An upper motor neuron injury typically results in what type of paralysis?

Upper motor neuron injuries are characterized by damage to the motor pathways that originate in the brain and terminate in the spinal cord. This type of injury disrupts the normal control over muscle activity, leading to specific manifestations. Spastic paralysis, which results from upper motor neuron lesions, is marked by an increase in muscle tone and exaggerated reflexes.

This occurs because the injury affects the pathways that inhibit reflex activity, resulting in increased excitability of the lower motor neurons. As a consequence, the affected muscles may become rigid and exhibit spasticity, causing muscle contractions and a lack of coordinated movement. It’s important to understand that this is distinct from flaccid paralysis, which is more commonly associated with lower motor neuron injuries wherein the muscle tone is decreased, and reflexes are diminished or absent.

While complete paralysis involves total loss of voluntary movement and partial paralysis pertains to the loss of strength in certain muscles, spastic paralysis specifically describes the hyperactive reflexes and increased muscle tone that define upper motor neuron damage. Therefore, spastic paralysis is the correct manifestation associated with upper motor neuron injury.