Introduction to Skeletal System - Surface Landmarks of the Skull.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

Bones: Axial Skeleton • Consists of bones, cartilage, joints & ligaments (ligaments connect bones & reinforce joints) • Joints (articulations) – junctions between skeletal elements • 206 named bones of human skeleton are grouped into axial or appendicular skeleton o Axial  Long axis of the body  80 named bones  Arranged into three major categories: skull, vertebral column & thoracic cage  Supports head, neck & trunk  Protects brain, spinal cord & thoracic organs o Appendicular  Bones of upper & lower limbs  Pectoral (shoulder) that attach upper limbs  Pelvic girdles that attach lower limbs Skull • Body’s most complex bony structure • Formed by cranial & facial bones (viscerocranium) • Enclose & protect the brain & provide attachment sites for head & neck muscles • Facial bones o Form framework of the face o Form cavities for organs of sight, taste & smell o Provide openings for passage of air & food o Hold teeth o Anchor muscles of the face • Most skull bones are flat & are firmly united by interlocking, immovable joints called sutures • Suture lines have an irregular saw-toothed appearance • Longest sutures – coronal, sagittal, squamous & lambdoid sutures o Connect cranial bones • Most other skull sutures connect facial bones & named according to specific bones they connect • Bregma: Sagittal suture meets coronal suture • Pterion o 4 different bones coming together (frontal, posterior termporal & sphenoid) o Weakest point of skull (not solid bone) o VERY THIN; Easy to break o Inside of skull, there is a major artery o Middle meningeal runs along pterion Overview • With lower jaw removed – skull resembles lopsided, hollow, bony sphere • Facial bones form anterior aspect • Cranium forms the rest • Cranium is divided into o Vault – calvaria or skullcap  Forms the superior, lateral & posterior aspects of skull & forehead region o Base  Inferior part  Internal prominent body ridges divide base into three distinct fossae (steps) – anterior, middle & posterior cranial fossae • Brain is said to occupy cranial cavity • Also contains smaller cavities o Middle ear cavity – lateral aspect of cranial base o Inner ear cavity – lateral aspect of cranial base o Nasal cavity – in & posterior to nose o Orbits – house eyeballs • Air-filled sinuses that occur in several one around nasal cavity are paranasal sinuses • Has 85 named openings (foramina, canals & fissures) • Most important of these provide openings for spinal cord, major blood vessels for brain & 12 pairs of cranial nerves Cranial Bones • 8 large bones o Paired parietal & temporal bones o Unpaired frontal, occipital, sphenoid & ethmoid bones • Superior aspect is curved – skull is self-bracing • Bones are thin & egg-shell like Petrous Ridge Edge between middle and posterior Parietal Bones & Major Sutures • Two large parietal bones - shaped like curved rectangles • Make up the bulk of calvaria – form superior aspect & lateral walls of skull • Sites at which parietal bones articulate (form a joint) with other cranial bones are 4 largest sutures: o Coronal suture  Running in coronal plane  Occurs anteriorly – parietal bones meet frontal bone o Squamous suture  Lateral aspect of skull  Occurs where each parietal bone meets temporal bone inferiorly o Sagittal suture  Occurs where right & left parietal bones meet superiorly in the midline of cranium o Lambdoid suture  Occurs where parietal bones meet occipital bone posteriorly  Resembles Greek letter lambda – hence the name • Sutures vary in appearance in different skulls • As a person ages – sutural lines close up – making sutures less noticeable Sutural Bones • Small bones that occur within sutures – especially lambdoid suture • Irregular in shape, size & location • Not all people have them • Develop between major cranial bones during fetal period & persist throughout life • Significance is unknown Frontal Bone • Forms forehead & roofs of orbits • Just superior to orbits – protrudes slightly to form superciliary arches (lie just deep to eyebrows) • Supraorbital margin or superior margin of each orbit is pierced by a hole or by a notch - called supraorbital foramen or supraorbital notch • Opening transmits supraorbital nerve (branch of cranial nerve V) & artery – supply the forehead • Smooth part of frontal bone between superciliary arches in midline is glabella • Just inferior to it – frontal bone meets nasal bones at frontonasal suture • Regions of frontal bone lateral to glabella contain air-filled frontal sinuses • Internally – frontal bone contributes to anterior cranial fossa – holds large frontal lobes of brain Occipital Bone • Makes up posterior part of cranium & cranial base • Articulates with parietal bones at lambdoid suture & with temporal bones at occipitomastoid sutures • Several features occur on external surface o External occipital protuberance  Knob in the midline  Junction of base & posterior wall of skull o External occipital crest  Extends anteriorly from protuberance to foramen magnum  Secures ligamentum nuchae – elastic, sheet-shaped ligament that lies in median plane of posterior neck & connects neck vertebrae to skull o Superior nuchal lines  Extend laterally from occipital protuberance  Marks upper limit of neck  Nuchal lines & body regions between them anchor many muscles of neck & back o Inferior nuchal lines  Running laterally from point halfway along occipital crest  Nuchal lines & body regions between them anchor many muscles of neck & back • Internally – forms walls of posterior cranial fossa – holds cerebellum • In the base – foramen magnum (large hole) o Inferior part of the brain connects with spinal cord • Foramen Magnum - flanked laterally by 2 rocker-like occipital condyles – articulate with first vertebra of (head is allowed to