ALS involves degeneration and death of which neurons?

• A. Upper motor neurons
• B. Lower motor neurons
• C. Both upper and lower motor neurons
• D. Peripheral nerves

Answer: (C)

ALS involves degeneration of both upper and lower motor neurons. The upper motor neurons start in the motor cortex and send signals down the corticospinal tract to the lower motor neurons located in the brainstem and spinal cord. When both populations are affected, you get a mix of signs: upper motor neuron features like increased muscle tone and brisk reflexes, and lower motor neuron features such as weakness with muscle wasting and fasciculations. Sensation is typically relatively preserved early on because the sensory system is not primarily targeted in ALS, which helps distinguish it from other neuropathies that affect peripheral nerves.