Chapter 6: The Skeletal System - The Axial SAkeleton

Axial Skeleton

• 80 bones in axial (206 in axial + appendicular)

• forms long axis of body, supports neck and trunk, protects brain, spinal cord, and thoracic organs

• consists of 3 major regions: skull, vertebral column, bonny thorax

the skull

• formed by cranial and facial bones

• flat bones connected by suture (but mandible)

• cranium divided into 1) cranial vault (roof of skull) and 2) cranial base (anterior, middle, and posterior cranial fossae)

• 85 named openings (foramina, canals, fissures, lacerum)

• 8 cranial, 14 fascial bones

frontal bone

• cranial bone

• glabella: midline of frontal bone

• frontal squama: forehead

• supraorbital margins: bony recess supporting and protecting the eyeballs

• supraorbital foramen: opening above orbits, transmits supraorbital artery/nerve

• lacrimal fossa: tear gland that lubricates eye surface

parietal bones

• cranial bone (paired)

• superior/inferior temporal lines: rides on external surface, attachment of temporalis muscle (closes mouth)

• parietal eminence: smooth surface superior to temporal lines

occipital bone

• cranial bone

• foramen magnum: hole where spinal cord passes, connected to brain

• occipital condyles: facets on base, articulate with superior facets of atlas

• hypoglossal canals: passageway for cranial nerve XII, at lateral base of condyle

• basioccipital: articulation between occipital bone and sphenoid, bone anterior to foreman magnum

• external occipital crest and protuberance: midline crest extends posterior from foramen magnum to protuberance

• superior/inferior nuchal lines: horizontal ridge intersecting external occipital crest, attachment of muscle and ligaments stabilizing articulation between atlas and occipital condyles

temporal bones

• cranial (paired)

• squamous region: 1) squama 2) cerebral surface 3) zygomatic process: zygomatic arch (defines projection of cheek)

• tympanic region: surrounds external acoustic meatus, styloid process: attachment site for ligaments, “part of petrous region”

• mastoid region: posterior to ear, “incorporated with petrous region”, mastoid process: anchors some neck muscles

• petrous region: lateral region, 1) jugular foramen 2) carotid canal 3) foreman lacerum 4) internal acoustic meatus

sphenoid

• cranial bone, “bat shaped”

• sphenoid body + 3 pairs of processes: 1) greater wings 2) lesser wings 3) pterygoid process (attachment site for pterygoid muscles)

• sella turcica: 1) hypophyseal fossa: houses hypophysis (pituitary gland), 2) anterior clinoid process, 3) tuberculum sellae, 4) dorsum sellae, 5) posterior clinoid process, inferior surface form part of orbit, superior part form superior orbital fissure, 6) optic groove, 7) optic canal

5 important openings of sphenoid

1) optic foremen: anterior to sella turcica, CN II

2) superior orbital fissure: slit between greater/less wings, CN III, IV, VI (controls eye movement control)

3) foramen rotundum: lateral to sella turcica, CN V

4) foramen ovale: posterior to sella turcica, CN V

5) foremen spinosum: inferior suspect, middle meningeal artery

ethmoid

• cranial bone, between nasal cavity and orbits, 3 major parts

• cribriform plates: 1) olfactory foramina, 2) crista galli: attached to falx cerebri

• ethmoidal labyrinth: superior/middle nasal conchae

• perpendicular plate: superior part of nasal septum, lateral masses

cranial bone sutures

• coronal suture

• squamous suture

• sagittal suture

• lambdoid suture

• frontonasal suture

• occipitomastoid suture

mandible

• facial bone

• 1) mandibular body

• 2) rami of mandible

• 3) mandibular angles

• 4) alveolar margin

• 5) condylar processes: forms mandibular condyles

• 6) coronoid process: temporalis muscle attachment

• 7) mandibular notch:

• 8 ) mental foramina: 1) mylohyoid line of mandible: origin of mylohyoid muscle, 2) submandibular fossa: submandibular salivary gland is located, 3) mandibular process:

maxillae

• paired facial