Sleep and Arousal
Ascending reticular activating system maintains a state of wakefulness by indirect projections to cortex.
ARAS… diencephalons… intralaminal nuclei of thalamus… cortex
Hypothalamus… forebrain
ARAS travels in the central tegmental tract after leaving the brainstem.
During wakefulness many pedunculopontine nuclei are active but NOT during sleep.
Electroencephalogram is a gross potential record of the sum of all electrical fluctuations in the brain and postsynaptic summation through pyramidal cells. Awake state is indicated by EEG activity in alpha and beta patterns.
Stages of Sleep
Four stages of sleep (1-4) characterized by progressively SLOWER frequency of wavers and HIGHER VOLTAGE activity. 1-4 progression takes 45 min.
After 45 min, regression in REVERSE order back to stage 1. Characterized by relaxed muscles, decreased heart rate and decreased respiration.
After 90 minutes the EEG becomes desynchronized, low voltage and fast activity. Loss of muscled tonus and increase in RAPID EYE MOVEMENT (REM.) driven by phasic bursts of activity in the PGO (pons, geniculate bodies, occulomotor nuclei).
REM sleep is “dream sleep”. As successive sleep cycles progress the amount of time spent in REM sleep increases.
Initially stage 3 and 4 dominate sleep (delta sleep) but as night progresses until stage 2 is dominate at early morning hours.
REM induces increased blood flow to the anterior cingulated cortex, amygdala and pons tegmentum. LIMBIC SYSTEM. Also increase in AP from pontine reticular formation.
Dorsolateral prefrontal cotex (rational thought) and posterior cingulated gyrus activity decreases during REM sleep.
During Wakefulness: Cholinergic Neurons/Locus Ceruleus/Raphe Nuclei-… ACTIVE
During Non-REM Sleep: All above are decreased.
REM Sleep: Cholinergic Neurons ACTIVE Raphe and LC are INACTIVE
In REM sleep Off… LC is ACTIVE
Mechanisms of Sleep
Wakefullness
-increase output of REM off cells; Raphe Nuclei (seratonin), Locus Ceruleus (Noradrenaline)
-low discharge during REM sleep
-self inhibitory to post synaptic neurons and inhibit REM on cells
REM sleep
-increase activity of REM on cells; mesencephalic medullary junction cells
-all use acetylcholine and excitatory
in
Ventrolateral preoptic nucleus induces sleep through aminergic secretions medullary nuclei (raphe, tuberomamillary, LC).
REM sleep declines over age from 80% prenatal to 20% in adults. Sharp decline in deep sleep after age 10. REM sleep is necessary for function; deprivation of REM sleep increases the “REM rebound” or need to recover amount of REM displaced.
Diseases
Insomnia caused by disruption of circadian rythym (jet lag) and aging. Depression, anxiety and drug abuse also decrease REM sleep.
Somnambulism (sleep walking) does not occur in REM sleep but in stage 3 and 4 of sleep. Common in children .
Narcolepsy is irresistible urge to sleep 5-30 minutes at a time. Abrupt loss of muscle tone and auditory and visual hallucinations. Enter DIRECTLY into REM sleep.
Tags: Cholinergic Neurons, Dorsolateral, hypothalamus, insomnia, Limbic system, Locus Ceruleus, mesencephalic medullary junction, Narcolepsy, posterior cingulated gyrus, rapid eye movement, REM, sleep stagges, Somnambulism, Ventrolateral preoptic nucleus
