1. Biological Rhythms and Sleep

2. 10 Biological Rhythms and Sleep: Part I
Many Animals Show Daily Rhythms in Activity
The Hypothalamus Houses an Endogenous Circadian Clock

3. 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

4. 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 cycles repeat less than once a day

5. 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

6. 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

7. Figure 10.2 How Activity Rhythms Are Measured (Part 1)
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8. 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”

9. Figure 10.2 How Activity Rhythms Are Measured (Part 2)
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10. 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

11. Figure 10.3 The Effects of Lesions in the SCN
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12. 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

13. Figure 10.5 Brain Transplants Prove That the SCN Contains a Clock
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14. 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

15. 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

16. Figure 10.6 Components of a Circadian System
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17. 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

18. 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)

19. 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

20. Figure 10.7 A Molecular Clock in Flies and Mice
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21. 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

22. Figure 10.8 When the Endogenous Clock Goes Kaput
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23. 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

24. Figure 10.9 Humans Free-Run Too
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25. 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

26. 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

27. 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

28. Figure 10.10 Electrophysiological Correlates of Sleep and Waking
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29. 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

30. 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

31. 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

32. 10 Human Sleep Exhibits Different Stages
Late stage 3 sleep
Delta waves are present about half the time

33. 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

34. 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

35. Figure 10.11 A Typical Night of Sleep in a Young Adult
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36. 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

37. Figure 10.12 How I Hate to Get Out of Bed in the Morning!
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38. 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

39. 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

40. 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

41. Figure 10.14 Sleep in Marine Mammals
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42. 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

43. Figure 10.15 The Trouble with Babies
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44. Figure 10.16 Human Sleep Patterns Change with Age
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45. 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

46. Figure 10.17 The Typical Pattern of Sleep in an Elderly Person
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47. 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

48. Figure I Need Sleep!
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49. 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

50. Figure 10.19 Sleep Recovery after 11 Days Awake

51. 10 Manipulating Sleep Reveals an Underlying Structure
Sleep deprivation can be fatal
Total sleep deprivation compromises the immune system and leads to death
The disease fatal familial insomnia is inherited—in midlife people stop sleeping and die 7–24 months after onset of the insomnia

52. 10 What Are the Biological Functions of Sleep?
Four functions of sleep:
Energy conservation
Niche adaptation
Body restoration
Memory consolidation

53. 14 What Are the Biological Functions of Sleep?
One role of sleep is to conserve energy
Muscular tension, heart rate, blood pressure, temperature, and rate of respiration are reduced

54. 10 What Are the Biological Functions of Sleep?
Sleep helps animals avoid predators—animals sleep during the part of the day when they are most vulnerable The ecological niche for each species is the unique assortment of opportunities and challenges in its environment

55. Figure 10.20 Sleep Helps Animals to Adapt an Ecological Niche
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56. 10 What Are the Biological Functions of Sleep?
Sleep restores the body by replenishing metabolic requirements, such as proteins Most growth hormone is only released during SWS Proper sleep is essential for immune function

57. 10 What Are the Biological Functions of Sleep?
Sleep may aid memory consolidation:
Sleep during the interval between learning and recall may reduce interfering stimuli
Memory typically decays and sleep may slow this down
Or sleep, especially REM, may actively contribute through processes that consolidate the learned material

58. 10 What Are the Biological Functions of Sleep?
A challenge to sleep theories is the existence of a few people who hardly sleep at all yet are normal and healthy Whatever the function of sleep, these people fill it with a brief nap

59. Figure A Nonsleeper
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60. 10 At Least Four Interacting Neural Systems Underlie Sleep
Sleep is an active state mediated by:
A forebrain system—displays SWS
A brainstem system—activates the forebrain
A pontine system—triggers REM sleep
A hypothalamic system—affects the other three

61. 10 At Least Four Interacting Neural Systems Underlie Sleep
Transection experiments showed that different sleep systems originate in different parts of the brain
The isolated brain is made by an incision between the medulla and the spinal cord
Animals showed signs of sleep and wakefulness, proving that the networks reside in the brain

62. Figure 10.22 Transecting the Brain at Different Levels (Part 2)
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63. 10 At Least Four Interacting Neural Systems Underlie Sleep
An isolated forebrain is made by an incision in the midbrain
The electrical activity in the forebrain showed constant SWS, but not REM—thus, the forebrain alone can generate SWS

