see 78267 chapter 06

Skeletal System: Bones and Joints6

c H a P t E rc H a P t E r

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Module5 SkeletalSystem

lEarnToPrEDictDr.thomasMooreandDr.robertarutledgehadworkedtogether for almost two decades, and roberta knewsomething was bothering thomas. She noticed himwincing in pain whenever he bent down to retrievesomething from a bottom shelf, and he was short-temperedratherthanhisusualhappyself.robertaknewthomaswouldneveradmittobeinginjuredif itmeanthe couldnt care for his patients, even if only for a fewdays.Finally,robertaconvincedhimtoletherx-rayhislowerback.rightaway,whenrobertashowedthomasthex-ray,hepointedtothecauseofthepainhedbeensuffering.

using knowledge of the vertebral column, predictthesourceofthomasspain,basedonhisx-rayshowninthis photo. also, using your knowledge of vertebralanatomy, predict the region of the injury and explainwhythisregionofthevertebralcolumnismorepronetothistypeofinjurythanotherregions.

limitedmovement;othersallownoapparentmovement.Thestruc-tureofagivenjointisdirectlycorrelatedtoitsdegreeofmovement. Althoughtheskeletonisusuallythoughtofastheframeworkofthebody,theskeletalsystemhasmanyotherfunctionsinaddi-tiontosupport.Themajorfunctionsoftheskeletalsysteminclude:

1. Support.Rigid,strongboneiswellsuitedforbearingweightandisthemajorsupportingtissueofthebody.Cartilageprovidesfirmyetflexiblesupportwithincertainstructures,suchasthenose,externalear,thoraciccage,andtrachea.Ligamentsarestrongbandsoffibrousconnectivetissuethatattachtobonesandholdthemtogether.

2. Protection.Boneishardandprotectstheorgansitsurrounds.Forexample,theskullenclosesandprotectsthebrain,andthevertebraesurroundthespinalcord.Theribcageprotectstheheart,lungs,andotherorgansofthethorax.

6.1 FunctionSoFtHESKElEtalSYStEMLearning Outcome After reading this section, you should be able to

A. Explainthefunctionsoftheskeletalsystem.

Sitting,standing,walking,pickingupapencil,andtakingabreathall involvetheskeletalsystem.Withouttheskeletalsystem,therewould be no rigid framework to support the soft tissues of thebody and no system of joints and levers to allow the body tomove.Theskeletalsystemconsistsofbones,suchasthoseshowninfigure6.1,aswellastheirassociatedconnectivetissues,whichinclude cartilage, tendons, and ligaments. The term skeleton isderivedfromaGreekwordmeaningdried.Buttheskeletonisfarfrombeingdryandnonliving.Rather,theskeletalsystemconsistsofdynamic,livingtissuesthatareabletogrow,detectpainstimuli,adapttostress,andundergorepairafterinjury. A joint,oranarticulation, isaplacewheretwobonescometogether.Manyjointsaremovable,althoughsomeofthemallowonly

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SkeletalSystem:BonesandJoints 111Skeletal

3. Movement.Skeletalmusclesattachtobonesbytendons,whicharestrongbandsofconnectivetissue.Contractionoftheskeletalmusclesmovesthebones,producingbodymovements.Joints,wheretwoormorebonescometogether,allowmovementbetweenbones.Smoothcartilagecoverstheendsofboneswithinsomejoints,allowingthebonestomovefreely.Ligamentsallowsomemovementbetweenbonesbutpreventexcessivemovement.

4. Storage.Somemineralsinthebloodprincipally,calciumandphosphorusaretakenintoboneandstored.Shouldbloodlevelsofthesemineralsdecrease,themineralsarereleasedfromboneintotheblood.Adiposetissueisalsostoredwithinbonecavities.Ifneeded,thelipidsarereleasedintothebloodandusedbyothertissuesasasourceofenergy.

5. Blood cell production.Manybonescontaincavitiesfilledwithredbonemarrow,whichproducesbloodcellsandplatelets(seechapter11).

6.2 ExtracEllularMatrixLearning Outcome After reading this section, you should be able to

A.Describethecomponentsoftheextracellularmatrix,andexplainthefunctionofeach.

Thebone,cartilage,tendons,andligamentsoftheskeletalsystemare all connective tissues. Their characteristics are largely deter-minedbythecompositionoftheirextracellularmatrix.Thematrixalways contains collagen, ground substance, and other organic

molecules,aswellaswaterandminerals.Butthetypesandquan-titiesofthesesubstancesdifferineachtypeofconnectivetissue. Collagen (koll-jen; koila, glue + -gen, producing) is atough,ropelikeprotein.Proteoglycans(prt--glkanz;proteo,protein+glycan,polysaccharide)arelargemoleculesconsistingofpolysaccharidesattachedtocoreproteins,muchastheneedlesofapinetreeareattachedtothetreesbranches.Theproteoglycansformlargeaggregates,muchaspinebranchescombinetoformawholetree.Proteoglycanscanattractandretainlargeamountsofwaterbetweentheirpolysaccharideneedles. Theextracellularmatrixof tendons and ligaments containslarge amounts of collagen fibers, making these structures verytough, like ropesor cables.The extracellularmatrixofcartilage(karti-lij) contains collagen and proteoglycans. Collagenmakescartilage tough, whereas the water-filled proteoglycans make itsmoothandresilient.Asaresult,cartilageisrelativelyrigid,butit springs back to its original shape after being bent or slightlycompressed.Itisanexcellentshockabsorber. Theextracellularmatrixofbonecontainscollagenandminer-als,includingcalciumandphosphate.Theropelikecollagenfibers,likethereinforcingsteelbarsinconcrete,lendflexiblestrengthtothe bone.Themineral component, like the concrete itself, givesthe bone compression (weight-bearing) strength. Most of themineralinboneisintheformofcalciumphosphatecrystalscalledhydroxyapatite(h-droks-ap--tt).

Predict 2

What would a bone be like if all of the minerals were removed? What would it be like if all of the collagen were removed?

acaSEinPoint

Brittle Bone Disease

Maytrix isa10-year-oldgirlwhohasahistoryofnumerousbrokenbones.atfirst,physicianssuspectedshewasavictimofchildabuse,buteventually theydetermined that shehasbrittle bone disease,orosteogenesis imperfecta,which literallymeans imperfect boneformation.May is short for her age, andher limbs are short andbowed.Hervertebralcolumnisalsoabnormallycurved.Brittlebonedisease is a raredisorder causedbyanyoneofanumberof faultygenes that results in either too little collagen formationor poorqualitycollagen.asaresult,thebonematrixhasdecreasedflexibilityandismoreeasilybrokenthannormalbone.

6.3 GEnEralFEaturESoFBonELearning Outcomes After reading this section, you should be able to

A. Explainthestructuraldifferencesbetweencompactboneandspongybone.

B. outlinetheprocessesofboneossification,growth,remodeling,andrepair.

Therearefourcategoriesofbone,basedontheirshape:long,short,flat,andirregular.Long bonesarelongerthantheyarewide.Mostofthebonesoftheupperandlower limbsare longbones.Short bones areapproximatelyasbroadas theyare long;examplesarethebonesofthewristandankle.Flat boneshavearelativelythin,

Skull

Sternum

RadiusUlna

Vertebralcolumn

Ribs

Clavicle

Humerus

Femur

Tibia

Fibula

Pelvis

Figure 6.1 Major Bones of the Skeletal System


112 Chapter 6Skeletal

StructureofalongBoneAlongboneservesasausefulmodelforillustratingthepartsofa typical bone (figure 6.2). Each long bone consists of a centralshaft,calledthediaphysis(d-afi-sis;growingbetween),andtwo

flattenedshape.Examplesofflatbonesarecertainskullbones,theribs, the scapulae (shoulder blades), and the sternum. Irregular bones include thevertebraeandfacialbones,whichhaveshapesthatdonotfitreadilyintotheotherthreecategories.

