The human spinal column is composed of 33 bones, or vertebrae, that are grouped into distinct regions. The uppermost region, located in the neck, is known as the cervical spine and consists of seven vertebrae, numbered C1 through C7. The letter “C” simply stands for cervical, and the numbering system proceeds sequentially from the base of the skull downward. C5, C6, and C7 represent the lower portion of this cervical section, acting as a transitional zone between the highly mobile upper neck and the more stable upper back. These three vertebrae are structurally similar to one another, forming the subaxial spine along with C3 and C4. They support the weight of the head while allowing for extensive head and neck movement.
Pinpointing the Location in the Neck
The C5, C6, and C7 vertebrae are situated in the lower half of the neck, directly above the first bone of the thoracic spine, T1. This segment is often referred to as the lower cervical spine, marking the area where the neck transitions into the torso. A key landmark is the C7 vertebra, commonly called the vertebra prominens because its spinous process is usually the most prominent bump felt at the base of the neck.
The bony structures are defined by their vertebral bodies, separated by intervertebral discs that function as shock absorbers. The C5-C6 and C6-C7 discs cushion movement between the adjacent vertebrae. This unit is reinforced posteriorly by facet joints, which guide the range of motion and allow for forward, backward, and twisting motions of the neck.
These lower cervical vertebrae are the smallest of the true vertebrae but bear a significant load. The C3 through C7 vertebrae have a more typical structure compared to the specialized C1 (atlas) and C2 (axis) vertebrae. The C5-C7 segment provides attachment points for numerous muscles and ligaments necessary for stabilizing the head and coordinating neck posture.
Motor and Sensory Functions Controlled by C5-C7
The C5, C6, and C7 spinal nerves exit the spinal column near their corresponding vertebrae and form the brachial plexus, the network of nerves responsible for motor and sensory function in the shoulder, arm, and hand. The nerve roots from this segment control specific groups of muscles, known as myotomes, and supply sensation to defined areas of skin, called dermatomes. Understanding these links is fundamental to assessing nerve health in the upper extremity.
The C5 nerve root primarily controls the myotome for shoulder abduction, which is the action of lifting the arm away from the side of the body, largely involving the deltoid muscle. The sensory function, or dermatome, of C5 provides sensation to the skin over the lateral aspect of the upper arm down to the elbow. This nerve root also contributes to elbow flexion, along with C6.
C6 Nerve Root
The C6 nerve root innervates the myotome that controls elbow flexion, involving the biceps muscle, and wrist extension. The sensory distribution of C6 extends down the thumb side of the forearm and hand, including the thumb and index finger.
C7 Nerve Root
The C7 nerve root controls the myotome for elbow extension, primarily through the triceps muscle, as well as wrist flexion. Its dermatome supplies sensation to the skin on the back of the arm and into the middle finger.
Common Conditions Affecting This Spinal Segment
The C5-C7 segment is a common site for degenerative changes and injury due to the high degree of movement and stress it endures. A frequent consequence of problems in this area is cervical radiculopathy, which is the term for symptoms that result from the compression or irritation of a cervical nerve root. This compression can lead to pain, tingling, numbness, or weakness that radiates along the dermatomal and myotomal patterns associated with the affected nerve.
Disc herniation frequently affects the intervertebral discs in this region, particularly at the C5-C6 and C6-C7 levels. A herniated disc occurs when the soft, inner material pushes through the tough outer layer, potentially pressing on a nearby nerve root. Herniation at C5-C6 typically affects the C6 nerve root, while herniation at C6-C7 most often affects the C7 nerve root.
Another condition is spinal stenosis, which involves the narrowing of the spinal canal or the foramina, the smaller openings where the nerve roots exit. This narrowing is often caused by the wear and tear of aging, such as bone spurs or bulging discs. Foraminal stenosis in the C5-C7 area directly reduces the space for the C5, C6, or C7 nerve roots, causing irritation or pinching. Degenerative changes affecting the uncovertebral joints also contribute to nerve root impingement in this lower neck segment.