The cervical spine (C-spine) forms the bony structure of the neck, consisting of seven vertebrae, numbered C1 through C7. This column connects the skull to the upper back, providing support and a wide range of motion. The numbering system begins at the top (C1) and ends at the base of the neck (C7), where it transitions into the thoracic spine. The C6 and C7 vertebrae and their associated nerve roots govern much of the function and sensation in the arms and hands.
Mapping the Location and Structure of C6 and C7
The C6 and C7 vertebrae are situated in the lower portion of the neck, acting as a transition point between the mobile upper cervical spine and the more stable thoracic region. C7 is known as vertebra prominens due to its distinct, long spinous process that protrudes toward the skin at the back of the neck. This prominent bump is the most easily felt bony landmark when running a finger down the back of the neck.
The C6 vertebra is located immediately above C7. While similar, its spinous process is typically smaller and often has a bifid (split) end, unlike the non-bifid C7 process. These lower vertebrae feature larger bodies compared to those higher up, helping support the increasing weight of the head and neck. They also contain a transverse foramen, an opening that allows passage for the vertebral artery and veins, although the C7 foramen is often smaller.
The Functional Role of the C6 and C7 Nerve Roots
The spinal nerve roots exiting near C6 and C7 are responsible for motor control and sensation in specific areas of the upper limb. The C6 nerve root exits above the C6 vertebra, and the C7 nerve root exits above the C7 vertebra. These nerves contribute to the brachial plexus, a network that supplies the shoulder, arm, and hand.
The C6 nerve root is associated with elbow flexion (controlling the biceps muscle) and wrist extension. The sensory area (dermatome) covers the outer side of the forearm, extending into the thumb and index finger. Conversely, the C7 nerve root controls elbow extension (primarily the triceps muscle) and wrist flexion. The C7 sensory distribution runs down the back of the arm and forearm, terminating in the middle finger.
Key Conditions Affecting the C6-C7 Segment
The C6-C7 segment is a common site for degenerative changes and injury due to its location at the base of the neck. The intervertebral disc here absorbs significant shock and allows movement. Conditions that narrow the space around the nerve roots are the primary cause of C6 and C7 symptoms.
Disc herniation is a frequent cause of compression, occurring when the disc’s center pushes out through a tear. A protrusion between C6 and C7 typically presses on the C7 nerve root, causing inflammation. Cervical spondylosis (osteoarthritis) also affects this segment through bone spurs (osteophytes) that impinge on the nerve roots or spinal cord. Spinal stenosis, a generalized narrowing of the spinal canal, is another mechanism leading to nerve root compression.
Specific Symptoms Associated with C6/C7 Involvement
Irritation or compression of the C6 and C7 nerve roots produces cervical radiculopathy, commonly known as a “pinched nerve.” The resulting pain, numbness, and weakness follow the functional map of the affected nerve root.
C6 radiculopathy typically manifests as pain or tingling that radiates down the outside of the arm into the thumb and index finger. This condition is also characterized by weakness when attempting to bend the elbow or extend the wrist.
If the C7 nerve root is compressed, the pain and numbness follow the back of the arm and forearm, extending into the middle finger. Weakness associated with C7 involvement is most apparent in the triceps muscle, making it difficult to fully straighten the elbow. Recognizing these patterns helps determine which cervical level is the source of the nerve irritation.