Home :: Chapter 14 :: Summary & Outline

Chapter 14 Summary & Outline

Biological Rhythms

Many living systems show circadian rhythms that can be entrained by environmental stimuli, especially light. These rhythms synchronize behavior and body states to changes in the environment. Review Figure 14.1, Web Activity 14.1

Study questions: 1 | 2 | 3 | 4 | 5 | 6

Neural pacemakers in the suprachiasmatic nucleus (SCN) of the hypothalamus are the basis of many circadian rhythms. The basis of light entrainment is a specialized pathway from the retina to the SCN. Review Figures 14.2 and 14.6
Ultradian rhythms (shorter than 24 hours) and infradian rhythms (longer than 24 hours) are evident in both behavior and biological processes. Review Figures 14.8 and 14.10
Several proteins, including, clock, cycle, and period interact in a cyclic fashion, increasing and decreasing in a cyclic fashion that takes about 24 hours. Thousands of SCN neurons, each keeping time through this molecular clock, pool this information to provide the circadian biological clock. Review Figure 14.7, Web Activity 14.2

Study questions: 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18

Seasonally breeding animals will continue to show annual cycles in body physiology and fur composition, even when kept in constant conditions in the laboratory. The brain region mediating this circannual rhythm has not been determined, but it is not the SCN.

Study questions: 19 | 20

During sleep, almost all mammals alternate between two main states: slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep. Review Figures 14.11, 14.12, and 14.15
Human SWS shows four stages defined by electroencephalography (EEG) criteria that include bursts of sleep spindles and persistent trains of large, slow delta waves. During SWS, muscle tension, heart rate, respiratory rate, and temperature decline progressively. Review Figure 14.11 and Table 14.2
REM sleep is characterized by a rapid EEG of low amplitude—almost like the EEG during active waking behavior—and intense autonomic activation, but the postural muscles are flaccid because of profound inhibition of motoneurons.
In adult humans, SWS and REM sleep alternate every 90–110 minutes. Smaller animals have shorter sleep cycles and spend more overall time asleep. Review Figures 14.12 and 14.15, Web Activity 14.3
Mental activity does not cease during sleep. Subjects awakened from REM sleep frequently report vivid perceptual experiences (dreams); subjects awakened from SWS often report ideas or thinking. Review Web Activities 14.4 and 14.5

Study questions: 21 | 22 | 23 | 24 | 25 | 26

SWS seems widespread among animal species, but REM sleep appears restricted to mammals and birds. It is unknown whether REM was inherited from a common ancestor of birds and mammals, or evolved independently in the two groups.

Study questions: 27 | 28 | 29 | 30

The characteristics of sleep-waking cycles change during the course of life. Mature animals sleep less than the young, and REM sleep accounts for a smaller fraction of their sleep. Review Figures 14.12, 14.18, and 14.19
The prominence of REM sleep in infants suggests that REM sleep contributes to development of the brain and to learning. Review Figure 14.18

Study questions: 31 | 32 | 33 | 34

Deprivation of sleep for a few nights in a row leads to impairment in tasks that require sustained vigilance. During recovery nights following deprivation, the lost SWS and REM sleep are partially restored over several nights. Review Figure 14.21

Study questions: 35 | 36 | 37 | 38 | 39

Researchers have suggested several biological roles for sleep, including conservation of energy, niche adaptation, restoration of the body, and consolidation of memory. Review Figure 14.23
The fact that prolonged sleep deprivation can lead to death suggests that sleep promotes health. No pill can guarantee a normal night of sleep. Review Box 14.1

Study questions: 40 | 41 | 42 | 43 | 44 | 45 | 46

General anesthetics, which seem to mimic slow wave sleep, act as non-competitive agonists to boost the inhibitory activity of GABA_A receptors. Review Figure 14.25
Four brain structures are involved in the initiation and maintenance of sleep. A basal forebrain system promotes SWS, the brainstem reticular formation promotes arousal, a pontine system appears to trigger REM sleep, and a hypothalamic system of hypocretin-releasing neurons regulates these three centers to control the sleep-waking cycle. Review Web Activity 14.6
Narcolepsy is the sudden, uncontrollable intrusion of sleep, which may be accompanied by cataplexy, during wakefulness. Disruption of hypocretin signaling, brought about by the lack of either hypocretin or hypocretin receptors, causes narcolepsy. Review Web Activity 14.7

Study questions: 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57

Sleep disorders fall into four major categories: disorders of initiation and maintenance of sleep (e.g., insomnia); disorders of excessive drowsiness (e.g., narcolepsy); disorders of the sleep-waking schedule; and dysfunctions associated with sleep, sleep stages, or partial arousals (e.g., sleepwalking). Review Table 14.2

Study questions: 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65