Vertebrae Definition
Vertebrae are bones located within the vertebral column. In humans, they are a series of 33 bones that run from the base of the skull to the coccyx. The irregularly shaped bones form the roughly S-shape of the spinal cord. Between each vertebra is an intervertebral disc, which helps provide shock absorption and protect the vertebrae.
Each vertebrate species, which gets its name from the vertebrae that make up its column, has a similarly shaped vertebrae. The biggest differences occurbetween land-dwelling and aquatic species because of their different movement requirements.
Parts of Vertebrae
Vertebrae vary in their shape based upon the region of the body that they are found in, as well as what species they belong to. The main portion of the vertebra is the body, which is divided into two parts: the centrum and the posterior vertebral arch (also called the neural arch).
The vertebrae bodies are made of a spongy form of bone called cancellous bone. They are covered in cortical bone, which is denser, harder bone. The bodies have roughened attachment places for the intervertebral discs.
The vertebrae have seven processes that jut out from their central body, including the main spinous process, four articular processes, and two transverse processes. The spinous process serves as an attachment point for muscles.
The transverse processes also serve as muscle and ligamentous attachment sites, including the intertransverse ligaments. This area articulates with the ribs within the thoracic vertebrae. The articular processes restrict the amount of movement possible and are joined by part of the vertebral arch.
Types of Vertebrae
There are several different types of vertebrae found within most vertebrates, named for the parts of the body they are located in.
Cervical vertebrae
At the base of the skull, the vertebral column starts with the cervical vertebrae. There are seven of these, and they are numbered C1 through C7. C1 is also dubbed the atlas, while C2 is the axis; both of these have more unique shapes—due to how they support the skull—in comparison with the other vertebrae.
It’s the cervical vertebrae that allow our necks the full range of motion they have. Somewhat surprisingly,a giraffe has the same number of cervical vertebrae that a person does—they’re just larger.
Thoracic Vertebrae
The thoracic vertebrae are the next 12 vertebrae, moving down the body. They articulate with the ribs, helping to protect the chest cavity containing the heart and lungs. These are larger than the cervical vertebrae.
Lumbar Vertebrae
The next five vertebrae are the lumbar vertebrae, and these are the largest of the vertebrae. They produce a natural curvature to the spine and support the greatest weight of the vertebrae. They allow for flexion, extension, and side-bending. Chimpanzees only have three lumbar vertebrae.
Sacrum and Coccyx
The remaining vertebrae are the five vertebrae that form the fused sacrum, as well as the three to five vertebrae that form the coccyx or tailbone. The sacral and coccygeal vertebrae do not have intervertebral discs.
These bones are sometimes referred to as the caudal vertebrae and have the most variation in number, with some species having a few and others having 50 caudal vertebrae.
Vertebrae Function
Vertebrae are important structurally in vertebrates. They support the head and neck, allowing movements such as turning the neck. The vertebrae also provide attachment points for muscles and ligaments, allowing many of the motions that the body is able to go through, such as bending and twisting.
The vertebrae also protect the spinal cord, which runs down openings in the vertebrae. As a result of this protection, the risk of damage due to trauma and everyday activities is minimized. There are openings known as foramina that allow the spinal nerves to pass through, providing nervous innervation to different tissues.
There is no blood supply to the intervertebral discs, so the movements of the vertebrae provide the mechanism by which the discs receive vital nutrients and remove waste build-up. This is managed by the hyaline ligament between each vertebrae that separates the cancellous bone from each disc.
Different issues can affect the vertebrae, including irregularly shaped vertebrae leading to abnormal bending of the spine, such as in scoliosis. Disc herniations can occur when some of the intervertebral disc material protrudes and puts pressure on the spinal column, potentially resulting in paresis or pain. In degenerative disc disease, the body’s discs degenerate, which can be a very painful process.