Neuroscience/Objectives/Lecture 47
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Objectives: 27 - 28 - 29 - 30 - 31 - 32 - 33 - 34 - 35 - 36 - 37 - 38 - 39 - 40 - 41-42 - 43 - 44-45 - 46 - 47 - 48 - 49 - 50 - 51 - 52 - 53 - 54
Objectives: 27 - 28 - 29 - 30 - 31 - 32 - 33 - 34 - 35 - 36 - 37 - 38 - 39 - 40 - 41-42 - 43 - 44-45 - 46 - 47 - 48 - 49 - 50 - 51 - 52 - 53 - 54
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Sleep and consciousness
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Explain the basic principles of electroencephalography and its applications.
Electroencephalography (EEG) uses a series of bilaterally symmetric electrodes placed on the scalp. Each electrode measures the electrical activity (ie, electrical potential changes) of millions of neurons beneath it. Potential differences are recorded between each pair of electrodes, transmitted to an amplifier, and then recorded as an electroencephalogram, which plots voltage versus time.
Because the brain's electrical activity changes with different states of alertness, EEGs are commonly used to study sleep and consciousness.
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Describe sleep patterns and stages and their underlying physiological mechanisms.
| State | EEG characteristics | Mesopontine cholinergic nuclei | Locus coeruleus | Raphe nuclei |
|---|---|---|---|---|
| Awake, eyes open | ↓Voltage, ↑frequency (14-60 Hz beta waves) | Active | Active | Active |
| Awake, eyes closed | ↓Voltage, ↑frequency (8-13 Hz alpha waves) | Active | Active | Active |
| Stage 1 sleep | ↑Voltage, ↓frequency | Decreased | Decreased | Decreased |
| Stage 2/3 sleep | ↑Voltage, ↓frequency, sleep spindles, K complex | Decreased | Decreased | Decreased |
| Stage 4 (slow-wave) sleep | ↑↑Voltage, ↓↓frequency (delta waves) | Decreased | Decreased | Decreased |
| REM sleep on | ↓Voltage, ↑frequency (resembles wakefulness) | Active (PGO waves) | --- | Inactive |
| REM sleep off | ↓Voltage, ↑frequency | -- | Active | -- |
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Delineate various states of consciousness and their anatomical/physiological correlates.
- Clouding of consciousness
- Reduced awareness and loss of attention. Substantial clouding results in confusional state with external stimuli being misinterpreted. Reflects general brain dysfunction.
- Deliriuim
- A deeper impairment resulting in disorientation, irritability, inaccurate perception of sensory stimuli, and hallucinations.
- Optundation
- Mild reduction in alertness and decreased interest in environment, associated with drowsiness.
- Stupor
- Characterized by deep sleep from which the individual can only be aroused by strong, repeated stimuli. Cerebral hemispheres, paramedian diencephalon, and upper brainstem are implicated in stupor and coma.
- Coma
- State of unresponsiveness from which individual cannot be aroused. EEG resembles stage 4 (slow wave) sleep. Cerebral hemispheres, paramedian diencephalon, and upper brainstem are implicated in stupor and coma.
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Understand the neurological evaluation of patients with stupor or coma.
| Lesion | Respiratory pattern | Pupil size/reactivity | Oculocephalic and -vestibular responses | Motor responses |
|---|---|---|---|---|
| Early (superior) diencephalic | Cheyne-Stokes or eupneic (normal) with deep sighs and yawns | Small, reactive pupils | Normal doll's head and ice water caloric responses | Bilateral Babinski, paratonic resistance |
| Late (inferior) diencephalic | Cheyne-Stokes | Small, reactive pupils | Normal doll's head and ice water caloric responses | Decorticate rigidity (legs extend, arms flex) |
| Midbrain-pons junction | Sustained, regular hyperventilation | Fixed pupils | Impaired doll's head response, dysconjugate ice water caloric response (due to bilateral MLF lesion) | Decerebrate rigidity |
| Pons-medulla junction | Eupneic (but shallow) | Fixed pupils | Absent doll's head and ice water caloric responses | No muscle tone |