make a “yes” movement) • Hidden medial & superior to each occipital condyle hypoglossal canal – cranial nerve XII runs through • Anterior to foramen magnum – occipital bone joins sphenoid bone via basilar part of occipital bone Temporal Bones • Best viewed laterally • Lie inferior to parietal bones & form inferolateral region of skull & parts of cranial floor • Temporal/temple – gray hairs first appear at temples (passage of time) • Each temporal bone has intricate shape & has 3 major parts o Squamous  Plate-shaped  Abuts squamous suture  Has bar-like zygomatic process – projects anteriorly to meet zygomatic bone of face • Together make zygomatic arch – cheek bone  Oval mandibular fossa on inferior surface of zygomatic process receives condylar process of mandible (lower jaw bone) - forming movable temporomandibular joint o Tympanic  Surrounds external acoustic meatus or external ear canal  Through this canal that sound enters ear  External acoustic meatus & tympanic membrane (eardrum) at its deep end are parts of external ear  In dried skull – tympanic membrane has been removed • Part of the middle ear cavity deep to tympanic region is visible o Petrous  Contributes to cranial base  Forms body wedge between occipital bone posteriorly & sphenoid bone anteriorly  Form within cranial cavity – very dense region looks like a mountain ridge  Posterior slope of ridge lies in posterior cranial fossa  Anterior slope of the ridge lies in middle cranial fossa – holds temporal lobes  Housed inside – cavities of middle & inner ear (sensory apparatus of hearing/balance) • Several foramen penetrate petrous part o Large jugular foramen  Located where petrous parts join occipital bone  Largest veins of the head pass through - internal jugular vein  Cranial nerves IX, X, XI o Carotid canal opens on skull’s inferior aspect – anterior to jugular foramen  Internal carotid artery (main artery to brain) passes through o Foramen lacerum  Jagged opening between medial tip of petrous part & sphenoid bone  Almost completely closed by cartilage in living person but visible in dried skull o Internal acoustic meatus  Lies in cranial cavity on posterior face of petrous part  Transmits cranial nerves VII & VIII • Projecting inferiorly from petrous part is needle-like styloid process o Attachment point for some muscles of tongue & pharynx o Attachment point for ligament that connects skull to hyoid bone of neck • Lateral & posterior to styloid process is mastoid process o Breast-shaped o Anchoring site for some neck muscles o Can be felt as lump just posterior to ear o Full of air sinuses called mastoid air cells – lie just posterior to middle ear cavity  Mastoiditis (infection) can spread from throat to middle ear to mastoid cells • Spread to brain – mastoid air cells are separated by a thin roof of bone • Stylomastoid foramen o Located between styloid & mastoid processes o Branch of cranial nerve CII leaves skull through this foramen Sphenoid Bone • Spans width of cranial floor • Resemble a bat with wings spread • Keystone of cranium – forms central wedge that articulates with every other cranial bone • Portions are viewable from most aspects of skull • Consists of o Central body o 3 pairs of processes: greater wings, lesser wings & pterygoid processes • Superior surface of body bears saddle-shaped prominence: sella turcica o Seat of saddle: hypophyseal fossa – holds pituitary gland or hypophysis • Within body are paired sphenoidal sinuses • Greater wings o Protect laterally from body – forming parts of middle cranial fossa & orbit o Externally, form lateral wall of skull anterior to squamous part of temporal bones • Lesser wings o Horn-shaped o Form part of the floor of anterior cranial fossa & part of orbit • Pterygoid processes o Trough-shaped (winglike) o Project inferiorly from greater wings o Have medial & lateral plates o Attachment sites for pterygoid muscles that help close the jaw in chewing • 5 important openings on each side o Optic canal  Lies just anterior to sella turcica  Cranial nerve II passes through hole from orbit into cranial cavity o 4 other openings lie in crescent-shaped row just lateral to body on each side  Superior orbital fissure • Most anterior • Long slit between greater & lesser wings • Transmits several structures to & from orbit (cranial nerve III, IV, VI) • Seen in anterior view of orbit  Foramen rotundum • Lies in medial part of greater wing • Usually oval (despite name which means round) • Allow passage for large branches of cranial nerve V exiting cranium  Foramen ovale • Oval hole posterolateral to foramen rotundum • Allow passage for large branches of cranial nerve V exiting cranium  Foramen spinosum • Small & posterior & lateral to foramen ovale • Short spine that projects from its margin on inferior aspect of skull • Middle meningeal artery (supplies blood to broad inner surfaces of parietal bones & squamous part of temporal bones) passes through Ethmoid Bone • Most deeply situated • Lies anterior to sphenoid bone & posterior to nasal bones • Forming most of the medial bony area between nasal cavity & orbits • Thin-walled, delicate & only small portions are visible • Superior surface is formed by paired, horizontal cribriform plates o Contribute to roof of nasal cavities & floor of anterior cranial fossa o Perforated by tiny holes cribriform foramina o Filaments of cranial nerve I passes through holes as they run from nasal cavity to brain • Between cribriform plates, in the midline, is superior projection crista galli • Fibrous membrane falx cerebri attaches to crista galli & helps to secure brain in cranial cavity • Perpendicular plate o Projects inferiorly in median plane o Forms superior part of nasal septum – vertical partition that divides nasal cavity into R & L • Ethmoidal Labyrinth o Flanking perpendi
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