skeletal tissue & the axial skeleton human anatomy sonya schuh-huerta, ph.d
TRANSCRIPT
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