Skeletal Tissue & The Axial Skeleton Human Anatomy Sonya Schuh-Huerta, Ph.D

Skeletal Tissue & The Axial SkeletonSkeletal Tissue & The Axial Skeleton

Human AnatomyHuman AnatomySonya Schuh-Huerta, Ph.D.Sonya Schuh-Huerta, Ph.D.

Skeletal Tissue, Ch 6

The Skeletal System

• Composed of bones, cartilages, & joints

that form the internal framework of body

-We’ll explore the microscopic & gross structure

of the skeletal tissues & system

Cartilage

• Location & basic structure– Found throughout adult body

• Ear & epiglottis

• Articular cartilages & costal cartilage

• Larynx, trachea, & nose

• Intervertebral discs, pubic symphysis, & articular discs

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Cartilages

Cartilage inexternal ear

Cartilages innose

Articular cartilageof a joint

Costal cartilageCartilagein intervertebraldisc

Pubicsymphysis

Articular cartilageof a joint

Meniscus (padlikecartilage inknee joint)

CartilageEpiglottis

Larynx

Trachea

Cricoidcartilage

Lung

Respiratorytube cartilagesin neck and thorax

Thyroidcartilage

Cartilage

• Is surrounded by perichondrium

• Consists primarily of water

• Resilient tissue it springs back to original shape

Types of Cartilage – Review!

• Hyaline cartilage (glassy) – Most abundant cartilage– Provides support through flexibility

• Elastic cartilage contains many elastic fibers– Able to tolerate repeated bending

• Fibrocartilage resists strong compression & strong tension– An intermediate between hyaline & elastic

Gelatinous groundsubstance

Chondrocyte in a lacuna

Elastic fibersLacuna

Matrix

Chondrocytein a lacuna

Perichondrium

Chondrocyte in a lacuna

Collagen fibers

(a) Hyaline cartilage (180)

(b) Elastic cartilage (470)

(c) Fibrocartilage (285)

Cartilages in the Adult Body (remember these?…)

Growth of Cartilage

• Appositional growth – Chondroblasts in surrounding perichondrium

produce new cartilage

• Interstitial growth – Chondrocytes within cartilage divide &

secrete new matrix

• Cartilage stops growing when the skeleton stops growing

Tissues in Bone

• Bones contain several types of tissues– Dominated by bone CT– Contain nervous tissue & blood– Contain cartilage in articular cartilages– Contain ET lining blood vessels

Function of Bones

• Support – provides hard framework• Movement – skeletal muscles use bones as levers• Protection of underlying organs• Mineral storage – reservoir for important minerals Ca2+

• Blood-cell formation – bone contains red marrow• Energy metabolism – osteoblasts secrete

osteocalcin; & yellow marrow stores fat

Bone Tissue

• Bone tissue– Organic components cells, fibers, & ground

substance– Inorganic components mineral salts that

invade bony matrix (calcium phosphate)

Extracellular Matrix

• Unique composition of matrix– Gives bone exceptional properties– 35% organic components

• Contributes to flexibility & tensile strength

– 65% inorganic components• Provide exceptional hardness, resists compression!

Cells in Bone

• 3 types of cells in bone produce or maintain bone:– Osteogenic cells stem cells that

differentiate into osteoblasts– Osteoblasts actively produce & secrete

bone matrix• Bone matrix = osteoid

– Osteocytes housed within lacunae, keep bone matrix healthy

• Osteoclasts – 4th type of cell– Responsible for resorption of bone– Secrete hydrochloric acid (HCl) & lysosomal

enzymes to break down bone

– The “Grim Reaper”

of bone

Cells in Bone

http://faculty.une.edu/com/abell/histo/histolab3.htm

Classification of Bones

• Long bones longer than wide; a shaft plus ends

• Short bones roughly cube-shaped

• Flat bones thin and flattened, usually curved

• Irregular bones various shapes, do not fit into other categories

Classification of Bones

Gross Anatomy of Bones

• Compact bone dense outer layer of bone

• Spongy bone internal network of bone

Structure of a Typical Long Bone

• Diaphysis = “shaft” of a bone• Epiphysis = ends of a bone• Blood vessels well vascularized • Medullary cavity = hollow cavity filled

with yellow marrow• Membranes

– Periosteum, perforating fibers, &

endosteum

Structure of a Long Bone

Proximalepiphysis

Yellowbone marrow

Endosteum

Epiphysealline

Articular cartilage

Periosteum

Spongy bone

Compact bone

Medullarycavity (linedby endosteum)

