Sleep and dreaming 2 - stages of sleep

STAGES OF SLEEP - sleep is categorized by decreased response to stimuli.
1. EEG measures stages of sleep. averages electrical potentials. EEG records rises or falls. EEG compares different activity at different times of sleep.
  1. a polysomnograph combines EEG and eye movement
2. STAGE 1: irregular, low-voltage, jagged waves. brain activity higher than other stages. STAGE 2: sleep spindles and k-complexes.
  1. STAGES 3 & 4: slow-wave sleep. large waves, heart rate, breathing and brain activity decrease. by S4, sensory input to the cerebral cortex is reduced
    1. PARADOXICAL OR REM SLEEP. deep = postural muscles (and head support) are relaxed. light sleep as low, fast irregular waves indicate neuronal activity
3. Stage 1 = 5% of sleep, stage 2 = 50% of sleep, stages 3 & 4 = 15-20% of sleep, REM = 20-25% of sleep.
4. Pass through stages 2,3,4 and then 4,3,2, REM. each cycle is 90 mins. early on stages 3&4 dominate then later on REM dominates.
  1. Dement and Kleitman (1957) found that REM sleep is almost synonymous with dreaming. REM reported dreams 80-90% of the time.
5. Interruptions of consciousness
  1. coma is extended period of unconsciousness, low level of brain activity in a coma. can't wake. little or no response to stimuli.
  2. a vegative state alternates between periods of sleep and moderate arousal. a painful stimulus produces autonomic response, but no purposeful activity
  3. a minimally conscious state has occasional periods of purposeful activity and limited speech comprehension.
  4. brain death is when there is no brain activity and no response to stimuli
BRAIN MECHANISMS
1. BRAIN STEM: includes reticular formation and posterior hypothalamus, receives sensory info, maintains wakefulness.
  1. Mouzzi & Morgan - stimulation of reticular formation, awakens / energises animals.
  2. mid brain relays sensory information. cut though midbrain decreases arousal by damaging reticular formation
2. NEUROTRANSMITTERS
  1. Inhibitory: GABA -- decrease temp and metabolic rate. Excitatory: acetylcholine and histamine, increase arousal, maintains wakefulness
  2. GABA is main inhibitory neurotransmitter. GABA responsible for sleep. body temp and metabolism decrease. GABA inhibits synaptic activity.
    1. GABA levels cut the activity short and prevent axons from spreading stimulation to other areas. so can't become conscious of it
3. Sleep walking - awake in some parts of the brain but not others
4. During REM, cells in the pons send messages that inhibit the motor neurons that control the body's large muscles.
  1. normally when you wake up cells in the pons shut off and regain muscle control, but sometimes the pons remain in REM when awake and can't move
5. Brain function in REM sleep: PET - radioactive chemical. During REM activity increases in the pons and limbic system.
  1. activity decreases in the primary visual cortex, motor cortex, and dorsolateral prefrontal cortex, increased in temporal and parietal
  2. REM sleep has a distinct pattern of high amplitude electrical potentials known as PGO WAVES. at the end of deprivation, unusually high density of PGO
  3. REM sleep depends on the relationship between the neurotransmitters serotonin and acetlycholine
SLEEP DISORDERS - DYSSOMNIAS (changes in amount, restfulness) and PARASOMMNIAS (abnormal behaviour around sleep)
1. DYSSOMNIAS
  1. INSOMNIA - hard to fall / stay asleep, affects 2/3 people, women, caused by stress, depression, obesity, breathing, alcohol. also result of parkinsons
    1. related to shifts in circadian rhythms, fall asleep when temp is declining normally, if phase-delayed trouble sleeping at normal time
  2. OBSTRUCTIVE SLEEP APNEA - may stop breathing 5-50 times an hour. wake up to breathe, obesity, age, genetics, hormones cause
    1. in sleep apnea, multiple brain regions seem to have lost neurons, deficiencies in learning, reasoning, attention etc.
    2. unknown if brain abnormalities led to sleep apnea or other way. sleep impairments led to cognitive loss.
  3. NARCOLEPSY - sleep during the day, no gene identified. gradual / sudden attacks, muscle weakness, sleep paralysis, dream like experiences.
    1. Narcolepsy caused by neurotransmitter orexin, people with nar lack hypothalamic cells that produce / release orexin. orexin maintains wakefulness
  4. Periodic limb movement disorder / restless leg syndrome. involuntary leg movements. lack of sleep, genetic, affects any age.
  5. REM BEHAVIOUR DISORDER - move around vigorously, acting out dreams, injure themselves / others / damage.
2. evening people tolerate sleep deprivation more than morning people
3. PARASOMNIAS
  1. NIGHT TERRORS - intense anxiety, occur in NREM, more common in children
  2. SLEEP WALKING - runs in families, mostly in children. in stages 3 & 4 of sleep. occurs when sleep deprived / stressed.
  3. SEXSOMNIA - engage in sexual behaviour when asleep. ruins relationships.

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Sleep and dreaming 2 - stages of sleep

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	Created by becky.waine over 11 years ago