Ch 7 axial skeleton

•Axial skeleton: skull, vertebral column, and thoracic cage

•Appendicular skeleton: shoulder and hip bones and those of the upper and lower extremities

•Cranial bones:

•Unpaired: ethmoid, frontal, occipital, and sphenoid

•Paired: parietal and temporal

•Facial bones:

•Unpaired: vomer and mandible

•Paired: maxillae, nasal, lacrimal, zygomatic, palatine, and inferior nasal conchae

Contains many cavities, the largest being the cranial cavity which houses the brain

Immovable joints between skull bones

•Coronal suture: between frontal and parietal bones

•Lambdoid suture: between occipital and parietal bones

•Sagittal suture: between parietal bones

•Squamous suture: between temporal and parietal bones

May contain sutural bones variable in size, number, and location

Calvaria: Skullcap; roof of cranium

•Made of parietal bones and parts of frontal and occipital bones

Base of cranium: floor

•Made of parts of ethmoid, sphenoid, occipital and temporal bones

fossa is a depression in a bone

The floor of the cranial cavity contains three cranial fossae:

•Anterior cranial fossa

•Middle cranial fossa

Posterior cranial fossa

The nasal complex is composed of bones and cartilages forming the nasal cavities and paranasal sinuses

Superior border: cribriform plate of ethmoid, parts of frontal and sphenoid

Inferior border: maxillae and palatine bones

Lateral walls: ethmoid, maxillae, inferior nasal conchae, palatine bones, and lacrimal bones

air-filled spaces within the skull bones surrounding the nasal cavity

-protect the eyes, and the orbital complex consists of multiple bones that form each orbit

•Roof of orbit: frontal bone and lesser wing of sphenoid bone

•Floor: mainly the maxilla bone

•Medial wall: maxilla, lacrimal, and ethmoid bones

•Lateral wall: zygomatic, greater wing of sphenoid, and frontal bones

•Posterior wall: mainly the sphenoid bone

Three tiny bones in petrous part of each temporal bone are for hearing:

•Malleus

•Incus

•Stapes

between the mandible and larynx

•Does not articulate with another bone

•Contains a midline body and two hornlike processes, the greater cornu and lesser cornu

Human male and female skulls show differences in shape and size

female are delicate and small,

male are larger, sturdier, and bulkier

Infant cranial bones are connected by flexible areas of dense regular connective tissue called fontanelles

•Mastoid fontanelle

•Sphenoidal fontanelle

•Posterior fontanelle

•Anterior fontanelle

cervical vertebrae (C₁-C₇) form the bones of the neck

thoracic vertebrae (T₁-T₁₂) form the superior regions of the back

•Each thoracic vertebra articulates with a pair of ribs

lumbar vertebrae (L₁-L₅) form the lower back

sacrum (S₁-S₅) five fused sacral vertebrae

coccyx (“tailbone”) four coccygeal vertebrae (Co₁-Co₄) 

•Begin to fuse during puberty

•Cervical curvature

•Thoracic curvature

•Lumbar curvature

•Sacral curvature

appear in fetal development

•Thoracic and sacral curvatures

•Secondary curves appear at 3–4 months of age

•Cervical and lumbar curvatures

•Help shift trunk’s weight over the legs

•Body: weight-bearing region

-Adjacent bodies separated by pad of fibrocartilage (intervertebral disc)

•Vertebral arch: attaches to body to form vertebral foramen

-Pedicles: feet of the arch

-Laminae: posterior extensions of the arch

-Stacked vertebral foramina form vertebral canal (contains spinal cord) and intervertebral foramina (passage for spinal nerves)

•Processes:

-Spinous processes project posteriorly

-Transverse processes project laterally

-Inferior articular processes of each vertebra attach to the superior articular processes of the vertebra immediately inferior to it

-Each articular process has smooth articular facet

triangular bone forming posterior wall of pelvic cavity

•Apex: points inferiorly; base is broad superior surface

•Transverse ridges mark fusion points of the five vertebrae

•Sacral canal is continuation of vertebral canal

•Sacral hiatus in inferior opening

•Anterior and posterior sacral foramina allow nerves to exit

•Has an auricular surface at sacroiliac joint

•fusion of four small vertebrae

•Attachment site for ligaments and muscles

•Coccygeal cornua are the laminae of the first coccygeal vertebrae

•Thoracic vertebrae posteriorly

•Ribs laterally

•Sternum anteriorly

Protects heart, lungs, trachea, esophagus, and other thoracic organs

“breastbone” in anterior midline of thoracic wall

•Manubrium

•Body

•Xiphoid process

articulate posteriorly with thoracic vertebrae and end in the anterior wall of the thorax

Articular facets on the head and tubercle of each rib articulate with vertebral body and transverse process, respectively

•True ribs: 1–7; articulate anteriorly with the sternum via costal cartilages

•False ribs: 8–12; their costal cartilages do not attach directly to the sternum

•Floating ribs: false ribs (pairs 11 and 12) that do not articulate with the sternum

Many bones fuse as we age

Skeletal mass and density become reduced

Bones can become more porous and brittle (osteoporosis), enhancing chance of fracture

Articulating surfaces deteriorate, contributing to arthritic conditions

bones form from cartilage

Flat skull bones develop from mesenchyme

Sternum develops from cartilaginous sternal bars that fuse medially