Electromyography Flashcards
Electromyography (EMG)
recording of the action potentials occurring in skeletal muscle fibres
Extra-cellular recording: both electrodes outside the muscle fibres. Record the emf (potential) between 2 locations both outside the cells
Other examples of extra-cellular recordings
Where are the electrodes?
ECG (EKG), electrocardiogram, recording action potentials from the heart. Electrodes on limbs, or chest.
EEG, electroencephalogram, recording action potentials from the brain. Electrodes on the scalp.
Difference between intracellular and extracellular recording
What are you measuring the voltage between?
Intracellular recording: one electrode inside the cell.
Measure voltage between inside and outside cell.
Inside of cell is more negative with respect to the outside
both electrodes outside the muscle fibres
Measure voltage between 2 sites outside the fibres
Difference between intracellular and extracellular recording What are you measuring the voltage between? Exemplar graph (slide 12, lecture 6)
Intracellular recording: one electrode inside the cell.
Measure voltage between inside and outside cell.
Inside of cell is more negative with respect to the outside
Extracellular recording: both electrodes outside the muscle fibres
Measure voltage between 2 sites outside the fibres
Measuring voltage between inside and outside on one place and the inside and outside on another place (different from action potential graph)
Difference between intracellular and extracellular recording What are you measuring the voltage between? Exemplar graph (slide 12, lecture 6)
Intracellular recording: one electrode inside the cell.
Measure voltage between inside and outside cell.
Inside of cell is more negative with respect to the outside
Extracellular recording: both electrodes outside the muscle fibres
Measure voltage between 2 sites outside the fibres
Measuring voltage between inside and outside on one place and the inside and outside on another place (different from action potential graph)
Voluntary contraction
As force exerted by muscle increases?
As force exerted by muscle increases, EMG amplitude on recording increases
What converts force to electrical signal
Transducer
Stronger artificial stimulus effect on muscle
Leads to action potentials and stronger/larger twitch
Increasing frequency of stimulus leads to ?
a more homogenous output, without distinct outputs, summating output to produce a larger force
Tetanus
: contraction where twitches are so rapid that they produce a fused tetanic contraction, without distinct contractions
Electric shock:
What is required?
What happens?
If 50Hz mains, muscles undergo tetanic contraction, and can’t let go because muscles clamping
