The vertebral column is a flexible column, formed by a series of bones called vertebrae. It is part of the axial skeleton and consists of seven cervical, 12 thoracic, five lumbar, five sacral, and four coccygeal vertebrae. Its major function is to enclose and protect the spinal cord and provide structural support to the head and trunk.
Description
The vertebral column—or spinal column—is composed of a series of 33 separate bones known as vertebrae. It is located in the trunk of the body and extends from the base of the skull to the pelvis. It belongs to the axial skeleton, meaning that portion of the skeleton associated with the central nervous system that also includes the bones of the cranium, ribs, and breastbone. The vertebral column consists of seven cervical—or neck—vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae, followed by the sacrum, composed of five fused vertebrae, and by four coccygeal vertebrae which are sometimes fused together and called the coccyx. The coccyx—or tailbone—is the last bone of the vertebral column.
Vertebrae are stacked on top of one another from the first cervical vertebra, called C1 or the atlas, to the sacrum. Only the first 24 vertebrae are considered movable. Both the superior and inferior surfaces of each vertebra are covered by a thin layer of cartilage joined to disk-shaped pads of fibrous cartilage, called intervertebral disks, that cushion the vertebrae and stabilize the vertebral column while allowing it to move. Each disk has a jelly-like core, the nucleus pulposus surrounded by a ring of tough fibrous tissue, the annulus fibrosus. The vertebrae are also bound together by two strong ligaments running the entire length of the vertebral column and by smaller ligaments between each pair of connecting vertebrae. Several groups of muscles are also attached to the vertebrae, providing additional support as well as movement control. The length of the vertebral column depends on the height of the vertebrae and the thickness of the intervertebral disks.
There are four normal curvatures in the vertebral column of the adult that align the head with a straight line through the pelvis. In the region of the chest and sacrum, they curve inwards and each is known as a kyphosis. In the lower back and neck regions, they curve outward and each is known as a lordosis.
All vertebrae have common features. A typical vertebra consists of two parts: an arch that encloses an opening called a vertebral foramen; and a body. Since the vertebrae are all stacked on top of one another, the foramina form the vertebral canal that houses the spinal cord from which the spinal nerves emerge. The body of a vertebra is a round, stocky part on the surface of which the inter-vertebral disk lies and it has two projections, called pedicles, that connect around the foramen to similar bony projections on the arch called facets. Besides enclosing the foramen with its facets, an arch also has three bony spikes, a spinous process located directly opposite the body and two transverse processes on each side of the foramen. These bony elements serve as important sites of attachment for deep back muscles. There are also differences between vertebrae, depending on their location in the column:
The cervical vertebrae. The seven cervical vertebrae are numbered C1 to C7. Together, they make up the bony axis of the neck. Typical cervical vertebrae have large vertebral foramina, and oval-shaped vertebral bodies. They are the smallest vertebrae of the column, but their bone density is higher than that of all the other vertebrae. The transverse processes of the cervical vertebrae are special because they also contain transverse foramina, which are passageways for arteries leading to the brain. The two first cervical vertebrae are special, because they provide a seat for the head. C1 directly supports and balances the skull. It has practically no body and looks like a ring with two transverse processes. On its upper surface, C1 also has two kidney-shaped facets that link it to the skull. The other special cervical vertebra is C2. It forms an axis which bears a tooth-like odontoid process on its body. This bony spike projects upward and lies in the ring of C1. As the head is turned from side to side, C1 thus pivots around the odontoid process of C2.
The thoracic vertebrae. The thoracic vertebrae are numbered T1 to T12 and are located in the chest area. They are larger than the cervical vertebrae. They have round foramina and long, pointed spinous processes that slope downward. Thoracic vertebrae have a unique feature, additional facets on the sides of their bodies that join them with the ribs. Starting with T3 and moving down, their bodies increase in size.
The lumbar vertebrae. The lumbar vertebrae are numbered L1 to L5. They feature large, massive bodies, triangular foramina, and robust spinous and transverse processes. Their facets are oriented so as to favor a wide range of bending flexibility. Lumbar vertebrae also contain small extra bony processes on their bodies that serve as sites of attachment for back muscles.
The sacrum. In the adult, the sacrum consists of five vertebrae that are fused together. It has a characteristically wide body curved upon itself and a triangular foramen. It is shorter and wider in the female than in the male. It links with L5 above and the coccyx below and it articulates on each side with the bones of the pelvis forming the sacroiliac joints with the iliac bones on either side. In addition to its characteristic shape, it contains two additional foramina through which spinal nerves pass.
The coccyx. The tailbone is a small triangular bone consisting of four fused rudimentary vertebrae. The number of coccygeal vertebrae may be five or three. They all lack pedicles and spinous processes, but a primitive body and transverse processes can be recognized in each of the first three vertebrae. The last vertebra is a mere small nodule of bone.
KEY TERMS
Annulus fibrosus—Peripheral ring of fibrous tissue in an intervertebral disk.
Atlas—The atlas is the first cervical vertebra, C1, the one upon which the base of the skull rests. Along with C2, it provides the pivot assembly around which the skull rotates.
Axial skeleton—The skeleton associated with the central nervous system and that consists of the cranium, all the bones of the vertebral column, the ribs, and the sternum. Those portions of the skeleton not associated with the central nervous system are associated with the appendicular skeleton or the skeleton of the extremities, such as the arms and legs.
