The spinal column is a complex, segmented structure providing support for the body and protection for the central nervous system. It is divided into distinct regions, with the cervical spine (C-spine) forming the neck and supporting the head’s weight. The C-spine consists of seven individual bones, called vertebrae, stacked vertically and separated by cushioned discs. This structure allows for a wide range of motion while safeguarding the spinal cord, which transmits messages between the brain and the rest of the body.
Exact Location of the C5-C6 Segment
The C5-C6 segment is located in the middle-to-lower portion of the neck. Cervical vertebrae are numbered C1 (beneath the skull) down to C7 (connecting to the thoracic spine). The segment is defined by the C5 vertebra, the C6 vertebra below it, and the intervertebral disc between them, often called the C5-C6 disc space.
This segment is part of the subaxial cervical spine, responsible for most neck movement, including flexion, extension, and rotation. The C5 and C6 vertebrae are larger than the upper cervical vertebrae, reflecting the need for greater structural support. Its location marks a transition point where the spine moves from a highly mobile upper section to a more stable lower section.
Essential Functions Controlled by C5 and C6
The C5-C6 segment is highly mobile and plays a significant role in the biomechanics of the neck and upper limbs. Due to its position, it is one of the most mechanically stressed areas in the cervical spine. The C5 and C6 spinal nerve roots exit here, carrying signals that control specific muscles and sensation in the arm and hand.
The C5 nerve root primarily controls the deltoid muscles, allowing for shoulder abduction (lifting the arm away from the body). It also contributes to biceps function and sensation over the upper outer arm. The C6 nerve root is responsible for elbow flexion (bending the arm) and wrist extension.
The C6 nerve supplies sensation to the thumb side of the forearm and hand, including the thumb and index finger. This nerve root is involved in the biceps and brachioradialis reflexes, which are tested to assess nerve pathway health. Together, the C5 and C6 nerve roots are components of the brachial plexus, the nerve network governing motor and sensory functions of the upper extremity.
Common Injuries and Resulting Symptoms
The high mobility and weight-bearing function make the C5-C6 segment a frequent site for degenerative changes and injury. Disc herniation is common here, often compressing the exiting C6 nerve root. This occurs when the soft inner material of the C5-C6 disc pushes through its outer wall, creating pressure on nearby neural structures.
Compression of the C6 nerve root often leads to cervical radiculopathy, characterized by symptoms that radiate away from the neck. Patients experience sharp or burning pain traveling down the arm into the thumb and index finger. Muscle weakness in the biceps and wrist extensor muscles is a motor symptom associated with C6 nerve root compression.
Beyond acute injury, the C5-C6 segment is susceptible to chronic issues like spinal stenosis and cervical spondylosis (osteoarthritis). These conditions involve the narrowing of the spinal canal or the growth of bone spurs (osteophytes) from the vertebrae. This can impinge on the nerve roots or the spinal cord. Symptoms of nerve compression include numbness and tingling along the specific C6 sensory distribution.