The axial skeleton is one of the two parts of the skeletal system. It has 80 bones that compose the skull, ribs, spine/vertebrae, sternum, ear ossicles and the hyoid bone. The axial system can be broken down even further. The skull has 22 bones, 8 in the cranium and 14 in the face; there is one hyoid bone, 6 auditory ossicles, 26 vertebrae, 1 sternum and 24 ribs.
The Skull is made up of cranial and facial bones. In general, the skull serves as a place for cavities, paranasal sinuses, mandible and suture bones.
The frontal bone is a part of the cranium. There is only one. It forms the forehead, roof of the orbits (eyes) and anterior cranial floor. The coronal suture connects the frontal bone to the parietal bones.
The parietal bones are the 2nd and 3rd bones of the cranium. They form the roof of the cranium. There are four sutures involved with the parietal bones: the first is the coronal suture that connects the parietal bones to the frontal bone. The second is the saggital suture that connects the two parietal bones together. The lamboid suture connects the parietals to the occipital bone. The squamous suture connects the parietal bones to the temporal bones.
The occipital bone is the 4th bone of the cranium. There is only one. It is the back of the skull and base of the cranium. There is the foramen magnum that is the opening for the spinal cord, vertebral and spinal arteries to leave the head. The external occipital protuberance (a projection that sticks out from the occipital bone) is the bump just above our necks. This joins together with the axis of the vertebrae to allow us to nod our head yes. The ligament that allows us to do this is called the ligamentum nuchae. The lamboid suture connects the occipital bones to the parietal bones.
The temporal bones are the 5th and 6th bones of the cranium. They are the sides of our cranium, as well as the floor. It is also the floor and side of each orbital. The squamous suture attaches the temporal bones to the parietal bones. The temporal bones are the location of the external acoustic (auditory) meatus, the mastoid process (neck muscle attachment point), the styloid process (one of the tongue muscle attachment points) and the zygomatic process.
The sphenoid bone is the 7th bone and base of the cranium, sides of the skull, floor and sides of the orbits. It has a sella tuchica and the sphenoid sinus.
The ethmoid bone is the 8th bone of the cranium. It makes up the anterior portion of the cranial floor, the medial walls of the orbits. The perpendicular plate makes our septum and is on the ethmoid bone.
There are 14 facial bones: 2 nasal, 2 maxillae, 2 zygomatic, 2 lacrimal, 2 palentine, 2 inferior nasal conchae, 1 mandible, and 1 vomer. I'm not going to cover the palentine or lacrimal bones because we aren't going to be tested on them.
The maxillary bones are the floor of our orbits, the nasal cavity or hard palate. A cleft plate occurs when the amxillae don't fuse together.
The zygomatic bones are the prominences of our cheeks. They form the lateral walls and floor of our orbits. The temporal process joins to the zygomatic process of the temporal bone.
The nasal bones make up the bridge of our nose.
The vomer is our nasal septum. It divides the nose into left and right cavities. If someone has a deviated septum, the septum is not directly in the middle of the nose.
The mandible is the only movable part of our skull. It is horseshoe shaped with a flat ramus going upward at the ends. The mandibular condyle is a fossae of the temporals. The mandibular notch is between the condylar and coronoid processes.
The orbits, as I've mentioned, have 7 bones that make them up. The roof is formed by the frontal and sphenoid bones. The lateral wall is formed by the zygomatic and sphenoid bones. The floor is the maxilla, zygomatic and sphenoid. The medial wall is made of the maxilla, lacrimal, ethmoid and sphenoid.
The hyoid bone is the only bone in the body that does not articulate with another bone. It is u-shaped. It is suspended by ligaments and muscle from the skull. It helps support the tongue, and provides attachment for the tongue, neck and pharyngeal muscles.
Moving onto the Vertebral Column
The vertebral column is composed of 7 cervical vertebrae, 12 thoracic vertebrae, 5 fused vertebrae, a sacrum (5 fused vertebrae) and a coccyx (4 fused vertebrae). Each of the four curvatures of the vertebrae make sense. The cervical vertebrae make the cervical curvature, the thoracic vertebrae make the thoracic curvature, the lumbar curvature comes from the lumbar vertebrae and the sacrum and coccyx make up the pelvic curvature. (Which makes sense because the top of the sacrum and the top of the pelvic girdle match up).
The vertebrae are separated by intervertebral discs. These help absorb vertical shock. The discs permit various movements within the column. They are a fibrocartilagenous with a pulpy center. When one or more of the discs are injured, the nucleus pulposes protrudes into the ring, which causes pressure to be put on the spinal nerves. Surgically removing a disc is called laminectomy.
Every vertebrae has several parts. Different vertebrae have different prominent parts. The body is the weight bearing part and is anterior to the rest of the vertebrae. The vertebral foramen is the opening for blood vessels and the spinal cord. There are seven processes (projections). There are two transverse processes, one spinous process and four articular processes. The intervertebral notch forms the intervertebral foramen with the next vertebrae.
The spinal canal is the vertebral foramen all linked together. Intervertebral foramen allow the spinal cord to leave leave the spine.
The seven cervical vertebrae are at the top of the spine. The first one is called the atlas. It allows the skull to say yes. The second vertebrae is called the axis. It is the only one to have a dens. The dens allows the head to say no. Cervical vertebrae 3-6 are typical vertebrae. The 7th, vertebrae pominens is different, it has a more prominent spinous process.
Thoracic vertebrae articulate with ribs. There are 12 of them and they have larger and stronger bodies. Thoracic vertebrae also have longer transverse and spinous processes. Facets and demifacets articulate from the body of the vertebrae to the head of the ribs.
Lumbar vertebrae are the largest and strongest.
The sacrum is the union of 5 vertebrae by age 30. The median sacral crest was the spinous process. The sacral ala is a fused transverse process.
The coccyx is the union of 4 fused vertebrae by age 30. Caudal or epidural anesthesia is inserted into the sacral to anesthetize sacral and coccygeal nerves.
The Thorax is the extire chest. It consists of sternum, costal cartilage, ribs and bodies of thoracic vertebrae. The thorax is a bony cage that is flattened from front to back. The sternum consists of the manubrium (1st and 2nd ribs); it is the sternal angle junction within the body. The body of the sternum is the costal cartilage of ribs 2-10. The sternum's xiphoid is at the most inferior of the sternum. It has the xiphisternal joint and is the location for CPR as well as a connection site for abdominal muscles.
We have 24 ribs. They increase in length from ribs 1-7. After the 7th rib, they decrease in size. The head and tubercle articulate with facets of the vertebrae. The tubercle of the rib articulates with the transverse process of the vertebrae, while the head articulates with the vertebral bodies.