The transverse processes of each cervical vertebra have openings (called foramens, or foramina) to accommodate passage of the vertebral arteries. Rotation or tipping of the vertebrae can twist or put pressure on these arteries, reducing the flow of blood, as in a plastic garden hose; if you put a bend in it, you reduce or shut off the flow of water. The amount of blood passing through these vertebral arteries depends on the position of the upper cervical vertebrae in the neck.
