The 'back' is divided into:
1.) Cervical Spine (the neck) - The cervical spine starts at C1, the vertebrae which are located directly under your skull. There are 7 cervical vertebrae in most people. Symptoms in the neck can refer pain into the shoulders, into the mid-back, into the arms. Nerve irritation from the cervical spine can cause radiating pain, numbness or tingling into the shoulders, arms and/or fingers. Usually, this is in a very specific pattern.
2.) Thoracic Spine (the midback) - There are 12 Thoracic vertebrae in most people. The most common area's affected are thoracic ribs or between the shoulder blades (interscapular pain).
3.) Lumbar Spine (the low back) - There are 5 lumbar vertebrae in most people. Symptoms in the low back can refer into the flanks, the groin, the hips or into the legs. Nerve irritation from the low back can cause radiating pain, numbness or tingling into the legs, thighs, calves and/or toes. Again, this is usually in a very specific pattern. This is commonly known as Sciatica.
4.) Sacrum and Pelvis (tailbone and hips) - The Sacrum is also known as the tailbone and consists of usually five unfused vertebrae which begin to fuse between ages 16-18 and are usually completely fused into a single bone by age 26. The Pelvic bones are located on either side of the Sacrum. The joint between the Sacrum and the Pelvic bones is called the Sacroiliac joint. Intervertebral discs are found between each vertebra. The discs are flat, round structures about a quarter to three-quarters of an inch thick with tough outer rings of tissue called the annulus fibrosis that contain a soft, white, jelly-like center called the nucleus pulposus. Flat, circular plates of cartilage connect to the vertebrae above and below each disc. Intervertebral discs separate the vertebrae, but they act as shock absorbers for the spine. They compress when weight is put on them and spring back when the weight is removed. Joints between the bones in our spine are what allow us to bend backward and forward and twist and turn. The facet joints are a particular joint between each vertebral body that help with bending, twisting motions and rotation of the spine. The facet joints are part of the posterior elements of each vertebra. Each vertebra has facet joints that connect it with the vertebrae above and the vertebrae below in the spinal column. The surfaces of the facet joints are covered with smooth cartilage that helps these parts of the vertebral bodies glide smoothly on each other. There are five 5 muscle layers surrounding the spine which are the multifidi, rotators, erector spinae, iliocostalis, and quadratus lumborum. These muscles work synergistically to move and support the spine. Although bending forward at the waist doesn't look all that complicated, it is a highly complex sequence of events: the central nervous system (brain and spinal cord) coordinate the precise intensity and timing of contraction of each muscle group to make the spine move as intended. Other soft tissue structures involve ligaments, which restrict and control joint motion, tendons which attach muscle to bone, and joint capsules which surround joints and adding further stability and containing the lubricant, synovial fluid.