The cervical spine, or neck, is the uppermost section of the vertebral column, providing support and mobility for the head. This region consists of seven individual bones, labeled C1 through C7, which protect the spinal cord that runs through their center. The C5 and C6 vertebrae form a functional unit. Understanding the location and role of this segment is important for anyone experiencing neck pain or arm symptoms.
Anatomical Placement of C5 and C6
The C5 and C6 vertebrae are situated in the lower half of the neck, with C4 positioned above them and C7 below. These bones are part of the cervical lordosis, the natural inward curve of the neck, which aids in shock absorption and balance. The C5-C6 segment allows for forward, backward, and side-to-side motion of the head and neck.
Each vertebra has a cylindrical body in the front and a protective arch in the back, forming the vertebral foramen where the spinal cord travels. Between the C5 and C6 bodies lies an intervertebral disc, a cushion composed of a tough outer ring and a gel-like center that provides flexibility and shock absorption. The bones are also connected by facet joints, which permit smooth, limited movement and help stabilize the spine.
Neurological Role of the C5-C6 Segment
The function of the C5-C6 segment is defined by the C6 spinal nerve root, which exits the spinal canal between the C5 and C6 vertebrae. This nerve root is composed of motor fibers (controlling movement) and sensory fibers (relaying sensation). The C6 nerve root is a component of the brachial plexus, the network of nerves that supplies the entire upper limb.
The motor function (myotome) associated with the C6 nerve root primarily governs the muscles responsible for elbow flexion and wrist extension. Weakness in the biceps muscle and the wrist extensor muscles is often tied to C6 nerve root signals. The sensory function (dermatome) of the C6 nerve root is responsible for sensation in the lateral forearm, the thumb, and the index finger.
Common Structural Issues Affecting C5 and C6
Due to its high mobility and load-bearing nature, the C5-C6 segment is highly susceptible to wear and tear, often leading to structural issues that impact adjacent nerves. Cervical spondylosis, or degenerative disc disease, is a common condition where the intervertebral disc loses height and hydration over time. This drying and stiffening can lead to instability and the formation of bone spurs (osteophytes) around the edges of the vertebrae.
A primary concern at this level is a cervical disc herniation, where the soft, gel-like center of the disc pushes through a tear in the outer ring. The C5-C6 level is one of the most common locations for this to occur in the neck. This protrusion can press directly on the C6 nerve root as it exits the spinal canal through the neural foramen. Furthermore, the narrowing of the spinal canal or the neural foramen due to bone spurs and disc changes is known as spinal stenosis, which also contributes to nerve root compression.
Specific Symptoms Associated with C5-C6 Impingement
When the C6 nerve root is compressed or irritated by a structural issue at the C5-C6 level, it causes a condition known as cervical radiculopathy. The most recognizable symptom is pain that radiates from the neck and shoulder down into the arm, forearm, and often into the hand, following the path of the nerve. Patients frequently describe this discomfort as a sharp, burning, or electric-shock sensation.
The sensory fibers of the C6 nerve root manifest symptoms as numbness or tingling, often described as a “pins and needles” feeling, that is felt specifically in the thumb and index finger. Motor impingement results in observable muscle weakness in the upper extremity. This weakness is typically noted when attempting to flex the elbow, such as when curling a weight, or when extending the wrist. These specific patterns of pain, sensory changes, and weakness help medical professionals confirm that the C6 nerve root is the source of the patient’s symptoms.