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Reticular formation
diffuse nuclei of tegmentum of brainstem; primary integrating area of brainstem relating to consciousness
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Tegmentum
elongated gray mass that extends b/w medulla and midbrain
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What is the primary global integration area of the brainstem?
tegmentum
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What are the 3 zones/columns reticular formation?
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Which zone/column of the reticular formation is closest to midline?
median
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Which zone/column of the reticular formation is the middle part?
medial
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What is the median zone/column of the reticular formation responsible for?
- pain modulation
- inhibition of pain perception
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What structure is found in the median zone/column of the reticular formation?
raphe nuclei
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What is the median zone/column of reticular formation's primary neurotransmitter?
serotonin
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Where does the median zone/column of the reticular formation project to?
spinal cord
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Why does the median zone/column of the reticular formation project to the spinal cord?
to modulate pain transmission to conscious centers
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Is the median zone/column of the reticular formation important in ARAS?
no
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Where is the medial zone/column of the reticular formation found?
primarily in medulla and pons
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What is the function of the medial zone/column of the reticular formation?
makes sense of input
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What is the function of the efferent component of the medial zone/column of the reticular formation?
- influence basic activities of body:
- sleep cycle
- drowsiness
- alertness
- awareness
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What is contained in the medial zone/column of the reticular formation?
nuclei
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Where can nuclei of the medial zone/column of the reticular formation project to?
- hypothalamus
- thalamus
- spinal cord
- other tegmental nuclei
- cranial nerve nuclei
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Which tracts terminate with LMN of the medial zone/column of the reticular formation?
rubrospinal and reticulospinal tracts
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What does the medial zone/column of the reticular formation add to ARAS?
efferent component
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What does the lateral zone/column of the reticular formation add to ARAS?
primary afferent component
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What is the function of the lateral zone/column of the reticular formation?
recieves input from collaterals, neurons associated w/ major ascending pathways
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Is the lateral zone/column of the reticular formation an important part of ARAS?
yes
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What does ARAS stand for?
ascending reticular activating system
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What does ARAS control?
various states of arousal
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What is ARAS?
functional system of reticular formation
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What makes ARAS?
medial and lateral zones/columns
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Where does ARAS recieve input from?
- cranial nerves and CNS
- ascending sensory systems from spinal nn
- cerebral areas of cortex
- cerebellum
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What are the functions of ARAS?
- if ARAS is not working right, then cortex is not getting information:
- sleep cycle
- drowsiness
- awareness
- alertness
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What is the clinical significance of ARAS?
anesthesia acts by hyperpolarizing neurons in ARAS to decrease output, thus deactivating nuclei in reticular formation by competing for binding sites
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What makes up the afferent input of ARAS?
lateral column of reticular formation
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What makes up the efferent component of ARAS?
medial column
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What are the outcomes of ARAS?
- sleep cycle
- drowsiness
- alertness
- awareness
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What is a conscious experience?
you are aware of feelings, ideas, dreams, and thoughts
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What are the states of consciousness?
- normal consciousness
- lethargy
- stupor
- coma
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What level is normal consciousness?
level 1
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What is speech like at the normal consciousness state?
spontaneous (voluntary) speech at a normal rate
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What is motor activity like at the normal consciousness state?
normal voluntary and reflex somatic motor activity
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What are the eyes like in the normal consciousness state?
open, normal oculomotor activity
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What is speech like in level 2 lethargy?
spontaneous sentences, spoken slowly
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What is motor activity like at level 2 lethargy state?
decreased speed of voluntary motor activity
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What are the eyes like in level 2 lethargy state?
open, decreased oculomotor activity
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What is speech like in level 3 lethargy?
spontaneous words, spoken infrequently
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What is motor activity like at level 3 lethargy?
decreased speed and coordination of voluntary motor activity
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What are the eyes like in level 3 lethargy?
open or closed; decreased oculomotor activity
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What are the levels of the stupor state of consciousness?
