The cervical spine begins just below the skull and extends down to about shoulder level. It contains the first seven vertebrae of the spine. These vertebrae are smaller and more mobile than those in the rest of the spine.
The cervical spine is unusual in another way as well. Unlike the rest of the spine, the vertebrae of the cervical spine contain openings that allow arteries to pass through and carry blood to the brain.
The first two segments at the top of the cervical spine, called the atlas and the axis, are shaped differently than the other vertebrae. The atlas (first vertebra) is more like a ring, and the axis (second vertebra) has a bony knob on top. The knob of the axis pivots in the atlas, allowing the neck to rotate. The next five vertebrae also provide large degrees of motion, but it is primarily side-to-side bending.
Neck motions fall into four categories: rotation (side-to-side movements), flexion (chin-to-chest movements), lateral flexion (ear-to-shoulder movements), and hyperextension (looking up). These motions are made possible by the coordinated action of a series of muscle groups.
When muscles are the cause of neck pain, there is a good chance that the origin is the trapezius muscle, the sternomastoid muscle, or the scalene muscles. The trapezius is a flat, triangular muscle that covers the upper and back part of the neck and shoulders. The sternomastoid (also called the sternocleidomastoid) muscle and the three muscles known collectively as the scalene muscle group run along the side of the neck.