Deep tendon reflexes

A 24 year old man is brought to the physician because of a 3 day hsitory of progressive numbness of both feet that now has ascended to the level of his thighs. In the last 24 hours, he has developed numbness and tingling of his hands. Physical examination shows an ataxic gait. Deep tendon reflexes are diminished in the upper extremities and absent at the knees and ankles. Sensation to vibration and joint position is abent in the fingertips and feet bilaterally. There is mild weakness of the distal upper extremities and moderate weakness of the lower extremities. A process involving which of the following structures is the most likley explanation for these sensory findings? 1. Dorsal spinocerebellar tract 2. Faciculus cuneatus 3. Faciculus gracilis 4. Myelinated primary afferents 5. Unmyelinated primary afferents 6. Ventral spinocerebellar tract