The cervical spine, commonly known as the neck, represents the uppermost segment of the vertebral column. This complex structure is an arrangement of bones, soft tissues, and nerves that acts as a link between the head and the rest of the body. Its primary role is to support the weight of the human head, which averages between 10 and 13 pounds, and to allow for the wide range of motion necessary for sight and interaction with the environment. The cervical spine is composed of the first seven stacked bones, or vertebrae, designated from C1 at the skull base down to C7 at the top of the chest. This structural configuration protects the central nervous system pathway that extends from the brain.
Structural Components of the Cervical Spine
The bony architecture of the cervical spine is made up of seven distinct vertebrae, labeled C1 through C7, which are connected by specialized joints. The first two vertebrae have unique shapes and functions that facilitate most of the head’s mobility. The Atlas, or C1, is a ring-shaped bone that lacks a typical vertebral body and rests directly beneath the skull. It allows for the nodding motion of flexion and extension.
The Axis, or C2, sits directly beneath the Atlas and features a unique bony projection called the odontoid process, or dens. This dens extends upward into the ring of the Atlas, acting as a pivot point around which the Atlas rotates. This specialized articulation between C1 and C2 is responsible for approximately 50% of the neck’s side-to-side rotation. The lower five cervical vertebrae, C3 through C7, are structurally more similar to each other, featuring a vertebral body in the front and facet joints in the back. These vertebrae contribute to the remaining range of motion and form a protective central canal for the spinal cord.
Supporting Elements
Between the vertebral bodies, from C2 down to C7, are the intervertebral discs, which act as fibrocartilaginous shock absorbers. Each disc consists of a tough, flexible outer ring called the annulus fibrosus, which encircles a softer, gel-like inner core known as the nucleus pulposus. This structure allows the spine to absorb impacts from daily activities, like walking and running, while also providing enough space for the spinal nerves to exit. The discs are thicker on the anterior side, which contributes to the natural inward curve, or lordosis, of the cervical spine.
Stability is provided by a network of strong ligaments that connect the bones, resisting excessive or damaging movements. The anterior and posterior longitudinal ligaments, for example, run the length of the spine and help to prevent extreme forward and backward bending. Running alongside and branching out from the spinal cord are eight pairs of cervical nerves, labeled C1 through C8, which exit through small openings between the vertebrae. These nerves transmit motor signals to control muscles in the neck, shoulders, and arms, and sensory signals for sensation in the upper extremities. The phrenic nerve, formed by nerve roots C3, C4, and C5, controls the diaphragm, the primary muscle for breathing.
Primary Functions of the Neck
The cervical spine performs a dual role centered on protection and mobility. Its protective function involves encasing the spinal cord within the vertebral canal formed by the stacked vertebrae, safeguarding this delicate extension of the central nervous system from external forces. Additionally, the transverse processes of the C1 through C6 vertebrae contain small holes, known as transverse foramina, which provide a protected pathway for the vertebral arteries. These arteries are a major source of blood supply to the brain.
The second primary function is to provide a wide range of motion for the head, allowing humans to orient their senses toward the world. The neck is capable of significant movement in multiple directions, including tilting the head forward (flexion) and backward (extension), lateral bending from side to side, and rotation. The cervical spine can achieve approximately 80 to 90 degrees of total rotation to each side, with roughly half of that motion occurring at the C1-C2 joint. This high degree of flexibility, supported by the surrounding muscles, is necessary for navigating the environment and maintaining visual focus.