Epiphysis

Articular cartilage

Diaphysis

Compact bone

Medullary cavity (containsred marrow in juveniles andyellow marrow in adults)

Periosteum

Endosteum

Epiphyseal linesin adults

Epiphyseal platesin juveniles

Diaphysis

Spongy bone

Adult bone

Young bone

Endosteum

Central canals

Connecting vessels

Osteons(haversian systems)

Inner layer

Outerlayer

Compact bone

Medullarycavity

Periosteum

Spongy bonewith trabeculae

Adult bone

Figure 6.2 Structure of a Long Bone(a)Younglongbone(thefemur)showingtheepiphysis,epiphysealplates,anddiaphysis.(b)adultlongbonewithepiphyseallines.(c)internalfeaturesofaportionofthediaphysisin(a).

(a)

(c)

(b)



HistologyofBoneThe periosteum and endosteum contain osteoblasts (ost--blasts; bone-forming cells), which function in the formation ofbone, as well as in the repair and remodeling of bone. Whenosteoblastsbecomesurroundedbymatrix,theyarereferredtoasosteocytes(ost--stz;bonecells). Bone is formed in thin sheets of extracellularmatrix calledlamellae (l-mel; plates), with osteocytes located between thelamellae within spaces called lacunae (l-koon; a hollows)(figure6.3).Cellprocessesextendfromtheosteocytesacrosstheextracellularmatrixofthelamellaewithintinycanalscalledcana-liculi(kan--lik-l;sing.canaliculus,littlecanal). Therearetwomajortypesofbone,basedontheirhistologicalstructure.Compact boneismostlysolidmatrixandcells.Spongy bone,orcancellous(kans-ls)bone,consistsofalacynetworkofbonewithmanysmall,marrow-filledspaces.

Compact BoneCompactbone(figure6.3)formsmostofthediaphysisoflongbonesandthe thinnersurfacesofallotherbones.Mostof the lamellaeofcompactboneareorganizedintosetsofconcentricrings,witheachsetsurroundingacentral canal,orHaversian(ha-vershan)canal.Bloodvesselsthatrunparalleltothelongaxisoftheboneare containedwithin the central canals.Eachcentral canal,withthe lamellae and osteocytes surrounding it, is called an osteon(ost-on),orHaversian system.Eachosteon,seenincrosssection,lookslikeamicroscopictarget,withthecentralcanalasthebulls-eye(figure6.3).Osteocytes,locatedinlacunae,areconnectedtooneanotherbycellprocessesincanaliculi.Thecanaliculigivetheosteontheappearanceofhavingtinycrackswithinthelamellae.

ends,eachcalledanepiphysis(e-pifi-sis;growingupon).Athinlayerofarticular(ar-tik-lr;joint)cartilagecoverstheendsoftheepiphyseswherethebonearticulates(joins)withotherbones.A long bone that is still growing has an epiphyseal plate, orgrowth plate, composedof cartilage,betweeneachepiphysis andthediaphysis(figure6.2a).Theepiphysealplateiswherethebonegrows in length.When bone growth stops, the cartilage of eachepiphysealplate is replacedbyboneandbecomesanepiphyseal line(figure6.2b). Bonescontaincavities,suchasthelargemedullary cavityinthediaphysis, aswellas smallercavities in theepiphysesof longbones and in the interiorofotherbones.These spaces are filledwith soft tissue calledmarrow. Yellow marrow consists mostlyof adipose tissue. Red marrow consists of blood-forming cellsandistheonlysiteofbloodformationinadults(seechapter11).Childrens bones have proportionately more red marrow thando adult bones because, as a person ages, redmarrow ismostlyreplacedbyyellowmarrow.Inadults, redmarrowisconfinedtothebonesinthecentralaxisofthebodyandinthemostproximalepiphysesofthelimbs. Mostoftheoutersurfaceofboneiscoveredbydenseconnec-tive tissue called theperiosteum (per--ost-m;peri, around+osteon,bone),whichcontainsbloodvesselsandnerves(figure6.2c).Thesurfaceofthemedullarycavityislinedwithathinnerconnec-tivetissuemembrane,theendosteum(en-dost-m;endo,inside).

Lamellae between osteons

Periosteum

Blood vesselconnecting to a central canalbetween osteons

Blood vesselsconnecting to a central canal

Blood vesselswithin a central(Haversian) canal

Lamellae on surface of boneConcentric rings

of lamellae

OsteonOsteon

Blood vessel withinthe periosteum

CanaliculiOsteocytes inlacunae

CanaliculiLacunae

Central canal

LM 400x

(a) (b)

Figure 6.3 Structure of Bone Tissue(a)Photomicrographofcompactbone.(b)Finestructureofcompactbone.



BoneossificationOssification (osi-fi-kshn;os, bone+ facio, tomake) is theformation of bone by osteoblasts. After an osteoblast becomescompletely surrounded by bone matrix, it becomes a maturebone cell, or osteocyte. In the fetus, bones develop by two pro-cesses,eachinvolvingtheformationofbonematrixonpreexistingconnectivetissue(figure6.5).Boneformationthatoccurswithinconnective tissue membranes is called intramembranous ossifi-cation, and bone formation that occurs inside cartilage is calledendochondralossification.Bothtypesofboneformationresultincompactandspongybone.

Nutrients leave the blood vessels of the central canals anddiffuse to the osteocytes through the canaliculi.Waste productsdiffuseintheoppositedirection.Thebloodvesselsinthecentralcanals, inturn,areconnectedtobloodvessels intheperiosteumandendosteum.

Spongy BoneSpongybone,socalledbecauseofitsappearance,islocatedmainlyin the epiphyses of longbones. It forms the interior of all otherbones. Spongy bone consists of delicate interconnecting rods orplates of bone called trabeculae (tr-bek-l; beams), whichresemblethebeamsorscaffoldingofabuilding(figure6.4a).Likescaffolding, the trabeculae add strength to a bone without theaddedweight thatwouldbepresent if thebonewere solidmin-eralizedmatrix.Thespacesbetween the trabeculaeare filledwithmarrow.Eachtrabeculaconsistsofseverallamellaewithosteocytesbetweenthem(figure6.4b).Usually,nobloodvesselspenetratethetrabeculae, and the trabeculae have no central canals.Nutrientsexitvesselsinthemarrowandpassbydiffusionthroughcanaliculitotheosteocytesofthetrabeculae.

Trabeculae

Spaces containingbone marrow andblood vessels

Compact bone

Spongybone

Osteoblast

Osteoclast

Osteocyte

Lamellae Canaliculus

Trabecula

Parietalbone

Ossificationcenter

OssificationcenterSuperior part

of occipitalbone

Inferior partof occipital bone

Temporal bone

Vertebrae

Styloidprocess

Mandible

MaxillaZygomatic bone

Frontal bone

Nasal boneEthmoid bone

Sphenoid bone

Intramembranousbones forming

Fontanel

Cartilage

Endochondralbones forming

Figure 6.4 Spongy Bone(a)Beamsofbone,thetrabeculae,surroundspacesinthebone.inlife,thespacesarefilledwithredoryellowbonemarrowandwithbloodvessels.(b)transversesectionofatrabecula.