Compact bone

Compact bone

Periosteum

Perforating(Sharpey’s)fibers

Nutrientarteries

Diaphysis

Distalepiphysis

Endosteum

Microscopic Structure of Compact Bone

• Compact Bone– Contains passage ways for blood vessels,

lymph vessels, & nerves– Osteons long cylindrical structures

• Function in support• Structurally – resembles rings of a tree in c.s.

Compact bone

Endosteum lining bony canals and covering trabeculae

Perforating (Volkmann’s) canal

Perforating (Sharpey’s) fibers

Periosteal blood vessel

PeriosteumLamellae

Circumferentiallamellae

Osteon(Haversian system)

Central(Haversian) canal

Spongy bone

Interstitial lamellae

Lacunae

Lamellae

Centralcanal

Lacuna (with osteocyte)

NerveVeinArtery

Canaliculi

Osteocytein a lacuna

Lacunae

Lamellae

Central canal

Microscopic Structure of Compact Bone

Microscopic Structure of Compact Bone

• Osteons contain:– Lamellae– Central canal– Perforating canals– Canaliculi

Interstitial lamellae

Lacuna (with osteocyte)

Lacunae

Lamellae

Centralcanal

Structuresin thecentralcanal

Artery withcapillaries

Vein

Nerve fiber

Lamellae

Collagenfibersrun indifferentdirections

Twistingforce

Microscopic Structure of Compact Bone

Microscopic Structure of Spongy Bone

• Spongy Bone– Is less complex than compact bone– Trabeculae contain layers of lamellae &

osteocytes• Are too small to contain osteons (no “tree rings”)

Trabecula

Osteocytes

Endosteum

Marrow space

Osteoblasts

Microscopic Structure of Spongy Bone

Compact bone

Trabeculae

Spongy bone(diploë)

Structure of Short, Irregular, & Flat Bones

– Contain bone marrow but no marrow cavity

– Diploë= Internal spongy

bone of flat bones

Load here(body weight)

Head offemur

Compressionhere

Point of no stress

Tensionhere

Gross Anatomy of Bones

• Bone design & stress– Anatomy of a bone

reflects stresses– Compression &

tension greatest at external surfaces

Bone Markings

• Superficial surfaces of bones reflect stresses on them

• 3 broad categories of bone markings:– Projections for muscle attachment– Surfaces that form joints– Depressions & openings

Bone Markings

Bone Development

• Ossification (osteogenesis) = bone-tissue formation– Membrane bones formed directly from

mesenchyme (during embryonic period)• Intramembranous ossification

– Other bones develop initially from hyaline cartilage

• Endochondral ossification

Intramembranous Ossification

Mesenchymalcell

CollagenfiberOssificationcenter

Osteoid

Osteoblast

Osteoid

Osteocyte

Newly calcifiedbone matrix

Osteoblast

Ossification centers appear in the fibrous connective tissue membrane.• Selected centrally located mesenchymal cells cluster

and differentiate into osteoblasts, forming an ossification center.

Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies.• Osteoblasts begin to secrete osteoid, which is

calcified within a few days.• Trapped osteoblasts become osteocytes.

1 2

Intramembranous Ossification

Mesenchymecondensingto form theperiosteum

Blood vessel

Trabeculae ofwoven bone

Fibrousperiosteum

Osteoblast

Plate ofcompact bone

Diploë (spongybone) cavitiescontain redmarrow

Woven bone and periosteum form.• Accumulating osteoid is laid down between embryonic

blood vessels in a random manner. The result is a network (instead of lamellae) of trabeculae calledwoven bone.

• Vascularized mesenchyme condenses on the externalface of the woven bone and becomes the periosteum.

Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken and

are later replaced with mature lamellar bone, forming compact bone plates.

• Spongy bone (diploë), consisting of distinct trabeculae, persists internally, and its vascular tissue becomes red marrow.

3 4

Endochondral Ossification

• All bones except some bones of the skull & clavicles

• Bones are 1st modeled in hyaline cartilage

• Begins forming late in the 2nd month of embryonic development

• Continues forming until early adulthood

Primary ossification centers in the skeleton of a 12-week fetus

Radius

Ulna

Humerus

Tibia

Frontalbone ofskull

Parietalbone

Femur

Occipitalbone

Clavicle

Scapula

Ribs

Vertebra

Ilium

Mandible

Hyalinecartilage

Area ofdeterioratingcartilage matrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificationcenter

Bloodvessel ofperiostealbud

Medullarycavity

Articularcartilage

Childhood to adolescenceBirthWeek 9 Month 3

Spongybone

Bone collar

Primaryossificationcenter

Bone collar forms around hyaline cartilage model.

Cartilage in the center of the diaphysis calcifies and then develops cavities.

The periosteal bud invades the internal cavities, and spongy bone begins to form.

The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5.

The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

1 2 3 4 5

Stages in Endochondral Ossification

• In epiphyseal plates of growing bones:– Cartilage is organized for quick, efficient

growth– Cartilage cells form tall stacks

• Chondroblasts at the top of stacks divide quickly

– Pushes the epiphysis away from the diaphysis– As chondrocytes die, osteoblasts replace them

& secrete bone matrix lengthens bone

Anatomy of Epiphyseal Growth Areas

Anatomy of Epiphyseal Growth Areas

• Older chondrocytes signal surrounding matrix to calcify

• Older chondrocytes then die & disintegrate– Leaves long trabeculae (spicules) of calcified

cartilage on diaphysis side– Trabeculae are partly eroded by osteoclasts– Osteoblasts then cover trabeculae with bone tissue– Trabeculae finally eaten away from their tips by

osteoclasts

Organization of Cartilage within Epiphyseal Plate of Growing Long Bone

Calcified cartilagespicule

Osseous tissue

Resting zone

Proliferation zoneCartilage cells undergo mitosis.

Hypertrophic zoneOlder cartilage cells enlarge.

Ossification zoneNew bone formation is occurring.

Calcification zoneMatrix becomes calcified; cartilage cells die; matrix begins deteriorating.

1

2

3

4

Postnatal Growth of Endochondral Bones

• During childhood & adolescence:– Bones lengthen entirely by growth of the

epiphyseal plates– Cartilage is replaced with bone CT as quickly

as it grows– Epiphyseal plate maintains constant thickness– Whole bone lengthens

Hormonal Regulation of Bone Growth

• Growth hormone produced by the pituitary gland– Stimulates epiphyseal plates (lengthens bones)

• Thyroid hormone ensures that the skeleton retains proper proportions

• Sex hormones (estrogen & testosterone)– Promote bone growth– But also later induces closure of epiphyseal

plates (~stop growing shortly after puberty!)

Postnatal Growth of Endochondral Bones

• As adolescence draws to an end:– Chondroblasts divide less often– Epiphyseal plates become thinner

• Cartilage stops growing• Replaced by bone tissue no more addition

– Long bones stop lengthening when diaphysis & epiphysis fuse

Postnatal Growth of Endochondral Bones

• Growing bones widen as they lengthen– Osteoblasts add bone tissue to the

external surface of the diaphysis– Osteoclasts remove bone from the

internal surface of the diaphysis

• Appositional growth growth of a bone by addition of bone tissue to its surface

Bone Remodeling

• Bone is dynamic living tissue– 500 mg of calcium may enter or leave the

adult skeleton each day!!!– Some bone of the skeleton is replaced every

3–4 years– Compact bone is replaced every 10 years

Bone Remodeling

• Bone deposit & removal– Occurs at periosteal & endosteal surfaces

• Bone remodeling – Bone deposition accomplished by

osteoblasts– Bone reabsorption accomplished by

osteoclasts

Osteoclast: A Bone-Degrading Cell

• A giant cell with many nuclei• Crawls along bone surfaces• Breaks down bone tissue (reabsorption)

