PSY208 Chapter Notes - Chapter 8-11: Circadian Clock, Nathaniel Kleitman, Michel Jouvet
Chapter 8 – Wakefulness and Sleep
MODULE 8.1 RHYTHMS OF WAKING AND SLEEPING
ENDOGENOUS RHYTHMS
• Endogenous means generated from within
• Endogenous Circannual Rhythm: birds generate a rhythm that prepares them
for seasonal changes
• Endogenous Circadian Rhythms: last about a day
• E.g. if you go without sleep all night you feel sleepier and sleepier as the night
goes on but as morning arrives you will feel more alert (the light from the sun)
• Urge to sleep depends on the time of day
• Humans also generate 24-hour wake-sleep rhythms we can modify them only
a little
• Circadian rhythms in eating, drinking, urination, hormone secretion,
metabolism, sensitivity to drugs, etc.
• Have circadian rhythms in mood (biologically driven circadian rhythm in our
emotional well-being)
SETTING AND RESETTING THE BIOLOGICAL CLOCK
• Readjust our internal workings daily to stay in phase with the world
• Sometimes misadjust them (e.g. on weekends)
• Circadian rhythms persist without light but light is critical for resetting them
• Zeitgeber: stimulus that resets the circadian rhythm
• Light is the dominant zeitgeber for land animals
• Secondary Zeitgebers: exercise (arousal of any kind), meals, temperature
JET LAG
• A disruption of circadian rhythms due to crossing time zones (circadian clock
and external time)
• Sleepiness during the day, sleeplessness during the night, depression, impaired
concentration
• Easier to adjust to times going west than east
• Phase-delay: stay awake at night and then awaken late the next morning
• Phase-advance: going east go to sleep earlier and awaken earlier
• Adjusting to jet lag is often stressful (elevates blood levels of adrenal hormone
cortisol)
• Prolonged elevations leads to damage in the hippocampus (memory)
SHIFT WORK
• Duration of sleep depends on when they go to sleep
• Feel groggy on the job, sleep poorly, body temperature peaks
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• Have more accidents
• Does not reliably change the circadian rhythm
• Short-wavelength (bluish) light helps to reset the circadian rhythm
MORNING PEOPLE AND EVENING PEOPLE
• Circadian rhythms differ among individuals
• Morning People (larks): awaken early, reach their peak of productivity early,
become less alert later in the day
• Evening People (owls): warm up more slowly, reaching their peak in the late
afternoon or evening, tolerate staying up all night better
• Many people are intermediate between the two extremes
• Staying up later as you get older results from increased levels of sex hormones
MECHANISMS OF THE BIOLOGICAL CLOCK
• Curt Richter (1967): introduced concept that the brain generates its own
rhythms (a biological clock)
• Is insensitive to most forms of interference
• Blind/deaf animals generate circadian rhythms but drift out of phase with the
external world
• Hardy, robust mechanism
THE SUPRACHIASMATIC NUCLEUS (SCN)
• Main driver for sleep and body temperature (part of the hypothalamus)
• Get its name from its location just above the optic chiasm
• After damage the body’s rhythms become erratic
• Generate circadian rhythms in a genetically controlled manner
• Single isolated cell can also maintain a rhythm
HOW LIGHT RESETS THE SCN
• A small branch of the optic nerve (retinohypothalamic path) from the retina to
the SCN alters the SCN’s settings
• Comes from a special population that have their own photopigment
(melanopsin)
• Receive input from rods and cones
THE BIOCHEMISTRY OF THE CIRCADIAN RHYTHM
• Suprachiasmatic Nucleus: produces circadian rhythms
GENE – PERIOD (PER) AND TIMELESS (TIM)
• The concentration of the two proteins promote sleep/inactivity over a day
based on feedback interactions among neurons
• The messenger RNA levels responsible for producing PER and TIM start low
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• Increase during the day (increase synthesis of the protein) but the process
takes time (lag behind)
• During the night PER and TIM concentrations are high RNA is declining
• Light activates a chemical that breaks down the TIM protein
MELATONIN
• The SCN regulates waking/sleeping by controlling activity levels in the pineal
gland (endocrine gland, posterior to the thalamus)
• The pineal gland releases the hormone
• Melatonin influences both circadian and circannual rhythms
• Secreted mostly at night
• Pineal Gland Tumours: stay awake for days at a time
• Increases 2-3 hours before bedtime
MODULE 8.2 STAGES OF SLEEP AND BRAIN MECHANISMS
SLEEP AND OTHER INTERRUPTIONS OF CONSCIOUSNESS
• Coma: an extended period of unconsciousness
• Caused by head trauma, stroke, disease
• Low level of brain activity and little response to stimuli
• Either die or begins to recover in a few weeks
• Vegetative State: alternates between periods of sleep and moderate arousal
• During the more aroused state the person shows no awareness of surroundings
• Breathing is more regular
• Painful stimulus produces increased heart rate, breathing, sweating
• Minimally Conscious State: one stage higher with occasional, brief periods of
purposeful actions and a limited amount of speech comprehension
• Can last for months or years
• Brain Death: condition with no sign of brain activity and no response to any
stimulus
• Physicians usually wait 24 hours before pronouncing brain death
THE STAGES OF SLEEP
• Polysomnograph: combination of EEG and eye-movement records
• Alpha Waves: frequency of 8-12 per second
• Characteristic of relaxation not of all wakefulness
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