Figure 6.5 Bone Formation in a Fetus(a)intramembranousossificationoccursina12-week-oldfetusatossificationcentersintheflatbonesoftheskull(yellow).Endochondralossificationoccursinthebonesformingtheinferiorpartoftheskull(blue).(b)radiographofan18-week-oldfetus,showingintramembranousandendochondralossification.intramembranousossificationoccursatossificationcentersintheflatbonesoftheskull.Endochondralossificationhasformedbonesinthediaphysesoflongbones.theepiphysesarestillcartilageatthisstageofdevelopment.

(a)

(b)

(a)

(b)



increase in number, enlarge, and die. Then the cartilagematrixbecomescalcified(figure6.6,step2).Asthisprocessisoccurringin thecenterof thecartilagemodel,bloodvesselsaccumulate inthe perichondrium. The presence of blood vessels in the outersurfaceoffuturebonecausessomeoftheunspecifiedconnectivetissuecellsonthesurfacetobecomeosteoblasts.Theseosteoblaststhen produce a collar of bone around part of the outer surfaceof thediaphysis, and theperichondriumbecomesperiosteum inthatarea.Bloodvesselsalsogrowintothecenterofthediaphyses,bringing in osteoblasts and stimulating ossification. The centerpartof thediaphysis,wherebonefirstbeginstoappear, iscalledtheprimary ossification center (figure 6.6, step 3).Osteoblastsinvadespacesinthecenteroftheboneleftbythedyingcartilagecells. Some of the calcified cartilagematrix is removed by cellscalled osteoclasts (ost--klastz; bone-eating cells), and theosteoblastslineupontheremainingcalcifiedmatrixandbeginto

Intramembranous(intr-membr-ns)ossificationoccurswhen osteoblasts begin to produce bone in connective tissuemembranes. This occurs primarily in the bones of the skull.Osteoblastslineuponthesurfaceofconnectivetissuefibersandbegin depositing bone matrix to form trabeculae. The processbegins in areas calledossification centers (figure 6.5a), and thetrabeculaeradiateoutfromthecenters.Usually,twoormoreossi-ficationcentersexist ineach flat skullbone,and the skullbonesresultfromfusionofthesecentersastheyenlarge.Thetrabeculaeare constantly remodeled after their initial formation, and theymayenlargeorbereplacedbycompactbone. Thebonesat thebaseoftheskullandmostoftheremainingskeletal system develop through the process of endochondral ossification from cartilage models. The cartilage models havethegeneralshapeofthematurebone(figure6.6,step1).Duringendochondral ossification, cartilage cells, called chondrocytes,

Perichondrium

Cartilage

Perichondrium

Bone collar

Uncalcifiedcartilage

Calcified cartilage

Periosteum

Blood vesselto periosteum

Epiphysis

Epiphysis

Diaphysis

A cartilage model, with the general shape of the mature bone, is produced by chondrocytes. A perichondrium surrounds most of the cartilage model.

2. The chondrocytes enlarge, and cartilage is calcified. A bone collar is produced, and the perichondrium of the diaphysis becomes the periosteum.

3. A primary ossification center forms as blood vessels and osteoblasts invade the calcified cartilage. The osteoblasts lay down bone matrix, forming trabeculae.

4. Secondary ossification centers form in the epiphyses of long bones.

Perichondrium

Bone collar

Cartilage

Calcified cartilage

Periosteum

Blood vessel

Primaryossificationcenter

Trabecula

Medullary cavity

Secondaryossificationcenter

Spongybone

Cartilage

Blood vessel

Calcifiedcartilage

Spongy bone

PeriosteumBone collar

Blood vessel

Medullary cavity

Space inbone

1 2

43

Perichondrium

Cartilage

Perichondrium

Bone collar

Uncalcifiedcartilage

Calcified cartilage

Periosteum

Blood vesselto periosteum

Epiphysis

Epiphysis

Diaphysis

A cartilage model, with the general shape of the mature bone, is produced by chondrocytes. A perichondrium surrounds most of the cartilage model.

2. The chondrocytes enlarge, and cartilage is calcified. A bone collar is produced, and the perichondrium of the diaphysis becomes the periosteum.

3. A primary ossification center forms as blood vessels and osteoblasts invade the calcified cartilage. The osteoblasts lay down bone matrix, forming trabeculae.

4. Secondary ossification centers form in the epiphyses of long bones.

Perichondrium

Bone collar

Cartilage

Calcified cartilage

Periosteum

Blood vessel

Primaryossificationcenter

Trabecula

Medullary cavity

Secondaryossificationcenter

Spongybone

Cartilage

Blood vessel

Calcifiedcartilage

Spongy bone

PeriosteumBone collar

Blood vessel

Medullary cavity

Space inbone

1 2

43

PROCESS Figure 6.6 Endochondral Ossification of a Long Bone



ofthebone,causingthebonetoelongate.Thenthechondrocytesenlargeanddie.Thecartilagematrixbecomescalcified.Muchofthe cartilage that formsaround the enlargedcells is removedbyosteoclasts, and the dying chondrocytes are replaced by osteo-blasts. The osteoblasts start forming bone by depositing bonelamellae on the surface of the calcified cartilage. This processproducesboneonthediaphysealsideoftheepiphysealplate.

Predict 3

Describe the appearance of an adult if cartilage growth did not occur in the long bones during childhood.

BoneremodelingBone remodelinginvolvestheremovalofexistingbonebyosteoclastsandthedepositionofnewbonebyosteoblasts.Boneremodelingoccursinallbone.Remodelingisresponsibleforchangesinboneshape,theadjustmentofbonetostress,bonerepair,andcalciumionregulationinthebodyfluids.Remodelingisalsoinvolvedin

formbonetrabeculae.Asthebonedevelops,itisconstantlychanging.Amedullarycavityformsinthecenterofthediaphysisasosteo-clastsremoveboneandcalcifiedcartilage,whicharereplacedbybonemarrow.Later, secondary ossification centers form in theepiphyses(figure6.6,step4).

BoneGrowthBonegrowthoccursbythedepositionofnewbonelamellaeontoexisting bone or other connective tissue. As osteoblasts depositnewbonematrixonthesurfaceofbonesbetweentheperiosteumand the existing bone matrix, the bone increases in width, ordiameter. This process is called appositional growth. Growth inthelengthofabone,whichisthemajorsourceofincreasedheightinanindividual,occursintheepiphysealplate.Thistypeofbonegrowth occurs through endochondral ossification (figure 6.7).Chondrocytes increase in number on the epiphyseal side of theepiphysealplate.Theylineupincolumnsparalleltothelongaxis

Calcified cartilageis replaced by bone.

Chondrocytesdivide and enlarge.

Length of boneincreases.

Thickness ofepiphysealplate remainsunchanged.

Bone isadded todiaphysis.

Bone of diaphysis

Epiphysealplate

1

2

3

4

Femur

Patella

Epiphysis

Epiphysealplate

Diaphysis

New cartilage isproduced on the epiphyseal sideof the plate as thechondrocytes divideand form stacksof cells.

Chondrocytesmature and enlarge.

Matrix is calcified,and chondrocytesdie.

The cartilage onthe diaphyseal sideof the plate isreplaced by bone.

