P1246341509XNTRF

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Circadian Rhythms Sleep

• Circadian Rhythms (9.1)
• endogenous cycles
• role of the suprachiasmatic nucleus
• setting/resetting biological clocks
• Sleep (9.2)
• why sleep?
• stages of sleep
• Dreaming (9.3)
• why dream?

Extra review session Mon Feb 21, 630 730,
KRB 105
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Circadian Rhythms

• Endogenous circadian rhythms
• rhythms that last about a day
• humans last around 24.2 h
• Examples
• -activity
• -temperature
• -waking and sleeping
• -secretion of hormones
• -eating and drinking

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Suprachiasmatic Nucleus (SCN)
SCN - main control center for sleep and
temperature circadian rhythms
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What sets the Clock?
Zeitgeber a stimulus that resets the biological
clock (eg. bright light, exercise, temperature)
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What Resets the Clock?

• Light
• retinal ganglion cells send direct projections
  to the SCN
• this provides information about light to the
  SCN
• light can also alter blood-borne factors
• SCN is highly vascularized
• Melatonin
• secreted from the pineal gland
• increased levels of melatonin make you sleepy
• melatonin can act on receptors in the SCN to
  phase-advance the
• biological clock

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Sleep
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Sleep Stages
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REM Sleep

• REM rapid-eye movement
• lots of brain activity - EEG shows low voltage
  fast waves
• postural muscles are most relaxed during REM
  sleep
• loose associative thinking
• PGO waves - start in the pons ? geniculate
  nucleus of thalamus ? occipital cortex

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REM Sleep

• neurons within the pons send inhibitory messages
  to the spinal cord during REM sleep
• this message inhibits motor neurons that project
  to large muscles
• REM sleep is still observed after damage to the
  pons
• but, no inhibition of muscle neurons

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Function of REM Sleep

• REM sleep deprivation
• subjects attempt to ? REM
• mild, temporary personality changes
• when uninterrupted, increased REM
• Memory Storage
• animals ? REM after learning something
• Getting Oxygen to the Corneas

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Why Sleep?

• Repair and Restoration Theory
• sleep enables the body and brain to repair itself
  after working hard all day
• going without sleep causes people to be
  irritable, dizzy, and to have hallucinations and
  impaired concentration
• sleep-deprived rats bodies work harder
• BUT, how much we sleep does not depend on how
  much we worked that day

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Why Sleep?

• Evolutionary Theory
• we evolved to sleep so that we would conserve
  energy when we were least efficient
• during sleep body temperature decreases
• predicts that species will sleep different
  amounts depending on how much they must look for
  food and watch for predators

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Why Dream?

• Activation-Synthesis Hypothesis
• dreams begin with episodic bursts of spontaneous
  activity in the Pons (PGO waves)
• these PGO waves partially activate certain
  regions of the cortex
• this haphazard input is combined with previous
  (waking) input
• cortex synthesizes a story to make sense of
  all the input it is receiving

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Sleep Disorders

• Insomnia
• habitual sleeplessness
• possible causes excessive noise, stress,
  drugs, medications, pain, uncomfortable
  temperature, sleep apnea, periodic limb movement
  disorder
• three forms onset, maintenance, termination
• Narcolepsy
• Frequent, unexpected periods of sleepiness
  during the day
• affects about 1 in 1000 people
• symptoms extreme daytime sleepiness,
  cataplexy, sleep paralysis, hypnagogic
  hallucinations
• involvement of orexin

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Sleep Disorders

• Night Terrors
• experience of intense anxiety from which a
  person awakens screaming in terror
• occur during nonREM sleep
• more common in children
• Sleep Walking
• occurs mostly in children
• runs in families
• expressed early in the night during stage 3 and
  4 sleep