lecture 5: electromyography Flashcards
what is extracellular recording?
this is when both electrodes are located outside the muscle fibre
what is an ECG?
this is an electrocardiogram which records the action potentials in the heart
what is an EEG ?
this is an electroencephalogram
what is an intracellular recording?
- one electrode is in the cell and the other is outside the cell and the zero value is the outside cell measurement
show a diagram of where the reading is zero : EMG
there is no difference between the two electrodes so the EMG measures zero
show a diagram where the reading has a positive indent : EMG
as the AP passes along the muscle fibre it is detected by the skin so a brief positive deflection is seen by the EMG
show a diagram where the reading has a negative indent: EMG
the AP passes to the next electrode and this time a negative deflection is shown as the polarity is opposite
what is the downward deflection? what is the upward deflection? what is the delay between the stimulus to the action potential ? INSERT PIC
downward deflection: stimulus artefact upwards deflection: action potential the delay: this is defined as the latency
what is tetany?
this is when multiple forces fuse to form a plateau effect of contraction - this is sustained contraction
what induces tetany?
multiple sampling frequency stimuli if the intervals are short
show a diagram on a EMG of tetany
INSERT PIC
what happens to the muscles after prolonged contraction
- they start to hurt due to the build of of lactic acid
what has a higher frequency of action potentials in tetany? voluntary contraction or stimulated contraction?
voluntary contraction
where is the EEG performed?
- the medial aspect of the forearm at the wrist - the ulnar groove at the elbow
what is measured in a EEG?
- the latency is measured at each location this is the time difference between stimulation and response
