The spine or the vertebral column is a column normally composed of 33 vertebrae (bony segments forming the spine), of which 24 are articulated (3 sections in the upper portion) and 9 are fused (2 sections in the lower portion). Inside the spinal column is the spinal canal that houses and protects the spinal cord.
The spine is divided into five sections, namely: cervical (composed of 7 vertebrae), thoracic (12 vertebrae), lumbar (5 vertebrae), sacral (composed of 5 fused vertebrae), and coccygeal (4 fused vertebrae).
A typical vertebra is composed of two essential parts, namely: an anterior (front) arch called the vertebral body; and a posterior segment known as the vertebral neural arch wherein the vertebral foramen lies.
In between each of the vertebrae are discs (intervertebral discs) which serve as cushions or shock absorbers and also allow for a certain degree of movement between the vertebral bodies. There are also special joints known as facet joints between each of the vertebral bodies. These special joints enable the individual spinal vertebra to move and rotate with respect to each other.
The cervical spine is the neck section of the spinal column; and consists of the first 7 vertebrae (designated as C1, C2, C3, C4, C5, C6 and C7). It starts at the base of the skull and ends just above the first thoracic vertebra. This section of the spine contains eight pairs of cervical nerves (also abbreviated as C1 through C8). The cervical nerves C1 and C2 innervate the head and neck; C3 supplies the diaphragm; C4 supplies the upper body muscles (i.e. deltoids, biceps); C5 and C6 act as wrist extensors; C7 supplies the triceps; while C8 supplies the hands.
The cervical spine is shaped like an inverted “C” and is remarkably more mobile than either of the thoracic or lumbar section of the spine. In contrast to the other sections of the spine, the vertebrae in the cervical spine are smaller and contain special openings for the arteries that carry blood to the brain.
The firs two (C1 and C2) of the seven vertebrae in the cervical spine are known as the atlas and the axis. Because the atlas is the vertebra responsible for carrying the weight of the head, it was named after a mythical Greek god believed to carry the weight of the world on his shoulders. The atlas and the axis cervical vertebrae are distinct from the rest of the vertebrae because they are designed mainly for the purpose of rotation.
The cervical spine mainly acts to protect the spinal cord, support the skull and allow for various head movements, including side-to-side rotation and forward-backward flexion.
The cervical spine contains a complex network of ligaments, tendons and muscles, which helps support and stabilize this section of the spine. Ligaments act to restrict too much movement that could cause serious injury. Muscles contribute to the maintenance of spinal balance and stability and help facilitate movement by contracting or relaxing in response to nerve impulses coming from the brain.
The anterior arch of the atlas vertebra is thick while its posterior arch is thin. The axis lies just beneath the atlas and has a bony prominence called the odontoid process, which sticks out through the hole in the atlas. This mechanism is responsible for the head’s ability to turn from side to side.