The spine provides structure and support to the body. Without a spine, an individual would not be able to stand, bend or even move.
The spine is made up of block–shaped bones called vertebrae that are stacked on top of each other to form a column. At birth, a person typically has 33 vertebral bones. However, some vertebrae in the lower back fuse so that by adulthood there are 26 vertebrae. The spine is divided into several regions:
Cervical: seven vertebrae located in the neck
Thoracic: 12 vertebrae located in the upper back
Lumbar: five vertebrae located in the lower back
Below the lumbar vertebrae is the sacrum. This triangular bone makes up the back part of the pelvis. In children, the sacral spine begins as five vertebrae that eventually fuse into the single adult bone.
The sacral region also contains the coccyx (tailbone), which is at the bottom of the spine. The coccyx begins as several vertebrae, usually four, that fuse into one adult bone. The sacral region also contains the nerves that control bowel and bladder function and provide sensation to the pelvic area.
Intervertebral discs separate most of the vertebrae. These tough but elastic discs act as shock absorbers between the vertebrae, shielding the bones from the impact of activities such as jumping or certain forms of exercise. They degenerate as a person ages.
Ligaments and tendons also work together to connect bones to bones and bones to muscles. There are also a number of joints in the spinal column that connect the vertebrae and give the body flexibility to move.
The vertebral column is curved at various points to help align the head with a vertical line through the pelvis. The normal curve of the spine is shaped like an “S,” allowing the weight of the body to be evenly distributed.
The main purpose of the vertebral column is to support the weight of the head and trunk and to provide protection for the spinal cord. The spinal cord is an extension of the brain, and all information from the brain travels through the spinal cord to nerve fibers that stimulate the rest of the body. This pathway of information is necessary for bodily functions (breathing, heartbeat) sensations and movement.
Developmental problems, everyday stresses and sudden trauma can cause many spinal disorders. These include scoliosis, herniated discs, sciatica, arthritis, spinal stenosis, osteoporosis, fractures, spinal cord injuries and whiplash. Sometimes these conditions are minor, temporary or easily treated, but in other cases they can cause chronic pain and disability.
About spinal anatomy
Spinal anatomy includes bones, tendons, muscles, ligaments and nerves that promote a combination of strength and flexibility. It includes strong bones, flexible ligaments and tendons, large muscles and sensitive nerves.
The spine is one of the most important parts of the body as it provides strength and structure and protects the sensitive spinal cord. Also known as the vertebral or spinal column, the spine is made up of 24 block–shaped bones called vertebrae and two fused bones below them. The bones of the vertebral column are grouped into several categories:
Cervical spine (seven vertebrae)
Thoracic spine (12 vertebrae)
Lumbar spine (five vertebrae)
Sacral region (sacrum and coccyx)
At birth, there are usually 33 vertebrae. The sacrum includes five vertebrae that eventually fuse to one bone. The coccyx has three to five vertebrae (typically four) that fuse to one bone. Thus the approximately 33 vertebrae in an infant appear as 26 bones in an adult.
An intervertebral disc separates each of the vertebrae in most people, except the first and second cervical vertebrae. These discs are made up of tough, fibrous type of cartilage that is elastic. They act as shock absorbers between the vertebrae, cushioning the bones from the impact of activities such as jumping or certain forms of exercise. They also add stability to the spine while still allowing for movement between the bones. Each disc is made up of a core of jelly–like material (nucleus pulposus) surrounded by a covering of tough, fibrous material (annulus fibrosis). These discs begin degenerating in early adulthood.
Each vertebra is made up of a main body (ventral segment), and a smaller section called the vertebral or neural arch that includes structures called pedicles and laminae. These sections join together to form an open ring. At the vertebral arch, the vertebrae are joined to one another above and below by two zygapophysial joints, commonly known as Z or facet joints.
In the average male, the vertebral column measures 28 inches (71 centimeters [cm]). In women, the average is 24 inches (61 cm).
The vertebral column is normally curved at various points to help align the head with the pelvis. In the thoracic and sacral regions, the curves are concave anterior, meaning the spine curves forward and outward. An exaggeration of the thoracic curve is called kyphosis, or humpback, caused by conditions including osteoporosis. In the cervical and lumbar regions, the curves are convex anterior, meaning the spine curves inward. An exaggeration of the lumbar curve is called lordosis. Sideways curves are not part of the spine’s normal anatomy, and the condition is known as scoliosis.
