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Psychology 3325 Lecture Notes - Suprachiasmatic Nucleus, Preoptic Area, Retina

Course Code
Psychology 3325
John Usher

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Brain Mechanisms of Sleep
several brain regions have special roles in sleep and biological rhythms
all living organisms show rhythmic changes in their physiological processes and behaviour
some of these rhythms are simply responses to environmental changes
mammals have two biological clocks that play role in sleep
circadian rhythms daily rhythmical change in behaviour or physiological process; oscillates
once a day
second clock controls cycles of slow-wave and REM sleep, oscillates several times a day
clock that controls circadian rhythms is located in small pair of structures located at bottom of
hypothalamus: the suprachiasmatic nuclei (SCN)
activity of neurons in SCN oscialltes once each day; neurons are active during day and
inactive at night
changes in activity control daily cycles of sleep and wakefulness
if person is kept in room with constant light their circadian rhythms will eventually get
out of synch but will be back in sych within a few days of being outside
resynchronization is accomplished by direct connection between eyes and SCN
each morning when we see light our biological clock resets
second biological clock in mammalian brain runs faster and continuously, unaffected by
periods of light and darkness
in humans it cycles on 90 minute period
first suggestion that 90 minute cycle occurs throughout day came from observation
that infants who are fed on demand show regular feeding cycles
later studies found 90 minute cycles of rest and activity, including such activities as
eating, drinking, smoking, heart rate, oxygen consumption, stomach motility, urine
production, and performance on tasks that make demands on person's ability to pay
basic rest-activity cycle (BRAC) 90 minute cycle (in humans) of waxing and
waning alterness controlled by biological clock in pons; duirng sleep it control cycles
of REM sleep and slow-wave sleep; term coined by Kleitman
pons also contains neural circuits that are responsible for REM neurons that begin a
period of REM sleep release acetylcholine
release of this neurotransmitter substance activates several other circuits of neurons:
activates cerebral cortex and causes dreaming
activates neurons in midbrain and causes rapid eye movements
acitvates set of inhibitory neurosn that paralyze us and precent us from acting out our
first evidence tha REM sleep was turned on by acetylcholine-secreting neurons came from
observation that overdoses of insecticides that excite such neurons also cause visual
acetylcholine-secreting neurons (REM-ON) are inhibited by neurons that secrete seratonin
drugs that decrease activity of seratonin-secreting neurons will permit REM-ON to become
drugs that increase activity of seratonin-secreting neurons will supress REM sleep
antidepressant drugs have this affect suggests that excess REM sleep may play role in
mood disorders
preoptic area region at base of brain just in front of hypothalamus; contains neurons that
appeaer to control occurence of slow-wave sleep
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