What about the spinal cord--isn't it also nourished by vertebral branches?
Vascular disease in the spinal cord is uncommon. Unlike arteries in the brain, spinal arteries are not particularly susceptible to atherosclerosis or embolization. However, infarction of the spinal cord can occur after aortic replacement or when a dissecting aneurysm of the aorta blocks radicular vessels. Collateral arteries supplying the spinal cord vary in size, and a catastrophic drop in blood pressure may result in ischemia in vulnerable segments (those at mid-thoracic levels are especially at risk). This is the spinal equivalent of a border zone infarct in the cerebral hemispheres.

When the anterior spinal artery is blocked, there is bilateral paralysis and a deficit in pain sensation below the level of the lesion. However, joint position and vibratory sensations are spared since the posterior columns and neighboring white matter are supplied by the smaller posterior spinal arteries.