Epiphyseal side

Diaphyseal side

1

2

3

4LM 400x

1

2

3

4

PROCESS Figure 6.7 Endochondral Bone Growth(a)locationoftheepiphysealplateinalongbone.(b)asthechondrocytesoftheepiphysealplatedivideandalignincolumns,thecartilageexpandstowardtheepiphysis,andtheboneelongates.atthesametime,theoldercartilageiscalcifiedandthenreplacedbybone,whichisremodeled,resultinginexpansionofthemedullarycavityofthediaphysis.thenetresultisanepiphysealplatethatremainsuniforminthicknessthroughtimebutisconstantlymovingtowardtheepiphysis,resultinginelongationofthebone.(c)Photomicrographofanepiphysealplate,demonstratingchondrocytedivisionandenlargementandtheareasofcalcificationandossification.

(c)

(b)

(a)



Compactbone

Periosteum

Medullarycavity

ClotDeadbone

Newbone

Compactbone atbreak site

Spongybone

Deadbone

Cartilage

Fibersand cartilage

Clot formation Callus formation Callus ossification Bone remodeling

1 When a bone is broken, a clot forms in the damaged area.

2 Blood vessels and cells invade the clot and produce a network of fibers and cartilage called a callus.

3 Osteoblasts enter the callus and form spongy bone.

4 Most of the spongy bone is slowly remodeled to form compact bone and the repair is complete.

Callus

PROCESS Figure 6.8 Bone Repair

bonegrowthwhennewly formedspongybone in theepiphysealplate forms compact bone.A long bone increases in length anddiameterasnewboneisdepositedontheoutersurfaceandgrowthoccursattheepiphysealplate.Atthesametime,boneisremovedfromtheinner,medullarysurfaceofthebone.Asthebonediameterincreases,thethicknessofthecompactbonerelativetothemedul-larycavitytendstoremainfairlyconstant.Ifthesizeofthemedullarycavity did not also increase as bone size increased, the compactboneofthediaphysiswouldbecomethickandveryheavy. Becauseboneisthemajorstoragesiteforcalciuminthebody,bone remodeling is important tomaintain blood calcium levelswithinnormallimits.Calciumisremovedfromboneswhenbloodcalciumlevelsdecrease,anditisdepositedwhendietarycalciumisadequate.Thisremovalanddepositionisunderhormonalcontrol(seeBoneandCalciumHomeostasislaterinthischapter). If too much bone is deposited, the bones become thick ordevelopabnormalspursor lumpsthatcan interferewithnormalfunction.Toolittleboneformationortoomuchboneremoval,asoccurs inosteoporosis,weakens thebonesandmakes themsus-ceptibletofracture(seeSystemsPathology,Osteoporosis).

BonerepairSometimesaboneisbrokenandneedstoberepaired.Whenthisoccurs, blood vessels in the bone are also damaged.The vesselsbleed, anda clot forms in thedamagedarea (figure6.8, step1).Two to three days after the injury, blood vessels and cells fromsurrounding tissuesbegin to invade theclot.Someof thesecellsproduceafibrousnetworkofconnectivetissuebetweenthebrokenbones,whichholdsthebonefragmentstogetherandfillsthegapbetweenthem.Othercellsproduceisletsofcartilageinthefibrousnetwork.Thenetworkoffibersandisletsofcartilagebetweenthetwobonefragmentsiscalledacallus(figure6.8,step2).

Osteoblastsenter thecallusandbegin formingspongybone(figure6.8,step3).Spongyboneformationinthecallusisusuallycomplete46weeksaftertheinjury.Immobilizationoftheboneiscriticaluptothistimebecausemovementcanrefracturethedeli-catenewmatrix.Subsequently,thespongyboneisslowlyremod-eledtoformcompactandspongybone,andtherepairiscomplete(figure6.8,step4).Althoughimmobilizationatafracturepointiscriticalduringtheearlystagesofbonehealing,completeimmobili-zationisnotgoodforthebone,themuscles,orthejoints.Notlongago,itwascommonpracticetoimmobilizeabonecompletelyforaslongas10weeks.Butwenowknowthat,ifaboneisimmobi-lizedforaslittleas2weeks,themusclesassociatedwiththatbonemayloseasmuchashalftheirstrength.Furthermore,ifaboneiscompletelyimmobilized,itisnotsubjectedtothenormalmechanicalstressesthathelpitform.Bonematrixisreabsorbed,andthestrengthofthebonedecreases.Inexperimentalanimals,completeimmobili-zationofthebackfor1monthresultedinuptoathreefolddecreasein vertebral compression strength. Modern therapy attempts tobalancebone immobilizationwithenoughexercise tokeepmuscleandbonefromdecreasinginsizeandstrengthandtomaintainjointmobility.Thesegoals areaccomplishedby limiting theamountoftimeacastisleftonthepatientandbyusingwalkingcasts,whichallowsomestressontheboneandsomemovement.Totalhealingofthefracturemayrequireseveralmonths.Ifabonehealsproperly,thehealedregioncanbeevenstrongerthantheadjacentbone.

6.4 BonEanDcalciuMHoMEoStaSiSLearning Outcomes After reading this section, you should be able to

A. Explaintheroleofboneincalciumhomeostasis.B. Describehowparathyroidhormoneandcalcitonininfluence

bonehealthandcalciumhomeostasis.


118 Chapter 6Skeletal Bone fractures can be classi-

fied as open (or compound), if the boneprotrudes through the skin, and closed(or simple), if the skin is not perforated.Figure 6a illustrates some of the differenttypes of fractures. if the fracture totallyseparates the two bone fragments, it iscalled complete; if it doesnt, it is calledincomplete. an incomplete fracture thatoccursontheconvexsideofthecurveofaboneiscalledagreenstick fracture.acom-minuted (komi-n-ted; broken into smallpieces) fracture is one in which the bonebreaks into more than two fragments. animpacted fractureoccurswhenoneof thefragmentsofonepartoftheboneisdrivenintothespongyboneofanotherfragment.

Fracturescanalsobeclassifiedaccord-ing to the direction of the fracture line aslinear(paralleltothelongaxis);transverse

(atrightanglestothelongaxis);orobliqueor spiral (at an angle other than a rightangletothelongaxis).

CLINICALIMPACT Bone Fractures

Complete

Linear

Incomplete

Comminuted

Transverse

Impacted

Oblique

Spiral

Figure 6A typesofbonefractures.

PTH

Osteoclastspromote Ca2+uptake frombone.

Osteoblasts promoteCa2+ deposition in bone.

Stimulatesosteoclasts

Inhibitsosteoclasts

Bone

Ca2+

Ca2+ Blood

Vitamin D

Kidney

Small intestine

Calcitonin

Decreased blood Ca2+ stimulates PTH secretion from parathyroid glands.

PTH stimulates osteoclasts to break down

bone and release Ca2+ into the blood.

In the kidneys, PTH increases Ca2+ reabsorption from the urine. PTH also stimulates active Vitamin D formation.

Vitamin D promotes Ca2+ absorption from the small intestine into the blood.

Increased blood Ca2+ stimulates calcitonin secretion from the thyroid gland.

Calcitonin inhibits osteoclasts, which allows for enhanced osteoblast uptake of Ca2+ from the blood to deposit into bone.

1

2

3

4

5

6

1

2

3

4

5

6

Posterior aspectof thyroid gland

Parathyroidglands

Thyroid gland

Increasedblood Ca2+

Decreasedblood Ca2+

PROCESS Figure 6.9 Calcium Homeostasis



Calcitonin (kal-si-tnin), secreted from the thyroid glandwhenbloodcalciumlevelsaretoohigh,decreasesosteoclastactivityand thus decreases blood calcium levels. Increasing blood cal-ciumlevelsstimulatecalcitoninsecretion.PTHandcalcitoninaredescribedmorefullyinchapter10.