The pelvic curve and the thoracic curve are known as primary curves, because they are the two curves that are present in a fetus. The cervical and lumbar curves are known as secondary (compensatory) curves, because they are developed after birth. The cervical curve develops once a child is able to hold the head up (3 to 4 months old) and to sit upright (9 months). The lumbar curve develops when the child begins to walk (12 to 18 months).
The sections of vertebral column include:
Cervical spine. This is located in the neck. It helps support the weight of the head and protects the brain stem and upper portion of the spinal cord. It includes seven vertebrae. The rotation of the cervical spine primarily comes from the top two segments of the cervical spine, the atlas and the axis, whereas flexion and extension movement (bending forward and backward) comes from the lower cervical vertebral segments. The cervical spine contains a convex curve (a backward C shape). It begins at the base of the skull and continues to the upper part of the back, joining the top of the thoracic spine. This cervical section of the spine is more flexible than other regions, allowing more fluid movement of the head and neck.
The cervical region is at risk for injury from sudden movements, such as whiplash. The vertebrae are smaller than those in the thoracic region and must support the weight of the head. In addition, there is limited muscle support in this small area.
Thoracic spine. The center portion of the spine located in the upper back. The rib cage attaches firmly at each level of the thoracic spine, providing stability and structural support to the upper back. In this way, the thoracic spine helps protect the heart and lungs. The thoracic spine contains a concave curve (C shape). This curve begins in the middle of the second thoracic vertebra and ends at the middle of the 12th thoracic vertebra.
Because this area of the upper back is not designed for motion, injuries to the thoracic spine are less common. In addition, the thoracic spine has larger vertebrae than the cervical and stronger muscles, allowing greater support and protection. Ribs are also attached to these vertebrae, giving additional support.
Lumbar spine. The lowest section of the spine located below the thoracic spine. The vertebrae in the lumber region are the largest in the spine. The lumbar spine contains a convex curve (backward C) similar to the cervical spine. It begins in the middle of the thoracic vertebra and ends at the base of spine. This curve is more marked in females than in males.
The lumbar region allows flexibility and strength in the spine. It is one of the most frequent areas for injury as it holds most of the body’s weight. People tend to place undo pressure on the lumbar region with lifting and twisting movements. Improper lifting or repetitive movements often cause lower back pain.
Sacral region. Just below the lumbar spine is the sacral spine or sacrum. The sacrum is a large triangle-shaped bone that makes up the back part of the pelvis. It connects the spine to the lower half of the body. The sacroiliac joints, which connect the sacrum to the pelvis, contain some of the strongest ligaments in the body. They are responsible for the stability and strength at the lower end of the spine.
Below the sacrum is the coccyx, more commonly known as the tailbone. It is the very bottom of the spine and marks the end of the spinal column. Most injuries in the sacral region occur where the lumbar and sacral regions connect. This area is subject to stress from many daily activities.
The vertebral column supports the body weight of the head and trunk, and provides protection for the spinal cord. It is primarily responsible for a person’s posture and contributes to the strength and flexibility of the body.
About the spinal cord
The spinal cord and the brain make up the central nervous system (CNS). The spinal cord relays information to and from the brain in the form of electrical signals that travel through nerve fibers between the brain and the rest of the body. This pathway of information is necessary for sensation, movement and autonomic functions such as heartbeat and bladder control. Any interruption in this process, such as that caused by traumatic injury or tumor, may result in loss of sensation, motor function or bodily functions.
The spinal cord is a delicate structure that closes to form a neural tube during fetal development. The entire CNS develops from the neural tube. The spinal cord itself usually extends down to the first lumbar vertebra and divides into several individual nerve roots.
Two spinal nerves extend out at each vertebral level. There are 31 pairs of these spinal nerves in the neck and back. In the part of the back where the spinal cord ends, a group of nerves called the cauda equina continue down. Compression of these nerves, a condition known as cauda equina syndrome, demands immediate medical attention. Left untreated, cauda equina syndrome can cause permanent neurological damage.
The spinal cord is encased in the spinal canal, which is formed by the alignment of the bones and ligaments of the spinal column. The spinal cord is covered with three membranes known as meninges. The tough outermost layer called the dura mater encloses the brain and spinal cord to prevent the protective cerebrospinal fluid from leaking into the central nervous system.
The epidural space is the region between the dura mater and the spinal canal. It is filled with tissues and vessels. Medications such as anesthetics and corticosteroids are sometimes injected into the epidural space to relieve pain and inflammation on nerve roots.
