Fairbanks Pain Clinic - An electromyograph (or likewise called EMG) is an apparatus designed for diagnosing neuromuscular disorders. The EMG records the electric activity of muscle fibers and the motor neurons which activate them. The EMG makes a visual image on a television monitor and an auditory record of the electric signal transmitted from the muscle to the electromyograph. The signals are measured in millivolts. The visual picture appears as a graph of a wave function. The auditory record produces a crackling sound. Together, the visual and auditory record could help to determine the reasons for muscle weakness and nerve damage.
There are two kinds of electromyography: surface EMG and intramuscular EMG.
The intramuscular EMG method utilizes a thin needle electrode which is inserted into the muscle. After inserting the needle into the muscle, a jolt of electrical activity is generated as the needle moves throughout the muscle. The signal fades because the resting muscle usually produces no electrical activity. Thus, any irregular electrical activity the EMG picked out while the muscle is resting, like fibrillation potentials, can indicate damage or disease.
When there is a contracting muscle it would produce an electrical pulse that could be measured by an intramuscular EMG. Also being measured are the strength of the contractions, which motor neurons are firing, and the density of motor units in certain areas of the muscle. Motor units means individual neurons and the muscle fibers they control. Severe nerve damage causes some motor neurons to generate new branches and take over muscle fibers once belonging to damaged nerves. A higher frequency is detected in these neurons which are compensating for the loss of the damaged neurons.
Intramuscular EMG could provide doctors with a great deal of information from which to make a likely diagnosis. EMG can help diagnose common neuromuscular diseases like compression of a nerve root due to a herniated disc, trauma damage to nerves, and muscular dystrophy. The needle would be inserted numerous times in order to sample adequate muscle tissue for a correct diagnosis.
Electric patches are on the surface of the skin for the surface EMG procedure. usually, the surface EMG would not provide detailed records of individual motor units as the needle can provide. Nevertheless, surface EMG is useful for making overall measurements of muscular activity in general regions of the body. It is used all through physical therapy with individuals who have nerve or muscle damage allowing them to see when their muscles are contracting and how strong their muscles are becoming. The surface EMG is therefore used a biofeedback device.