1.,2.Stages of Sleep

1.,2.Stages of sleep

- for humans, sleep is s state of decreased but not abolishedconsciousness, 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 toawaken than someone in depths of SWS

- 4-6 cycles per night

- as night progressesSWS episodes shorter and REM episodes longer, i.e. SWSearly in night, REM sleep at dawn

Slow-wave sleep (Serotonin)

- heart rate, BP, respiratory rate, and set point of hypothalamic thermostatdecrease; gut motility increases, blood flow to braindecreases (in thalamus, basal ganglia, and higher-order cortical association areas)

- muscle tonedecreases 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 gammamotor 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 isslow, 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 turnsthem off to cause sleep

- parts of both networks live in brainstem and forebrain

- wakefulnessincrease excitability of cortical neurons and depolarizethalamic neurons (tonic mode)

- suppressinginputsthalamic neurons go into burst mode, and a synchronized, slow-waveEEG 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 caudalhypothalamus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