Spasticity occurs from damage to which pathways?

• A. Extrapyramidal pathways
• B. Corticospinal tracts
• C. Peripheral nerves
• D. Spinocerebellar pathways

Answer: (A)

Spasticity comes from disruption of descending control over spinal reflex circuits. The extrapyramidal pathways, including brainstem tracts like the reticulospinal and vestibulospinal systems, normally set baseline muscle tone and modulate reflex activity. When these pathways are damaged, their inhibitory and modulatory influence on the spinal motor neurons is reduced, causing increased excitability of these neurons and a velocity-dependent resistance to passive movement—the hallmark of spasticity. Peripheral nerves and spinocerebellar pathways don’t produce this tone pattern, and while corticospinal (pyramidal) tract damage also contributes to upper motor neuron signs, the characteristic tone change described here aligns with extrapyramidal pathway disruption.