The+Axial+Skeleton

=The Axial Skeleton=

What is it?
The [|axial skeleton] is only one part of the human skeleton. The appendicular skeleton is the other. The central axis of the body is formed from the axial skeleton. The bones included in the axial skeleton are: the skull, the vertebral column, the ribs and the breastbone (formally known as the sternum).

The Skull
The [|skull] can be divided up into even more groups than just the axial skeleton. It consists of 28 bones located in both the cranium and the facial bones categories.



Pictures courtesy of bbbob_99 from Flickr.com. The first picture shows the human cranial bones and the second shows human frontal bones.

The Cranium
The cranium is made up of eight flat bones that are used to protect one of the most important organs of the human body: the brain. The focus of the cranium bones are on the frontal bone, the occipital bone, the occipital condyle, the foramen magnum, and the two temporal bones. The frontal bone is what forms the forehead and protects the front part of the brain, thus the name. The frontal bone also forms some portions of the eye sockets, also known as orbits. The occipital bone is located at the base of the skull and has two openings in it in which the occipital condyle are located. The occipital condyle is what allows the neck to move around. The foramen magnum is the large opening in the occipital bone where the spinal cord passes through. There are two temporal bones which are used for hearing. They are located, as one might assume, on either side of the cranium.

Picture courtesy of seaniz on Flickr.com. This picture shows the human cranium.

The Facial Bones
There are almost twice as many facial bones as there are cranial bones, since it is made up of 14 irregular bones. The lower jawbone is the only one of these irregular bones that is not attached to the cranium by way of sutures. The facial bones include the nasal bones, two jawbones, and cheekbones. The upper and lower jaws are what allows humans to bite and chew food to get the energy that they require. Both the upper and lower jaws have alveolar pockets, where teeth are fitted into. The root, the neck, and the crown are the three structures that make up a tooth. The root is attached to the alveolar pocket by a surrounding of strong connective tissue. The neck is the combining force between the root and the crown and the crown is what appears over the gum that most people associate the word "tooth" to. Dentine is a far harder substance than bone and surrounds the tooth from root to crown. At the tip of the root there is a tiny opening in which nerves and blood capillaries enter to give nutrients to the tooth. There are four types of teeth: the incisors, the canines, the premolars, and the molars. Each one has the root, neck, and crown that was just described above.

The Vertebral Column
The [|vertebral column] forms the central part of the skeleton. The two main functions of it are to support the skull and protect the spinal cord. However, it also serves the body as a convenient attachment place for the ribs, as well as the pectoral and pelvic girdles. The 33 vertebrae is what makes up the vertebral column, even though they are divided into separate sections. There are seven cervical (or neck) vertebrae, twelve thoracic (or chest) vertebrae, five lumbar vertebrae, five fused sacral vertebrae, and four fused vertebrae. Normal vertebra has a centrum, a neural arch, a neural spine, two transverse processes, and four articular processes with articulating surfaces. The centrum is made up of spongy bone surrounded by compact bone. The back part of the vertebra is the neural arch. A foramen (or opening) happens between the neural arch and the centrum and the spinal cord enters through this opening. The neural canal is formed by the vertebral foramina and the neural spine is directed backwards. Transverse processes are the attachment for both ligaments and muscles and the four articular processes with articulating surfaces are covered with hyaline cartilage.

Picture courtesty of h3ath3r on Flickr.com. This shows the vertebral column.

The Ribs
[|Ribs] are flat and narrow bones that can be identified by their bow-shaped curve. Each rib has a capitulum (or head), a tubercle, and the shaft. There are twelve pairs of ribs which are given motion by the twelve vertebrae of the thoracic region. The head of the rib is moved with the semi-circular facets that are formed by two successive thoracic vertebrae. Hyaline cartilage (or costal cartilage in this region of the body) joins the first seven ribs to the breastbone and because of this those first seven ribs are known as true ribs. The next three pairs of ribs, known as the vertebrochondral ribs, are connected to the ribs above them and the final pairs do not attach to the sternum at all. They are known as the floating ribs because of their lack of attachment. The vertebrochondral and floating ribs are known as false ribs.

The Sternum (or Breastbone)
The [|sternum] is between 15 and 18 cm long and is found in the center of the chest region. The sternum is a flat bone that is also classified as being long and dagger shaped. The upper end of the sternum is broadened to support the collar bones and the first seven pairs of ribs attach to its articulating facets on the sides. The thorax is formed by the sternum, the twelve thoracic vertebrae, and the twelve pairs of ribs. The main function of the thorax is to protect the heart and lungs, without which, the body would never be able to function.

Picture courtesty of biol347 on Flickr.com. This picture shows the human ribs and sternum.