Sleep and Dreaming - Rhythms of waking and sleeping

EARLY IDEA was that wake and sleep must depend on something outside the body such as light
1. HOWEVER Richter (1922) suggested that the body generates own activity / inacitivity
Mechanisms of the biological clock. Richter (1967) suggested we have a biological clock. our cycles remain stable despite changes in food, water, xray
1. Suprachiasmatic nucleus (SCN)
  1. the SCN provides the main control of the circadian rhythms for sleep and body temp. after damage the bodies rhythms become erratic.
  2. the SCN is part of the hypothalamus, located just above the optic chiasm. light resets the SCN via the retinohypothalmic path
    1. the path comes from a special population of ganglion cells that have their own photopigment, melanopsin. which respond directly to light no rods/cone
  3. RALPH et al., (1988) found in rats that a mutation caused a 20hr rhythm and when transplanted into another rat, they take on this rhythm. donor based
  4. even a single isolated SCN cell can maintain a circadian rhythm.
  5. even blind people with damage to rods and cones have enough input to melanopsin containing ganglion cells to have their cycle set to local sunlight
2. Freedman et al. (1999) even blind mole rats with no eye muscles or lens, or response to bright light can set their cycle to sunlight
  1. two types of genes responsible for generating circadian rhythm, PERiod & TIMeless.
    1. when per and tim are high they interact with a protein and induce sleepiness, when low = wakefulness.
3. the SCN regulates sleep / wake by controlling activity levels in pineal gland. this gland releases melatonin, which influences rhythms
  1. Melatonin pills work 2-3 hours before bed and are useful for travel across timezones.
ENDOGENOUS INFLUENCES (inside the body)
1. endogenous circannual rhythm - internal mechanisms on a yearly cycle
2. endogenous circadian rhythms - on a 24 hour internal cycle
3. light from the sun makes you feel less sleepy. in an unchanging environment (constant darkness) the self-generated cycle might be longer than 24 hours
  1. Kelly et al., 1999. people in submarines cut off from sunlight and have 18 hour schedules but they still retain rhythms of alertness at about 24.3 hrs
4. circadian rhythms for eating, drinking, urination, secretion of hormones, sensitivity to drugs etc... also for mood
  1. circadian rhythms differ among people, e.g. morning and evening people. (Taillard et al, 2003)
  2. people will find their way back to a 24 hour cycle even if their environment differs from that
5. Siffre (1975) spent 6 months in a cave and found that humans hold a 25 hour cycle when no external cues
EXOGENOUS INFLUENCES (outside the body)
1. circadian rhythms can persist without light although light is critical for resetting them.
  1. without something to reset the rhythm, it could gradually drift from the correct time. stimuli that resets the rhythm called a ZEITGEBER (time giver)
    1. light is the dominant Zietgeber although others include any arousal, exercise, meals, temperature. social stimuli are weak zeitgebers.
    2. Zeitgeber for marine animals are the tides
2. external stimuli affect our circadian rhythms, as when the change to daylight saving occurs, people remain ill-rested and inefficient for days after
3. Roenneberg et al., 2007. study on Germany's circadian rhythms. the sun time at the east differs half an hour to the west.
  1. They found that people on the eastern edge have a sleep midpoint 30 minutes earlier than people on the west.
4. blind people set their rhythms by noise, temp, meals etc. their rhythms are a little longer than 24 hours. cycle not with clock, experience insommnia
5. Jet lag majorly disrupts circadian rhythms. easier to travel west than east
  1. due to easier to adapt to phase-delay (stay awake later, rise later) than to phase-advance (sleep earlier, rise earlier)
    1. Cho (2001) found adapting caused stress and elevated hormone cortisol which impaired memory in flight attendants.
6. Shift workers find it hard to adapt even after many years. night-time workers have more accidents than daytime.

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Sleep and Dreaming - Rhythms of waking and sleeping

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