Overview of major regions supplied:
  • upper cervical spinal cord
  • brainstem and cerebellum
  • most of the thalamus and hypothalamus
  • cortex and deep white matter of the posterior medial parietal lobes, and medial and inferior temporal and occipital lobes
  • posterior part (splenium) of the corpus callosum
Diagrams  
The vertebral arteries usually arise from the subclavian arteries. They course through the cervical transverse foramina, run medially and ascend into the foramen magnum where they pierce the dura and enter the cranial cavity. The vertebral arteries run alongside the medulla, and give rise to vessels that participate in supplying the spinal cord as well as the brainstem.

Clinical Note: Cardiac emboli tend to enter the vertebral circulation far less frequently than they enter the carotid circulation. Several facts of vascular anatomy may account for this. Each vertebral artery takes off from the subclavian at a sharp angle, and has a much smaller diameter. By contrast, the internal carotid is about the same diameter as the common carotid, and makes only a slight bend at its origin. Finally, the vertebral basilar system handles only about 20% of the total cerebral blood flow, while the carotid system handles a much larger share.