Poliovirus-induced paralysis is caused by destruction of motor neurons in which part of the spinal cord?

• A. The anterior horn of the spinal cord.
• B. The posterior horn of the spinal cord.
• C. The dorsal root ganglia.
• D. The white matter of the spinal cord.

Answer: (A)

Poliovirus causes paralysis by destroying the lower motor neurons located in the anterior horn of the spinal cord. These anterior horn cells are the cell bodies of motor neurons that send impulses to skeletal muscles; when they’re damaged, you get flaccid paralysis with muscle weakness, atrophy, fasciculations, and reduced reflexes. The posterior (dorsal) horn contains sensory neurons and interneurons, so its destruction would lead to sensory problems rather than motor paralysis. The dorsal root ganglia are sensory neuron groups, and damage there would primarily affect sensation. The white matter contains nerve tracts, not the motor neuron cell bodies targeted by the virus.