The fifth and sixth cervical vertebrae, C5 and C6, are foundational components of the cervical spine. These structures support the head’s weight while providing the mobility necessary for daily activities. They are part of the seven cervical vertebrae (C1 through C7) that form the bony column protecting the upper spinal cord. C5 and C6 are important because they facilitate a large range of motion and house the nerve roots that control sensation and movement in the upper limbs.
Precise Anatomical Location
The C5 and C6 vertebrae are situated in the lower cervical spine, positioned just above C7, the last bone in the neck before the thoracic spine begins. C5 sits beneath C4, and C6 sits beneath C5, forming a continuous, stacked structure. This location places them within the subaxial spine, a region designed for both movement and stability.
Each vertebra consists of a vertebral body, the largest weight-bearing section, and a posterior vertebral arch that encloses the spinal cord. The C5 and C6 bodies are connected by an intervertebral disc. This disc has a tough outer ring and a soft, gel-like center that acts as a shock absorber, providing flexibility and smooth motion between the bones.
A distinguishing feature is the transverse foramen, a small hole on either side of the bone’s transverse process. This passageway allows the vertebral artery, which supplies blood to the brain, to ascend toward the skull. C5 and C6 also typically feature a bifid, or split, spinous process, which serves as an attachment point for neck muscles and ligaments. The structural design of this segment helps transition support toward the less mobile thoracic spine.
C5 and C6 Role in Neck Movement
The C5-C6 segment forms a motion unit that contributes significantly to neck mobility and postural balance. Facet joints, located at the back of the vertebrae, connect C5 to C6 and guide movement. These joints are covered in articular cartilage, allowing the vertebrae to glide smoothly during neck movements.
Flexion (bending the neck forward) and extension (bending backward) are substantially influenced by the C5-C6 segment. This area is highly active in the lower cervical spine, absorbing mechanical stress during these sagittal plane movements. C5-C6 primarily supports stability and the fundamental forward and backward tilting of the head.
Due to its high mobility and load-bearing function, the C5-C6 segment is susceptible to wear and tear. Degenerative changes, such as disc bulging or bone spurs, frequently affect this level. These structural changes can compromise the segment’s efficiency, leading to stiffness and reduced range of motion.
Nerve Roots and Corresponding Body Areas
The C5 and C6 vertebrae are associated with the C5 and C6 nerve roots, which exit the spinal column through openings called intervertebral foramina. The C5 nerve root exits above C5, and the C6 nerve root exits above C6. These roots form part of the brachial plexus, a complex network of nerves that controls the upper limb. They are responsible for both muscle movement (myotomes) and skin sensation (dermatomes) in the shoulder and arm.
C5 Nerve Root Function
The C5 nerve root primarily controls the deltoid muscle, responsible for lifting the arm (shoulder abduction). It also contributes to the biceps muscle. Sensory input from C5 supplies the skin over the shoulder and the upper outer arm.
C6 Nerve Root Function
The C6 nerve root is the dominant motor supply for the biceps muscle, controlling elbow flexion, and the wrist extensor muscles. Sensation from C6 supplies the skin along the outer forearm, extending to the thumb and index finger.
When a condition like a herniated disc or bone spur causes irritation or compression of the C5 or C6 nerve root, a person may experience radiculopathy. This manifests as weakness in the corresponding muscles, such as difficulty lifting the arm or bending the elbow. Sensory symptoms include pain, tingling, or numbness that radiates down the specific pathway of the nerve root, often traveling from the neck into the shoulder, arm, and hand.