Download Physiology 59 [5-12

Physiology 59: States of Brain Activity – Sleep, Brain Waves, Epilepsy, Psychoses
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Sleep = unconsciousness from which can be aroused by sensory or other stimuli
Coma = unconsciousness from which cannot be aroused
Two types of sleep:
o Slow-wave sleep = brain waves are strong, low frequency
 Most sleep; deep, restful state in first hour after being awake for long
 Decrease in peripheral vascular tone and vegetative functions (BP, respiratory
rate, and BMR)
 May have dreams but not remembered and without body movement
o Rapid eye movement sleep (REM sleep) = rapid eye movements while asleep
 Occurs in episodes (25% of sleep) recurring every 90 mins; vivid dreaming
 If extremely sleepy, bout is short or absent. If rested, bouts increase
 Active dreaming with bodily muscle movement
 More difficult to arouse by sensory stimuli (but may awaken spontaneously)
 Muscle tone depressed (inhibition of spinal muscle control areas) but irregular
muscle movement occurs
 HR and respiratory rate irregular
 Brain is highly active (metabolism increased).
 Paradoxical sleep on EEG
Theory of sleep -> reticular activating system fatigued (passive theory); current belief is sleep is
an active inhibitory process
o Center below midpontile level inhibits parts of brain -> sleep
Raphe nuclei in lower half of pons and in medulla can cause almost natural sleep
o Diffuse spread and secrete serotonin (NT associated with production of sleep)
o Lesions = high state of wakefulness (reticular nuclei of mesencephalon and pons
released from inhibition)
Nucleus of tractus solitarus can also cause sleep (enters via CN IX and X terminating in medulla
and pons)
Areas of diencephalon (i.e. rostral hypothalamus suprachiasmal area and diffuse thalamic
nuclei) can promote sleep
o Bilateral lesions = high state of wakefulness (reticular nuclei of mesencephalon and pons
released from inhibition)
Muramyl peptide = accumulates in CSF and urine when kept awake for several days; sleep
producing substance.
o Nonapeptide in blood and other substance in neuronal tissue = sleep factors
Drugs mimicking Ach increase REM sleep
Without sleep centers, reticular activating nuclei spontaneously active (excite CNS and PNS ->
positive feedback). Many hours later, neurons fatigue and sleep centers take over.
Sleep causes 1) nervous system effects and 2) other functional system effects.
o Prolonged wakefulness -> malfunction of thought process and abnormal behavior,
increased sluggishness, irritability
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Sleep functions: neural maturation, facilitation of learning or memory, cognition and
conservation of metabolic energy. Restores natural balances among neural centers.
Brain waves are recorded on an EEG (0-200 mV, frequency 0.5-50 per sec). Classified alpha,
beta, theta and delta waves.
o Alpha waves = 8-13 cycles/sec; in most adult EEGs when awake in resting state; most
intense in occipital region. ~50 mV -> disappear in deep sleep
o Beta waves = asynchronous, higher-frequency (15-80 cycles/sec), lower-voltage; replace
alpha when specific mental activity; in parietal and frontal regions
o Theta waves = 4-7 cycles/sec; in parietal and temporal regions in children or emotional
stress (disappointment and frustration) in adults; occur in degenerative brain states
o Delta waves = all EEG waves less than 3.5 cycles/sec; high-voltage; in deep (slow-wave)
sleep, infancy and organic brain disease; in cortex independent of lower brain activity
Intensity of brain wave = neurons and fibers firing in synchrony (nonsynchronous signals often
nullify if opposite polarity)
o Alpha waves from feedback oscillation in cortex via reticular nuclei of thalamus
o Delta waves from synchronous mechanism in cortex by itself without thalamus
Average frequency of EEG increases with higher cerebral activity
o Delta waves (stupor, anesthesia, deep sleep) -> theta waves (psychomotor state and
infants) -> alpha waves (relaxed states) -> beta waves (intense mental activity, alert
wakefulness)
 During mental activity, waves asynchronous (voltage falls)
Stage 1 sleep: EEG broken by sleep spindles (burst of alpha waves). Stage 2, 3, 4 sleep: EEG
frequency slows (theta to delta waves). REM sleep: desynchronized sleep, beta waves
Epilepsy = uncontrolled excessive activity of CNS; occurs when basal level of excitability rises
above threshold
o Grand Mal Epilepsy = extreme neuronal dischare in all brain areas; tonic seizures of
entire body followed by tonic-clonic seizures (tonic and spasmodic contractions); bite or
swallow tongue (may cause cyanosis); urination and defecation; postseizure depression
 High-voltage, high-frequency discharge in both halves simultaneously
 Can be initiated with pentylenetetrazol or insulin hypoglycemia
 Hereditary predisposition -> strong emotional stimuli, alkalosis (overbreathing),
drugs, fever and loud noises/flashing lights
 Stopped by neuronal fatigue and active inhibition
o Petit Mal Epilepsy = thalamocortical brain activating system; 3-30 secs of twitchlike
contractions (esp blinking) -> absence syndrome. First in late childhoold and gone by 30,
may initiate grand mal attack.
 Spike and dome pattern on EEG over most cortex
 Oscillation of inhibitory (GABA) thalamic reticular neurons and excitatory
neurons
o Focal epilepsy = local part of brain from organic lesion (scar tissue, tumor, destroyed
area, congenitally deranged local circuit); extremely rapid discharges spread over
adjacent regions (localized reverberating circuits)
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Spread to motor cortex -> “march” of contralateral muscle contractions from
mouth down = jacksonian epilepsy
 Psychomotor seizure = short period of amnesia, abnormal rage attack, sudden
anxiety, discomfort or fear, incoherent speech or mumbling (involve limbic
portion) -> low-frequency rectangular wave (2-4/second)
 Surgical excision prevents future attacks.
Huntington’s disease = loss of GABA neurons and Ach-neurons -> specific abnormal motor
patterns + dementia
Mental depression psychosis -> caused by diminished formation of norepinephrine and/or
serotonin (normally increase sense of well-being, happiness, contentment, good appetite, sex
drive, and psychomotor balance)
o Norepi neurons located in locus ceruleus. Serotonin neurons in midline raphe nuclei.
o MAO inhibitors, tricyclic antidepressants (imipramine and amitriptyline) used to treat
depression as well as “shock therapy”
o Bipolar disorder or manic-depressive psychosis = alternate between depression and
mania (treat with lithium compounds)
Schizophrenia = voices, delusions, fear, paranoia (sense of persecution); from blockage of
signals to prefrontal lobes (loss of response to glutamate), excessive excitement of dopamine
and/or abnormal function of limbic behavioral control system (hippocampus)
o Excess dopamine from neurons in ventral tegmentum = mesolimbic dompaminergic
system
o Treat with chlorpromazine, haloperidol, and thiothixene (decrease dopamine secretion
or effect on neurons)
o Hippocampus is often reduced in size in schizophrenia
Alzheimer’s Disease = premature aging of breain; amnesic memory impairment, deterioration
of language, visuospatial deficits, loss of neurons in memory pathway -> most common form of
dementia
o Increased amounts of beta-amyloid peptide (amyloid plaques) -> all mutations increase
β-amyloid peptide, Down syndrome have 3 copies of amyloid precursor gene, abnormal
apoE accelerates amyloid deposits, overproduction of amyloid precursor proteins leads
to memory deficit, anti-amyloid antibodies attenuates disease.
o Hypertension and atherosclerosis contribute to Alzheimer’s. cerebrovascular disease is
2nd cause of acquired cognitive impairment and dementia.