Understanding Your Spine
Simple Anatomy from the Michigan Spine Clinic
It is important to understand the shape and composition of the spine in order to understand the problems that may be causing you pain, numbness, tingling, or other symptoms in your back or in your extremities. The purpose of the spine is to support your upper body, neck, and shoulders. It allows you to stand up straight while also providing you with the flexibility to bend and twist. It is also responsible for protecting your spinal cord. It is one of the most important parts of your body. However, many demands are placed on the spine and over time, wear and tear from aging or damage from injuries can result in painful conditions affecting your everyday life.
Spine Segments and Curvature
The spine is made up of three larger segments: Cervical (the neck), thoracic (upper back), and lumbar (lower back) and two smaller segments: Sacrum and coccyx (tailbone). The cervical, thoracic and lumbar parts of the spine are composed of articulating vertebrae and when viewed from the side, these segments form “c-shaped” curves. It is these curves that allow us to stand upright and maintain balance. When these curves are too large or too small, there is a deformity in the spine. These spinal abnormalities are referred to as Kyphosis of the thoracic spine (“hunchback”) and Lordosis of the lumbar spine (“swayback”). Scoliosis is also a spinal abnormality. It is found when the spine forms an “S” or a “C” shape, rather than an “I” when viewing the spine from the front or back. The sacrum and coccyx are composed of vertebrae that are fused together and are not moveable.
The spine is made up of vertebrae that are stacked on top of one another. These bones form a canal that protects your spinal cord. There are 33 vertebrae in the spine. The upper or moveable part of the spine has 24 vertebrae. The cervical spine is made up of 7 small vertebrae that begin at the base of the skull and end at the upper chest. The thoracic spine is made of 12 vertebrae that start at the chest and end at the middle back. The vertebrae in the thoracic spine are also connected to the rib cage. There are 5 vertebrae in the lumbar spine. These vertebrae are larger in size as they carry more of your body’s weight. It is possible to have fewer or more vertebrae in one of these segments. In the lower part of the spine, 5 vertebrae are fused together to form the sacrum and 4 are fused to form the coccyx or tailbone.
The vertebrae are comprised of various parts that function to support and stabilize the spine while also providing protection for the spinal cord. The vertebral body bears most of the weight of the spine and serves as the attachment to the discs between each vertebra. The pedicles are the two “tube-like” projections connecting the vertebral body in the anterior (front) part of the spine to the posterior (back) part of the spine. The posterior vertebrae can be felt by pressing on your back. The “wings” or projections of the vertebrae are referred to as processes. The spinous process is the projection in the center of the vertebrae. The transverse processes come off of each side of the vertebrae and serve as an attachment to many muscles that help with bending, twisting, and standing still. Between these are small joints called facet joints. They allow you to move. It is possible for these joints to become sore and cause pain.
Spinal Cord and Nerves
The spinal cord is the center of your body’s nervous system and extends from the skull down to your lower back through the spinal canal. The space inside each vertebra acts as the tunnel through which the spinal cord travels. Nerves branch out from the spinal cord through the openings in the vertebrae and carry messages between the brain and the muscles. The spinal cord ends in the lower back and continues as nerve roots to the legs and feet. This is why symptoms such as pain, numbness, and tingling are often found in the arms and legs as a result of a spine condition.
Muscles and Ligaments
The muscles and ligaments that are attached to your spine provide support and stability for your spine as well as your upper body. Strong ligaments connect your vertebrae and help keep the spinal column in position.
Between each vertebra, in the moveable part of your spine, are intervertebral disks. They are flat and round and are about a half-inch thick. Each vertebral disk is made of two components: The nucleus pulpous, the jelly-like center of the disk that gives the disk flexibility and strength and the annulus fibrosus, the outer ring of the disk. These disks act as shock absorbers for the spine and help protect the vertebrae from becoming damaged. However, nerve endings supply the disks and as a result, an injury to the disk can cause pain.
On the posterior side of the vertebrae, between the spinous process and the transverse processes are facet joints. These joints, similar to your hip or knee joints, have a cartilage surface. They allow for the rotation of the spine. However, arthritis or wear and tear in the facet joint can be a source for back or neck pain.