In poliovirus infection, motor neuron destruction occurs in which region of the spinal cord to cause paralysis?

• A. The anterior horn of the spinal cord.
• B. The hippocampus.
• C. The dorsal root ganglia.
• D. The cerebellum.

Answer: (A)

Poliovirus causes paralysis by destroying the cells that form the final common path for voluntary muscle movement—the motor neurons whose cell bodies reside in the anterior (ventral) horn of the spinal cord. These anterior horn cells project their axons out through the ventral roots to innervate skeletal muscles. When the virus damages these neurons, the affected motor units lose their neural input, leading to flaccid paralysis, reduced muscle tone, and diminished reflexes in the muscles served by those segments.

The dorsal root ganglia house sensory neuron cell bodies, so damage there would produce sensory changes rather than the motor paralysis seen with poliovirus injury. The hippocampus is involved in memory, and the cerebellum coordinates movement; lesions in those regions produce different signs such as memory issues or ataxia, not the LMN-type paralysis caused by anterior horn destruction.