Download Bones of the Axial Skeleton Notes

Skeletal System – Bones of the Axial Skeleton
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Axial Skeleton: The Skull- Cranial Bones
o Frontal Bone- anterior cranium, articulates posteriorly with parietal bones
 frontal squama- forehead
 supraorbital ridges/margins- inferior end of frontal squama- thicken regions under eyebrows
 superior walls of orbits- posterior to ridges
 each pierced by supraorbital foramen- notch- allows supraorbital artery and nerve to pass
 glabella= smooth part between orbits, riddled with frontal sinuses laterally
 supraorbital fossae- supports frontal lobes of brain, back from margins and orbits
o Parietal bones- large, curved rectangular; forms most of superior and lateral aspects of skull- bulk of cranial vault4 large sutures attach to other bones
 coronal suture – to frontal bone anteriorly
 sagittal suture – superiorly to cranial midline (parietals meet)
 lambdoid suture- meet occipital posteriorly
 squamous suture- parietal and temporal meet on lateral aspect of skull
o Occipital Bone-most of skulls posterior walls and base- articulates with parietal (lambdoid suture), temporal
(occipitomastoid sutures) and sphenoid bones (basioccipital suture)
 Walls of posterior cranial fossae (interior)- supports cerebellum
 Foramen magnum- large opening where spinal cord connects with brain at base of skull
 occipital condyles- on laterals of foramen magnum- articulate with first vertebra (nodding, etc)
 external occipital protuberance (crest and nuchae)- superior to foramen magnum- knoblike- you can feel
just below most bulging posterior skull
o Temporal bones- articulate with parietals (squamous sutures) and= inferolateral aspects of skull and part of cranial
floor
 Latin root: temporum- time (gray hairs appear here first!)
 Zygomatic process- meets zygomatic bone of fac; bar shaped bone protruding forward
 Mandibular fossa- inferior surface of zygomatic process, receives condyle of mandible- part of
temporomandibular joint (TMJ)
 External auditory/acoustic meatus- (tympanic region) external ear canal- houses the ear, eardrum is the
deepest part
 styloid process- below meatus- attachment for tongue and neck muscles and ligaments secure hyoid
bone (more later) of neck to skull
 mastoid process- (mastoid region)- anchoring site for some neck muscels, lump posterior to ear
 full of sinuses- adjacent to middle ear= high-risk area for infections to spread from throat risk
of infection itself mastoid sinus infection  hard to treat, mastoid sinuses separate from brain
only by thin bony plate, risk infection spread to brain. Now treated with antibiotics, used to
surgically remove mastoid process
o Sphenoid- spans middle cranial fossa- keystone bone of cranium= articulates with all others- central body with 3
processes- greater wings, lesser wings and pterygoid processes
 sella turcica- superior surface has saddle-like prominence (where pituitary gland sits)
 Paired sphenoid sinuses
 greater wings- project laterally from body (part of middle cranial fossa, dorsal walls of orbits, and external
wall of skull, look like flags medial to zyg arch)
 optic foramina (canal)- in sphenoid, connecting by chiasmatic groove- anterior to sella turcicaa-optic
nerves pass through to eyes
 Foramen present for passage of many facial nerves
o Ethmoid- between sphenoid and nasal bones of face- deepest bone of skull- forms most of bony area between
nasal cavit and orbits
 cribiform plates- superior surface- help form roof of nasal cavities and floor anterior cranial fossa
 Foramen for passage of facial nerves
 ethmoid sinuses- lots in lateral mass on each side of plate (ethmos= sieve)
 middle nasal conchae- medial from lateral masses- protrude in nasal cavity
o Sutural- or Wormian- bones- groups irregular shaped bones seen within sutures. They vary in # and are not
regularly present in all skulls. Unusual finding, but not rare.
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The Skull- Facial Bones (14, most are paired)
o Men tend to be longer than women, women less angular (rounder)
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Functions of facial bones= 1) framework of face, 2) cavities for special sense organs (sight, taste and smell) 3)
openings for air and food, 4) secure teeth, 5) anchor facial muscles or expression
Mandible (unpaired, though starts as 2, fuses during infancy)- lower jaw bone- largest and strongest bone of face
 Body- chin
 Rami- upright angular portion that meets the skull
 coronoid processes- anterior= insertion point for large temporalis muscle (chewing)
 mandibular condyles- articulate with mandibular fossa of temporal bones (temporomandibular joint)
 alveoli- superior border- sockets for teeth
 mandibular foramen- 1 on each medial surface of rami, permit nerves responsible for tooth sensation to
pass to teeth in lower jaw- where dentist injects lidocaine
 mental foramen- openings on laterals of rami, allow blood vessels and nerves to skin of chin and lower lip
Maxillae- fused medially- upper jaw- central portion of facial skeleton, all bones articulate with except mandible=
keystone bones of facial skeleton (Also have alveoli- upper teeth)
 frontal processes- superior to frontal bone, forming lateral parts of bridge of nose
 maxillary sinus- largest of paranasal sinuses (more Monday) flank nasal cavity from orbits to roots of
upper teeth
 infraorbital foramen- allows infraorbital nerve and artery to reach face
Zygomatic- cheek bones
 Articulate with zygomatic processes of temporal posteriorly and zygomatic process of frontal bone
superiorly and zygomatic processes of maxillae anteriorly
 Zygomatic arch
Nasal- thin, rectangular (basically) bone fused medially to form the bridge of nose,
 articulate with: superior- frontal bone, lateral- maxillary bones, posterior- perpendicular plate of ethmoid,
inferior part is all cartilage that forms most of the external nose
Lacrimal- medial walls of orbits- very delicate
 Articulate with: superior- frontal bone, posterior- ethmoid bone- anterior- maxillae
 Lacrimal fossa- deep grove allows passage of tear ducts
Palatine- L shaped bone that creates posterior portion of hard palate (horizontal plates) and posterolateral walls of
nasal cavity and small part of orbits (perpendicular plates)
Vomer- nasal septum

