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George E. Carvell, PhD, PT   University of Pittsburgh
 
PERIPHERAL NERVE DYSFUNCTION VIII: LOWER MOTOR NEURON
    The EMG needle exam of a denervated muscle may show a prolonged period of insertional activity that outlasts the actual movement of the needle. The sarcolemma is hyperirritable. This is followed by fibrillation potentials and/or positive sharp waves at rest; an important sign of denervation (fig 13-24). At sub-maximal muscle contraction few motor unit potentials (MUPs) are seen; these abnormally large motor units suggest reinnervation of denervated muscle fibers rescued by surviving motor axons (figs 13-23, 13-25). At maximal (weak) contraction, the same MUPs are seen at higher rates of discharge; one sees incomplete interference pattern typical of a muscle
that has few surviving motor units.
Needle Insertion,
Muscle at Rest
Voluntary Contraction, Motor Unit Recruitment
Ben.  fig 13-23 p 414
Ben.  fig 13-24 p 414
Ben.  fig 13-25 p 415
GMOMM  2001
MUPs