Central nervous system (CNS)—One of two major divisions of the nervous system. The CNS consists of the brain, the cranial nerves and the spinal cord.
Cervical vertebrae—The seven vertebrae of the neck.
Coccyx—The last bone of the vertebral column just below the sacrum, also called the tailbone.
Condyle—A rounded enlargement that has an articulating surface.
Foramen—A hole in a bone usually for the passage of blood vessels and/or nerves.
Foramen magnum—Large opening at the base of the skull that allows passage of the spinal cord.
Ilium—The upper and largest part of the bony pelvic girdle, also called the iliac wing.
Intervertebral disk—Disk-shaped pads of fibrous cartilage interposed between the vertebrae of the vertebral column that provide cushioning and join the vertebrae together.
Nervous system—This is the entire system of nerve tissue in the body. It includes the brain, the brain-stem, the spinal cord, the nerves and the ganglia and is divided into the peripheral nervous system (PNS) and the central nervous system (CNS).
Nucleus pulposus—Jelly-like core of an intervertebral disk.
Pelvis—The basin-shaped cavity that contains the bladder and reproductive organs of the body.
Process—A general term describing any marked projection or prominence on a bone.
Sacroiliac joints—Joints that allow the sacrum and the ilium to articulate.
Sacrum—The triangular-shaped bone found between the fifth lumbar vertebra and the coccyx. It consists of five fused vertebrae and it articulates on each side with the bones of the pelvis (ilium), forming the sacroiliac joints.
Skull—All of the bones of the head.
Spinal cord—Elongated part of the central nervous system (CNS) that lies in the vertebral canal of the vertebral column and from which the spinal nerves emerge.
Vertebra—Flat bones that make up the vertebral column. The spine has 33 vertebrae.
Vertebral canal—Hollow part of the vertebral column formed by the vertebral foramina of all vertebrae. It encloses the spinal cord.
Vertebral foramen—The opening formed in vertebrae that allows passage of the spinal cord.
Function
The vertebral column has several major functions. It protects the sensitive spinal cord, which it encloses. It functions as a strong and flexible rod that allows movement of the trunk. It supports the head and acts as a pivot. It is also a point of structural attachment for the ribs.
Role in human health
The vertebral column plays a major protective role in human health because it encloses the spinal cord, that delicate bundle of nerve tissue which carries nerve impulses between the brain and the rest of the body. The vertebral column also plays another important role, not only in providing structural support for the chest, but also in maintaining the posture of the body and in locomotion.
Common diseases and disorders
Injuries to the vertebral column are common and are usually caused by one of three types of severe pressure:longitudinal compression, hinging, or shearing. Longitudinal compression usually occurs as a result of a fall from a height, and it crushes one vertebra lengthwise against another. Hinging can occur in whiplash injuries: it subjects the vertebral column to sudden and violent acceleration and recoil motions. Shearing, which can occur when a person is knocked over with great force, combines both hinging and twisting forces. Any of these forces can dislocate the vertebrae, fracture them, or rupture the ligaments that bind them together. Damage to the vertebrae and ligaments usually causes severe pain and swelling in the injured area. In severe cases, the spinal cord may be affected as well, and thus sensory and/or motor nerve functions. Other common disorders and diseases of the vertebral column include:
Degenerative disc disease (DDD). DDD affects the vertebral discs. As each disc is under constant pressure during flexion and extension of the vertebral column, the discs begin to wear and tear with age.
Discitis. Discitis, or disc space infection, is an inflammation of the intervertebral disc that occurs in adults but more commonly in children. Its cause is believed to be infectious.
Facet joint syndrome. The facet joints can get inflamed following injury or arthritis and cause pain and stiffness. It affects more commonly the facet joints of the cervical vertebrae and typically causes pain in this area as well headaches and difficulty rotating the head.
Hyperlordosis. Hyperlordosis, also simply called lordosis, refers to an exaggerated lordosis of the lumbar vertebrae. It can be caused by pregnancy or obesity.
Lumbar herniated disc. This condition represents a common cause of low back and leg pain. A herniated intervertebral disc is a ruptured disk. Symptoms may include dull or sharp pain, muscle spasm or cramping, and leg weakness or loss of leg function.
Osteoarthritis. Osteoarthritis is a degenerative form of arthritis, it is a progressive joint disease associated with aging. In the vertebral column, osteoarthritis can affect the facet joints, which allow the body to bend and twist.
Scheuermann's kyphosis. Scheuermann's kyphosis refers to an exaggerated kyphosis of the thoracic vertebrae. It can be caused by rickets or poor posture.
Scoliosis. Abnormal sideways curvature of the vertebral column.
Spondylolisthesis. A forward displacement of one vertebra on another, usually in the lower back region due to either a traumatic or a congenital defect.
Vertebral osteomyelitis. Vertebral osteomyelitis is the infection of the bones of the vertebral column. It may be caused by either a bacteria or a fungus. Bacterial or pyogenic vertebral osteomyelitis is the most common form.
BOOKS
Bryan, Glenda J. Skeletal Anatomy. Philadelphia: W. B. Saunders Co., 1996.
Simon, Seymour. Bones: Our Skeletal System (Human Body). New York: Morrow (Harper-Collins), 1998.
OTHER
"The Vertebral Column." Bartleby.com edition of Gray's Anatomy of the Human Body. <http://www.bartleby.com/107/19.html>.
Sign up with Facebook
