axial skeleton cranium. axial skeleton major divisions in the skeletal system: – axial: bones...

Axial Skeleton

Cranium

Axial skeleton

• Major Divisions in the skeletal system:– Axial: Bones along the

center axis (medial) of the body.• Skull, Vertebral column,

rib cage

The Skull• The skull is formed by two sets of bones:

1. The cranium encloses and protects the fragile brain tissue ( 8 cranial bones: Frontal bone, 2 parietal bones, 2 temporal bones, the occipital bone, the spenoid bone, ethmoid bone)

2. The facial bones hold the eyes in an anterior position (14 facial bones: 2 nasal bones, 2 maxillae, 2 zygomatic bones, the mandible, 2 lacrimal bones, 2 palatine bones, 2 inferior nasal conchae, vomer)

• All but one of the bones of the skull are joined together by sutures, which are interlocking, immovable joints

Frontal Bone

• Frontal Bone: Forms the forehead, the bony projections under the eyebrows, and the superior part of each eye orbit

Parietal Bones• The paired parietal

bones form most of the superior and lateral walls of the cranium

• They meet in the midline of the skull at the sagittal (front to back) suture, and form the coronal (up and down) suture where they meet the frontal bone

Temporal Bones

• The temporal bones lie inferior to the parietal bones

• The temporal bones and parietal bones are joined at the squamous (sideways) sutures

Occipital Bone

• It is the most posterior bone of the cranium

• It forms the floor and back wall of the skull

• The occipital bone joins the paretial bones anteriorly at the lambdoidal (along the back) suture

Sphenoid Bone

• The butterfly-shaped bone spans the width of the skull and forms part of the floor of the cranial cavity

Ethmoid Bone

• The ethmoid bone is very irregularly shaped and lies anterior to the sphenoid

• It forms the roof of the nasal cavity and part of the medial wall of the orbits(eye sockets)

FrontalParietal

Occipital

Temperal

Sphenoid

Ethmoid

Coronal suture Squamous suture

Lambdoidal suture

Bone Surface Markings• Bones have characteristic surface markings– Structural features adapted for specific functions

• There are two major types of surface markings:– 1) Depressions and openings• Allow the passage of blood vessels and nerves or form

joints– 2) Processes• Projections or outgrowths that form joints or serve as

attachment points for ligaments and tendons

Temporal Bones Markings

• External auditory meatus: a canal that leads to the eardrum and the middle ear

• Styloid process: a sharp needle projection. Many neck muscles use the styloid process as an attachment point

• Zygomatic process: a thin bridge of bone that joins with the cheek bone

• Mastoid process: a rough projection posterior and inferior to the external auditory meatus, which is full of air cavities

Temporal Bones Markings

Temporal Bones Markings• Jugular foramen

(hole): the junction of the occipital and temporal bones, allows passage of the large jugular vein which drains the brain

• Just anterior to it is the carotid canal through which the carotid artery runs, supplying blood to most of the brain

Occipital Bone Markings

• Foramen magnum (large hole): surrounds the lower part of the brain and allows the spinal cord to connect with the brain

Sphenoid Bone Markings

• Sella turcica: holds the pituitary gland in place

Facial Bone• 2 Maxillae or maxillary

bones, fuse to form the upper jaw

• All facial bones except the mandible join the maxillae, thus they are the main or keystone bones of the face

• The maxillae contains sinuses, which drain into the nasal passages: Paranasal sinuses

Palatine Bones

• The paired palatine bone are posterior to the palatine processes of the maxillae

• Failure of these results in cleft palate

Facial Bones

• Zygomatic bones: Are commonly referred to as the cheekbones

• Lacrimal Bones: fingernail size bones forming part of the medial wall to each orbit (eye socket)

Facial Bones

• Nasal Bones: The small rectangular bones forming the bridge of the nose (the lower part of the nose is made up of cartilage)

• Vomer Bone: The single bone in the median line of the nasal cavity

Facial Bones

• Inferior conchae: Thin curved bones projecting form the lateral walls of the nasal cavity

• Mandible: The lower jaw. The largest and strongest bone of the face

The Hyoid Bone

• Lies inferior to the mandible

• It is the only bone with no direct articulation with any other bone

• Acts as a movable base for the tongue