Body Rhythms

Body Rhythms

Teachers everywhere complain that students don’t remember what they were taught. Maybe schedules, not daydreaming, are to blame.

The brain of every living creature responds to the environment with natural rhythms that rise and fall by the hours, days, and seasons. For example, body weight and height are affected by time of year: Children’s growth rate increases for height in summer and for weight in winter. Some biorhythms are on a day–night cycle that occurs approximately every 24 hours, called the circadian rhythm. (Circadian means “about a day.”) Puberty affects both seasonal and daily biorhythms.

The hypothalamus and the pituitary regulate the hormones that affect patterns of stress, appetite, sleep, and so on. At puberty, these hormones cause a phase delay in the circadian sleep–wake cycles. The delay is in the body’s reaction to daylight and dark.

For most people, daylight awakens the brain. That’s why people experiencing jet lag are urged to take an early morning walk. The phase delay at puberty makes many teens wide awake and hungry at midnight but half asleep, with no appetite or energy, all morning.

In addition to circadian changes in adolescent bodies, some individuals (especially males) are naturally more alert in the evening than in the morning, a genetic trait called eveningness. Exacerbated by pubertal phase delay, eveningness puts adolescents at risk for antisocial activities because they are awake when adults are asleep. Another result, if school is scheduled for adults, not teenagers, is that students are sleep deprived (Carskadon, 2011). In many nations, sleep deprivation increases during adolescence (see Figure 14.2 (Links to an external site.) Links to an external site.) (Roenneberg et al., 2012).

FIGURE 14.2

Sleepyheads Three of every four high school seniors are sleep deprived. Even if they go to sleep at midnight, as many do, they must get up before 8, as almost all do. Then all day they are tired.

 

To make it worse, “the blue spectrum light from TV, computer, and personal-device screens may have particularly strong effects on the human circadian system” (Peper & Dahl, 2013, p. 137). Watching late-night TV, working on the computer, or texting friends at 10 p.m. interferes with normal nighttime sleepiness. Sleeping late on weekend mornings is a sign of deprivation, not compensation.

Sleep deprivation and irregular sleep schedules lead to several specific dangers, including insomnia, nightmares, mood disorders (depression, conduct disorder, anxiety), and falling asleep while driving. In addition, sleepy people do not learn as well as they might when rested. Many adults ignore these facts, as the following Opposing Perspectives explains.

FIGURE 14.3
Dreaming and Learning? This graph shows the percentage of U.S. students who, once a week or more, fall asleep in class or are too tired to exercise. Not shown are those who are too tired overall (59 percent of high school students) or who doze in class “almost every day” (8 percent).

Sex Hormones

Late in childhood, the pituitary activates not only the adrenal glands but also the gonads, or sex glands (ovaries in females; testes, or testicles, in males), following another sequence called the HPG (hypothalamus-pituitary-gonad) axis. One hormone in particular, GnRH (gonadotropin-releasing hormone), causes the gonads to enlarge and dramatically increase their production of sex hormones, chiefly estradiol in girls and testosterone in boys. These hormones affect the body’s shape and function and produce additional hormones that regulate stress and immunity (Young et al., 2008).

Estrogens (including estradiol) are female hormones and androgens (including testosterone) are male hormones, although both sexes have some of both. The biochemical messages from the HPG axis activate the ovaries to produce high levels of estrogens and the testes to produce dramatic increases in androgens. This “surge of hormones” affects bodies, brains, and behavior before any visible signs of puberty appear, “well before the teens” (Peper & Dahl, 2013, p. 134).

The activated gonads produce mature sperm or ova, released in menarche or spermarche. Conception is possible, although fertility peaks several years later.

Hormonal increases and differences may also underlie sex differences in psychopathology. Compared to the other sex, adolescent males are almost twice as likely to develop schizophrenia and adolescent females more than twice as likely to develop depression. Of course, hormones are not the sole cause of psychopathology in anyone (Tackett et al., 2014; Rudolph, 2014).

One psychological effect of hormones at puberty has been proven: Hormones awaken interest in sex. The first sexual objects are usually unattainable—a film star, a teacher—but by mid-adolescence, fantasies typically settle on another teenager.

Emotional surges and lustful impulses may begin with hormones, but remember that body, brain, and behavior always interact. Sexual thoughts themselves can cause physiological and neurological processes, not just result from them.

Cortisol levels rise at puberty, and that makes adolescents quicker to become angry or upset (Goddings et al., 2012; Klein & Romeo, 2013). Then those emotions, in turn, increase levels of various other hormones. Bodies, brains, and behavior each affect the other two.

For example, when other people react to emerging breasts or beards, that evokes thoughts and frustrations in the adolescent, which then raise hormone levels, propel physiological development, and trigger emotions, which then affect people’s reactions. Thus the internal and external changes of puberty each impact the other.