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3.2. Topic content.

Electromyography is a functional method that allows to registrate graphically electrical muscular activity while its excitement. With other words, it is registration method of skeletal muscles electrical potential oscillations occurrence under rest, at tonic tension and arbitrary movements. At muscular contractions visual observation under muscle or nerve irritation one tells about electrical excitability investigation.

EMG allows to study structure and function of neuro-motor apparatus consisting of functional elements named as motor units (MU). MU is an integrity of motoneuron and muscular fibers group innervated by it. On EMG potentials oscillations in neuro-muscular endings (motor plates) occurring under impulses action from medulla oblongata and spine motors are fixated. EMG-record is performed at paper and tape movement velocity equal to 4-5 cm/sec and 20 cm/sec for oscillations quantity estimation.

The curve receiving at this method usage is named electromyogram. It is the result of interference of multiply action potential that appear asynchronically in different muscular fibers and is registrated by means of intracellular electrodes.

There are 3 main electromyogram kinds:

  1. interferential – muscular biopotentials are taken off from large surface while applying the electrodes on skin;

  2. local – separate motor units activity is registrated by means of needle electrodes;

  3. stimulatory – the registration of electrical muscle answer to the stimulation of nerve innervating it.

At EMG with needle electrodes it is necessary to make EMG record under rest and at the investigated muscles weak tension. At necessity one can investigate muscles reaction to nerve electrical irritation or doctor can apply dosated muscular loading, reaction to fatigue and different pharmacological substances (for example, proserin, at myasthenia).

Muscular potentials bringing out is performed by means of electrodes:

  • needle – they are involved in the muscle and bioelectric potentials of separate muscular fibers are registrated;

  • surface – they registrate summary muscles activity from many muscular fibers.

At EMG analysis one should takes into account:

  • altitudes level;

  • potentials oscillations frequency;

  • common oscillograms structure (osclillations monotony or division into volleys, volleys form, duration and frequency).

Parameters of motor units are different because non-equal amount of muscular fibers are included in motor unit. That is why for taking information about state of motor unit of a given muscle it is essential to registrate not less than 20 action potentials. Action potential duration is 5-13 msec. Under norma in a resting state (at local bringing out with needle electrodes) the bioelectrical potentials oscillations don’t increase (at summary EMG one can see low-altituded weak oscillations up to 10-15 mcV). Reflectory tonus increasing is accompanied by insignificant rising up of electrical activity (up to 50-100 mcV). At arbitrary tension frequent high oscillations (1000-2000 mcV) are occured. In healthy people summary EMG dependently on muscular force has altitude up to 400 mcV and frequency up to 400 fluctuations per 1 second.

EMG have different picture at movement disorders that are connected with anomalies of central and perypheral nervous system and muscular apparatus as itself. The muscular bioelectrical activity changes are delt with pathological process topics, severity and course stages. EMG helps at diagnostics of central, segmentary, neurithic and myopathic motor disturbances, it helps to determine typical disorders at early disease stage under conditions of low-expressed symptoms. It also gives the opportunity to observe process dynamics and treatment effectiveness. Sometimes in neurological practice tthey use electroneuromyography – complex investigation method including in it:

  • registration and analysis of muscles and nerves stimulated potentials parameters (stimulated potentials parameters latent period, form, altitude and duration);

  • functionning motor units determining;

  • impulses transmission velocity through peripheral nerves motor and sensor fibers et al.

  • At interpherential EMG one should determine such parameters as:

  • altitude;

  • duration and

  • temporary course of bioelectrical activity during functional probes;

  • symmetrical muscles activity correlation;

  • activity distribution in muscles of one and different groups.

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