16 to 18 hours per day. By the time a child is three to five years old, total sleep time averages 10 to 12 hours, and then it further decreases to 7 to 8 hours per night by adulthood. One of the most prominent age-related changes in sleep is a reduction in the time spent in the deepest stages of NREM (Stages 3 and 4) from childhood through adulthood. In fact, this change is prominent during adolescence, when about 40 percent of this activity is lost and replaced by Stage 2 NREM sleep. In addition to these changes, the percentage of time spent in REM sleep also changes during development. Newborns may spend about 50 percent of their total sleep time in REM sleep. In fact, unlike older children and adults, infants fall asleep directly into REM sleep. Infant sleep cycles generally last only 50 to 60 minutes. By two years of age, REM sleep accounts for 20 to 25 percent of total sleep time, which remains relatively constant throughout the remainder of life. 15 Young children have a high arousal threshold, which means they can sleep through loud noises, especially in the early part of the night. For example, one study showed that 10-year-olds were undisturbed by a noise as loud as the sound of a jet airplane taking off nearby.

Although most humans maintain REM sleep throughout life, brain disorders like Alzheimer’s and Parkinson’s are characterized by decreasing amounts of REM sleep as the diseases progress. Also, elderly individuals exhibit more variation in the duration and quality of sleep than do younger adults. Elderly people may also exhibit increased sleep fragmentation (arousals from sleep that occur as either short or more extended awakenings).

9) An internal biological clock, called the circadian clock, regulates the timing for sleep in humans. True ____ False ____

TRUE . The activity of this clock makes us sleepy at night and awake during the day. Our clock cycles with an approximately 24-hour period and is called a circadian clock (from the Latin roots circa = about and diem = day). In humans, this clock is located in the hypothalamus in the brain in a very small structure consisting of a pair of pinhead-size regions, each containing only about 10,000 neurons out of the brain’s estimated 100 billion neurons.

Clocks enable organisms to adapt to their surroundings. The circadian clock in most humans has a natural day length of just over 24 hours… The cue that synchronizes the internal biological clock to the environmental cycle is light. Photoreceptors in the retina transmit light-dependent signals to the pinhead-size structures in the hypothalamus (called the Suprachiasmatic Nucleus - SCN).

The biological clock controls the cycle of body temperature, which is lowest in the biological night and rises in the biological daytime, and the release of the hormone melatonin, which levels rise during the night and decline at dawn in both nocturnaland diurnal species…Research has demonstrated that administering melatonin can produce shifts in circadian rhythms in a number of species including rats, sheep, lizards, birds, and humans. Melatonin is available as an over-the-counter nutritional supplement. Although claims are made that the supplement promotes sleep, the evidence for this is inconclusive. Potential side effects of long-term administration of melatonin remain unknown, and its unsupervised use by the general public is discouraged.

Circadian rhythm problems include:

• Jet lag . The circadian cycle afflicts travelers who rapidly cross multiple time zones. Jet lag produces a number of unwanted effects including excessive sleepiness, poor sleep, loss of concentration, poor motor control, slowed reflexes, nausea, and irritability. Jet lag results from the inability of our circadian clock to make an immediate adjustment to the changes in light cues that an individual experiences when rapidly crossing time zones.
• Monday morning blues. By staying up and sleeping in an hour or more later than usual on the weekends, we provide our biological clock different cues that push it toward a later nighttime phase. By keeping a late sleep schedule both weekend nights, our internal clock becomes two hours or more behind our usual weekday schedule. When the alarm rings at 6:30 a.m. on Monday, our body’s internal clock is now set for 4:30 a.m. or earlier.
• Seasonal affective disorder (SAD). A change of seasons in autumn brings on both a loss of daylight savings time (fall back one hour) and a shortening of the daytime. As winter progresses, the day length becomes even shorter. During this season of short days and long nights, some individuals develop symptoms similar to jet lag but more severe. These symptoms include decreased appetite, loss of concentration and focus, lack of energy, feelings of depression and despair, and excessive sleepiness. Too little bright light reaching the biological clock in the SCN appears to bring on this recognized form of depression in susceptible individuals. Consequently, treatment often involves using light therapy.
• Shift work. Unlike some animals, humans are active during daylight hours. This pattern is called diurnal activity. Animals that are awake and active at night (for example, hamsters) have what is known as nocturnal activity. For humans and other diurnally active animals, light signals the time to awake, and sleep occurs during the dark. Modern society, however, requires that services and businesses be available 24 hours a day, so some individuals must work the night shift. These individuals no longer have synchrony between their internal clocks and external daylight and darkness signals, and they may experience mental and physical difficulties similar to jet lag and SAD.

10) Caffeine has no biological influence on sleepiness. True ____ False ____

FALSE. The precise mechanism underlying the pressure that causes us to feel a need to sleep remains a mystery. What science does know is that the action of nerve-signaling molecules called neurotransmitters and of nerve cells (neurons) located in the brainstem and at the base of the brain determines whether we are asleep or awake. Additionally, there is recent evidence that the molecule adenosine (composed of the base adenine linked to the five-carbon sugar ribose) is an important sleepiness factor: it appears to "keep track" of lost sleep and may induce sleep. Interestingly, caffeine binds to and blocks the same cell receptors that recognize adenosine. 21, 30 This suggests that caffeine disrupts sleep by binding to adenosine receptors and preventing adenosine from delivering its fatigue signal. The homeostatic regulation of sleep helps reinforce the circadian cycle. We usually sleep once daily because the homeostatic pressure to sleep is hard to resist after about 16 hours, and then while we sleep, our closed eyes block the light signals to the biological clock.

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