Chapter 8 (1)

• The skeleton is divided into two: Axial and Appendicular. There are 206 bones in the average adult person but originally we are all born with 270 bones. The reduction of quantity is a result of bone fusion.
• The axial skeleton forms the central supporting axis of the body, such as the skull, vertebrae, sternum, ribs, sacrum, and hyoid. The Appendicularskeleton on the other hand is made up of appendages (arms, legs, and such) like the pectoral girdle, upper extremity, pelvic girdle, and lower extremity.
• An articulated skeleton: is held together by wire and rods and it shows spatial relationships between bones WHILE Disarticulated bones: are taken apart so that their surface features can be studied in detail.
• The skull is the most complex part of the skeleton. It is made up of 22 bones that are joined together by sutures (immovable joints). The skull has several cavities: the cranial cavity (braincase), orbits (eye sockets), nasal cavity, oral (buccal) cavity, middle- and inner-ear cavities, and paranasal sinuses.
• The foramina are holes that allow passage for nerves and blood vessels. Paranasal sinuses are frontal, sphenoid, ethmoid, and maxillary. The sinuses are lined by mucous membranes and are air-filled. They also act as chambers that add resonance to the voice and lighten the skull.
• The cranium (braincase). The meninges (membranes) separate the brain from the bones and the dura mater is the thickest membrane. The cranium consists of two parts: the calvaria (skullcap) and the cranial base.

  
• The cranial base of the cranium is divided into 3 basins: The anterior (towards the front of the skull) cranial fossa holds the frontal lobe of the brain. The middle cranial fossa holds the temporal lobes of the brain. And the posterior (towards the back of the skull) cranial fossa contains the cerebellum and ALWAYS has that hole for the spinal cord. There are 8 cranial bones: 1 frontal, 2 parietal, 2 temporal, 1 occipital, 1 sphenoid, and 1 ethmoid.

  
• The frontal bone forms the forehead and part of the roof of the cranium. The coronal suture is the posterior boundary of the frontal bone. The supraorbital foramen provides passage for the nerve, artery, and vein in the frontal bone and the frontal bone contains the frontal sinus.
• The parietal bones form most of the cranial roof and part of its lateral walls. It is bordered by four sutures; Sagittal: between parietal bones. Coronal: at anterior margin. Lambdoid: at posterior margin. And Squamous: at the lateral border. The parietal bones have two temporal lines for the attachment of the temporalis muscle.
• The temporal bone is the lateral wall and part of the floor of the cranial cavity. It has four parts; the squamous, tympanic, mastoid, and petrous
• The different lobes as well as sutures:

  
• Squamous part of the temporal bones:

  • Encircled by a squamous suture
  • Contains the zygomatic process and a mandibular fossa
• Tympanic part of the temporal bones:

  • Contains the external auditory meatus and the styloid process
• Mastoid part of the temporal bones:

  • Contains the mastoid process, the mastoid notch, the mastoid foramen, and the stylomastoid foramen
• Petrous part of the temporal bones:

  • Part of the cranial floor
  • Separates the middle from the posterior cranial fossa
  • Houses middle- and inner-ear cavities, as well as receptors for hearing and balance
  • Contains the opening for the CN VIII (vestibulocochlear nerve) in the internal auditory meatus
  • Contains the carotid canal and the jugular foramen
• The occipital bone is at the rear and base of skull. It houses or "hosts" the foramen magnum which is the opening for the spinal cord (the "hole") as well as the occipital condyles which are the knobs resting on the spinal column. The tiny things highlighted in purple are the occipital condyles.

  
• The ethmoid bone is located between the eyes. The bone contributes to the medial wall of the orbit, walls, and roof of the nasal cavity, and the nasal septum. The perpendicular plate in this bone forms the superior two-thirds of the nasal septum. The ethmoid bones' cribriform plate forms the roof of the nasal cavity. The superior and middle nasal conchae are scroll-like plates that project into the nasal fossa. Along with an inferior concha (a separate bone), these plates occupy most of the nasal cavity, create turbulence of airflow, and help humidify air.