PSYC 2800 Lecture Notes - Circadian Rhythm, Biorhythm, Seasonal Affective Disorder

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20 Apr 2012
Lecture # 1n *final+
Why Do We Sleep and Dream?
Origins of Biological Rhythms
Biorhythm: Inherent timing mechanism that controls or initiates various
biological processes
Many aspects controlled by bio rhythms (eating, sleep, exercise)
Linked to the cycle of days and seasons produced by the Earth’s
rotation around the sun
Animals living near the poles of the Earth are more affected by
seasonal changes than animals living in equatorial regions
Human behavior is governed more by : daily cycles than by : seasonal
We breed all year round, not just at given times of the year
Biological Clocks
Behavior is not simply driven by external cues from the environment
Rhythms are endogenous (control comes from within)
Biological clock: Neural system that times behavior.
Allows animals to anticipate events before they happen
Example: Birds migrate before it gets cold. Internal cue
to get going.
Biological Rhythms
Time required to complete a cycle of activity
Ex: A day, one sleep wake cycle for humans
Circannual: Rhythm
Yearly (e.g., migratory cycles of birds)
Infradian: Rhythm
Less than a year (e.g., human menstrual cycle montly, also known as
lunar cycle)
Circadian: Rhythm
Daily rhythms (e.g., human sleep cycle)
Peak in BP first thing in the morning, bowel morning usually in the
morning, testosterone highest in morning, alertness highest in
morning (based 8 am, 10 pm cycle). Body temp., highest in evening.
Body temp. related to when you eat.
Ultradian: Rhythm
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Less than a day (e.g., eating cycle)
Free-Running Rhythm: Rhythm of the bodys own devising in the absence of
all external cues
Without input from external cues, our bodies have their own rhythms
with periods of 25 to 27 hours
Sleep-wake cycle shifts an hour or so everyday
Animals expand: and contract: their sleep periods as the sleep-
related lighting period expands or contracts
Zeitgebers: Environmental event/external cue that entrains biological rhythms; a
“time giver
Example: light resets biological rhythms
Determination or modification of the period of a biorhythm
Jet Lag: Fatigue and disorientation from rapid travel through time zones an
exposure to a changed light-dark cycle
Easier to fly east to west, only need to stay up later instead of wake up
Neural Basis of the Biological Clock
Suprachiasmatic Nucleus (SCN) *within hypothalamus+
Main pacemaker of circadian rhythms located just above the optic
Retinohypothalamic Pathway *important in sleep/wake cycle+
Neural route from a subset of cone receptors in the retina to the
suprachiasmatic nucleus of the hypothalamus; allows light to entrain
the rhythmic activity of the SCN
Why people have seasonal affective disorder. Can’t retrain to new
time in winter and get depressed. Related to melatonin (main
hormone of SCN). All they want to do is sleep but can’t so affects
Other pacemakers exist in the retina and pineal gland, but the SCN is the
main one
Immortal Time
Lesion SCN, bio rhythms removed
Endogenous rhythm is not learned
Martin and colleagues: transplantation studies in hamsters
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