– Secretes concentrated HCl

– Lysosomal enzymes are released

– Derived from blood stem cells

Osteocyte withina lacuna

Bone matrix

Ruffled borderof osteoclast

Nuclei

Injuries to Bone:Common Types of Fractures

Common Types of Fractures

Common Types of Fractures

Stages of Healing a Fracture

Hematoma Externalcallus

Newbloodvessels

Spongybonetrabecula

Internalcallus(fibroustissue andcartilage)

A hematoma forms. Fibrocartilaginous callus forms.

Bony callus forms.

Bonycallus ofspongybone

Healedfracture

Bone remodeling occurs.

1 2 3 4

Disorders of Bones

• Osteoporosis– Characterized by low bone mass

• Bone reabsorption outpaces bone deposition

• Occurs most often in women after menopause (no/low estrogen!)

• Also aging men (with low T)

Osteoporosis

Disorders of Bones

• Osteomalacia– Occurs in adults bones are inadequately mineralized (not enough Ca2+ & phosphorus)

• Rickets– Occurs in children analogous to osteomalacia – Vit D/Ca2+/P deficiency not enough Ca2+ absorbed– Bones are brittle, weak, deteriorate– Common in industrial Europe (little sunlight)– Now in most countries milk, etc. fortified w/ Vit D– But Rickets on the rise in U.S. & many countries

Disorders of Bones

• Paget’s disease– Characterized by excessive rate of bone deposition

enlarged & deformed bones, can lead to pain, arthritis, deformities, fractures, & other complications

– Prevalence 1-8% ( > 40 yrs old)

• Osteosarcoma– Most common form of bone cancer– Occurs mainly at the ends of long bones– ~68% survival rates

The Skeleton Throughout Life

• Cartilage grows quickly in youth• Skeleton has fewer chondrocytes in the elderly• Bones are a timetable

– Mesoderm• Gives rise to embryonic mesenchyme cells

– Mesenchyme• Produces membranes & cartilage

– Membranes & cartilage ossify (harden)– New bone is added during childhood & youth

The Skeleton Throughout Life

• Skeleton grows until age ~18–21 years• In children & adolescents: bone formation exceeds rate

of resorption• In young adults: bone formation &

resorption are in balance• In old age: resorption predominates• Bone mass declines with age

Healthy diet, moderate sunlight, & exercise can help keep your bones in better shape as you age!

The Axial Skeleton, Ch 7(also to be used as Lab Guide)

The Skeleton

• Consists of:– Bones, cartilage, joints, & ligaments

• Composed of 206 bones grouped into 2 divisions:– Axial skeleton (80 bones)– Appendicular skeleton (126 bones)

Axial Skeleton

• Formed from 80 named bones

• Consists of skull, vertebral column, & bony thorax

Skull

Thoracic cage(ribs and sternum)

Facial bones

Cranium

Sacrum

Vertebralcolumn

Clavicle

ScapulaSternumRibHumerus

VertebraRadiusUlna

Carpals

PhalangesMetacarpalsFemurPatella

Tibia

Fibula

TarsalsMetatarsalsPhalanges

(a) Anterior view

Axial Skeleton

(b) Posterior view

Cranium

Clavicle

Bones ofpectoralgirdle

Bones ofpelvic girdle

Upperlimb

Scapula

RibHumerus

VertebraRadiusUlna

CarpalsPhalangesMetacarpalsFemur

Lowerlimb

Tibia

Fibula

The Skull – Cranial & Facial Bones

• Facial bones serve to:– Form framework of face– Form cavities for the sense organs of sight,

taste, & smell– Provide openings for passage of air & food– Hold the teeth in place– Anchor muscles of face

Facial Bones

• Unpaired bones– Mandible & vomer

• Paired bones– Maxillae– Zygomatic bones– Nasal bones– Lacrimal bones– Palatine bones– Inferior nasal conchae

