ALS is best described as degeneration of which neural structures?

• A. Only upper motor neurons
• B. Only lower motor neurons
• C. Both upper and lower motor neurons
• D. Sensory neurons

Answer: (C)

ALS involves degeneration of both upper motor neurons, located in the motor cortex and forming the corticospinal tract, and lower motor neurons, the anterior horn cells in the spinal cord and motor nuclei in the brainstem. This dual loss explains the mixed clinical signs: spasticity and brisk reflexes from the upper motor neuron component, along with weakness, muscle wasting, and fasciculations from the lower motor neuron component. Sensory pathways are typically spared, so sensation remains relatively normal. Hence, the description that fits ALS best is degeneration of both upper and lower motor neurons.