Orbits, Nasal Cavity, Sinuses and Hyoid Bone
o Orbits- bony cavities that hold and cushion (with fatty tissue) the eyes
 Muscles that move the eyes and the lacrimal glands also are in orbits
 Walls are formed by 7 bones: frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid
o Nasal Cavity- bone and hyaline cartilage
 Mucus secreting mucosa cover nasal septum and conchae- helps moisten, heat, and filter air entering
respiratory sys- conchae shape allows air to swirl for extra contact
o Paranasal Sinuses- because clustered around nasal cavity, air-filled, small openings connect to nasal cavity
 Mucosa lined- helps warm air
 Lighten skull and increase resonance of voice
o Hyoid Bone- movable base for tongue, just inferior to mandible (anterior neck)
 Does not articulate with any bones; (stylohyoid) ligaments anchor it to styloid process of temporal bones
 Body and two “horns”- attachment for neck muscles- raise and lower larynx during swallowing and speech

The vertebral column (Spine)
o 26 irregular bones with flexible curved structure for axial support of trunk- skull to pelvis
 33 separate vertebrae in fetus, 9 in bottom fuse to form sacrum and coccyx, other 24 stay individual with
intervertebral discs that form between them
o surrounds spinal cord and is attachment for ribs and muscles of back and neck
o 5 main divisions, progressively bigger from top to bottom
 cervical vertebrae= 7, C1-C7
 thoracic vertebrae= 12, T1-T12
 lumbar vertebrae= 5, L1-L5
 sacrum
 coccyx
o general vertebral structure - body (centrum)- weight bearing region, vertebral arch- together with body enclose
vertebral foramen- stacked together= vertebral canal through which spinal cord passes
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7 processes project from arch. The spinous process in the middle; transverse process on each side;
superior and inferior articular processes on each side of top and bottom.
 Smooth surfaces or facets are covered with hyaline cartilage allowing movable articulations with
vertebrae on top and bottom
 Intervertebral foramina are openings between vert where nerves can get through
 Structure differs slightly in different regions by function. In general, movements include flexion and
extension, and rotation
 Cervical vertebrae - body is oval, except C7 (easy one to find because see through skin, land mark for
counting vert), spinous process is short, foramen is large and triangular
 1st two cervical vertebrae are special
o C1= atlas- no body or spinous process, just a ring with articular facets; allow nodding
(Carry skull like atlas carried earth)
o C2= axis- has body and spine, but also has dens- another process superiorly- articulates
with missing body of atlas- pivot for nodding
 Thoracic vertebrae - all articulate with ribs- first a lot like C7, last 4 progress towards lumbar- get
progressively bigger, body is roughly heart shaped, each has 2 small facets- on superior edge and 2 on
inferior= superior and inferior facet allow rotation, prevents flexion and extension, foramen is circular,
spinous process long and points down, articulate with tubercles of ribs
 Lumbar vertebrae – small/curve of back, under most stress, spinous process is short and flat, foramen is
triangular, articulation allows to lock in place and give stability by preventing rotational movement
 Sacrum- S1-S5 in adults, fused
 Coccyx- tailbone- 4 (or for some 3-5) vert fused together, articulates superiorly with sacrum
 nearly useless- sometimes babies are born with it unusually long, doc snips
Intervertebral discs- are cushion-like pads between vertebral bodies- to absorb shock and allow spine to flex and
extend and bend laterally
 thickest in lumbar and cervical regions to give more flexibility
 when compressed, discs flatten and bulge out a bit between vertebrae
Thoracic Cage (Rib Cage)
o Thoracic Cage-thoracic vert (post/dorsal), ribs (lateral), sternum and costal cartilages (ant/vent)- protective cage
for vital organs (heart, lungs, great blood vessels), supports shoulder girdles and upper limbs and serves as a site of
attachment for many muscles of neck, back, chest and shoulders
 Sternum- anterior midline of thorax- flat bone= fusion of 3 bones- manubrium (superior portion, knot in a
necktie) articulates with clavicles (clavicular notches) and 1st pair of ribs, body- midportion- sides are
notched to articulate with ribs and cartilages of 2nd and 7th ribs, xihpoid process- inferior end- hyaline cart
in youth, ossified in adults- attachment for some abdominal muscles- careful with CPR!
 Ribs- 12 pairs- all attach posteriorly to thoracic vertebrae
 Intercostal spaces are filled with intercostal muscles- left and depress thorax when breathing
 Increase in size 1-7, decrease 8-12
 Typically bowed flat bone and easily felt in normal size people (except 1, under clavicle)
 True or vertebrosternal ribs- 1st 7 attach directly to sternum by individual costal cartilages (bars
of hyaline cart)
 False ribs- last 5- indirectly attach to sternum or not at all
o 8-10 indirectly through costal cart above it; also called vertebrochondral ribs
o 11-12 not at all; also called floating ribs- costal cartilages are embedded in muscles of
body wall