6.5 GEnEralconSiDErationSoFBonEanatoMYLearning Outcome After reading this section, you should be able to

A. listanddefinethemajorfeaturesofatypicalbone.

It is traditional to list 206 bones in the average adult skeleton(table 6.1), although the actual number varies from person topersonanddecreaseswithageassomebonesfuse. Anatomists use several common terms to describe the fea-turesofbones(table6.2).Forexample,aholeinaboneiscalledaforamen(f-rmen;pl.foramina,f-rmin-;foro,topierce).Aforamenusuallyexistsinabonebecausesomestructure,suchasanerveorbloodvessel,passesthroughtheboneatthatpoint.Iftheholeiselongatedintoatunnel-likepassagethroughthebone,

Boneisthemajorstoragesiteforcalciuminthebody,andmove-ment of calcium into and out of bone helps determine bloodcalcium levels, which is critical for normalmuscle and nervoussystem function.Calcium (Ca2+)moves intobone asosteoblastsbuildnewboneandoutofboneasosteoclastsbreakdownbone(figure6.9).Whenosteoblast andosteoclast activity is balanced,themovementsofcalciumintoandoutofaboneareequal. When blood calcium levels are too low, osteoclast activityincreases, osteoclasts release calcium from bone into the blood,and blood calcium levels increase. Conversely, if blood cal-ciumlevelsaretoohigh,osteoclastactivitydecreases,osteoblastsremovecalciumfromthebloodtoproducenewbone,andbloodcalciumlevelsdecrease. Calcium homeostasis is maintained by two hormones.Parathyroid hormone (PTH), secreted from the parathyroidglandswhenbloodcalciumlevelsaretoolow,stimulatesincreasedbonebreakdownandincreasedbloodcalciumlevelsbyindirectlystimulatingosteoclastactivity.PTHalsoincreasescalciumuptakefromtheurineinthekidney.Additionally,PTHstimulatesthekid-neystoformactivevitaminD,whichincreasescalciumabsorptionfromthesmallintestine.DecreasingbloodcalciumlevelsstimulatePTHsecretion.

TABle6.1 Named Bones in the Adult Human Skeleton

Bones NumberThoracic Cage ribs 24 Sternum(3parts,sometimesconsidered3bones) 1

total thoracic cage 25

total axial skeleton 80

Appendicular Skeleton

Pectoral Girdle Scapula 2 clavicle 2

Upper Limb Humerus 2 ulna 2 radius 2 carpalbones 16 Metacarpalbones 10 Phalanges 28

total girdle and upper limb 64

Pelvic Girdle coxalbone 2

Lower Limb Femur 2 tibia 2 Fibula 2 Patella 2 tarsalbones 14 Metatarsalbones 10 Phalanges 28

total girdle and lower limb 62

total appendicular skeleton 126

total bones 206

Bones NumberAxial Skeleton

Skull Braincase Paired Parietal 2 temporal 2 unpaired Frontal 1 occipital 1 Sphenoid 1 Ethmoid 1

Face Paired Maxilla 2 Zygomatic 2 Palatine 2 nasal 2 lacrimal 2 inferiornasalconcha 2

unpaired Mandible 1 Vomer 1

total skull 22

Auditory Ossicles Malleus 2 incus 2 Stapes 2

total 6

Hyoid 1

Vertebral Column cervicalvertebrae 7 thoracicvertebrae 12 lumbarvertebrae 5 Sacrum 1 coccyx 1

total vertebral column 26



TABle6.2 Anatomical Terms for Features of BonesTerm DescriptionMajor Features

Body,shaft Mainportion

Head Enlarged(oftenrounded)end

neck constrictedareabetweenheadandbody

condyle Smooth,roundedarticularsurface

Facet Small,flattenedarticularsurface

crest Prominentridge

Process Prominentprojection

tubercle,ortuberosity Knoborenlargement

trochanter largetuberosityfoundonlyon proximalfemur

Epicondyle Enlargementnearoraboveacondyle

Openings or Depressions

Foramen Hole

canal,meatus tunnel

Fissure cleft

Sinus cavity

Fossa Depression

itiscalledacanalorameatus(m-tus;apassage).Adepressionin abone is called a fossa (fos).A lumponabone is called atubercle(toober-kl;aknob)oratuberosity(toober-osi-t),andaprojectionfromabone iscalledaprocess.Most tuberclesandprocesses are sites ofmuscle attachment on the bone. Increasedmuscle pull, as occurs when a person lifts weights to build upmusclemass,canincreasethesizeofsometubercles.Thesmooth,roundedendofabone,whereitformsajointwithanotherbone,iscalledacondyle(kondl;knuckle). Thebonesof the skeletonaredivided intoaxialandappen-dicularportions(figure6.10).

6.6 axialSKElEtonLearning Outcomes After reading this section, you should be able to

A. namethebonesoftheskullanddescribetheirmainfeaturesasseenfromthelateral,frontal,internal,andinferiorviews.

B. listthebonesthatformthemajorityofthenasalseptum.C. Describethelocationsandfunctionsoftheparanasalsinuses.D. listthebonesofthebraincaseandtheface.e. Describetheshapeofthevertebralcolumn,andlistits

divisions.F. Discussthecommonfeaturesofthevertebraeandcontrast

vertebraefromeachregionofthevertebralcolumn.G. listthebonesandcartilageoftheribcage,includingthethree

typesofribs.

Theaxialskeletoniscomposedoftheskull,thevertebralcolumn,andthethoraciccage.

SkullThe22bonesoftheskullaredividedintothoseofthebraincaseandthoseoftheface(seetable6.1).Thebraincase,whichenclosesthecranialcavity,consistsof8bones that immediatelysurroundandprotect the brain; 14 facial bones form the structure of theface.Thirteenof the facialbonesare rather solidlyconnected toformthebulkoftheface.Themandible,however,formsafreelymovablejointwiththerestoftheskull.Therearealsothreeaudi-toryossicles(osi-klz)ineachmiddleear(sixtotal). Manystudentsstudyinganatomyneverseetheindividualbonesoftheskull.Eveniftheydo,itmakesmoresensefromafunctional,or clinical, perspective to studymostof thebones as they appeartogetherintheintactskullbecausemanyoftheanatomicalfeaturesof theskullcannotbefullyappreciatedbyexaminingtheseparatebones.Forexample,severalridgesontheskullcrossmorethanonebone,andseveralforaminaare locatedbetweenbonesratherthanwithinasinglebone.Forthesereasons,itismorerelevanttothinkof the skull, excluding themandible, as a singleunit.Themajorfeaturesoftheintactskullarethereforedescribedfromfourviews.

