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1.,2. Stages of sleep
- for humans, sleep is s state of decreased but not abolished consciousness, from which we can be
aroused
- sleep is an actively induced state
- sleep stages defined by EEG criteria (measures movement of ions across cell membranes in
layers 4-5 of cortex), 2 types:
1. synchronized, slow-wave EEF (slow-wave sleep, SWS)
2. desynchronized, low-voltage EEG (rapid eye movement, REM sleep)
- stages are W (awake)  1 (REM occurs here)  2  3  4
- once we fall asleep  EEG larger, slower, more synchronized (= falling more deeply asleep)
- intervals every 90 minutes
- REM Sleep  EEG condition that looks like awake or lightly asleep state; individuals harder to
awaken than someone in depths of SWS
- 4-6 cycles per night
- as night progresses  SWS episodes shorter and REM episodes longer, i.e. SWS early in
night, REM sleep at dawn
Slow-wave sleep (Serotonin)
- heart rate, BP, respiratory rate, and set point of hypothalamic thermostat decrease; gut motility
increases, blood flow to brain decreases (in thalamus, basal ganglia, and higher-order cortical
association areas)
- muscle tone decreases due to inhibition of gamma motor neurons,
- dreams have little imagery or are not reported at all
- appears restful and restorative
REM sleep (Ach)
- increased heart rate, BP, respiratory rate; muscle tone disappears completely, due to inhibition of
both alpha and gamma motor neurons
- hypothalamic thermostat shuts off, we take on temperature of room
- bursts of rapid eye movements and muscle twitches
- cerebral blood flow increases almost to waking levels (not in higher-order cortical areas)
- dreams with detailed visual imagery and content
Sleep appetite
- we need both SWS and REM sleep; if deprived of REM  spend more time in REM after
period of deprivation
- amount of REM sleep changes over our lifespan; newborns spend 50% of their sleep time in
REM; adults only spend 20 % in REM, and progressively less stages of SWS as they get older.
3. Major CNS structures and NT systems involved in sleep-wake cycle
- transection in rostral midbrain  sleep-like state of forebrain that is constant; EEG is slow,
synchronized, eyes act asleep; damage to midbrain reticular formation
- transection in caudal midbrain  constant wakefulness- EEG is low-voltage, desynchronized,
eyes act awake
- there is a network of wakefulness-promoting areas of brain and a network of areas that turns
them off to cause sleep
- parts of both networks live in brainstem and forebrain
- wakefulness  increase excitability of cortical neurons and depolarize thalamic neurons
(tonic mode)
- suppressing inputs  thalamic neurons go into burst mode, and a synchronized, slow-wave
EEG is the result
Brainstem
- to maintain consciousness  cholinergic cells in midbrain reticular formation (with
monoaminergic fibers passing through it) necessary
- midbrain reticular formation  ascending reticular activating system (ARAS)  promotes
wakefulness by affecting thalamus and cortex
- ARAS  thalamic relay and association nuclei (tonic mode)
- ARAS  projects to midline and intralaminar nuclei of thalamus  these project to cortical
areas activating them
- monoaminergic fibers project through medial forebrain bundle to cortical areas
- reticular structures in rostral medulla and caudal pons turn ARAS off and on (sleep and
wakefulness)
- lesion in midpons disconnecting caudal structures leaves ARAS on constantly
Forebrain centers
- damage to 3rd ventricle walls in caudal hypothalamus  drowsiness and lethargy
- damage in lamina terminalis  inability to sleep
- collection of monoaminergic neurons in hypothalamus near mammillary bodies  project to
widespread CNS areas, releasing histamine  depolarizes thalamic and cortical neurons (turning
these neurons off  drowsiness, like antihistamines)
- cholinergic neurons of basal nucleus increase excitability of cortical neurons
- neurons of preoptic region and anterior hypothalamus inhibit tuberomammillary nucleus 
cause sleep
REM centers
- in brainstem; after midpontine transection  forebrain is awake constantly; parts of brain
caudal to cut begin to cycle through parts of REM sleep  muscle tone vanishes and twitches of
lateral recti eye muscles
- firing of raphe nuclei and locus ceruleus neurons terminates episodes of REM sleep
4. Location of circadian clock and how it is entrained
- physiological rhythms with a period of a day located in suprachiasmatic nucleus of
hypothalamus
- if cues about day length removed  clock and rhythms run with a 25-hour period
- light/dark info reaches suprachiasmatic nucleus from retina and entrains it to a 24-hour period
- photic influence enhanced by cyclic secretion of melatonin by pineal gland
- other entraining inputs to the suprachiasmatic nucleus travel through serotenergic fibers from
raphe nuclei