chapter 9 notes

chapter 9 notes - CHAPTER 9: Sleep Stages of sleep:...

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CHAPTER 9: Sleep Stages of sleep: Electroencephalogram (EEG) Electromyogram (EMG) – recording of muscle activity Electro-oculogram (EOG) – recording of eye activity During wakefulness, a person's EEG shows 2 basic patterns of activity: alpha and beta. Alpha activity consists of regular, medium-frequency waves of 8-12 Hz, and is produced when the person is resting quietly, not particularly engaged in mental activity; eyes usually closed, but also occurs when open. Beta activity consists of irregular, low-amplitude waves of 13-30 Hz. Beta waves show desynchrony, reflecting the fact that many various neural circuits are processing info. This activity (desynchronized) occurs when a person is alert, attentive to environment. Stage 1 sleep is marked by some theta activity (EEG: 3.5-7.5 Hz), which occurs intermittently during early stages of slow-wave sleep and REM sleep. Theta activity indicates that the firing of neurons in the neocortex is becoming more synchronized. During Stage 1 (transition between waking and sleep), eyelids may open/close, eyes roll. Stage 2 sleep has an irregular EEG, containing theta activity, sleep spindles (short bursts of 12-14 Hz waves occuring between 1-5x/min during stages 1-4), and K complexes (sudden, sharp waveforms; usually only found during stage 2; spontaneously occur about 1x/min, often triggered by sudden noises, in which case they are inhibitory mechanisms to protect the sleep from awaking; K complexes appear to be the forerunner of delta waves). Stage 3 sleep is signaled by high-amplitude delta activity (less than 3.5 Hz). Stages 3 and 4 (referred to as slow-wave sleep because of EEG activity) are similar; stage 3 has 20-50% delta activity, and stage 4 contains over 50%. Most important feature of slow-wave sleep are slow oscillations of less than 1 Hz. Each oscillation consists of a single high-amplitude biphasic (down/up) wave. First part indicates a down state: period of inhibition; neurons of neocortex totally silent. Neocortical neurons are able to rest during the down state. Second part: up state- period of excitation; neurons briefly fire at a high rate. Other short-wave sleep components (K complexes, sleep spindles, delta waves) are synchronized with these slow oscillations. Slow oscillations play an important role in learning and memory. About 90 mins after beginning of sleep/45 mins after onset of stage 4 (the deepest stage), EEG suddenly becomes mostly desynchronized, with some theta waves (similar to stage 1). Rapid eye movements begin (REM sleep); during this stage, there is no EMG reading (zero muscle movement), meaningful stimuli such as sound of name can awaken the sleeper (though not meaningless noise, usually) and they will be alert and attentive; dreams occur. Throughout the night sleep alternates between periods of REM and non-REM – each cycle
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chapter 9 notes - CHAPTER 9: Sleep Stages of sleep:...

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