polyphasic potential
Motor unit potential with multiple phases, indicating muscle fiber desynchronization or reinnervation changes.
Full Definition
A polyphasic potential is a motor unit action potential that crosses the baseline more than four times, creating five or more phases. Normal motor units typically show two to four phases, so polyphasic potentials suggest abnormal motor unit architecture. They commonly occur in neurogenic conditions due to collateral sprouting and reinnervation, where nerve fibers supply muscle fibers at varying distances, causing temporal dispersion of muscle fiber action potentials. Polyphasic potentials may also be seen in myopathic conditions due to muscle fiber loss and architectural disruption. The percentage of polyphasic potentials in a muscle sample provides quantitative assessment of motor unit pathology.
Usage
Usage note: Quantified as percentage of total potentials analyzed; threshold is typically >25% abnormal.
In Context
- "Thirty percent of motor units showed polyphasic potentials, suggesting chronic reinnervation." — EMG report
- "The polyphasic potential morphology indicated active denervation-reinnervation processes." — Electromyography interpretation