Lateral ViewTheparietal bones(p-r-tl;wall)andtemporal(temp-rl)bonesformalargeportionofthesideofthehead(figure6.11).(Theword temporal refers to time,and the temporalbone is sonamedbecausethehairsofthetemplesturnwhite,indicatingthepassageoftime.)Thesetwobonesjoineachotheronthesideoftheheadatthesquamous(skwms)suture.Asutureisajointunitingbonesof theskull.Anteriorly, theparietalbone is joinedtothefrontal(forehead)bonebythecoronal(kr-nl;corona,crown)suture,andposteriorlyitisjoinedtotheoccipital(ok-sipi-tl;backofthehead)bonebythelambdoid(lamdoyd)suture.Aprominentfea-tureofthetemporalboneisalargeopening,theexternal auditory canal,acanal thatenablessoundwaves toreachtheeardrum.Themastoid(mastoyd)processofthetemporalbonecanbeseenandfeltasaprominentlumpjustposteriortotheear.Importantneckmusclesinvolvedinrotationoftheheadattachtothemastoidprocess. Partofthesphenoid(sfnoyd)bonecanbeseenimmediatelyanteriortothetemporalbone.Althoughitappearstobetwosmall,pairedbonesonthesidesoftheskull,thesphenoidboneisactuallyasinglebonethatextendscompletelyacrosstheskull.Itresemblesabutterfly,with itsbody in thecenterof the skull and itswingsextendingtothesidesoftheskull.Anteriortothesphenoidboneisthezygomatic(z-g-matik)bone,orcheekbone,whichcanbeeasilyfelt.Thezygomatic arch,whichconsistsofjoinedprocessesof the temporal and zygomatic bones, forms a bridge across thesideofthefaceandprovidesamajorattachmentsiteforamusclemovingthemandible. Themaxilla (mak-sil; jawbone) forms the upper jaw, andthemandible (mandi-bl; jaw) forms the lower jaw.Themaxillaarticulatesbysuturestothetemporalbone.Themaxillacontainsthesuperiorsetofteeth,andthemandiblecontainstheinferiorteeth.

Frontal ViewThemajorstructuresseenfromthefrontalviewarethefrontalbone,thezygomaticbones,themaxillae,andthemandible(figure6.12a).Theteethareveryprominentinthisview.Manybonesofthefacecanbeeasilyfeltthroughtheskin(figure6.12b).



UlnaRadius

Carpal bonesMetacarpalbones

PhalangesCoxalbone

Femur

Patella

Tibia

Fibula

Tarsal bonesMetatarsal bonesPhalanges

Anterior view Posterior view

Axial Skeleton

Skull

Vertebralcolumn

Mandible

Ribs

Sacrum

Coccyx

Appendicular Skeleton

Clavicle

Scapula

Humerus

Axial Skeleton

Skull

Vertebralcolumn

MandibleHyoid bone

Sternum

Ribs

Sacrum

Figure 6.10 Complete SkeletonBonesoftheaxialskeletonarelistedinthefarleft-andright-handcolumns;bonesoftheappendicularskeletonarelistedinthecenter.(theskeletonisnotshownintheanatomicalposition.)



Coronal suture

Parietal bone

Temporal bone

Occipital bone

Squamous suture

Lambdoid suture

External auditory canal

Styloid process

Zygomatic arch

Frontal bone

Sphenoid boneNasal boneLacrimal bone

Ethmoid bone

Zygomatic bone

Maxilla

Mental foramen

Nasolacrimal canal

Mastoid process

Mandible

Mandibular condyle

Coronoid process

Lateral view

Figure 6.11 Skull as Seen from the Right Side (The names of bones are in bold.)

Fromthisview, themostprominentopenings into the skullaretheorbits(rbitz;eyesockets)andthenasal cavity.Theorbitsarecone-shapedfossae, sonamedbecause theeyesrotatewithinthem.Thebonesoftheorbitsprovidebothprotectionfortheeyesandattachmentpointsforthemusclesthatmovetheeyes.Theorbitisagoodexampleofwhyitisvaluabletostudytheskullasanintactstructure.Nofewerthansevenbonescometogethertoformtheorbit,andforthemostpart,thecontributionofeachbonetotheorbitcannotbeappreciatedwhenthebonesareexaminedindividually. Each orbit has several openings through which structurescommunicate with other cavities (figure 6.12a). The largest ofthesearethesuperiorandinferior orbital fissures.Theyprovideopenings throughwhich nerves and blood vessels communicatewiththeorbitorpasstotheface.Theopticnerve,forthesenseofvision,passesfromtheeyethroughtheoptic foramenandentersthecranialcavity.Thenasolacrimal(n-z-lakri-ml;nasus,nose+lacrima,tear)canal(seefigure6.11)passesfromtheorbitintothenasalcavity.Itcontainsaductthatcarriestearsfromtheeyestothenasalcavity.Asmalllacrimal(lakri-ml)bonecanbeseenintheorbitjustabovetheopeningofthiscanal.

Predict 4

Why does your nose run when you cry?

Thenasalcavityisdividedintorightandlefthalvesbyanasal septum(septm;wall)(figure6.12a).Thebonypartofthenasalseptum consists primarily of the vomer (vmer) inferiorly andtheperpendicular plateoftheethmoid(ethmoyd;sieve-shaped)bonesuperiorly.Theanteriorpartofthenasalseptumisformedbycartilage. The external part of thenose is formedmostly of cartilage.Thebridgeofthenoseisformedbythenasal bones. Each of the lateral walls of the nasal cavity has three bonyshelves, called the nasal conchae (konk; resembling a conchshell).Theinferiornasalconchaisaseparatebone,andthemiddleandsuperiorconchaeareprojectionsfromtheethmoidbone.Theconchaeincreasethesurfaceareainthenasalcavity.Theincreasedsurfaceareaoftheoverlyingepitheliumfacilitatesmoisteningandwarmingoftheairinhaledthroughthenose(seechapter15). Severalofthebonesassociatedwiththenasalcavityhavelargecavities within them, called the paranasal (par--nsl; para,alongside)sinuses (figure6.13),whichopen into thenasal cavity.Thesinusesdecrease theweightof theskullandactasresonatingchambersduringvoiceproduction.Compareanormalvoicewiththevoiceofapersonwhohasacoldandwhosesinusesarestoppedup.Thesinusesarenamedfortheboneswheretheyarelocatedandincludethefrontal,maxillary,ethmoidal,andsphenoidalsinuses.



formingthefloorofthecranialcavity,fromanteriortoposterior,arethefrontal,ethmoid,sphenoid,temporal,andoccipitalbones.Several foramina can be seen in the floor of the middle fossa.These allow nerves and blood vessels to pass through the skull.Forexample,theforamenrotundumandforamenovaletransmitimportantnervestotheface.Amajorarterytothemeninges(themembranesaroundthebrain)passesthroughtheforamenspino-sum.Theinternalcarotidarterypassesthroughthecarotidcanal,andtheinternaljugularveinpassesthroughthejugularforamen(see chapter 13). The large foramen magnum, through whichthe spinal cord joins the brain, is located in the posterior fossa.

Theskullhasadditionalsinuses,calledthemastoid air cells,which are located inside themastoid processes of the temporalbone.Theseaircellsopenintothemiddleearinsteadofintothenasalcavity.Anauditorytubeconnectsthemiddleeartothenaso-pharynx(upperpartofthroat).

Interior of the Cranial CavityWhenthefloorofthecranialcavityisviewedfromabovewiththeroofcutaway(figure6.14),itcanbedividedroughlyintothreecra-nialfossae(anterior,middle,andposterior),whichareformedasthedevelopingskullconformstotheshapeofthebrain.Thebones

Superior orbital fissure

Supraorbital foramen

Optic foramen

Coronal suture

Inferior orbital fissure

Infraorbital foramen

Mental foramen

Nasal cavity

Middle nasal concha

Sphenoid bone

Frontal bone

Parietal bone

Mandible

Orbit

Temporal boneNasal boneLacrimal bone

Zygomatic bone

Perpendicular plateof ethmoid bone

Vomer

Inferior nasal concha

Maxilla

Nasalseptum

Frontal view

Zygomaticbone

Maxilla

Frontal bone

Mandible

Nasal bone

(b)

(a)

Figure 6.12 Skull and Face (The names of bones are in bold.)(a)Frontalviewoftheskull.(b)Bonylandmarksoftheface.


