EEG and EMG Flashcards
What does EEG record
Electrical activity in the outer regions of the brain, primarily cortex
Records mass acuity of 1000s-millions of neurones firing
What is the mass discharge recorded by EEG
EEG Used to examine
Coma, brain defects, brain death, epilepsy
EEG Method
Electrodes placed at anatomically defined points
19 recordings, 1 reference
What is each electrode connected to
Input amplifier (1000-100,000 times)
What does EEG signal represent
Difference between voltages at 2 electrode sites
Bipolar montage
Each channel represents difference between 2 adjacent electrodfe
What is a montage
Can record eeg between different electrode combinations = montage
What is used as a common reference
Average signal
Normal activity is described in terms of:
Rhythmic activity and transients
Rhythm is activity is divided into…
Frequency bands
Describe delta waves
0-4Hz
Highest amplitude, slowest waves
Seen in slow wave sleep
Describe theta waves
4-7Hz
Young children
Drowsiness and arousal in adults
Meditation
Describe alpha waves
8-12Hz
Seen on closing eyes and relaxation
Disappears on opening eyes and mental maths
Describe beta waves
12-30Hz
Disappear with motor movement
Describe beta waves
12-30Hz
Disappear with motor movement
Associated with busy or anxious thinking
Describe new-born waves
Mainly irregular theta and delta waves
Lacks rhythmic activity
What is wakefulness characterised by
Alpha waves
Drowsiness is characterised by:
Increased amplitude, slower alpha waves
Reduced HR and muscle artefact
EEG and stage 1 sleep characterised by
Alpha waves suppressed, beta waves increase, some theta waves
Stage 2 sleep:
Background beta and theta activity with some delta
Sleep spindles (sigma) 12-14Hz
Also K complexes - sharp wave followed by delta and spindle
Stage 3 sleep:
Large amplitude delta waves <1Hz
Sleep spindles and K complexes remain
Stage 4 sleep:
More prominent delta waves
Some K complexes
Hyperventilation and EEG
Hypocapnia, decr BP, cerebral vasoconstriction
Increased theta waves
Intermittent photic stimulation and EEG
Light lashes at 4-20Hz
Cause visual evoked potentials
Can be used to: identify sites of lesions and provoke epileptic activity
Characteristic of epileptic EEG
Spike and wave activity
Localised in focal
Seen in every electrode in general
focal can spread giving secondary generalised activity
What does EMG record
Electrical activity from skeletal muscles
What type of electrodes are used on EMG
Surface electrodes
Intramuscular needle electrodes
What is EMG used to distinguish
Neurogenic and myopathies causes of motor unit dysfunction
What do nerve conduction studies involve
Stimulating nerve from 2 sides eg near elbow and at wrist
EMG procedure
Fine needle inserted intramuscularly
Potentials from fibres in vicinity of tip recorded
Compound action potentials from fibres in the same motor unit recorded
Upon insertion brief discharge normally subsides after a few sewconds
EMG activity is examined for what
Activity at rest
Number of motor units under voluntary control
Duration and amplitude of AP in each motor unit
What happens in weak voluntary contraction
Series of motor unit potentials recorded as different motor units are recruited
What happens in maximal contraction
Potentials overlap, impossible to identify single potentials
What is amplitude determined by
The number of fibres within the motor unit
Characteristics of myopathic disease
Number of muscle fibres in each unit reduced as fibre atrophy and die
