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The Axial Skeleton Axial Skeleton • the skull is actually several bones that come together as an embryo develops • the cranial bones protect the brain, ears and eyes • some cranial bones provide attachment points for muscle → movement of head, jaw, and neck Axial Skeleton • the cranial bones are divided into the calvaria and the cranial base calvaria = frontal, occipital, parietal, temporal cranial base = ethmoid, sphenoid • the rest of the skull is made of 14 facial bones Axial Skeleton • several of the bones of the skull contain sinuses = cavities lined with ciliated epithelial cells that secrete mucous Axial Skeleton • the left and right frontal sinuses are posterior to the frontal bone – not present at birth – begin development from age 2 to 5 – fully develop in the late teens – function: lighten skull, warm air Axial Skeleton the frontal bone • forms the forehead and eyebrow ridges • flat vertical = forehead • lower concave = orbits ( Axial Skeleton comparative anatomy note: • males have a thicker orbital ridge than females • the eyebrows of a male sit lower on the orbital ridge Axial Skeleton the temporal bone • complex shape • distinct features noteworthy features of the temporal bones: – mastoid process – styloid process – tympanic region – zygomatic process Axial Skeleton mastoid process • attachment of neck muscles • complex of cavities = mastoid sinuses – mastoid sinuses connected to inner ear – vulnerable to bacterial infection that affects ears and throat – adjust inne ear to pressure changes Axial Skeleton styloid process • varies in length from individual to individual • important attachment point for muscles and tendons of the neck and throat Axial Skeleton tympanic region • houses the internal components of the ears; includes the 3 small bones of the malleus ( incus ( stapes ( these bones develop from the facial bones in an embryo Axial Skeleton zygomatic process • forms the zygomatic arch with the zygomatic bone (facial) • forms the cheek • attachment for muscles used in chewing Axial Skeleton The parietal bone • forms the top, side, and posterior portion of the cranium • protects the posterior portion of the brain Axial Skeleton The occipital bone • forms the posterior base of the cranial vault • series of bones fused together in an embryo • an opening is left = foramen magnum or occipital foramen Axial Skeleton The occipital bone • the spinal cord enters through the occipital foramen • occipital condyles provide attachment of the head to the vertebral column, allow head movement Axial Skeleton The sphenoid bone • in contact with almost all other skull bones • helps form facial features • contains sphenoidal sinuses – connected to, and help form nasal cavities • major blood vessels and nerves of the eyes and face pass through the sphenoid • forma a structure, sella turica, which protects the pituitary gland Axial Skeleton The ethmoid bone • passageway for the nerves that detect smell • contains the ethmoid labyrinth – cleans and moistens air that enters the nose Axial Skeleton Most of a person’s facial features are determined by the 1) mandible 2) maxillary bones 3) zygomatic bones Axial Skeleton zygomatic bones • zygomatic arch maxillary bones • upper jaw • larger facial bones • form area around nose (lateral surfaces) • area under eyes (medial border of orbits) Axial Skeleton maxillary bones • passageway for major blood vessels and nerves = inferior orbital foramen • teeth develop on the lower surface Axial Skeleton palatine bones • between the maxillary and sphenoid bones • help form the 1) the walls of the nasal cavity 2) the roof of the mouth 3) the bottom of the orbits • this bone pair grows in height as facial features mature birth → adolescence Axial Skeleton mandible • largest facial bone • body of the mandible contains teeth • condyle of the mandible articulates with the temporal bones • contains passageways for blood vessels and nerves to the the chin and lower lip = mental foramen Axial Skeleton mandible • only skull bone not fused to other bones of the skull (ear bones, hyoid) hyoid bone • horshoe-shaped bone • suspended below mandible by muscles • anchors muscles of the neck • attaches to muscles of the tongue Axial Skeleton teeth • bones that grow out of an alveolus in the mandible or maxilla • has a crown – projects above the gum • has a root – embedded in the alveolus • a hard enamel covers the crown Axial Skeleton The remainder of the facial bones are tiny bones: nasal, lacrimal, vomer Axial Skeleton Axial Skeleton The vertebral column and ribs Axial Skeleton vertebral column region # association/articulation cervical 7 neck thoracic 12 rib cage lumbar 5 lower back sacral 5* hip bones coccygeal 3 - 5* tail end Axial Skeleton most vertebrae have a • vertebral body • vertebral arch • vertebral foramen Axial Skeleton vertebral body • supports weight of body Axial Skeleton vertebral arch • dorsal to the body • has several features – pedicles (2) – articular processes (4) – transverse processes (2) – lateral – spinous process • processes provide muscle attachment = movement of appendages, head, neck, vertebral column Axial Skeleton vertebral foramen • passageway for spinal cord Axial Skeleton cervical • smaller body • small transverse processes • short, bifurcated* spinous process unique feature: 2 transverse foramina for major blood vessels to the skull cervical 1 & 2 = atlas and axis Axial Skeleton atlas • supports the skull • lacks a body • large articular surfaces attach to the occipital bone axis • large protrusion = dens (odontoid process) → rotation and free movement of the atlas and skull Axial Skeleton thoracic • larger body • long, narrow spinous process unique features: each transverse process (2) has a facet for articulation with a rib another facet is located on the dorsal portion of the body → articulation that allows the ribs to flex during breathing Axial Skeleton lumbar • largest • thickest • support most of the body’s weight • anchor the back muscles = balance while moving, sitting, or standing • short stubby spinous process → bend backward Axial Skeleton sacral • form the sacrum • have large, lateral articular surfaces = fuse with hip bone • in females: sacrum is shorter wider less curved Axial Skeleton In most individuals the vertebral arch is not present on the last 2 vertebra = sacral canal The spinal cavity is exposed in the sacral canal The spinal cord ends in the lumbar region Result = opportunity to collect spinal fluid with minimal risk of nerve damage Axial Skeleton coccygeal • coccyx (tailbone) • no foramen • muscle attachment of upper leg muscles Axial Skeleton The rib cage consists of: costal cartilage ribs sternum • serves as a protective structure • assists in breathing Axial Skeleton normally 12 ribs, but . . . some individuals develop small cervicacl and lumbar ribs Why? Scientists have discovered that each vertebra has the genetical potential to become a rib Axial Skeleton 7 upper ribs = true ribs • attach directly to the sternum by costal cartilage ribs 8, 9, & 10 = false ribs • attached by costal cartilage to the rib above last 2 ribs = floating ribs • not attached ventrally Axial Skeleton The sternum serves as: • an articulation with the clavicles • an articulatioin with ribs 1 – 7 • an attachment for the chest and shoulder muscles • an attachment for the stomach muscles Axial Skeleton