124 Chapter 6Skeletal Frontal sinus

Ethmoidal sinus

Sphenoidal sinus

Maxillary sinus

Lateral view Anterior view

Sphenoid bone

Foramen rotundum

Internal auditory canal

Foramen magnum

Frontal sinuses

Crista galli

Cribriform plateEthmoid bone

Frontal bone

Optic foramen

Sella turcica

Foramen ovaleForamen spinosum Carotid canal

Jugular foramen

Parietal bone

Occipital bone

Superior view

Temporal bone

Hypoglossal canal

Anterior cranial fossa

Middle cranial fossa

Posterior cranial fossa

Figure 6.13 Paranasal Sinuses

(a) (b)

Figure 6.14 Floor of the Cranial Cavity (The names of bones are in bold.)theroofoftheskullhasbeenremoved,andthefloorisviewedfromabove.



palatine(pal-tn)bones.Theconnectivetissueandmusclesthatmakeupthesoft palateextendposteriorlyfromthehard,orbony,palate. The hard and soft palates separate the nasal cavity andnasopharynxfromthemouth,enablingustochewandbreatheatthesametime.

Hyoid BoneThehyoid bone(figure6.16)isanunpaired,U-shapedbone.Itisnotpartoftheskull(seetable6.1)andhasnodirectbonyattach-menttotheskull.Musclesandligamentsattachittotheskull.Thehyoidboneprovidesanattachmentforsometonguemuscles,andit isanattachmentpointforimportantneckmusclesthatelevatethelarynx(voicebox)duringspeechorswallowing.

VertebralcolumnThevertebral column,orbackbone,isthecentralaxisoftheskel-eton,extendingfromthebaseoftheskulltoslightlypasttheendofthepelvis.Inadults, itusuallyconsistsof26individualbones,grouped into five regions (figure 6.17; see table 6.1): 7 cervical(serv-kal;neck)vertebrae(vert-br;verto,toturn),12thoracic(th-rasik) vertebrae, 5 lumbar (lmbar) vertebrae, 1 sacral(skrl)bone,and1coccyx (koksiks)bone.Theadultsacraland

Thecentralregionofthesphenoidboneismodifiedintoastruc-tureresemblingasaddle,thesella turcica(seltrs-k;Turkishsaddle),whichcontainsthepituitarygland.

Base of Skull Viewed from BelowManyof thesameforaminathatarevisible in the interiorof theskullcanalsobeseeninthebaseoftheskull,whenviewedfrombelow, with themandible removed (figure 6.15). Other special-izedstructures,suchasprocessesformuscleattachments,canalsobe seen. The foramenmagnum is located in the occipital bonenearthecenteroftheskullbase.Occipital condyles(ok-sipi-tlkondlz),thesmoothpointsofarticulationbetweentheskullandthevertebralcolumn,arelocatedbesidetheforamenmagnum. Two long, pointed styloid (stloyd; stylus or pen-shaped)processesprojectfromtheinferiorsurfaceofthetemporalbone.Themusclesinvolvedinmovingthetongue,thehyoidbone,andthepharynx(throat)originatefromthisprocess.Themandibular fossa,where themandiblearticulateswith the temporalbone, isanteriortothemastoidprocess. Thehard palate (palt) forms the floor of the nasal cavityand the roof of themouth. The anterior two-thirds of the hardpalate is formed by themaxillae, the posterior one-third by the

Figure 6.15 Base of the Skull as Viewed from Below (The names of bones are in bold.)themandiblehasbeenremoved.

Inferior orbital fissure

Foramen ovaleForamen spinosum

External auditory canal

Jugular foramen

Occipital condyle

Incisive fossa

Maxilla

Hard palate

Palatine process of maxillary bone

Horizontal plate of palatine bone

Vomer

Zygomatic bone

Styloid processMandibular fossaCarotid canal

Mastoid process

Temporal bone

Occipital bone

Foramen magnum

Sphenoid bone

Nuchal lines

Inferior view



coccyxbonesfusefrom5and34individualbones,respectively.Forconvenience,eachofthefiveregionsisidentifiedbyaletter,andthevertebraewithineachregionarenumbered:C1C7,T1T12,L1L5,S,andCO.Youcanrememberthenumberofvertebraeineachregionbyrememberingmealtimes:7,12,and5. The adult vertebral column has fourmajor curvatures. Thecervical regioncurvesanteriorly, the thoracicregioncurvespos-teriorly, the lumbar region curves anteriorly, and the sacral andcoccygealregionstogethercurveposteriorly. Abnormalvertebralcurvaturesarenotuncommon.Kyphosis(k-fsis)isanabnormalposteriorcurvatureofthespine,mostlyintheupperthoracicregion,resultinginahunchbackcondition.Lordosis (lr-dsis; curving forward) is an abnormal anteriorcurvatureofthespine,mainlyinthelumbarregion,resultinginaswaybackcondition.Scoliosis(sk-l-sis)isanabnormallateralcurvatureofthespine. Thevertebralcolumnperformsthefollowingfivemajorfunc-tions:(1)supportstheweightoftheheadandtrunk;(2)protectsthespinalcord; (3)allowsspinalnerves toexit thespinalcord;(4)providesasiteformuscleattachment;and(5)permitsmove-mentoftheheadandtrunk.

General Plan of the VertebraeEachvertebra consists of a body, an arch, andvariousprocesses(figure6.18).Theweight-bearingportionofeachvertebra is thebody.Thevertebralbodiesareseparatedby intervertebral disks(seefigure6.17),whichareformedbyfibrocartilage.Thevertebral archsurroundsalargeopeningcalledthevertebral foramen.Thevertebral foraminaofall thevertebrae form thevertebral canal,where the spinal cord is located. The vertebral canal protectsthe spinal cord from injury. Each vertebral arch consists of two

Figure 6.16 Hyoid Bone

Figure 6.17 Vertebral Columncompletecolumnviewedfromtheleftside.

Body

Body

Anterior view

Lateral view(from the left side)

Cervicalregion(curvedanteriorly)

Thoracicregion(curvedposteriorly)

Lumbarregion(curvedanteriorly)

Sacral and coccygealregions(curvedposteriorly)

First cervical vertebra(atlas)Second cervical vertebra(axis)

Seventh cervical vertebraFirst thoracic vertebra

Intervertebral disk

Twelfth thoracic vertebra

Intervertebral foramina

First lumbar vertebra

Body

Transverse process

Spinous process

Fifth lumbar vertebra

Sacrum

Coccyx

Lateral view

Sacral promontory



pedicles(ped-klz),whichextendfromthebodytothetransverseprocessofeachvertebra,andtwolaminae(lami-n;thinplates),whichextendfromthetransverseprocessestothespinousprocess.Atransverse processextendslaterallyfromeachsideofthearch,between the pedicle and lamina, and a single spinous processprojectsdorsally fromwherethetwolaminaemeet.Thespinousprocessescanbeseenandfeltasaseriesoflumpsdownthemid-line of the back (see figure 6.24b). The transverse and spinousprocessesprovideattachmentsitesforthemusclesthatmovethevertebral column.Spinalnerves exit the spinal cord through theintervertebral foramina, which are formed by notches in thepediclesofadjacentvertebrae(seefigure6.17).Eachvertebrahasasuperiorandinferiorarticular processwherethevertebraearticu-latewith each other. Each articular process has a smooth littlefacecalledanarticular facet(faset).

