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Physiology 59: States of Brain Activity – Sleep, Brain Waves, Epilepsy, Psychoses - - - - - - 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 - - - - 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) - - - 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.