Lower Motor Neuron Lesions: Trauma, infection (poliomyelitis), vascular disorders, degenerative diseases, and neoplasms may all produce a lesion of the lower motor neuron by destroying the cell body in the anterior gray column or its axon in the anterior root or spinal nerve.
Sign & Symptom of Lower Motor Neuron Lesion
The following clinical signs are present with lower motor neuron lesions:
- Flaccid paralysis of muscles supplied.
- Atrophy of muscles supplied.
- Loss of reflexes of muscles supplied.
- Muscular fasciculation. This is twitching of muscles seen only when there is the slow destruction of the lower motor neuron cell.
- Muscular contracture. This is a shortening of the paralyzed muscles. It occurs more often in the antagonist muscles whose action is no longer opposed to the paralyzed muscles.
- The reaction of degeneration. Normally innervated muscles respond to stimulation by the application of faradic (interrupted) current, and the contraction continues as long as the current is passing. The galvanic or direct current causes contraction only when the current is turned on or turned off. When the lower motor neuron is cut, a muscle will no longer respond to interrupted electrical stimulation 7 days after nerve section, although it still will respond to direct current. After 10 days, the response to direct current also ceases. This change in muscle response to electrical stimulation is known as the reaction of degeneration.
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