What vessel is formed when the vertebral arteries unite in the skull?

When the vertebral arteries unite at the base of the skull, they form the basilar artery. This vessel plays a crucial role in supplying blood to the posterior part of the brain, including areas responsible for critical functions such as balance, coordination, and various autonomic responses. The basilar artery runs along the brainstem and eventually branches off to supply various regions of the brain, emphasizing its importance in cerebral circulation.

In contrast, the common carotid artery is a major artery supplying blood to the head and neck but is not formed by the union of the vertebral arteries. The Circle of Willis is an arterial structure that provides collateral circulation for the brain; it is not directly formed by the merging of the vertebral arteries. The internal jugular vein, on the other hand, is responsible for draining blood from the brain but is unrelated to the formation of any arterial structure from the vertebral arteries. Understanding the anatomical relationship and functions of these vessels highlights the significance of the basilar artery within the cerebral vascular system.