脑电图（EEG），清醒和睡眠（可编辑）

脑电图（EEG），清醒和睡眠（可编辑） 脑电图(EEG)，清醒和睡眠 Electroencephalogram EEG Brain Waves State of the Brain Normal brain function involves continuous electrical activity Patterns of neuronal electrical activity recorded are called brain waves Brain waves change with age sensory stimuli brain disease and the chemical state of the body An electroencephalogram EEG records this activity EEGs can be used to diagnose and localize brain lesions tumors infarcts infections abscesses and epileptic lesions A flat EEG no electrical activity is clinical evidence of death Electroencephalogram EEG Measures synaptic potentials produced at cell bodies and dendrites Create electrical currents Used clinically diagnose epilepsy and brain death EEG Patterns Alpha low-amplitude slow synchronous waves indicating an idling brain Recorded from parietal and occipital regions Person is awake relaxed with eyes closed 10-12 cyclessec 50 100 V Mechanism of EEG Continuous graph of changing voltage fields at scalp surface resulting from ongoing synaptic activity in underlying cortex Inputs from subcortical structures Thalamus Brainstem reticular formation II Wakefulness and Sleep Sleep Sleep is a behavior and an altered state of consciousness Sleep is associated with an urge to lie down for several hours in a quiet environment Few movement occur during sleep eye movements The nature of consciousness is changed during sleep We experience some dreaming during sleep We may recall very little of the mental activity that occurred during sleep We spend about a third of our lives in sleep A basic issue is to understand the function of sleep EEG Sleep Patterns There are two major types of sleep Non-rapid eye movement NREM Rapid eye movement REM REM rapid eye movement Dreams occur Low-amplitude high-frequency oscillations Similar to wakefulness beta waves Non-Rem resting High-amplitude low-frequency waves delta waves Types of Sleep One passes through four stages of NREM during the first 30-45 minutes of sleep REM sleep occurs after the fourth NREM stage has been achieved Non-REM Sleep Alpha delta theta activity are present in the EEG record Stages 1 and 2 Alpha waves Stages 3 and 4 delta activity synchronized Termed slow-wave sleep SWS Light even respiration Muscle control is present toss and turn Dreaming could but not vivid rational Difficult to rouse from stage 4 SWS resting brain Types and Stages of Sleep NREM Stage 1 – eyes are closed and relaxation begins the EEG shows alpha waves one can be easily aroused Stage 2 – EEG pattern is irregular with sleep spindles high-voltage wave bursts arousal is more difficult REM Sleep Presence of beta activity desynchronized EEG pattern Physiological arousal threshold increases Heart-rate quickens Breathing more irregular and rapid Brainwave activity resembles wakefulness Genital arousal Pontine-Geniculate-Occipital PGO waves Loss of muscle tone paralysis Vivid emotional dreams May be involved in memory consolidation Sleep Stage Cycles Importance of Sleep Sleep is necessary for survival Sleep appears necessary for our nervous systems to work properly During the SWS growth hormone secretion increase and important for the infants growth and physical restorative process of adult During REM brain blood flow and protein synthesis increase and it is important for the mental development of infants and long-term memory and mental restoration in adults Daily sleep requirements decline with age What Happens if We are Deprived of Sleep Lack of alertness Fatigue Memory problems Irritability Depression Lack of motivation Accidents Fibro Myalgia Tips for Getting a Good Nights Sleep Avoid caffeine and alcohol after dinner Keep a routine Dont nap during the day Dont go to bed hungry or right after eating Exercise Stop smoking Rules for Optimal Sleep Get an adequate amount of sleep every night Establish a regular sleep schedule Get continuous sleep Make up for lost sleep Chemical Control of SleepWaking Sleep is regulated loss of SWS or REM sleep is made up somewhat on following nights Does the body produce a sleep-promoting chemical during wakefulness or a wakefulness-promoting chemical during sleep Unlikely that sleep is controlled by blood-borne chemicals in the general circulation given Siamese twins