EMG By Sara salah Physiology department Electromyography EMG

EMG By Sara salah Physiology department

• Electromyography (EMG) : • is an electrodiagnostic medicine technique for evaluating and recording the electrical activity produced by skeletal muscles. • EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram

• Medical uses: • _EMG is used as a diagnostics tool for identifying neuromuscular diseases • _EMG is most often used when a person has symptoms of weakness, pain, or abnormal sensation.

• EMG recording techniques • _EMG recordings can be performed by means of intramuscular (needle) or non-invasive (surface) electrodes.

• Needle EMG (n. EMG): • _n. EMG permits local recording from deep muscles by means of insertion of a needle electrode into the muscle tissue.

• n. EMG has greater sensitivity and accuracy in the recording of high-frequency signals such • However, n. EMG has several limitations First, it reflects the activity of only a small number of active MUs whose fibers are close to the position of the detection site (not representative of all the fibers in the MU, due to its small detection volume).

• Second, n. EMG is painful especially during muscle activation, and prolonged n. EMG recording is not possible • Furthermore, n. EMG is time and temperature sensitive

Needle EMG (n. EMG):

• Surface EMG (s. EMG): • s. EMG is a technique to measure muscle activity noninvasively using surface electrodes placed on the skin overlying the muscle,

• s. EMG has several advantages. First, s. EMG recording is painless • s. EMG electrodes record from a wide area of muscle territory providing a more global view of Mus

• However, s. EMG has a relatively low-signal resolution, is highly susceptible to movement artifacts and body temperature. In addition, s. EMG signals are dominated by the contributions of superficial MUs, while deeper MUs are not assessed; conditions that increase skin resistance subsequently disturb the s. EMG signal (e. g. obesity and edema).

Surface EMG (s. EMG):

• Normal Results : • There is normally very little electrical activity in a muscle while at rest. Inserting the needles can cause some electrical activity, but once the muscles quiet down, there should be little electrical activity detected. • When you flex a muscle, activity begins to appear. As you contract your muscle more, the electrical activity increases and a pattern can be seen. This pattern helps your doctor determine if the muscle is responding as it should.

• EMG is often done with nerve conduction study (NCS)

• NCS: • __Nerve signals are electrical impulses that travel quickly throughout your nervous system. • Sometimes, problems with the electrical activity in your nerves can cause pain, tingling, or weakness in your muscles. • NCS measures how fast and how strong the electrical activity is in a nerve. The test can tell whether a nerve has been damaged.

nerve conduction study (NCS)