Levels 4-6
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What is speech like in level 4 stupor?
vocalization only to stimuli that cause pain
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What is motor activity like at level 4 stupor?
marked decrease in spontaneous motor activity
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What are the eyes like in level 4 stupor?
generally closed, some spontaneous eye movement
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What is speech like in level 5 stupor?
no vocalization
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What is motor activity like in level 5 stupor?
appropriate defensive movements (generally flexor) to movements that cause pain
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What are the eyes like in level 5 stupor?
generally closed
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What is speech like in level 6 stupor?
no vocalization
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What is motor activity like in level 6 stupor?
mass movements to stimuli that cause pain
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What are the eyes like in level 6 stupor?
closed, decreased spontaneous conjugate eye movement
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What level is the coma state of consciousness?
level 7
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What is speech like in coma?
no vocalization
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What is motor activity like in coma?
decrebrate posturing to stimuli that causes pain, or no response
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Decerebrate posturing:
postural change that occurs in some comatose pts consisting of episodes of axial rigidity, rigid extension of limbs, internal rotation of UEs, and marked PF of feet
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What are the eyes like in coma?
eyes closed, absent spontaneous eye movements
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What scale is used to grade comas?
Glasgow Coma Scale
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What is a coma?
extensive damage to cerebral cortex; general sensations do not get there
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In addition to damage of the cerebral cortex, where else may damage occur from a coma?
reticular formation of midbrain and upper pons, and thalamus
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What part of the reticular formation is damaged during coma?
nuclei of reticular formation, not ascending pathway
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What happens to information in the reticular formation during coma?
info goes up to the thalamus, but collaterals are not synapsing w/ nuclei of reticular formation, so there is no info in the brainstem
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What is a toxic coma?
caused by medications, drugs
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Can liver failure cause coma?
yes, build up of high levels of toxins which are toxic to neurons. Renal failure can do the same thing
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What is the range of the Glasgo coma score?
3-15
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What does the Glasgow coma score mean?
high is good; low is bad
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What is the criteria for the Glasgow coma score?
- best eye movement (4 pts)
- best verbal response (5 pts)
- best motor response (6 pts)
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What are the cardinal signs for cerebral death?
- coma
- absence of brain stem reflexes
- apena
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What is the prerequisite to cerebral death?
all appropriate diagnostic and therapeutic procedures have been performed
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What is the criteria to be present (from cerebral death) for 30 minutes at least 6 hours after the onset of coma and apnea?
- coma with cerebral unresponsivity
- absence of brain stem reflexes
- apenea
- cephalic reflexes
- EEG silence
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Cerebral unresponsivity:
state in which pt doesn't respond purposefully to externally applied stimuli, obeys no commands, and does not utter sounds spontaneously or in response to a painful stimulus
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Apnea:
absence of spontaneous respiration, manifested by need for controlled ventilation for at least 15 minutes
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Cephalic reflexes:
papillary, corneal, oculoauditory, oculovestibular, oculocephalic, ciliospinal, snout, pharyngeal, cough, and swallowing
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EEG silence:
EEG w/ absence of electrical potentials of cerebral origin
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What are the different waking states?
- alert wakefulness
- relaxed wakefulness
- relaxed drowsiness
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What is the alert wakefulness of the waking state?
- awake, alert, eyes open
- Beta rhythm >13 Hz/sec
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What is the relaxed wakefulness of the waking state?
- awake, relaxed (not alert), and eyes open
- Alpha rhythm, 8-13 Hz/sec
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What is the relaxed drowsiness of the waking state?
- fatigued, tired, eyelids may narrow/close, head may droop, lapses of alertness and attention, and still awake but not asleep
- decrease in alpha wave amplitude and some decrease in frequency--closer to the 8 Hz
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Is sleep a part of ARAS?
yes
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Sleep is a form of:
attentiveness
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What is sleep?
altered state of consciousness: the brain is still aware of the environment and still receives input and is very active processing sensory info
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What is the Sleep-Wake cycle?
natural endogenous cycle/rhythm of the body
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Cyclic:
the natural physiologic processes (HR, BP) that vary throughout the day
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Sleep-Wake cycle tunes your body to:
day and night (circadian cycle)
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What are the parts of the circadian cycle?
- suprachiasmatic nucleus
- sleep center
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What does the suprachiasmatic nucleus contain?
retinal cells sensitive to light
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Where is the suprachiasmatic nucleus located?
hypothalamus, above optic chiasm
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What does the suprachiasmatic nucleus do?
maintain circadian rhythm and biological clock
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What does the primary biological clock allow?
the body to stay w/in cycle
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What is sleep influenced by?
suprachiasmaatic nucleus (it is not dependent upon it)
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Where is the sleep center located?
w/in reticular formation of pons
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Is the sleep center excitatory or inhibitory in nature?
inhibitory, puts us in a sleep state
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What does the sleep center interact with?
ARAS (excitatory) as a feedback loop
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What does the sleep center involve?
a slow accumulation and dissipation of transmitter substances (NT/NM)
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Why is sleep an active process?
sleep is not the absence of wakefulness; the brain is not inactive
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What happens during sleep?
