EMG Flashcards
Describe the 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
How do we understand what is happening in the brain
To understand what is happening in the brain we need to analyse distal sites, such as the fingers and muslces.
Describe some other examples of extra-cellular recordings
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.
Describe intracellular recordings
one electrode inside the cell.
Measure voltage between inside and outside cell.
Describe extra-cellular recordings
both electrodes outside the muscle fibres
Measure voltage between 2 sites outside the fibres
What happens when an action potential occurs
The outside of the membrane becomes negative. May see a downward or upward deflection (depending on which electrode is the reference) this then comes back down to the resting value as the action potential moves away from that site.
Is an EMG extra-cellular or intra-cellular recording
Extra-cellular
When stimulating the nerves that innervate the muscles in the hand , for example the ulnar nerve, what two responses should you expect
Motor response- movement of the hand
Sensory response- the patient feels the stimulus
If no activity is seen, what could this indicate
You may have set the equipment up incorrectly, increase the stimulus.
Why will the patient feel the stimulus prior to the motor response
The sensory axons are large, and myelinated and so are more accessible to the stimulus, meaning that they will be activated at a lower strength stimulus than the motor neurons, which are small and myelinated.
Why are pain fibres only activated at larger stimuli
They are small and unmyelinated, and so are only accessible at larger strength stimuli.
What is used to measure the force
A transducer
How can this transducer be used to measure the force
The more the thumb pulls on the transducer (signal) converted into the electrical signal, which represents the force
What is an EMG representative of
A visual representation of the electrical activity inside a muscle.
What happens as you contract more
Electrical activity of the muscle increased amplitude on EMG. This corresponds with an increase in force generated too.
