Where does poliovirus primarily cause damage in the nervous system during paralytic disease?

• A. Cerebral cortex
• B. Anterior horn cells of the spinal cord and motor nuclei of the brainstem
• C. Basal ganglia
• D. Cerebellar Purkinje cells

Answer: (B)

Poliovirus in paralytic disease mainly targets motor neurons, specifically the anterior horn cells of the spinal cord and the motor nuclei of the brainstem. When these anterior horn neurons are damaged, signals from the brain can’t reach the muscles, producing the hallmark lower motor neuron signs: flaccid weakness, decreased or absent reflexes, and muscle atrophy, often with fasciculations. If brainstem motor neurons are involved, bulbar symptoms such as difficulty with swallowing or speech and sometimes respiratory compromise can occur.

In contrast, involvement of the cerebral cortex would tend to produce upper motor neuron signs with spasticity, and damage to the basal ganglia or cerebellar Purkinje cells would cause movement disorders or ataxia, which are not characteristic of classic paralytic poliomyelitis.