Electromyography (EMG)

Recording of action potentials of muscle fibers near the needle electrode in a muscle.The equipment for EMG consists of: --electrodes ( disc electrodes or needle electrodes) -Amplifier -Displayer ( visual)/ printer

basic unit of EMGThe basic unit of EMG signals is motor unit action potential (MUP).It is the sum of the action potentials produced in the muscle supplied by an anterior horn.Amplitude of MUP is 0.5-3mv, duration is 5-12 ms, frequency up to 500Hz and it is mostly triphasic.

analysis 3 types of signals observed in EMGInsertional activitySpontaneous activityVoluntary activity

Applications of EMG Mainly used to diagnose nerve and muscle injury.Neurogenic disease like anterior horn cell disease, Amylotropic lateral sclerosisMyogenic disease like Duchennes muscular dystrophy, muscle trauma, muscle cramps etc.

Fibrillationcontraction of individual muscle fiber which cannot be seen through skin. Abnormal spontaneous activity are seen in EMGIt may be due to denervation of motor neuronAmplitude 10-100mv, duration 1-2ms , frequency 10 Hz

Fasiculation

Coarse contraction of individual motor units; 50-500mv, 2-4ms, 2-20HzCan be visible through skinOccasionally it can be seen normally like in muscle cramps. Occurs in anterior motor neuron disease like poliomyelitis