The spinal system contains not just bones, but also nerves and muscles. The function of the bony components of the spine is to protect the spinal cord and nerve roots that are contained within the spinal canal and provide a site of attachment for muscles and ligaments. Movement of the spine is controlled by the contraction of the muscles which attach to the spine.
The spine has three curves. The upper (cervical) and lower (lumbar) portions both have a lordotic or c-shaped curve. The middle (thoracic) segment has a kyphotic or reverse c-shaped curve.
The cervical spine is in the neck. It consists of 7 vertebrae. The first vertebra is a ring which the skull sits on. Most flexion and extension movement occurs between the skull and C1. The second vertebra is a block of bone with a peg sticking upward inside the ring of C1. The articulation between C1 and C2 is where most rotation movement of the neck occurs. The remaining 5 vertebrae in the cervical, thoracic and lumbar spine are rectangular blocks of bone.
Discs are shock absorbing structures that are located between each vertebrae throughout the spine (except between C1 and C2 where there is no disc.) The vertebrae and discs form front of the spine, also called the anterior column.
Pedicles are pillars of bone that join the vertebrae in front to the arch of bone at the back of the spine. The arch of bone at the back of the spine consists of 2 lamina which form a roof over the spinal canal and spinous processes that project backward. Muscles and ligaments attach to the spinous processes and lamina to control movement of the spine.
The second part of the spine is the thoracic spine which consists of 12 vertebrae all of which have ribs attached. The third and lowest portion of the spine is the lumbar spine which consists of 5 vertebrae. The lumbar spine attaches to the sacrum which is part of the pelvis.
The spinal canal is the area enclosed in bone that contains the spinal cord and nerve roots. The posterior arch also has 2 joints called zygapophyseal or facet joints. The structure of the spine allows some forward bending (flexion), backward bending (extension) lateral or side bending and rotation or twisting movements. It also prevents translational movements between the vertebrae.