Facial Bones

Parietal bone

Squamous part of frontal bone

Nasal boneSphenoid bone(greater wing)

Temporal boneEthmoid boneLacrimal bone

Zygomatic bone

Maxilla

Mandible

Infraorbital foramen

Mentalforamen

Mentalprotuberance

Frontal bone

Glabella

Frontonasal suture

Supraorbital foramen(notch)

Supraorbital margin

Superior orbital fissure

Inferior orbital fissure

Middle nasal concha

Inferior nasal concha

Vomer

Optic canal

Perpendicular plateEthmoidbone

Mandible

• The lower jawbone is the largest & strongest facial bone

• Composed of 2 main parts– Horizontal body– 2 upright rami

Coronoidprocess

Mandibular foramen

Mentalforamen

Mandibularangle

Ramusofmandible

Mandibularcondyle

Mandibular notch

Mandibular fossaof temporal bone

Body of mandible

Alveolarmargin

Temporomandibularjoint

Mandible

Maxillary Bones (Maxillae)

• Articulate with all other facial bones except the mandible

• Contain maxillary sinuses largest paranasal sinuses

• Forms part of the inferior orbital fissure

• Are the “keystone” bones of the face

Maxillary Bones

Frontal process

Articulates with frontal bone

Anterior nasalspine

Infraorbitalforamen

Alveolarmargin

(b) Maxilla, right lateral view

Orbital surface

Zygomaticprocess(cut)

Maxilla(palatine process)

Hardpalate

Zygomatic bone

Incisive fossa

Median palatine sutureIntermaxillary suture

Infraorbital foramenMaxillaSphenoid bone(greater wing)

Foramen ovale

Pterygoid process

Foramen lacerumCarotid canal

External acoustic meatusStylomastoidforamenJugular foramen

Foramen magnum

Occipital condyle

Inferior nuchal line

Superior nuchal line

Temporal bone(zygomatic process)

Mandibular fossa

Vomer

Styloid process

External occipital crest

External occipitalprotuberance

Mastoid processTemporal bone(petrous part)

Basilar part ofthe occipital bone

Occipital bone

Palatine bone(horizontal plate)

Foramen spinosum

Inferior View of the Skull

Other Bones of the Face

• Zygomatic bones– Form lateral wall of orbits (& cheekbones!)

• Nasal bones– Form bridge of nose

• Lacrimal bones– Located in the medial orbital walls

• Palatine bones– Posterior part of the hard palate (roof of mouth)

• Vomer– Forms the inferior part of the nasal septum

• Inferior nasal conchae – Thin, curved bones that project medially from the

lateral walls of the nasal cavity

The CraniumBones of cranium (cranial vault)

Lambdoidsuture

Facialbones

Squamoussuture

(a) Cranial & facial divisions of the skull

Coronalsuture

The Cranium

• Is the body’s most complex bony structure

• Formed by cranial & facial bones

• The cranium– Encloses & protects the brain– Provides attachment for head & neck muscles

Anterior cranialfossa

Middle cranialfossa

Posterior cranialfossa

(b) Superior view of the cranial fossae

Frontal lobeof cerebrum

Temporal lobeof cerebrum

Cerebellum

PosteriorMiddleAnterior

Cranialfossae

(c) Lateral view of cranial fossae showing the contained brain regions

Overview of Skull Geography

• Facial bones form anterior aspect• Cranium is divided into cranial vault & base• Internally, prominent bony ridges divide skull into

distinct fossae

Overview of Skull Geography

• The skull contains smaller cavities– Middle & inner ear cavities in lateral

aspect of cranial base– Nasal cavity lies in & posterior to the nose– Orbits house the eyeballs– Air-filled sinuses occur in several bones

around nasal cavity

Overview of Skull Geography

• The skull contains about 85 openings:– Foramina, canals, & fissures– Provide openings for important structures

• Spinal cord• Blood vessels serving the brain• 12 pairs of cranial nerves

– You do not need to learn all of these openings, only a few….