64. Figure 10.22 Transecting the Brain at Different Levels (Part 3)
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65. 10 At Least Four Interacting Neural Systems Underlie Sleep
The constant SWS activity in the forebrain is generated by the basal forebrain, a ventral region
Neurons in this region become active at sleep onset and release GABA
GABA activates receptors in the nearby tuberomamillary nucleus
GABA receptors are also stimulated by general anesthetics to produce slow waves resembling SWS

66. 10 At Least Four Interacting Neural Systems Underlie Sleep
The reticular formation is able to activate the cortex
Electrical stimulation of this area will wake up sleeping animals
Lesions of this area promote sleep
The forebrain and reticular formation seem to guide the brain between SWS and wakefulness

67. Figure 10.23 Brain Mechanisms Underlying Sleep
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68. 10 At Least Four Interacting Neural Systems Underlie Sleep
An area of the pons, near the locus coeruleus, is responsible for REM sleep Some neurons in this region are only active during REM sleep They inhibit motoneurons to keep them from firing, disabling the motor system during REM sleep

69. Figure 10.24 Acting Out a Dream
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70. 10 At Least Four Interacting Neural Systems Underlie Sleep
The study of narcolepsy revealed the hypothalamic sleep center.
Narcolepsy sufferers:
Have frequent sleep attacks and excessive daytime sleepiness
Do not go through SWS before REM sleep
May show cataplexy—a sudden loss of muscle tone, leading to collapse

71. 14 At Least Four Interacting Neural Systems Underlie Sleep
Narcoleptic dogs have a mutant gene for a hypocretin receptor
Hypocretin normally prevents the transition from wakefulness directly into REM sleep
Interfering with hypocretin signaling leads to narcolepsy

72. Figure 10.25 Canine Narcolepsy
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73. 10 At Least Four Interacting Neural Systems Underlie Sleep
Hypocretin neurons in the hypothalamus project to other sleep system centers: the basal forebrain, the reticular formation, and the locus coeruleus Axons also go to the tuberomamillary nucleus, whose inhibition induces SWS The hypothalamus seems to contain a hypocretin sleep that controls wakefulness, SWS sleep, or REM sleep

74. Figure 10.26 Neural Degeneration in Humans with Narcolepsy
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75. 10 At Least Four Interacting Neural Systems Underlie Sleep
Sleep paralysis is the brief inability to move just before falling asleep, or just after waking up It may be caused by the pontine center continuing to signal for muscle relaxation, even when awake

76. 10 Sleep Disorders Can Be Serious, Even Life-Threatening
Sleep disorders in children:
Night terrors and sleep enuresis (bed-wetting) are associated with SWS
Somnambulism (sleepwalking) occurs during stage 3 SWS, and may persist into adulthood

77. 14 Sleep Disorders Can Be Serious, Even Life-Threatening
REM behavior disorder (RBD) is characterized by organized behavior, from an asleep person
It usually begins after age 50 and may be followed by beginning symptoms of Parkinson’s disease
This suggests damage in the brain motor systems

78. 10 Sleep Disorders Can Be Serious, Even Life-Threatening
Sleep-onset insomnia is a difficulty in falling asleep, and can be caused by situational factors, such as shift work or jet lag Sleep-maintenance insomnia is a difficulty in staying asleep and may be caused by drugs or neurological factors

79. 10 Sleep Disorders Can Be Serious, Even Life-Threatening
In sleep apnea, breathing may stop or slow down when muscles in the chest and diaphragm relax too much or respiratory neurons in the brain stem don’t signal properly
Sleep apnea may be accompanied by snoring
Sleep state misperception occurs when people report insomnia even when they were asleep

80. 10 Sleep Disorders Can Be Serious, Even Life-Threatening
Sudden infant death syndrome (SIDS) is sleep apnea resulting from immature respiratory pacemaker systems or arousal mechanisms Putting babies to sleep on their backs can prevent suffocation due to apnea

81. Photo, p Back to Sleep
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82. 10 Sleep Disorders Can Be Serious, Even Life-Threatening
Most sleeping pills bind to GABA receptors throughout the brain.
Continued use of sleeping pills:
Makes them ineffective
Produces marked changes in sleep patterns that persist even when not taking the drug
Can lead to drowsiness and memory gaps