Final answer:
The dorsal columns and Lissauer's tract of the spinal cord are spared in a complete occlusion of the anterior spinal artery because they are located posteriorly and are supplied by the posterior spinal arteries.
Step-by-step explanation:
In the case of a complete occlusion of the anterior spinal artery, the areas of the spinal cord that are typically spared are the dorsal columns and Lissauer's tract (also known as the posterolateral tract). The dorsal column system is responsible for carrying information about touch and proprioception and crosses the midline in the medulla, while the spinothalamic tract, which is primarily responsible for pain and temperature sensation, crosses the midline at the spinal cord level where it enters. The dorsal column and Lissaeur's tract are located posteriorly and receive their blood supply from the posterior spinal arteries, so they are not usually affected by anterior spinal artery occlusion.
The anterior spinal artery provides blood to the anterior two-thirds of the spinal cord, including the anterior and lateral corticospinal tracts, which are involved in the motor function. These areas would be affected by an occlusion, leading to potential motor deficits. Nonetheless, as both the left and right anterior corticospinal tracts lie adjacent to each other, it is unlikely that a spinal cord trauma would result in the damage of one anterior column while completely sparing the other.