Spasticity is primarily due to pathology in which tract?

• A. Basal ganglia
• B. Cerebellum
• C. Brainstem
• D. Corticospinal tract

Answer: (D)

Spasticity comes from injury to the corticospinal tract, the main pathway carrying voluntary motor commands from the cortex to the spinal cord and normally keeping spinal reflexes in check. When this upper motor neuron tract is damaged, its inhibitory influence on stretch reflex circuits at the spinal level is reduced. That leads to hyperexcitability of the reflexes and a velocity-dependent increase in muscle tone—classic upper motor neuron syndrome.

This pattern is most consistent with corticospinal tract pathology. Other motor regions influence tone differently: basal ganglia lesions produce rigidity and bradykinesia rather than the velocity-dependent spasticity; cerebellar lesions cause ataxia and coordination problems rather than increased, reflex-driven tone. While brainstem lesions can involve motor pathways, spasticity is best attributed to disruption of the corticospinal tract.