The Axial Skeleton

Formed by two sets of bones. ◦ Cranium: encloses and protects the fragile brain

tissue◦ Facial bones: hold the eyes in an anterior position

and allow the facial muscles to show our feelings

Skull

Sutures are interlocking, immovable joints. All but the mandible (jawbone) are joined

together by sutures.

Sutures

Cranial “cavity” – houses brain Smaller cavities

◦ Housing middle and inner ear◦ Nasal cavity◦ Orbits◦ Sinuses

Openings (foramina, canals, fissures) for:◦ Spinal cord◦ Blood vessels◦ Twelve cranial nerves: I-XII

Composed of eight large, flat bones Except for two paired bones ( the parietal

and temporal), they are all single bones 1. Frontal bone – forms the forehead, the

bony projections under the eyebrows, and the superior part of each eye’s orbit

2 &3. Parietal bones – paired bones that form the superior and lateral walls of the cranium, meeting at the midline of the skull

Cranium

4 & 5. Temporal bones – lie inferior to parietal bones and have several important bone markings◦ External acoustic meatus – canal that leads to the

eardrum◦ Styloid process- attachment point for neck muscles◦ Zygomatic process- thin bridge of bone that joins with

the cheekbone (zygomatic bone)◦ Mastoid process – behind ear, contains mastoid

sinuses and point of attachment for neck muscles◦ Jugular foramen, Internal acoustic meatus, and carotid

canal – passageways for blood vessels and nerves

Cranium Continued

6. Occipital bone – most posterior bone of the cranium, forms the floor and back wall of the skull◦ In the base of there is a large hole, foramen

magnum, that surrounds the lower part of the brain and allows the spinal cord to connect with the brain

Cranium continued

7. Sphenoid bone – butterfly- shaped bone that spans the width of the skull and forms part of the floor of the cranial cavity. ◦ Contains Turk’s saddle, which holds the pituitary

gland in place ◦ Contains foramen ovale so the cranial nerves can

pass through

Cranium continued

8. Ethmoid bone- irregular and lies anterior to the sphenoid, forms the roof of the nasal cavity and part of the medial walls of the orbits.

Cranium Continued

Facial bones (anterior aspect of skull)◦ Form framework of face◦ Form cavities for sense organs of sight, taste

and smell◦ Provides openings for passage of air and food◦ Hold the teeth◦ Anchor the muscles of the face

Facial Bones

Fourteen bones Following are all paired:

◦ Maxillae, zygomatics, palatines, nasals, lacrimals, and inferior nasal conchae

Unpaired:◦ Vomer and mandible

Hyoid: not really a skull bone, supported in the neck only by ligaments

Facial Bones

Only bone which does not articulate with any other bone

Moveable base for the tongue

Points of attachment for neck muscles that raise and lower the larynx during swallowing

Hyoid bone

Maxillae : upper jaw Palatine: posterior part of hard palate Zygomatic: Cheekbones, form part of

lateral orbital walls Lacrimal: medial walls of orbits, groove

serves as tear passage Nasal bones: nose bridge

Facial Bones

Of bone and cartilage Roof is ethmoid Floor formed by

palatine processes of the 2 maxillae and horizontal plates of palatine bones◦ These nasal-floor

structures form roof of the mouth, called the hard palate

Nasal cavity nasal bone

ethmoid

vomer

inf nasal concha

(part of slide 18)

maxilla___________

Vomer bone: forms nasal septum Inferior conchae: lateral walls of the nasal

cavity Mandible: lower jaw

Facial bones

Remember that the Axial skeleton includes:

SkullVertebral columnThoracic cage

Axial skeleton is shown in green

Fetus and infant: 33 separate bones, or vertebrae

Adult: 24 vertebrae◦ Inferior 9 have fused forming

The sacrum (5) and The coccyx (4)

The Vertebral Column

Cervical – 7 Thoracic - 12 Lumbar - 5 Sacrum (5 fused) Coccyx (4 fused)

Vertebrae

Cervical and lumbar are concave posteriorly* (lordosis)

Thoracic and sacral are convex posteriorly* (kyphosis)

Abnormal◦ Too much of either◦ Scoliosis (more than 10

degrees of lateral curvature)

*when viewed from the side

Spinal curvatures

Abnormal curvatures

Structure of a typical vertebra

Cervical vertebrae (C1-C7)C1 (atlas)

C2 (axis)

Smallest Lightest Most flexible Triangular

vertebral foramen

Transverse processes have foramina (transverse foramen)

Spinous process bifid (forked) except for C7

Cervical Vertebrae

Heart shaped body

Additional small costal facets (costal=ribs)

Round or oval vertebral foramen

Form posterior part of rib cage

Thoracic Vertebrae T1-T12

Massive blocklike bodies

Short, thick hatchet-shaped spinous processes

Limited mobility

Lumbar Vertebrae L1-L5

The SacrumShapes posterior wall of pelvis

Composite bone of 5 fused vertebrae

Sacral foramina allow passage of vessels & nerves

Coccyx(the tailbone)

Remember that the Axial skeleton includes:

SkullVertebral columnThoracic cage

Axial skeleton is shown in green

The Thoracic Cage

Manubrium

Body

Xiphoid process

True ribs 1-7

False ribs 8-12

Floating ribs 11,12

Sternum Ribs

Vertebral and Sternal Articulations

Typical rib

Skulls of newborns contain fontanels (membranous areas), which allow brain growth.

The infant’s facial bones are very small compared to the size of the cranium

Fetal skull ossifies after 22-24 months

Fetal vs. Adult Skull

Fontanels Unossified remnants

of membranes Present at birth Anterior fontanel

largest Called “soft spots” Ossify by 1 ½ - 2

years

Continue to ossify into adulthood; the sutures can become fused in old age