– External & internal acoustic meatus– Foramen magnum– Obturator foramen

Cranial Bones

• Formed from 8 large bones– Paired bones include:

• Temporal bones• Parietal bones

– Unpaired bones include:• Frontal bone• Occipital bone• Sphenoid bone• Ethmoid bone

Parietal Bones & Sutures

• Parietal bones form superior & lateral parts of skull

• 4 sutures of the cranium– Coronal suture runs in the coronal plane

• Located where parietal bones meet the frontal bone

– Squamous suture occurs where each parietal bone meets a temporal bone inferiorly

Parietal Bones & Sutures

• 4 sutures of the cranium (cont…) – Sagittal suture occurs where right & left

parietal bones meet superiorly– Lambdoid suture occurs where the

parietal bones meet the occipital bone posteriorly

Sutural Bones

• Small bones that occur within sutures

• Irregular in shape, size, & location

• Not all people have sutural bones

Lambdoidsuture

Occipital bone

Superior nuchal line

External occipitalprotuberance

Sutural bone

Inferior nuchal line

Occipitalcondyle

External occipital crestOccipitomastoidsuture

Parietal bone

Sagittal suture

The Skull – Posterior View

Frontal Bone

• Forms the forehead & roofs of orbits• Supraorbital margin = superior margin of

orbits (=brow)

• Glabella = smooth part of frontal bone between superciliary arches– Frontal sinuses within frontal bone

• Contributes to anterior cranial fossa

Occipital Bone

• Forms the posterior portion of the cranium & cranial base

• Articulates with the temporal bones & parietal bones

• Forms the posterior cranial fossa

• Foramen magnum located at its base

Occipital Bone

• Features & structures: – Occipital condyles– Hypoglossal foramen– External occipital protuberance– Superior nuchal lines– Inferior nuchal lines

Maxilla(palatine process)

Hardpalate

Zygomatic bone

Incisive fossa

Median palatine sutureIntermaxillary suture

Infraorbital foramenMaxillaSphenoid bone(greater wing)

Foramen ovale

Pterygoid process

Foramen lacerumCarotid canalExt. acoustic meatusStylomastoidforamenJugular foramen

Foramen magnum

Occipital condyle

Inferior nuchal line

Superior nuchal line

Temporal bone(zygomatic process)

Mandibular fossa

Vomer

Styloid process

External occipital crest

External occipitalprotuberance

Mastoid processTemporal bone(petrous part)

Basilar part ofthe occipital bone

Occipital bone

Palatine bone(horizontal plate)

Foramen spinosum

Inferior Aspect of the Skull

Temporal Bones

• Lie inferior to parietal bones

• Form the inferolateral portion of the skull

• Term “temporal” comes from Latin word for time

• Specific regions of temporal bone:– Squamous, tympanic, petrous, & mastoid regions

Sphenoid bone(greater wing)

Coronal suture

Parietal bone

Squamous suture

Zygomatic process

Temporal bone

Lambdoid suture

Occipital bone

External occipitalprotuberance

Occipitomastoid suture

External acousticmeatus

Mastoid process Styloid process Mandibular ramus

Mandibular angle

Mental foramen

Frontal bone

Ethmoid boneLacrimal bone

Nasal bone

Lacrimal fossaZygomatic bone

Maxilla

Mandible

Coronoid process

Alveolarmargins

Mandibular condyle

Mandibular notch

Lateral Aspect of the Skull

The Temporal Bone

Mastoidregion

External acousticmeatus

Mastoid process

Styloid process Tympanicregion

Mandibularfossa

Zygomaticprocess

Squamousregion

The Temporal Bone

• The mastoid process– Site for neck muscle attachment– Contains air sinuses

• Petrous region– Projects medially, contributes to cranial base– Houses cavities of middle & internal ear

• Contributes to the middle & posterior cranial fossae

The Temporal Bone

• Foramina of the temporal bone– Jugular foramen– Carotid canal– Foramen lacerum– Extermal & Internal accoustic meatus

Inferior Aspect of the Skull

Hard palate

Mandibularfossa

Mastoidprocess

Zygomatic processof temporal bone

Zygomatic bone

Foramen ovale

Foramen lacerumCarotid canal

Styloid process

Jugular foramen

Occipital condyle

Foramen magnum

Superior nuchalline

Foramen spinosum

The Sphenoid Bone

• Spans the width of the cranial floor

• Resembles a butterfly or bat!