Disorders of spinal anatomy
Many disorders are associated with spinal anatomy. Some are congenital (present at birth). However, most are acquired, due more often to cumulative physical stress or aging than to sudden trauma. Disorders of the spine include:
Herniated disc. A frequently painful condition in which the cartilage of an intervertebral disc bulges through its protective covering and can press on a nerve. This causes pain that often begins in the back or neck and sometimes extends down a limb. Herniated discs are common causes of pinched nerves and sciatica.
Degenerative disc disease. A condition, associated with aging, in which the intervertebral discs deteriorate and can press upon nerves, causing pain.
Spinal stenosis. A narrowing of space inside the spine that causes compression of the spinal cord or nerve roots. It typically develops later in life as a result of degenerative changes in the spine that occur with aging.
Osteoporosis. A degenerative bone condition, associated with aging, that typically affects the spine and can involve vertebral fractures.
Whiplash and other causes of neck pain.
Facet (zygapophysial) joint pain. Pain in the joint between two vertebrae. Facet joints are one of the common sites of neck and back pain, especially after a whiplash injury.
Spinal cord injury (SCI). Most cases of SCI involve sudden trauma, such as from a motor vehicle accident, diving accident or gunshot wound, that dislocate or fracture vertebrae. Depending on the severity and location, SCI may cause permanent paralysis or result in a partial or nearly complete recovery of motor function and sensation.
Ankylosing spondylitis. A form of arthritis that primarily affects the spine.
Other forms of arthritis. Osteoarthritis often affects the spine. Rheumatoid arthritis sometimes restricts movement in the cervical spine. Reiter’s syndrome (reactive arthritis) often causes pain in the lumbar spine. Juvenile arthritis may affect the spine in children.
Paget’s disease. Skeletal disease in which bone is broken down and replaced with oversized but weakened tissue. This can compress the spinal cord or nerve roots, resulting in excruciating pain that may radiate down into the legs.
Meningitis. Inflammation of the meninges, the membranes that cover the spinal cord and brain. Viral or bacterial infections cause most cases of meningitis.
Spondylolysis. A stress fracture in a posterior vertebral area called the pars interarticularis. This usually affects the fifth (lowest) lumbar vertebra and is a common source of low back pain in school-age athletes but can affect anyone. Sometimes the damaged vertebra becomes so weak it slips out of place, a condition known as spondylolisthesis.
Scoliosis. An abnormal sideways curvature of the spine. Scoliosis is usually painless but can result in chronic back pain and other complications if left untreated.
Spina bifida. A birth defect in which part of the vertebral column fails to close. Many cases are caused by a deficiency of folic acid, a B vitamin. Surgery can often treat spina bifida. Some mild forms (spina bifida occulta) produce no symptoms and may never be identified.
Achondroplasia. Genetic disorder that slows the rate of bone formation during fetal development and in early childhood. Patients have a shortened stature, including a smaller spinal canal that pressures the spinal cord. This can cause severe back and leg pain and paralysis of the legs.
Neurofibromatosis. A genetic disorder that causes noncancerous (benign) tumors to develop on nerves in the eyes, ears, brain, spinal cord and limbs. Many cases are mild and do not require treatment. Neurofibromatosis may cause scoliosis.
Other tumors. Benign tumors or cancer, such as those of the spinal cord, meninges, brain or bones, may affect the spine.
Syringomyelia. Formation of a cyst (syrinx) within the spinal cord. MRI has improved early diagnosis of this disorder.
Ossification of the posterior longitudinal ligament. Occurs when calcium deposits turn fibrous tissue into bone on the ligament running up and down the spine inside the spinal canal. These deposits may cause pain if they press on the nerves of the spinal canal.
Skeletal fluorosis. Immobilization of the spine and joints due to high levels of fluoride in the body. This makes any kind of movement painful. Skeletal fluorosis usually results from long-term inhalation of industrial dusts or gases contaminated with fluorides, long-term consumption of water containing large amounts of fluoride and accidental ingestion of insecticides that contain fluoride. It is rare in the United States.
Questions for your doctor about spinal anatomy
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about spinal anatomy:
Which areas of my spine are most prone to injury?
Do I have any hereditary spinal conditions or anomalies?
How do age and osteoporosis affect my spine?
Does a physical examination indicate my spine appears to be in good health? Should I undergo any x-rays or other diagnostic tests?
How can I improve my posture and body mechanics?
Can exercise help maintain the health of my spine?
Are there other ways I can keep my spine healthy, such as eating a good diet, using safety equipment or not smoking?
Are there any exercises or activities I should avoid?
How can my spinal cord become injured?
What damage happens to my spine with whiplash?
How can I tell whether a spinal or back condition can be treated at home or if I need medical help?
When do I need therapy after whiplash or other trauma?
