Anatomy, Back, Cervical Vertebrae

Vertebrae, along with intervertebral discs, compose the vertebral column or spine. It extends from the skull to the coccyx and includes the cervical, thoracic, lumbar, and sacral regions. The spine has several major roles in the body that include: protection of the spinal cord and branching spinal nerves, support for the thorax and abdomen and allows for flexibility and mobility of the body. The intervertebral discs are responsible for this mobility without sacrificing the supportive strength of the vertebral column. The cervical region contains seven vertebrae, denoted C1-C7, which are the smallest of the vertebral column. The intervertebral discs, along with the laminae and the articular processes of adjacent vertebrae, create a space through which spinal nerves exit. The cervical vertebrae, as a group, produce a lordotic curve. While all vertebrae share most morphologic features, several notable features exist in the cervical region. Typical vertebrae consist of a vertebral body, a vertebral arch, as well as seven processes. The body bears the majority of the force placed on the vertebra. Vertebral bodies increase in size from superior to inferior. The vertebral body consists of trabecular bone, which contains the red marrow, surrounded by a thin external layer of compact bone. The arch, along with the posterior aspect of the body, forms the vertebral (spinal) canal, which contains the spinal cord. The arch consists of bilateral pedicles, cylindrical processes of bone that connect the arch to the body, and bilateral lamina, flat bone segments that form most of the arch, connecting the transverse and spinous processes. A typical vertebra also contains four articular processes, two superior and two inferior, which contact the inferior and superior articular processes of adjacent vertebrae, respectively. The point at which superior and articular facets meet is known as a facet, or zygapophyseal, joint. These maintain vertebral alignment, control the range of motion, and are weight-bearing in certain positions. The spinous process projects posteriorly and often inferiorly from the vertebral arch and may overlap the inferior vertebrae to various degrees, depending on the region of the spine. Lastly, the two transverse processes project laterally from the vertebral arch symmetrically. Typical cervical vertebrae have several features distinct from those typical of thoracic or lumbar vertebrae. The most notable distinction is the presence of one foramen in each transverse process. These transverse foramina encircle the vertebral arteries and veins. This is true of all cervical vertebrae except C7, whose transverse foramina contain only accessory veins. Another feature unique to the cervical vertebrae is the bifid spinous process (See “physiologic variants” section), which may increase the surface area for muscle attachment. The spinous process of cervical vertebrae increases as the spinal column descends. Cervical vertebrae tend to have superior articular facets that face posteromedially. Some studies have shown that more inferior cervical vertebrae have superior facets that face in a posterolateral direction – more akin to those of the thoracic region. Lastly, cervical vertebrae are known to have the greatest intervertebral disc height, which increases the range of motion.   There are three atypical vertebrae found in the cervical region. C1, also known as “atlas,” is unique among all vertebrae in that it lacks both a vertebral body and a spinous process. The relatively circular bone contains two bilateral masses that take the place of a body in its load-bearing capacity. The superior articular facets of these masses contact the occipital condyles of the skull, and the inferior facets articulate with superior facets of C2. C2, also known as “axis,” is distinct in that it contains bilateral masses to articulate with C1, a body through which weight is transmitted through C3 and below, and an odontoid process, or “dens,” on the superior aspect of the body. The dens articulates with the posterior surface of the anterior arch of C1. C7 may be considered typical or atypical but has two distinct features. The first is that, unlike the rest of the cervical vertebrae, the vertebral artery does not traverse the transverse foramen. The second is that it contains a long spinous process known as “vertebra prominens.”