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Biological Rhythms and Sleep

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  1. Biological Rhythmsand Sleep

  2. 10 Biological Rhythms and Sleep: Part I • Biological Rhythms • 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 cyclesrepeat 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 10.2How Activity Rhythms Are Measured (Part 1)

  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 10.2How Activity Rhythms Are Measured (Part 2)

  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 10.3The Effects of Lesions in the SCN

  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

  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 10.6Components of a Circadian System

  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 10.7A Molecular Clock in Flies and Mice

  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 10.8When the Endogenous Clock Goes Kaput

  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 10.9Humans Free-Run Too

  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 10.10Electrophysiological Correlates of Sleep and Waking

  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 10.11A Typical Night of Sleep in a Young Adult

  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 10.12How I Hate to Get Out of Bed in the Morning!

  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 10.14Sleep in Marine Mammals

  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 10.15The Trouble with Babies

  44. Figure 10.16Human Sleep Patterns Change with Age

  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 10.17The Typical Pattern of Sleep in an Elderly Person

  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 10.18I Need Sleep!

  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 10.19Sleep Recovery after 11 Days Awake