Created by CK-12 Foundation/Adapted by Christine Miller
You are watching: What are the two major divisions of the skeletal system
This rather macabre display (Figure 11.3.1) have the right to be regarded at the Slovak nationwide Museum in Bratislava, Slovakia. The skulls are meant to stand for normal human being skeletal anatomy. The skull is component of the axial skeleton, which is just one of the two major divisions of the person skeleton. The other division is the appendicular skeleton.
The axial skeleton, presented in blue in figure 11.3.2, consists of a full of 80 bones. Besides the skull, it has the rib cage and also vertebral column. It additionally includes the 3 tiny ossicles (hammer, anvil, and stirrup) in the middle ear and the hyoid bone in the throat, come which the tongue and also some various other soft tissues room attached.
The skull is the part of the human skeleton that offers a bony structure for the head. It is composed of 22 different bones. There room eight skeletal in the cranium, i m sorry encloses the brain, and 14 skeleton in the face.
The cranium forms the whole upper part of the skull. As shown in figure 11.3.3, it consists of eight bones: one frontal bone, two parietal bones, 2 temporal bones, one occipital bone, one sphenoid bone, and also one ethmoid bone. The ethmoid bone the end the sleep cavity from the brain. The sphenoid bone is just one of several bones, including the frontal bone, that help form the eye sockets. The various other bones the the cranium are large and plate-like. Castle cover and protect the brain. The bottom of the skull has openings for significant blood vessels and also nerves. A large opening, called the foramen, connect the spinal cord and also brain.Figure 11.3.3 The cranium is composed of eight bones that are fused with each other at their joints.
The 14 facial bones the the skull are located listed below the frontal bone of the cranium, and also they are illustrated in number 11.3.4. Large bones in the confront include the upper jaw bones, or maxillae (singular, maxilla), which type the middle part of the face and also the bottom the the 2 eye sockets. The maxillae are fused together, except for an opening in between them because that the nose. The reduced edge the the maxillae has sockets for the top teeth. The lower jaw bone, or mandible, is likewise large. The optimal edge of the mandible has sockets for the lower teeth. The mandible opens and also closes come chew food and also is managed by solid muscles. There room two zygomatic (or cheek) bones and also two nasal bones. The nasal region also includes seven smaller bones, as suggested in figure 11.3.4.
The vertebral column — likewise called the spine or backbone — is the flexible shaft of vertebrae (singular, vertebra) the connects the trunk with the skull and also encloses the spinal cord. It is composed of 33 vertebrae the are separated into 5 regions, as presented in figure 11.3.5: the cervical, thoracic, lumbar, sacral, and also coccygeal regions. Indigenous the neck down, the first 24 vertebrae (cervical, thoracic, and lumbar) space individual bones. The five sacral vertebrae space fused together, as are the four coccygeal vertebrae.
The vertebral column is composed of 24 separation, personal, instance vertebrae that are separated through intervertebral discs that cartilage. An additional nine vertebrae are fused with each other at the base of the spine. Note the S-shaped curve the the vertebral pillar in the profile watch in number 11.3.5 top top the left.
The person vertebral tower reflects adaptations for upright bipedal locomotion (walking upright on two legs). Because that example, the vertebral shaft is much less like a rigid pillar than an S-shaped feather (see profile watch in number 11.3.5). Although child infants have a reasonably straight spine, the curves build as the backbone starts acquisition on its support functions, together as keeping the stems erect, holding up the head, and helping to anchor the limbs. The S shape of the vertebral column allows it come act choose a shock absorber, soaking up much of the jarring the walking and also running therefore the forces are not transmitted straight from the pelvis to the skull. The S shape also helps safeguard the spine indigenous breaking, which would certainly be an ext likely through a straight, more rigid vertebral column. In addition, the S form helps to distribute the weight of the human body — an especially of the inner organs, for this reason the weight load is no all in ~ the bottom, together would occur with a straight spine.
The rib cage (also called thoracic cage) is suitable named, since it forms a sort of cage that holds in ~ it the guts of the upper part of the trunk, consisting of the heart and also lungs. It is displayed in numbers 11.3.6–11.3.8. The rib cage has the 12 thoracic vertebrae and also the sternum, and also 12 bag of ribs, which space attached in ~ joints to the vertebrae. The ribs are split into three groups, referred to as true ribs, false ribs, and floating ribs. The peak seven pairs of ribs room true ribs. They room attached by cartilage directly to the sternum. The following three pairs of ribs are false ribs. They are attached by cartilage to the ribs over them, fairly than directly to the sternum. The lowest 2 pairs the ribs are floating ribs. They space attached through cartilage to muscle in the ab wall. The attachments of false and also floating ribs permit the lower component of the rib cage expand to accommodate the interior movements of breathing.
Figure 11.3.6 True ribs are attached to both the vertebrae and also the sternum. In this image, true ribs space highlighted in red.
Figure 11.3.7 False ribs space attached to the vertebrae and to the ribs above them through cartilage. In this image, false ribs and also floating ribs space highlighted in red.
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Figure 11.3.8 Floating ribs space attached to vertebrae and also the the muscle in the ab wall. In this image floating ribs space highlighted in red.