Neuromuscular

EMG: PARTIAL DENERVATION

PARTIALLY DENERVATED MUSCLE
Rapid firing of a motor unit

Sweep speed = 10 ms/div; Sensitivity = 0.2 mV/div
Large, rapidly firing motor unit

Sweep speed = 10 ms/div; Sensitivity = 1.0 mV/div
  • Normal motor unit
    • Firing rate: 7 to 15 Hz; No repetitive firing less than 4 to 5 Hz
    • Size: Muscle fiber number innervated
      • Limbs: 100 to 300
      • Larynx: 5 to 10
    • Territory
      • 5 to 10 mm
      • Increases with age: Due to growth of muscle fibers
  • Denervation
    • Motor unit firing rate: Rapid; > 20 Hz
    • Motor unit size: Increased; Amplitude & Duration greater
from M. Al-Lozi

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8/13/2008