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Biological Rhythms and Sleep. 10 Biological Rhythms and Sleep: Part I. Biological Rhythms Many Animals Show Daily Rhythms in Activity The Hypothalamus Houses an Endogenous Circadian Clock. 10 Biological Rhythms and Sleep: Part II. Sleeping and Waking Human Sleep Exhibits Different Stages
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10 Biological Rhythms and Sleep: Part I • Biological Rhythms • Many Animals Show Daily Rhythms in Activity • The Hypothalamus Houses an Endogenous Circadian Clock
10 Biological Rhythms and Sleep: Part II • Sleeping and Waking • Human Sleep Exhibits Different Stages • Our Sleep Patterns Change across the Life Span • Manipulating Sleep Reveals an Underlying Structure • What are the Biological Functions of Sleep? • At Least Four Interacting Neural Systems Underlie Sleep • Sleep Disorders Can Be Serious, Even Life-Threatening
10 Many Animals Show Daily Rhythms in Activity • Biological rhythms are regular fluctuations in a living process • Circadian rhythms have a rhythm of about 24 hours • Ultradian rhythms such as bouts of activity, feeding, and hormone release repeat more than once a day • Infradian rhythms such as body weight and reproductive cyclesrepeat less than once a day
10 Many Animals Show Daily Rhythms in Activity • Diurnal—active during the light • Nocturnal—active during the dark • Circadian rhythms are generated by an endogenous (internal) clock
10 Many Animals Show Daily Rhythms in Activity • A free-running animal is maintaining its own cycle with no external cues, such as light • The period, or time between successive cycles, may not be exactly 24 hours
10 Many Animals Show Daily Rhythms in Activity • A phase shift is the shift in activity in response to a synchronizing stimulus, such as light or food • Entrainment is the process of shifting the rhythm • The cue that an animal uses to synchronize with the environment is called a zeitgeber or “time-giver”
10 The Hypothalamus Houses an Endogenous Circadian Clock • The biological clock is located in the suprachiasmatic nucleus (SCN)—above the optic chiasm in the hypothalamus • Studies in SCN-lesioned animals showed disrupted circadian rhythms • Isolated SCN cells maintain electrical activity synchronized to the previous light cycle
10 The Hypothalamus Houses an Endogenous Circadian Clock • Transplant studies proved that the SCN produces a circadian rhythm • Hamsters with SCN lesions received a SCN tissue transplant from hamsters with a very short period, ~20 hours • Circadian rhythms were restored but matched the shorter period of the donor
Figure 10.5 Brain Transplants Prove That the SCN Contains a Clock
10 The Hypothalamus Houses an Endogenous Circadian Clock • Circadian rhythms entrain to light-dark cycles using different pathways, some outside of the eye • The pineal gland in amphibians and birds is sensitive to light • Melatonin is secreted to inform the brain about light
10 The Hypothalamus Houses an Endogenous Circadian Clock • In mammals, light information goes from the eye to the SCN via the retinohypothalamic pathway • Some retinal ganglion cells project to the SCN • Most contain melanopsin, a special photopigment, that makes them sensitive to light
10 The Hypothalamus Houses an Endogenous Circadian Clock • Molecular studies in Drosophila using mutations of the period gene helped to understand the circadian clock in mammals • SCN cells in mammals make two proteins: • Clock • Cycle
10 The Hypothalamus Houses an Endogenous Circadian Clock • Clock and Cycle proteins bind together to form a dimer • The Clock/Cycle dimer promotes transcription of two genes: • Period (per) • Cryptochrome (cry)
10 The Hypothalamus Houses an Endogenous Circadian Clock • Per and Cry proteins bind to each other and also to Tau • The Per/Cry/Tau protein complex enters the nucleus and inhibits the transcription of per and cry • No new proteins are made until the first set degrades • The cycle repeats ~every 24 hours
10 The Hypothalamus Houses an Endogenous Circadian Clock • Gene mutations show how important the clock is to behavior in constant conditions: • In tau mutations the period is shorter than normal • Double Clock mutants—severely arrhythmic
10 The Hypothalamus Houses an Endogenous Circadian Clock • Sleep is synchronized to external events, including light and dark • Stimuli like lights, food, jobs, and alarm clocks entrain us to be awake or to sleep • In the absence of cues, humans have a free-running period of approximately 25 hours
