Q. A 65 year-old man presents to the clinic due for progressive difficulties with walking. He notes that 1 year ago, he could run 2 miles. Currently, he is wheelchair dependent. He also notes bilateral hand weakness, troubles swallowing, exertional shortness of breath, and muscle twitches. He has lost 50 pounds within 1 year. He denies any sensory deficits. On physical exam, his strength is 1/5 in his lower extremities and 3/5 in his upper extremities. He has generalized muscle atrophy and fasciculations. He had reduced reflexes. His sensation is intact. Which of the following spinal cord tracts is most likely affected in this patient?