The vertebral column, commonly called the spine, is a stacked series of bones extending from the base of the skull down to the pelvis. This structure forms the central axis of the body, providing primary support and allowing for movement. The uppermost portion is the cervical spine (C-spine), located in the neck. This region bears the weight of the head, which averages between 10 and 13 pounds, and provides the flexibility necessary for the wide range of head motions.
Understanding the Cervical Vertebrae
The cervical spine consists of seven individual bones, known as vertebrae, labeled C1 through C7. This numbering system starts at the base of the skull, with C1 being the highest, and proceeds downward to C7. Medical professionals rely on this standardized naming convention for accurate diagnosis and localizing damage or pain.
Cervical vertebrae are structurally distinct from the larger bones of the thoracic (mid-back) and lumbar (lower back) regions. They have smaller vertebral bodies because they carry less weight than the lower spinal segments. A unique characteristic is the presence of transverse foramina, small holes in the bone. These openings function as a protective passageway for the vertebral arteries, which carry blood flow up to the brain.
Specific Location of C5, C6, and C7
The C5, C6, and C7 vertebrae are located in the lower portion of the neck, forming the final segments of the cervical curve before the spine transitions into the upper back. C7 is often the easiest to locate through the skin because of its shape. This vertebra is known as the vertebra prominens because its spinous process, the bony projection on the back, is the longest and most prominent in the neck.
To find this segment, a person can feel the back of their neck where it meets the shoulders; the largest bump felt there is typically the C7 vertebra. The C5 and C6 vertebrae are situated immediately superior to C7. This lower cervical segment is a crucial transition zone between the mobile upper neck and the rigid thoracic spine, which begins with the T1 vertebra. The C5, C6, and C7 segments are similar in structure, having more classic features than the specialized C1 and C2 vertebrae above them.
Nerve Roots and Movement Control
The functional importance of the C5, C6, and C7 segments stems from the spinal nerve roots that exit the spinal cord at these levels. These nerve roots are components of the brachial plexus, a complex network of nerves that sends motor and sensory signals to the shoulder, arm, and hand. Each nerve root controls specific muscle groups, and injury at a particular level can result in predictable deficits in movement or sensation.
C5 Nerve Root
The C5 nerve root primarily influences the shoulder and upper arm, providing motor control to the deltoid and biceps muscles. Its function allows the ability to raise the arm out to the side (shoulder abduction) and to bend the elbow. The C5 nerve also transmits sensory information from the skin over the upper arm, extending toward the elbow.
C6 Nerve Root
The C6 nerve root contributes to both the biceps and the muscles that extend the wrist backward. It controls the ability to turn the forearm so the palm faces up (supination), as well as the reflex action of the biceps tendon. Sensations relayed by the C6 nerve are felt along the thumb side of the forearm and into the thumb.
C7 Nerve Root
The C7 nerve root is principally associated with the triceps muscle, which straightens the elbow, and the finger extensor muscles. This nerve controls the ability to push objects away from the body by extending the elbow joint. The sensory pathway for C7 runs along the back of the arm and terminates in the middle finger.