Chapter 5

Axial Skeleton

3 parts: skull, vertebral column, bony thorax

Skull: cranium and facial – all but one joined by sutures

• Cranium: 8 large flat bones – 2 paired – rest single– Frontal– Parietal (pair)

• Meet at sagittal suture• Coronal suture – btw

parietal and frontal

– Temporal (pair) – meet parietal at squamous suture• External acoustic meatus – canal to

eardrum• Styloid process – inferior to acoustic

meatus – neck muscle attachment• Zygomatic process – joins cheek bone• Mastoid process – posterior and inferior to

acoustic meatus–Mastoid sinuses – air cavities

• Jugular foramen – allow passage of jugular vein

– Occipital – joins parietal at lamboid suture• Foramen magnum – large opening for spinal

cord• Occipital condyles – sit on 1st vertebra

– Sphenoid bone – butterfly shaped – floor of cranial cavity• Sella turcia – depression that holds pituitary• Foramen ovale – opening for cranial nerve to

mandible• Optic canal and

superior orbital fissure – allow nerves for eye

– Ethmoid bone – anterior to sphenoid• Roof of nasal cavity and medial walls of

orbits• Crista galli – outer brain covering attaches• Cribriform plates – allow nerves through

• Facial: 14 bones – 6 paired – 2 single– Maxillae (maxillary bones)

• Upper jaw – keystone of face• Alveolar margin – holds teeth• Palatine processes – anterior portion of

hard palate• Paranasal sinuses –

openings – drain into nasal passage

– Palatine bones• Posterior to palatine processes• Posterior part of hard palate• Failure to fuse = cleft palate

– Zygomatic bones – cheekbones – Lacrimal bones

• Fingernail size• Medial wall of orbit• Grooved for tear

passage

– Nasal bones - bridge of nose– Vomer – single – nasal septum– Inferior Nasal Conchae

• Project from lateral walls of nasal cavity– Mandible – single

• Lower jaw• Only free movable joint of skull – meets

temporal bones• Body – horizontal part• Rami (ramus) –

upright bars

• Hyoid bone– Suspended in midneck region

• 2cm above larynx– Held by ligaments – touches

no other bones– Body and 2 pairs of horns

(greater and lesser)– Movable base for tongue

• Fetal skull– Fontanels – soft spots

• allow compression during birth

Vertebral column (spine)

• Before birth – 33 vertebrae• 9 fuse to form sacrum and coccyx• 24 single vertebrae

– 7 cervical – neck– 12 thoracic – back– 5 lumbar – lower back

• Vertebrae separated by intervertebral discs– Cushion and absorb shock

• Primary curvature– In thoracic and sacral – present from birth

• Secondary curvature– Cervical – appears when baby begins to raise

head– Lumbar – appears when baby begins to walk

• Vertebrae– Parts

• Body (centrum) – weight bearing – faces anterior• Vertebral arch – joining of lamina and pedicle• Vertebral foramen – canal for spinal cord• Transverse processes – projection off arch• Spinal processes –

projection off posterior• Superior and inferior

articular processes – Lateral to vertebral

foramen– Joints w/ other vertebrae

• Cervical – C1 – C7– 1st – atlas – no body

• Depressions in transverse processes to receive occipital condyles

• Allow nodding– 2nd – axis – acts as a pivot

• Dens – pivot point– All have transverse foramen for cranial nerves

• Thoracic – T1 – T12– Costal facets – receive ribs– Have long spinous processes

• Lumbar – L1 – L5– Short, chunky spinous processes

• Sacrum – 5 fused vertebrae– Alae – wings – articulate w/ hips– Median sacral crest – fused

spinous processes– Sacral foramen – openings– Sacral canal – for spinal cord – ends @ sacral hiatus

• Coccyx – 3-5 fused vertebrae – tailbone

Bony Thorax – thoracic cavity• Sternum – breastbone

– Fusion of manubrium, body, and xiphoid process

– 7 ribs attach– Jugular notch – upper border

of manubrium– Sternal angle – where

manubrium and body meet– Xiphisternal joint – where

body and xiphoid process meet

– Sternal puncture – w/draw hematopoietic tissue

• Ribs – 12– True ribs – 1st 7 – attach to

sternum– False ribs – next 5

• 3 – attach to ribs by costal cartilage

• 2 – floating – don’t attach to anything

– Intercostal space – btw ribs – filled w/ muscle