Electromyography
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  • 1. RK Goit, Lecturer Department of Physiology
  • 2. • Electromyography (EMG) – is a technique for evaluating & recording the electrical activity produced by skeletal muscles – is performed using an instrument called an electromyograph, to produce a record called an electromyogram • a resting muscle does not show recordable electrical potential but with increase force of contraction, amplitude of potential increases • an electromyograph detects electrical potential generated by muscle cells when these cells are electrically or neurologically activated
  • 3. Equipment • electrodes – Surface electrodes – Needle electrodes • a high-gain amplifier (10-5000Hz) – connected to an oscilloscope • oscilloscopic traces may be photographed or stored on magnetic tape – EMG signals may be fed to an audio unit for an on the spot feel of the signals • an arrangement for recording the output – EMG is best done in a specially constructed shielded room to prevent interference
  • 4. Pattern of EMG Recorded Findings Resting activity Muscle relaxed & needle not moving No activity Insertion activity Needle is moved to various sampling spots within insertion tract Brief action potentials Motor unit potential Needle is not moved while patient makes slight contraction A few motor unit action potentials, biphasic or triphasic, short duration Recruitment Subject makes progressively stronger muscle contraction until reaching maximum force Increase number of functioning movements until the baseline is obscured
  • 5. Motor unit potential (MUP) • the sum of the action potentials produced in the muscle • characterized by its duration, number of phases, amplitude, & rate of rise of first component
  • 6. Feature of MUP Duration • measured from the initial take-off to the point of return to the baseline • 5-15 ms Phases • portion of the MUP between the departure & the return to the baseline • triphasic (positive, negative, positive) • Polyphasic-MUP with more than four phase (5-15%) Amplitude • measured from maximum peak of negative phase to maximum peak of the positive phase • 0.5mV to 2mV Rise time • duration from the initial positive to subsequent negative peak • normal ↓ 500 µs
  • 7. Factors that effect MUP • Technical factors – Type of needle electrode – Characteristics of recording surface – Electrical characteristics of cable – Preamplifier & amplifier – Method of recording • Physiological factors – Age of the patient – Muscle examined – Temperature
  • 8. Analysis of EMG • Qualitative analysis – visual inspection of the record • Quantitative analysis – amplitude, duration, & frequency – power spectrum analysis
  • 9. Application of EMG • kinesiology- degree & sequence of contraction of various muscles participating in a movement • mechanism employed by the body for grading the force of muscular contraction • clinical diagnosis & follow up myopathies & responses of nerve & muscle to injury
  • 10. Fibrillation Fasciculation contraction of individual muscle fiber contraction of individual motor units cannot be seen through the skin visible through the skin when muscle fibers lose contact with their innervating axon occurs as a result of additional nerve impulses generated 10-100 µV in amplitude, 1-2 ms in duration, & 10 Hz in frequency 50-500 µV in amplitude, 2-4 ms in duration, & 2-20 Hz in frequency Neuropathy, myopathy Neuropathy
  • 11. References • Essentials of Clinical Neurophysiology, 3/E Karl & Thomas • Principles of Neural Science, 4/E Kandel ER, Schwartz JH, Jessell TM (editors) • Understanding Medical Physiology, 4/E Bijlani & Manjunatha
  • 12. Thank You