The vertebral arteries finally join near the pontomedullary junction (where the rostral medulla and caudal pons meet) to form the single basilar artery. Click here to see if you can identify the arteries of the posterior circulation. These two arteries join and descend along the anterior spinal cord.įIGURE 2. Roughly less than 1cm before joining, the vertebral arteries give rise to a final pair of vessels: the anterior spinal arteries. The PICA play a significant role in balance by supplying the lateral medulla (where the vestibular nuclei reside) and the entire posterior and inferior parts of the cerebellum (via the inferior vermian and tonsillar-hemispheric branches). The bottom of figure 2 shows the right and left PICA branching from the right and left vetebral arteries. Just after entering the cranial space, the right and left vertebral arteries give rise to the right and left posterior spinal arteries, which travel down the posterior spinal cord (not pictured in figure 2).Īpproximately 1-2cm before the vertebral arteries join they give rise to the posterior inferior cerebellar arteries (PICA). The vertebral arteries ascend via the cervical vertebrae and enter the cranium through the foramen magnum (literally the "big hole" where the spinal cord enters the skull). Although not classically considered part of the vertebral-basilar system, it is important to note these vessels because of a germaine condition discussed later called the " Subclavian Steal Syndrome." Subclavian simply refers to the arteries' position beneath/behind the clavicle ("collar bone"). These are the first branches of the subclavian arteries (see figure 1). The posterior circulation, or vertebral-basilar system, traditionally begins with the right and left vertebral arteries.
More appropriately for a balance and dizziness discussion, this page focuses on the posterior structures of the central nervous system and the posterior circulation. The anterior structures of the brain are supplied by the carotid arteries, and will not be covered here. Arterial Supply to the Structures of Balance Posterior Circulation 1