• Consists of a body & 3 pairs of processes

• Contains 5 important openings

• Is the “keystone” of the cranium

(a) Superior view

Opticcanal

Greaterwing

Sellaturcica

Lesser wing

Foramen rotundumForamen ovale

Foramen spinosumBody of sphenoid

The Sphenoid Bone

Figure 7.10a

Greaterwing

Body of sphenoid

Superior orbitalfissure

Lesser wing

Pterygoidprocess

(b) Posterior viewFigure 7.10b

The Sphenoid Bone

The Ethmoid Bone

• Lies between nasal & sphenoid bones

• Forms most of the medial bony region between the nasal cavity & orbits

The Ethmoid Bone • Cribriform plate superior surface of the

ethmoid bone– Contains olfactory foramina (= holes for

olfactory neurons)

• Crista galli attachment site for falx cerebri (=strong sheet of dura matter between right & left cerebral hemispheres)

• Perpendicular plate forms superior part of nasal septum

• Lateral masses contain air cells (nasal sinuses)

• Superior & middle nasal conchae– Extend medially from lateral masses

Orbitalplate

Ethmoidal air cells

Perpendicularplate

Middlenasal concha

Cribriformplate

Olfactoryforamina

Crista galli

Left lateralmass

The Ethmoid Bone

Special Parts of the Skull

• Orbits

• Nasal cavity

• Paranasal sinuses

• Hyoid bone

Nasal CavityFrontal sinus

Superiornasal conchaMiddlenasal concha

Ethmoidbone

Inferior nasal concha

Nasal bone

Maxillary bone(palatine process)

Palatine bone(perpendicularplate)

Palatine bone (horizontal plate)

Pterygoidprocess

(a) Bones forming the left lateral wall of the nasal cavity (nasal septum removed)

Sphenoidsinus

Sphenoidbone

Superior, middle, &inferior meatus

Anterior nasal spine

Vomer

Crista galliCribriformplate

Ethmoidbone Frontal sinus

Nasal bone

Septal cartilage

Alveolar marginof maxilla

Perpendicular plate of ethmoid bone

Sella turcica

Sphenoid sinus

Palatine bone

Palatine processof maxilla

(b) Nasal cavity with septum in place showing the contributions of the ethmoid bone, the vomer, & septal cartilage

Hardpalate

Nasal Septum

Paranasal Sinuses

• Air-filled sinuses are located within – Frontal bone– Ethmoid bone– Sphenoid bone– Maxillary bones

• Lined with mucous membrane

• Lighten the skull

Paranasal SinusesFrontal sinus

Ethmoidal air cells(sinus)

Maxillary sinus

Sphenoid sinus

(a) Anterior aspect

FrontalsinusEthmoidal air cells

Maxillarysinus

Sphenoid sinus

(b) Medial aspect

Orbits

Roof of orbit

Medial wall

Orbital plateof ethmoid bone

Sphenoid body

Supraorbital notch Optic canal

Floor of orbit

Orbital process ofpalatine bone

Orbital surface ofmaxillary bone

Lacrimal bone

Nasal bone

Frontal processof maxilla

Lateral wall of orbit Zygomatic processof frontal bone

Greater wing ofsphenoid bone

Orbital surface ofzygomatic bone

Zygomatic bone

Zygomatic bone

Inferior orbital fissure

Infraorbital groove

Infraorbital foramen

Superiororbital fissure

(b) Contribution of each of the 7 bones forming the right orbit

Lesser wing ofsphenoid bone

Orbital plate offrontal bone

The Hyoid Bone

• Lies inferior to the mandible

• The only bone with no direct articulation with any other bone

• Acts as a movable base for the tongue

Greater horn

Lesser horn

Body

Questions…?

What’s Next?Lab Today: BonesWed Lecture: Appendicular SkeletonWed Lab: Finish Bones;

Selected Joints