Chapter 7 - The Axial Skeleton

Axial skeleton

bones along the body’s axis: skull bones, auditory ossicles, hyoid bone, ribs, sternum, and bones of the vertebral column.

Appendicular skeleton

Bones of the upper and lower limbs and the bones forming the girdles.

Girdles

the bones that connect the limbs to the axial skeleton.

Number of bones in the axial skeleton

80

Number of bones in the appendicular skeleton

126

Total bones in the human body

206

Long bones

have greater length than width, consists of a shaft and epiphyses, and are slightly curved for strength.

Short bones

nearly equal in length and width. Most made of spongy bone tissue.

Flat bones

generally thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue.

Irregular bones

have complex shapes and vary in the amount of spongy and compact bone present.

Sesamoid bones

develop in certain tendons where there is considerable friction, tension, and physical stress. They vary in number and are not always completely ossified and are usually very small.

Sutural bones

small bones located in sutures (joints) between certain cranial bones. Their number varies greatly from person to person.

Red bone marrow is restricted to…

• Flat bones - ribs, sternum, skull

• Irregular bones - vertebrae, hip bones

• Long bones - proximal epiphyses of the femur and humerus

• Some short bones

Surface markings

Structural features on bone adapted for specific functions.

Depressions and Openings

allow the passage of soft tissues or form joints

Processes

projections or outgrowths that either help form joints or serve as attachment points for connective tissue.

Fissure

Narrow slit between adjacent parts of bones through which blood vessels or nerves pass.

Foramen

Opening through which blood vessels, nerves, or ligaments pass.

Fossa

Shallow depression

Sulcus

Furrow along bone surface that accommodates blood vessel, nerve or tendon.

Meatus

Tubelike opening

Condyle

Large, round protuberance with a smooth articular surface at the end of bone.

Facet

smooth, slat, slightly concave or convex articular surface

Head

usually rounded articular projection supported on neck of bone

Crest

prominent ridge or elongated projection.

Epicondyle

Typically roughened projection above condyle

Line

Long, narrow ridge or border (less prominent than crest)

Spinous process

Sharp, slender projection

Trochanter

very large projection

Tubercle

Variably sized rounded projection

Tuberosity

Variably sized projection that has a rough, bumpy surface.

Number of cranial bones

8

Number of facial bones

14

Orbits

eye sockets

Metopic suture

unites the left and right sides of the frontal bone after birth and disappears between the ages of 6 and 8.

Frontal squama

a scalelike plate of bone that forms the forehead of the skull.

Supraorbital margin

superior border of the orbitals where the frontal bone thickens.

Temporal squama

the thin, flat part of the temporal bone that forms the anterior and superior part of the temple.

Zygomatic process

projects from the infereior portion of the temporal squama and articulates (forms a joint) with the temporal process of the zygomatic (cheek) bone.

Zygomatic arch

formed with the zygomatic process of the temporal bone and the temporal process of the zygomatic bone together.

mandibular fossa

located on the inferior posterior surface of the zygomatic process of each temporal bone.

Articular tubule

a rounded elevation, anterior to the mandibular fossa.

Temporo-mandibular joint (TMJ)

the mandibular fossa and articular tubercle articulate with the mandible.

Mastoid portion of the temporal bone

located posterior and inferior to the external auditory meatus or ear canal.

Mastoid process

a rounded projection of the mastoid portion of the temporal bone posterior and inferior to the external auditory meatus. Point of attachment for several neck muscles.

Mastoid air cells

communicate with the hollow space of the middle ear

internal auditory meatus

the opening through which the facial (VII) nerve and vestibulocochlear nerve pass.

Styloid process

projects inferiorly from the inferior surface of the temporal bone and serves as a point of attachment for muscles and ligaments of the tongue and neck.

Stylomastoid process

between the styloid process and the mastoid process through which the facial nerve and stylomastoid artery pass.

