The Bones of the Human Spine
Edited by Chameleon, SmartyPants, SarMal
As vertebrates humans have a spine (also known as the vertebral column or backbone). Unsurprisingly, the vertebral column is the essential distinction in vertebrates, and consists of sections of bones with intervertebral discs in between. In contrast to invertebrates which are species without a backbone or spine, all vertebrates have a spine, even if (such is the case with sharks) the spine is made out of cartilage rather than bone. Our spine is part of our axial skeleton and it also helps to protect our spinal cord, a very important part of our nervous system.
The human spine is made up of 24 articulating vertebrae (singular: vertebra):
- 7 cervical vertebrae in the neck
- 12 thoracic vertebrae in the upper body, and
- 5 lumbar vertebrae in the lower body.
A trick to remember the number of vertebrae in each section of the spine is to think about the times of day when we eat certain meals: breakfast at 7 (7 cervical vertebrae), lunch at 12 (12 thoracic vertebrae), and dinner at 5 (5 lumbar vertebrae). In addition to these 24 articulating vertebrae, which have joints that allow us to move and bend, we also have 9 fused vertebrae that make up the sacrum and coccyx. Since the sacrum and coccyx are fused, this means that they do not have joints to allow for movement.
Vertebrae of the Human Spine
Depending on the level of the vertebra (i.e. cervical, thoracic, or lumbar), the spine can have a slightly different appearance. However, there are several common structures in each vertebra that serve important functions:
- 1This is the weight-bearing part of the vertebra; in articulating vertebrae, the bodies are separated by intervertebral discs.Body (or corpus):Advertisement
- 3This acts as an attachment point for muscles of the spine enable humans to stand upright; on thoracic vertebrae, this is also where the facet for the rib is located.Transverse process:
- 4Part of the vertebral (or neural) arch.Pedicle:
- 6Where a vertebra connects to the vertebra above it; the superior articular process of a vertebra connects to the inferior articular process of the vertebra above itSuperior articular process:
- 7Where a vertebra connects to the vertebra below it; the inferior articular process of a vertebra connects to the superior articular process of the vertebra below it.Inferior articular process:
- 9The space where nerves from the spinal cord can exit the spinal canal and go to the rest of the bodyIntervertebral foramen:
- 10Found only in cervical vertebrae; the space through which an important artery called the vertebral artery travels to go to the brainTransverse foramen:
- 11Found only in thoracic vertebrae; this is where the ribs connect to the spineFacet for rib:
There is a fibrocartilaginous disc between each articulating vertebrae called the intervertebral disc. The intervertebral disc acts as a shock absorber and allows flexibility in the spine. Each intervertebral disc has a nucleus pulposus that is encircled by the annulus fibrosis. As we age, the annulus fibrosis loses its flexibility and elasticity. As it becomes stiffer and is less able to bounce back or absorb the forces applied to it the nucleus pulposus can herniate (leak) out of the annulus fibrosis, which is known as a herniated disc or a slipped disc.
The cervical spine is part of our neck and supports our skull. The vertebrae in our cervical spine can be differentiated from other vertebrae by the following characteristics:
- They are smaller and more delicate than other vertebrae
- There is a transverse foramen, which is absent on thoracic or lumbar vertebrae
- The spinous processes are narrower and often have two points (bifid) instead of just one
- The vertebral foramen is large and triangular in shape
The uppermost two out of the seven cervical vertebrae are very unique: the atlas and the axis. These two cervical vertebrae allow for articulation of the skull on the spine.
On the axis, there is a structure called the odontoid process (or dens) that articulates with the atlas to form the atlanto-axial joint, which allows for shaking the head. The atlas also articulates with the occipital bone in the skill to form the atlanto-occipital joint, which allows for nodding of the head.
The thoracic spine is part of the trunk of our body and also supports the rib cage. The vertebrae in our thoracic spine is differentiated from other vertebrae by the following characteristics:
- The body of the thoracic vertebra is heart-shaped.
- There are spots on the transverse processes for the ribs to connect (with the exception of the bottom two thoracic vertebrae: T11 and T12, which have floating ribs that do not articulate with the spine).
- Spinous processes are shaped differently; larger than cervical vertebrae, but smaller than lumbar vertebrae.
- Abstract similarity in appearance to the head of a giraffe.
The lumbar spine is part of the lower back. The vertebrae in our lumbar spine is differentiated from other vertebrae by the following characteristics:
- The body of the lumbar vertebra is kidney-shaped.
- These are the largest vertebrae in the spine.
- The spinous processes of lumbar vertebrae are larger than the spinous processes of the cervical or thoracic vertebrae.
- Abstract similarity in appearance to the head of a moose.
Sacrum & Coccyx
The sacrum is made up of 5 fused vertebrae, and no intervertebral discs. The sacrum is part of the pelvic girdle and sits between the two pelvic bones called the ilia (singular is ilium). The sacrum appears different in males and females; in females, it is shorter, wider, and has more of a curve to allow space for offspring bearing; in males, it is longer, narrower, and not curved as much as in females.
The coccyx is attached to the sacrum and is made up of 4 fused vertebrae, which also means there are no intervertebral discs. The coccyx is more commonly known as the tailbone and is the very bottom of the spine. Like the sacrum, the coccyx also assists to form the pelvic girdle as an attachment for pelvic floor muscles.
Referencing this Article
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Categories : Biology
Recent edits by: SmartyPants, Chameleon