Divisions of the Skeleton

Divisions of the Skeleton

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Divisions of the Skeleton...

Divisions of the Skeleton:

The adult human skeleton has 206 named bones. In addition to the named bones there are two other types of bones that vary in number from one individual to another and do not have specific names. Sutural bones are small bones in the joints between certain cranial bones. Sesamoid bones are small bones that grow in certain tendons in which there is considerable pressure. The patella or the knee cap is an example of a sesamoid bone that is named, there are others that are not named.

For convenience, the bones of the skeleton are grouped in two divisions. The 80 bones of the axial skeleton form the vertical axis of the body. The appendicular skeleton consists of 126 bones and includes the free appendages and their attachments to the axial skeleton. The free appendages are the upper and the lower extremities.

SEE YOUR TEXTBOOK FOR A BREAKOUT OF THE TWO SKELETAL DIVISIONS

AXIAL SKELETON

This division consists of the skull, hyoid, vertebral column, ribs, breastbone or sternum.

SKULL

There are 28 bones in the skull. Eight bones form the cranium which houses the brain, the anterior aspect of the skull forms the face and consists of 14 bones, the remaining six bones form the auditory ossicles or the tiny bones of the middle ear. See your textbook for a complete accounting of the bones of the skull.

With the exception of the mandible or the lower jaw, and the 6 auditory ossicles, the bones in the skull are tightly interlocked along irregular lines called sutures. Some of the bones in the skull have spaces or cavities which are called sinuses.

Sinuses are air filled cavities that are lined with mucous membranes. The sinuses help to reduce the weight of the skull and also play an important part in the development of our resonance. Resonance meaning the tone or pitch of the way we speak. Four pairs of these sinuses open into the nose and are referred to as paranasal sinuses. They are the frontal, maxillary, sphenoid and ethmoid bones.

Allergies and infections may cause inflammation of the membranes, which results in sinusitis. Symptoms of sinusitis may include headache, toothache, fever, pain on palpation of the frontal or maxillary sinuses, increased nasal discharge which may be purulent or green tinged in color, fever, chills, nausea, and postnasal drip. Diagnostic procedures may include transillumination of the nasal passages, X-rays or based upon patient history. Treatment may consist of anti-infectives or antibiotics, decongestants, antihistamines, analgesics. Sinusitis may become chronic causing severe problems for the patient with repeated bouts of the infection. On occasions where all of the above therapies have been unsuccessful, there are procedures performed by an EENT provider that will allow for invasive drainage of the sinus cavities. A maxillary Caldwell-Luc is an example of this type of procedure.

Mastoiditis is an inflammation of the mastoid portion of the temporal bone. This is a very serious medical problem if not treated immediately. Exudate or infectious material may find its way into the mastoid air cells as a result of middle ear infections. The problem with this is that the mastoid air cells do not drain like the sinuses and the infectious material may accumulate and damage the thin bones that separate this area from the brain resulting in brain tissue exposure to infectious material.

The 8 bones of the cranium are interlocked together to enclose the brain. See your textbook for a graphic of the skull. The immovable joints of the skull are called sutures. The major sutures are the lambdoidal suture which is linked with the occipital bone, the squamous suture with the temporal and a portion of the sphenoid bone, and the coronal suture with the frontal bone.

The bones in the skull of the newborn infant are not completely joined together, but are separated by fibrous membranes. There are six large areas of membranes called fontanels or soft spots. The anterior fontanel is on the top of the head, at the junction of the frontal and parietal bones. The posterior fontanel is at the junction of the occipital and parietal bones. On each side of the head there is a mastoid fontanel near the mastoid region of the temporal bones and a sphenoid fontanel just superior to the sphenoid bone.

Fontanels allow some compression of the skull during birth without much risk of breakage of the skull bones. The fontanels fuse to form sutures before a baby is 2 years old.

Please note that you will be expected to know the bones of the skull and face as they play an important role in utilization of the skull for landmarks to describe locations of pain or trauma.

AUDITORY OSSICLES

The auditory ossicles are the three tiny bones that form a chain in each middle ear cavity in the temporal bone. These are the malleus, incus, and stapes. These bones transmit sound waves from the TM or tympanic membrane to the inner ear where sound receptors are located.

HYOID BONE

The hyoid bone is not really part of the skull, this is why it is listed separately. It is a U shaped bone in the neck between the mandible and the larynx. It is unique because it is the only bone in the body that does not articulate directly with another bone. It is suspended under the mandible and is anchored by ligaments. It functions as a base for the tongue and as an attachment for several muscles associated with swallowing.

VERTEBRAL COLUMN

This column extends from the skull to the pelvis and contains 26 bones called vertebrae. The bones are separated by pads of fibrocartilage called intervertebral disks. These disks act as shock absorbers and allow the column to bend. Normally, there are four curvatures that increase the strength and resilience of the column. They are named accordingly to the region in which they are located. The four normal curves of the spine are important functions. These curves give our rigid bony framework enough strength to support the weight of the rest of the body. They also provide balance that is necessary for us to stand and walk on two feet. A curved structure offers much more strength that a straight one.

Think of someone you may know or even yourself, who may have had a back problem. When you are hunched over and unable to stand erect there are many resulting problems that stem from this.

Poor posture or disease process may result in the lumbar curve to become abnormally exaggerated developing a condition known as “swayback” or lordosis.

An abnormal thoracic curvature is kyphosis or “hunchback”, and an abnormal side to side curvature is called a scoliosis. Scoliosis is relatively common and appears usually before adolescence and the cause is unknown.

Symptoms of abnormal spinal curvatures may be posture related, breathing interference or chronic back discomfort. Diagnostic measures may include physical exam with X-rays which look at the degree of malformation and the potential for any resulting disk injury. Treatment is based upon the degree of the deformity noted. Braces such as a Milwaukee brace may be applied, casting may be necessary or transcutaneous muscle stimulation to enhance muscle contraction and thus shortening may be used to pull the muscles up and thus lighten the pull of gravity on the spinal disks offering some degree of straightening. If these methods fail, surgery may be necessary with implantation of metal rods to keep the vertebral column in place while bone grafts to the vertebrae may heal and fuse.

All vertebrae have a common structural pattern. See your textbook! Although individual vertebrae are small bones, irregular in shape; they have several well defined parts. The thick, anterior, weight bearing portion is the body or the centrum. The body surrounds the central, large opening called the vertebral foramen. When all of the vertebrae are stacked together in a column, the foramina make a canal that contains the spinal cord. Transverse processes project laterally and in the posterior midline is the spinous process. These processes are places for muscle attachments and can be felt as bony prominences along the midline of the back.