The cervical spine consists of the first seven vertebrae of the spine (C1-C7), starting at the base of the skull. This part of the spine provides support for the head, holding it above the shoulders via the neck, as well as providing the ability to rotate the head at the top of the spine. The vertebrae of the spine act as a protective bony sheath for the spinal cord, as well as nerves and blood vessels that branch off from the main vessels to and from the head. The cervical vertebrae are smaller than the vertebrae elsewhere in the spinal column, but they have the same bone structure as illustrated at Spine Universe and are protected by a vertebral disc between each, supported by ligaments, tendons and muscles.
Atlas and axis (C1 and C2)
An exception to the standard vertebrae structure is C1 and C2. The first two vertebrae at the top of the spinal column are unique in that they fit into one another. C1, called the atlas, is a ring that fits over the odontoid process of C2, called the axis (as shown in this image). However, this interlocking allows rotation of the head.
Physiology of C3-C7
The other five cervical vertebrae allow flexion and extension, as explained by Dr. Peter Ullrich of Spine-health. Most neck movements are controlled by C5-C7. Diseases or injury of the spine can cause fusion of the vertebrae, eliminating the capacity to move the head and neck. Neck pain is often caused by wear and tear on the vertebral disc cushioning the vertebrae.
Eight cervical nerves (also denoted as C1-C8) of the peripheral nervous system branch off from the spinal cord in the cervical spine. Each controls a different region of the upper body, including movement, sensory innervations, and body functions, though not every resource agrees on the exact control each exerts and their functions overlap. Nerves C1 and C2 control the head and neck. Nerve C3 controls the diaphragm, and thus the muscles involved in breathing. Nerve C4 controls the upper body muscles of the shoulders and chest, including the ribs and diaphragm for expansion and contraction during breathing. Nerve C5 controls the upper body muscles of the shoulders and arms, including the deltoids and biceps, and wrist extensors. Nerve C6 controls the wrist extensors and some innervation to the biceps. Nerve C7 controls the triceps. And finally, nerve C8 controls the hands.