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Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. [1] [2] EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram.
Leads I, II and III are called the limb leads. The electrodes that form these signals are located on the limbs – one on each arm and one on the left leg. [41] [42] The limb leads form the points of what is known as Einthoven's triangle. [43] Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode:
At the onset of muscle contraction, gross changes in the muscle shape cause a large peak in the MMG. Subsequent vibrations are due to oscillations of the muscle fibres at the resonance frequency of the muscle. The mechanomyogram is also known as the phonomyogram, acoustic myogram, sound myogram, vibromyogram or muscle sound.
An electrode introduced into the brain of a living animal will detect electrical activity that is generated by the neurons adjacent to the electrode tip. If the electrode is a microelectrode, with a tip size of about 1 micrometre, the electrode will usually detect the activity of at most one neuron.
(c) The intact but dormant axon receives the stimulus and propagates an action potential to (d) the neuromuscular junction. (e) The corresponding muscle fibers contract and generate (f) muscle force. (g) A train of negative pulses is produced. (h) Depolarization occurs where negative current enters the axon at the "active" electrode indicated.
Electrode placement: Surface electrodes are strategically placed on the skin over the nerve being tested and on a muscle it supplies or further along the path of that same nerve. [10] These electrodes record the nerve's electrical response and are referred to as surface recording electrodes. [ 10 ]
Electromyoneurography is a technique that uses surface electrical probes to obtain electrophysiological readings from nerve and muscle cells. The nerve activity is generally recorded using surface electrodes, stimulating the nerve at one site and recording from another with a minimum distance between the two.
Any peripheral nerve that can be reached may be a target for microneurography recordings, typically in the arm or leg, although recording from facial nerves and the vagus nerve have also been achieved. In order to locate deep nerves, electrical stimulation through a needle electrode or ultrasonic monitoring is often used.