What do the vertebral arteries unite to form?

The vertebral arteries are critical components of the brain's vascular supply and play a significant role in cerebral circulation. As they ascend through the neck, the vertebral arteries travel alongside the cervical spine and enter the skull, where they converge. This junction of the two vertebral arteries creates the basilar artery.

The basilar artery is vital because it supplies blood to key areas of the brain, including the brainstem and the cerebellum. It is formed by the union of the two vertebral arteries at the base of the skull and serves as the main conduit for blood flow to the posterior circulation of the brain.

Understanding this anatomy is essential for comprehending how blood circulation in the brain is organized, particularly in the context of neurological health and diseases. The other options provided do not accurately represent the anatomical outcome of the union of the vertebral arteries. For instance, the anterior and middle cerebral arteries are branches arising from the internal carotid artery and thus are not formed by the vertebral arteries. The Circle of Willis is an arterial circle that connects the anterior and posterior circulations of the brain, but it is not directly formed by the union of the vertebral arteries. Hence, the formation of the basilar artery is the correct response to the