share the same circulatory system but sleep independently Bottle-nose dolphins the two hemispheres sleep independently Neural Regulation of Arousal Electrical stimulation of the brain stem induces arousal Dorsal path RF-- to medial thalamus -- cortex Ventral path RF -- to lateral hypothalamus basal ganglia and the forebrain Neurotransmitters involved in arousal NE neurons in rat locus coeruleus LC show high activity during wakefulness low activity during sleep zero during REM sleep LC neurons may play a role in vigilance Activation of ACh neurons produces behavioral activation and cortical desynchrony ACh agonists increase arousal ACh antagonists decrease arousal 5-HT stimulation of the raphe nuclei induces arousal whereas 5-HT antagonists reduce cortical arousal Neural Control of SWS The ventrolateral preoptic area VLPA is important for the control of sleep Lesions of the preoptic area produce total insomnia leading to death Electrical stimulation of the preoptic area induces signs of drowsiness in cats VLPA neurons promote sleep Neural Control of REM Sleep The pons is important for the control of REM sleep Pontine-Geniculate-Occipital PGO waves are the first predictor of REM sleep ACh neurons in the peribrachial pons modulate REM sleep Increased ACh increases REM sleep Peribrachial neurons fire at a high rate during REM sleep Peribrachial lesions reduce REM sleep Pontine ACh neurons project to the thalamus control of cortical arousal to the basal forebrain arousal and desynchrony and to the tectum rapid eye movements Pontine cells project via magnocellular cells within medulla to the spinal cord release glycine to inhibit alpha-motoneurons induce REM motor paralysis or atonia NT Interactions REM Sleep 9 Section 6 Electroencephalogram EEG Wakefulness and Sleep 1 Brain Waves The EEG be recorded with Scalp electrodes through the unopened skull or with electrodes on or in the brain A normal EEG Betahigh-amplitude waves seen in deep sleep and when reticular activating system is damped Strongest from frontal lobes near precentral gyrus Produced by visual stimuli and mental activity Evoked activity 13-25 cyclessec Alpha Block Replacement of the alpha rhythm by an asynchronous low-voltage beta rhythm when opening the eyes Theta more irregular than alpha waves Emitted from temporal and occipital lobes Common in newborn some sleep in adult Adult indicates severe emotional stress 5-8 cyclessec Delta high-amplitude waves Common during sleep and awake infant In awake adult indicate brain damage 1-5 cyclessec SPONTANEOUS CORTICAL ELECTRICAL POTENTIALS THE EEG Diagrammatic comparison of the electrical responses of the axon and the dendrites of a large cortical neuron 2 Mechanism of EEG Current flow to and from active synaptic knobs on the dendrites produces wave activity while AP are transmitted along the axon EEG signals generated by cortex Currents in extracellular space generated by summation of EPSPs and IPSPs 3 EEG Records During Epileptic Seizure Epilepsy is characterized by uncontrolled excessive activity of either a part or all of the central nervous system Grand mal epilepsy characterized by extreme neuronal discharges in all areas of the brain last from a few seconds to 3 to 4 minutes Petit mal epilepsy Characterized by 3 to 30 seconds of unconsciousness or diminished consciousness during which the person has several twitch-like contractions of the muscle 9 Stage 3 – sleep deepens theta and delta waves appear vital signs decline dreaming is common Stage 4 – EEG pattern is dominated by delta waves skeletal muscles are relaxed arousal is difficult 9 Pontine-geniculate-occipital PGO wave – A synchronized burst of electrical activity that originates in the pons and like a wave it activates the lateral geniculate nucleus first relay of visual information and then the occipital lobe specifically in the visual cortex which receives and puts together the visual information that comes from the lat geniculate nucleus PGO waves appear seconds before and during REM sleep A typical sleep pattern alternates between REM and NREM sleep SWS precedes REM sleep REM sleep lengthens over the night Basic sleep cycle 90 minutes The suprachiasmatic and preoptic nuclei of the hypothalamus regulate the sleep cycle 9 9