Petrous portion of the temporal bone

triangular part located at the base of the skull between the sphenoid and occipital bones, houses the internal ear and the muddle ear. Also contains carotid foramen.

Carotid foramen

through which the carotid artery passes.

Jugular foramen

Through which the jugular vein passes.

Foramen magnum

medulla oblongata connects with the spinal cord through this foramen. The vertebral and spinal arteries and the accessory nerve also pass through.

Occipital condyles

articulate with depressions on the first cervical vertebra to form the atlanto-occipital joint

Atlanto-occipital joint

allows you to nod your head “yes”.

External occipital protuberance

bump on the back of the head

Ligamentum nuchae

ligaments that extends from the external occipital protuberance to the seventh cervical vertebra to help support the head.

Sphenoid bone

keystone of the cranial floor because it articulates with all the other cranial bones and holds them all together.

Sphenoidal sinus

drains into the nasal cavity

Hypophyseal fossa

contains the pituitary gland

Optic foramen/canal

the optic nerve and ophthalmic artery pass through into the orbit.

Superior orbital fissure

blood vessels and cranial nerves pass through

Nasal septum

divides the nasal cavity into left and right sides.

Ethmoid bone

Major superior supporting structure of the nasal cavity and forms an extensive surface area in the nasal cavity.

Cribriform plate

forms the roof of the nasal cavity

Olfactory foramina

olfactory nerves pass through

crista galli

serves as a point of attachment for the falx cerebri

Falx cerebri

the membrane that separates the two sides of the brain

Perpendicular plate

forms the superior portion of the nasal septum

Lateral masses

compose most of the wall between the nasal cavity and the orbits and contain ethmoidal cells.

ethmoidal cells

air spaces (usually 3-18) that together, form the ethmoidal sinuses.

Nasal conchae

increase the vascular and mucous membrane surface area in the nasal cavity which warms and moistens inhaled air before it goes to the lungs.

Nasal bones

form the bridge of the nose

Lacrimal fossa

houses the lacrimal sac

Lacrimal sac

gathers tears and passes them into the nasal cavity

Inferior nasal conchae AKA turbinates

are considered separate bones and not part of the ethmoid bone.

Superior nasal conchae

involved in the sense of smell

Maxillae

articulate with every bone of the face except the mandible.

Hard palate

formed by the palatine processes of the maxillae and horizontal plates of the palatine bones. Separates the nasal cavity from the oral cavity.

Maxillary sinus

empties into the nasal cavity

Alveolar process of the maxilla

contains the alveoli (sockets) for the maxillary (upper) teeth.

Infraorbital foramen

infraorbital blood vessels and nerves pass through.

Incisive foramen

transmits branches of the greater palatine blood vessels and nasopalatine nerve.

The rami of the mandible

the two perpendicular portions of the mandible.

Angle of the mandible

where each ramus meets the body

Condylar process

articulates with the mandibular fossa and articular tubercle of the temporal bone to form the TMJ.

coronoid process

to which the temporalis muscle attaches.

Mandibular notch

the depression between the coronoid and condylar processes.

alveolar process of the mandible

contains the alveoli (sockets) for the mandibular (lower) teeth.

mandibular canal

inferior alveolar nerves and blood vessels pass through.

Three components of the nasal septum

vomer, septal cartilage and the perpendicular plate of the ethmoid bone.

This many bones of the skull join to form each orbit

7

The three cranial bones of the orbit

frontal, sphenoid and ethmoid.

The four facial bones of the orbit

palatine, zygomatic, lacrimal and maxilla.

5 openings associated with each orbit

1. optic foramen

2. superior orbital fissure

3. inferior orbital fissure

4. supraorbital foramen

5. lacrimal fossa.

Suture

an immovable joint that holds most skull bones together.

Coronal suture

unites the frontal bone and both parietal bones

Sagittal suture

unites the two parietal bones on the superior midline of the skull.

Lambdoid suture

unites the two parietal bones to the occipital bone

Squamous sutures

unite the parietal and temporal bones