The C2-through-C5 spinal motion segments are located in the middle portion of the cervical spine. They include 3 separate spinal motion segments: C2 C3, C3 C4, and C4 C5. Each segment consists of 2 adjacent vertebrae and the anatomical structures connecting them. These segments are less likely to experience degeneration and pain compared to segments lower in the cervical spine.
The adjacent vertebrae are connected in the back by a pair of facet joints that allow limited forward, backward and twisting motions. Articular cartilage enables the facet joints to move smoothly, while muscles, tendons, and ligaments help hold the vertebrae together. A strain or tear to any of these tissues can cause neck pain and stiffness.
Between the vertebrae is an intervertebral disc that provides flexibility and shock absorption. The disc is made up of a tough outer ring called the annulus fibrosus, which encapsulates a gel-like interior called the nucleus pulposus.
The spinal cord lies within the vertebral foramen, a space formed by the vertebral arch and vertebral body.
A spinal nerve branches out from the spinal cord and exits on each side through an intervertebral foramen. Each pair of nerves innervate a specific region of the body.
- The C3 spinal nerve typically innervates skin on parts of the neck and head. It also has a motor component that sends signals to various muscles, such as the lateral neck flexors.
- The C4 spinal nerve typically innervates skin on the shoulder and upper arm. It also sends signals to various muscles, such as the upper trapezius and levator scapulae.
- The C5 spinal nerve typically innervates skin on the upper arm. It also sends signals to various muscles, such as the deltoid and biceps.
- The C3, C4, and C5 nerves also help control the diaphragm for breathing.
Spinal conditions including disc herniation or facet joint osteoarthritis may irritate one or more of these spinal nerves and cause radicular pain, tingling, numbness, and/or weakness along the path of the nerve. If the spinal cord is compressed, it may cause pain and neurological deficits in the arms, legs, or anywhere below the level of compression.