The vertebral column, also known as the spine or spinal column, is the portion of the axial skeleton that supports both the skull and the trunk of the body. It extends from the base of the skull downward past its connection with the pelvis. In addition to providing support, the vertebral column makes all body movement possible, it accommodates the stress associated with that motion, and, probably most important, it protects the spinal cord. The vertebral column consists of a continuous chain of 33 vertebrae, as well as 23 intervertebral discs. An intervertebral disc is a flattened structure that sits between and cushions vertebrae. Discs are composed of a fibrocartilage ring, the annulus fibrosus, surrounding a gelatinous center, the nucleus pulposus. The length of an adult vertebral column, including vertebrae and intervertebral discs, is typically about 71 cm (28 in.).The spinal column is grouped into five different regions, each with a specific number of vertebrae. Vertebrae in each region are numbered sequentially from the top to the bottom of that region. The cervical region at the top of the spine includes the seven vertebrae in the neck; these are numbered C1–C7. Beneath the cervical region is the thoracic region which is the region of the spine in the chest that consists of 12 vertebrae, numbered T1–T12. The spine's lumbar region consists of five vertebrae in the lower back; these are numbered L1–L5. The five sacral vertebrae at the base of the spine, numbered S1–S5, follow the lumbar vertebrae. Finally, four tiny, unnumbered coccygeal vertebrae make up the coccyx, or vestigial tail of the spine. The total number of vertebrae is 33: 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 fused vertebrae making up the sacrum, and 4 fused vertebrae making up the coccyx. The sacrum is the region of the vertebral column that lies between the hip bones and is made up of fused vertebrae.
Five Regions of the Vertebral Column
Anatomy of the Vertebral Column
The term column as used to describe the spine is misleading, because the vertebral column is actually curved rather than straight. In adults the spine has four major curves that make up an S-shape. Two of these curves originated with the developing embryo's continuous C-shaped curve in the uterus. A newborn's vertebral column retains this C-shape until the infant can raise its head. At that point a curve develops in the cervical region. Later, when the infant can sit up and then begins walking, a curve forms in the lumbar region. Altogether the curves in an adult spine take on this alternating form, with curves described in the anterior direction: a convex curve in the cervical region, a concave curve in the thoracic region, a convex lumbar curve, and a concave curve in the combined sacral and coccygeal (pelvic) region. This S-shape in the human spine enables walking upright on two legs (bipedal locomotion).Abnormal curvatures of the spine disrupt this S-shape. Scoliosis, is a lateral, or sideways, bend in the vertebral column, usually in the thoracic region. Causes of scoliosis are unclear but are believed to include inherited factors. Lordosis is an abnormal, pronounced curvature of the vertebral column's lumbar region. Known as swayback, lordosis can be caused by osteoporosis or other spinal ailments, excessive abdominal weight, or participation in activities that load weight on the spine. Kyphosis is an abnormal spinal curvature that takes the form of an exaggerated concave bend in the vertebral column's thoracic region. This causes a humpback shape that is most often attributed to osteoporosis, as well as to some of the other causes of lordosis.
Abnormal Curvatures of the Vertebral Column
Anatomy of the Vertebrae, Sacrum, and Coccyx
Comparing Types of Vertebrae
The triangular coccyx, or tailbone, consists of three to five tiny fused vertebrae. Coccygeal vertebrae lack vertebral foramina and developed processes.
Anatomy of the Thoracic Cavity
The thoracic cavity, is the area of a human's body from the neck to the abdomen, including the area within the ribs, breastbone, and dorsal vertebrae and containing the heart, lungs, and associated blood vessels. The name is descriptive because the bones involved create a cage or chamber that surrounds the vulnerable organs. The structure is semirigid, meaning that respiratory muscles cause its volume to regularly expand and contract as air is inhaled and exhaled.
The thoracic cavity is made up of the thoracic vertebrae, 12 pairs of ribs, and the sternum. The sternum, also called the breastbone, is a sword-shaped bony plate located in front of the heart. It divides into three regions from top to bottom: the broad manubrium, the long body, and the narrow xiphoid process. The notch at the top of the manubrium, the jugular notch, can be felt just between the clavicles. The body of the sternum meets the manubrium at the sternal angle, felt as a ridge at the most forward part of the sternum. The small xiphoid process below the body is the attachment site for some abdominal muscles.Each of the 12 pairs of ribs attaches at its back (posterior) point to the thoracic vertebrae of the spine. In the front of the thoracic cavity, thin costal cartilage connects the first seven ribs directly to the sternum. These are designated as true ribs. Ribs 8–12 are termed false ribs because they lack this direct attachment to the sternum. Ribs 8–10 are connected to rib 7's costal cartilage. Ribs 11–12 do not connect to the sternum at all and are thus called the "floating ribs." Ribs also vary somewhat in structure. All ribs have a head that meets and articulates with the vertebral column. Ribs 1 to 10 each have a proximal head and tubercle (a small rounded projection or protuberance, especially on a bone connected by a narrow neck; ribs 11 and 12 have a head only. The tubercles form another point of articulation with the vertebral column. The first rib is flat and horizontal. Extending from the tubercle, ribs 2–10 make a sharp bend appropriately called the angle and then flatten into blades called shafts. Costal grooves in rib shafts form pathways for nerves and blood vessels. Ribs 1–10 articulate both with and between thoracic vertebrae. Because ribs 11–12 lack tubercles, they articulate only with vertebrae.