Biological Rhythms and Sleep

Biological Rhythms and Sleep

• Variations in consciousness are partly shaped by biological rhythms
• Rhythms are present throughout the world around us
• Examples of rhythms include the daily alternation of light and darkness, the annual seasons, and the phases of the moon
• Humans and other animals have biological rhythms that align with planetary rhythms
• Biological rhythms involve periodic fluctuations in physiological functioning
• Organisms possess internal "biological clocks" to monitor the passage of time

The Role of Circadian Rhythms

• Circadian rhythms are 24-hour biological cycles present in humans and other species
• Circadian rhythms significantly regulate sleep in humans
• Daily cycles cause rhythmic variations in blood pressure, urine production, hormone secretion, alertness, short-term memory, and cognitive performance
• Body temperature varies rhythmically on a daily cycle, peaking in the afternoon and reaching its lowest point at night
• People generally fall asleep as body temperature drops and awaken as it rises
• Circadian rhythms can physiologically prime individuals to fall asleep at a specific time of day
• The optimal sleep time differs, but each person has an "ideal" bedtime
• Ideal bedtimes can improve sleep quality
• Sleep quality may correlate more strongly with health and well-being than sleep quantity
• The day-night cycle resets human biological clocks
• Light exposure causes receptors in the retina to send inputs to the suprachiasmatic nucleus (SCN) in the hypothalamus
• The SCN signals the pineal gland to secrete melatonin, which adjusts biological clocks
• Multiple internal clocks regulate circadian rhythms in humans
• The central pacemaker is located in the SCN

Ignoring Circadian Rhythms

• Ignoring the biological clock and sleeping at unusual times can impair sleep quality
• Jet lag is caused by getting out of sync with circadian rhythms
• While traveling across time zones, the biological clock keeps time as usual, even if the official clock time changes
• The result is going to sleep at the "wrong" time, causing difficulty falling asleep and poor-quality sleep
• Poor sleep can continue for several days, leading to fatigue, sluggishness, and irritability

Figure 5.1 Examples of circadian rhythms

• Alertness, core body temperature, and growth hormone secretion typically fluctuate in a 24-hour rhythm
• Circadian rhythms are present in many other physiological functions

Realigning Circadian Rhythms

• Scientists are exploring ways to help people realign their daily rhythms because of the importance of circadian rhythms
• Research suggests small doses of melatonin regulate the human biological clock
• Melatonin can reduce the effects of jet lag by helping travelers resynchronize their biological clocks, but results are inconsistent
• When using melatonin to ameliorate jet lag, timing is crucial, and calculating the optimal timing is complicated
• Carefully timed exposure to bright light can realign circadian rhythms in rotating shift workers in industrial settings

Other Factors that impact circadian rhythms

• Chronic jet lag is associated with measurable deficits in cognitive performance
• People reset their biological clocks at different speeds when compensating for jet lag
• It takes a day for each time zone crossed to readjust
• It is generally easier to fly westward and lengthen the day rather than fly eastward and shorten the day
• Flying direction impacts sports teams
• Teams flying westward perform better than teams flying eastward in professional baseball and college football
• Shift rotation can affect sleep
• Just going to bed a couple of hours later than usual can affect sleep cycles
• Rotating work shifts affect about 20% of the United States workforce
• Shift rotation tends to be harder to adjust to than jet lag
• When workers go on rotating shifts, total sleep decreases and poorer quality sleep increases
• Shift rotation can negatively impact employee productivity, accident proneness, social relations, and physical and mental health
• Studies found shiftwork in females is associated with irregular menstrual cycles, reduced fertility, and an increased risk of premature births