10 Human Sleep Exhibits Different Stages • Electrical brain potentials can be used to classify levels of arousal and states of sleep • Electroencephalography (EEG) records electrical activity in the brain
10 Human Sleep Exhibits Different Stages • Two distinct classes of sleep: • Slow-wave sleep (SWS) can be divided into four stages and is characterized by slow-wave EEG activity • Rapid-eye-movement sleep (REM) is characterized by small amplitude, fast-EEG waves, no postural tension, and rapid eye movements
10 Human Sleep Exhibits Different Stages • The pattern of activity in an awake person contains many frequencies: • Dominated by waves of fast frequency and low amplitude (15 to 20 Hz) • Known as beta activity or desynchronized EEG • Alpha rhythm occurs in relaxation, a regular oscillation of 8 to 12 Hz
Figure 10.10Electrophysiological Correlates of Sleep and Waking
10 Human Sleep Exhibits Different Stages • Four stages of slow-wave sleep: • Stage 1 sleep • Shows events of irregular frequency and smaller amplitude, as well as vertex spikes, or sharp waves • Heart rate slows, muscle tension reduces, eyes move about • Lasts several minutes
10 Human Sleep Exhibits Different Stages • Stage 2 sleep • Defined by waves of 12 to 14 Hz that occur in bursts, called sleep spindles • K-complexes appear–sharp negative EEG potentials
10 Human Sleep Exhibits Different Stages • Early stage 3 sleep • Continued sleep spindles as in stage 2 • Defined by the appearance of large-amplitude, very slow waves called delta waves • Delta waves occur about once per second
10 Human Sleep Exhibits Different Stages • Late stage 3 sleep • Delta waves are present about half the time
10 Human Sleep Exhibits Different Stages • REM sleep follows SWS • Active EEG with small-amplitude, high-frequency waves, like an awake person • Muscles are relaxed—called paradoxical sleep
10 Human Sleep Exhibits Different Stages • In a typical night of young adult sleep: • Sleep time ranges from 7–8 hours • 45–50% is stage 2 sleep, 20% is REM sleep • Cycles last 90–110 minutes, but cycles early in the night have more stage 3 SWS, and later cycles have more REM sleep
10 Human Sleep Exhibits Different Stages • At puberty, most people shift their circadian rhythm of sleep so that they get up later in the day • However, most high schools require adolescents to arrive even earlier • Later starts improved attendance and enrollment, and reduced depression and in-class sleeping
10 Human Sleep Exhibits Different Stages • Vivid dreams occur during REM sleep, characterized by: • Visual imagery • Sense that the dreamer is “there” • Nightmares are frightening dreams that awaken the sleeper from REM sleep • Night terrors are sudden arousals from stage 3 SWS, marked by fear and autonomic activity
10 Human Sleep Exhibits Different Stages • REM sleep evolved in some vertebrates: • Nearly all mammals display both REM and SWS • Birds also display both REM and SWS sleep
10 Human Sleep Exhibits Different Stages • Dolphins do not show REM sleep, perhaps because relaxed muscles are incompatible with the need to come to the surface to breathe • In dolphins and birds, only one brain hemisphere enters SWS at a time—the other remains awake
10 Our Sleep Patterns Change across the Life Span • Mammals sleep more during infancy than in adulthood • Infant sleep is characterized by: • Shorter sleep cycles • More REM sleep—50%, which may provide essential stimulation to the developing nervous system
10 Our Sleep Patterns Change across the Life Span • As people age, total time asleep declines, and times awakened increase • The biggest loss is time spent in stage 3: • At age 60, only half as much time is spent as at age 20 • By age 90, stage 3 has disappeared
Figure 10.17The Typical Pattern of Sleep in an Elderly Person
10 Manipulating Sleep Reveals an Underlying Structure • Effects of sleep deprivation—the partial or total prevention of sleep: • Increased irritability • Difficulty in concentrating • Episodes of disorientation • Effects can vary with age and other factors
10 Manipulating Sleep Reveals an Underlying Structure • Sleep recovery is the process of sleeping more than normally, after a period of deprivation • Night 1—stage 3 sleep is increased, but stage 2 is decreased • Night 2—most recovery of REM sleep, which is more intense than normal with more rapid eye movements