- there is not an overall massive inhibition of neuronal activity
- neurons continue to fire and some areas of the brain are more active than others
- blood flow and oxygen demand do not decrease
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What is the purpose of sleep?
- 'catch-up time'
- important in long-term chemical and structural change that brain must undergo to make learning and memory possible
- purposes of adaptations of organisms
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What does it mean that sleep is "catch-up time"?
represents a period of rest for specific elements, during which time they can replenish substrates important for generation of AP (upregulation and downregulation of genes)
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What is an example of the purposes of adaption of organisms that occur during sleep?
animals are asleep in burrows, nothing will eat you
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What are the different EEG frequencies (rhythms)?
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What is the range for beta EEG rhythms?
13 Hz and up
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What is the range for alpha EEG rhythms?
13-8 Hz
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What is the range for theta EEG rhythms?
8-4 Hz
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What is the range for delta EEG rhythms?
2 Hz
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Does slow wave sleep involve REM sleep?
no, non-REM sleep
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How does one enter slow wave sleep?
from one of the stages of wakefulness
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What are the characteristics of slow wave sleep?
- no complex dreams
- primarily used for rest
- muscle tension is reduced but not eliminated
- movement minimal but possible
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How many stages are there in slow wave sleep?
4
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How long does it take to go through all 4 stages of the slow wave sleep?
30-40 minutes
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What are the characteristics of the stages of slow wave sleep?
each stage is repeatable and has an EEG pattern characterized by slower frequency and higher amplitude than previous stage
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Describe stage I of slow wave sleep:
- light sleep, easily aroused by moderate stimuli
- alpha-rhythm reduced to partial theta rhythm (4-8 Hz/sec)
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Describe stage II of slow wave sleep:
- further lack of sensitivity to activation and arousal
- primarily theta-rhythm (4-8 Hz/sec)
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Describe stage III of slow wave sleep:
- deep sleep, activation and arousal requires vigorous stimulation
- theta wave (4-8 Hz) activity, as well as delta wave (about 2 Hz/sec)
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Describe stage IV of slow wave sleep:
- true/deep sleep; arousal requires vigorous stimulation
- predominantly delta rhythm (2 Hz)
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When does REM sleep occur?
after one cycle of slow wave sleep, but can occur at every stage of sleep
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What is eye activity like during REM sleep?
burst eye movement activity superimposed over slow, rolling eye movement
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How often does REM sleep occur?
every 90 minutes and last about 20 minutes (at 13+Hz/sec)
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Why is REM sleep a paradox?
because EEG resembles that of a person who is awake, and oxygen use is higher than when you are awake
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Why is REM sleep a deeper state of sleep?
- based on criteria for external arousability
- --takes immense external stimuli to wake up; noise/movement
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What is the lightest state of REM sleep based on?
- criteria for internal arousability
- --little internal stimuli required to wake up; dream/heartburn/full bladder, etc
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What happens to muscles during REM sleep?
profound loss of muscle tone (hypotonia/flaccidity/paralysis) throughout the body
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Which muscles do not have hypotonia during REM sleep?
- mm of respiration
- mm of eye movement
- mm of inner ear (stapedius mm)
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What is the function of the stapedius mm?
modulate sound--modulates eardrum (dampens activity of sound transmission)
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When do dreams occur?
only in REM sleep
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When are penile and clitoral erection common during sleep?
REM
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What are some problems of sleep?
- nightmares
- narcolepsy
- REM sleep behavior disorder
- sleepwalking
- night terrors
- bed wetting
- snoring
- insomnia
- pathological conditions which interrupt ARAS
- bruxism
- obstructive sleep apnea
- sleep deprivation
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narcolepsy:
manifest REM; unintentional sleep episode w/ REM (amphetamines)
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REM sleep behavior disorder:
excessive, vivid dreams w/ movement
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Sleepwalking:
usually occurs during stage IV of non-REM sleep; body wakes up before mind does; not usually during REM sleep
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Night terrors:
wake up screaming (Stage IV)
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Bed wetting:
may occur at any stage; becomes a problem if continues after age 16
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Snoring:
any stage; generally occurs w/ obesity b/c oropharynx has lost space
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Insomnia:
defect of ARAS; often age-related
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Obstructive sleep apnea:
- blockage of airway; common in obese
- stop breathing for 20-30 seconds, and then take a deep breath
- can't die b/c respiratory reflex will take over
- really never reach stage IV, so people are always tired
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Sleep deprivation:
intentional absence of sleep
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