Regional Differences in VertebraeThe cervical vertebrae (figure 6.19ac) have very small bodies,except for the atlas, which has no body. Because the cervicalvertebraearerelativelydelicateandhavesmallbodies,dislocations

Figure 6.18 Vertebra

Superior articular process

Articular facet

Transverse process

Vertebral foramen

Body

Pedicle

Lamina

Vertebral arch

Spinous process

Anterior

Superior view

Posterior

Superiorarticular facet

Spinous process

Transverseprocess

Transverseforamen

Vertebral foramen

Body

Pedicle

Lamina

Posterior arch

Atlas (first cervical vertebra), superior view

Thoracic vertebra, superior view

Lumbar vertebra, superior view

Cervical vertebra, superior view

Superior articularfacet (articulates with occipital condyle)Facet for dens

Transverseprocess

Transverseforamen

Vertebral foramen

Anterior arch

Body

Spinous process

Transverseprocess

Vertebral foramen

Pedicle

Lamina


Facets for ribattachment


Spinous process

Transverseprocess

Vertebral foramenPedicle

Lamina

Body

Dens(articulateswith atlas)

Dens

Body

Axis (second cervical vertebra),superior view

Lateral view

Figure 6.19 Regional Differences in Vertebraetheposteriorportionliesatthetopofeachillustration.

(a)

(d)

(e)

(b)

(c)



Vertebralcanal (sacralcanal)

Posteriorsacralforamina

Median sacralcrest

Sacral hiatus

Articular facet (articulates with fifth lumbar vertebra)

CoccyxCoccyx


Anteriorsacralforamina

Sacral promontory

Figure 6.20 Sacrum

(a) (b)

of thebodyof the first sacralvertebrabulges to form thesacral promontory (promon-t-r) (see figure 6.17), a landmark thatcanbefeltduringavaginalexamination.Itisusedasareferencepointtodetermineifthepelvicopeningsarelargeenoughtoallowfornormalvaginaldeliveryofababy. The coccyx,or tailbone,usually consistsof fourmore-or-lessfusedvertebrae.Thevertebraeofthecoccyxdonothavethetypicalstructureofmostothervertebrae.Theyconsistofextremelyreducedvertebralbodies,without the foraminaorprocesses,usually fusedintoasinglebone.Thecoccyxiseasilybrokenwhenapersonfallsbysittingdownhardonasolidsurfaceorinwomenduringchildbirth.

ribcageTherib cage protectsthevitalorganswithinthethoraxandpre-ventsthecollapseofthethoraxduringrespiration.Itconsistsofthethoracicvertebrae,theribswiththeirassociatedcartilages,andthesternum(figure6.21).

acaSEinPoint

Rib Fractures

HanD.Manns ladder fell as hewasworkingonhis roof, andhelandedontheladderwithhischest.threeribswerefracturedonhisright side. itwasdifficult forHan tocough, laugh,orevenbreathewithout severepain in the right sideofhis chest.themiddle ribsare thosemost commonly fractured, and theportionof each ribthat forms the lateralwall of the thorax is theweakest andmostcommonlybroken.thepain from rib fracturesoccursbecause thebrokenendsmoveduring respirationandother chestmovements,stimulatingpain receptors. Broken rib ends candamage internalorgans, suchas the lungs, spleen, liver, anddiaphragm. Fracturedribsarenotoftendislocated,butdislocatedribsmayhavetobesetforproperhealingtooccur.Bindingthechesttolimitmovementcanfacilitatehealingandlessenpain.

andfracturesaremorecommoninthisareathaninotherregionsof the vertebral column. Each of the transverse processes has atransverse foramen through which the vertebral arteries passtowardthebrain.Severalofthecervicalvertebraealsohavepartlysplitspinousprocesses.Thefirstcervicalvertebra(figure6.19a)iscalledtheatlasbecauseitholdsupthehead,asAtlasinclassicalmythology held up theworld.Movement between the atlas andtheoccipitalboneisresponsibleforayesmotionofthehead.Italsoallowsaslighttiltingoftheheadfromsidetoside.Thesecondcervicalvertebra(figure6.19b)iscalledtheaxisbecauseaconsid-erableamountofrotationoccursatthisvertebra,asinshakingtheheadno.Thisrotationoccursaroundaprocesscalledthedens(denz),whichprotrudessuperiorlyfromtheaxis. Thethoracic vertebrae(figure6.19d)possesslong,thinspinousprocesses thataredirected inferiorly.Thethoracicvertebraealsohaveextraarticular facetsontheir lateral surfaces thatarticulatewiththeribs. Thelumbar vertebrae(figure6.19e)havelarge,thickbodiesandheavy,rectangulartransverseandspinousprocesses.Becausethelumbarvertebraehavemassivebodiesandcarryalargeamountofweight,rupturedintervertebraldisksaremorecommoninthisareathaninotherregionsofthecolumn.Thesuperiorarticularfacetsofthelumbarvertebraefacemedially,whereastheinferiorarticularfacets face laterally. This arrangement tends to lock adjacentlumbarvertebraetogether,givingthelumbarpartofthevertebralcolumnmorestrength.Thearticularfacetsinotherregionsofthevertebral columnhave amore openposition, allowing formorerotationalmovementbutlessstabilitythaninthelumbarregion. Thefivesacralvertebraearefusedintoasinglebonecalledthesacrum(figure6.20).Thespinousprocessesofthefirstfoursacralvertebraeformthemedian sacral crest.Thespinousprocessofthefifthvertebradoesnot form, leavingasacral hiatus (h--ts)attheinferiorendofthesacrum,whichisoftenthesiteofcaudalanestheticinjectionsgivenjustbeforechildbirth.Theanterioredge



6.7 aPPEnDicularSKElEtonLearning Outcomes After reading this section, you should be able to

A. identifythebonesthatmakeupthepectoralgirdle,andrelatetheirstructureandarrangementtothefunctionofthegirdle.

B. nameanddescribethemajorbonesoftheupperlimb.C. nameanddescribethebonesofthepelvicgirdleandexplain

whythepelvicgirdleismorestablethanthepectoralgirdle.D. namethebonesthatmakeupthecoxalbone.Distinguish

betweenthemaleandfemalepelvis.e. identifyanddescribethebonesofthelowerlimb.

Theappendicular(apen-dik-lr;appendage)skeletonconsistsofthebonesoftheupperandlowerlimbs,aswellasthegirdles,whichattachthelimbstotheaxialskeleton.

PectoralGirdleThepectoral (pekt-rl)girdle,or shoulder girdle (figure6.22),consistsoffourbones,twoscapulaeandtwoclavicles,whichattachtheupper limbtothebody.Thescapula (skap-l),orshoulder blade, is a flat, triangular bone with three large fossae wheremusclesextendingtothearmareattached(figures6.23and6.24;see figure6.10).A fourth fossa, theglenoid (glenoyd)cavity, iswheretheheadofthehumerusconnectstothescapula.Aridge,calledthespine,runsacrosstheposteriorsurfaceofthescapula.A projection, called the acromion (-krm-on; akron, tip+omos,shoulder)process,extendsfromthescapularspinetoformthe point of the shoulder.The clavicle (klavi-kl), or collarbone,articulateswiththescapulaattheacromionprocess.Theproximalendoftheclavicleisattachedtothesternum,providingtheonly

Ribs and Costal CartilagesThe12pairsof ribs canbedivided into true ribs and false ribs.Thetrue ribs,ribs17,attachdirectlytothesternumbymeansofcostalcartilages.Thefalse ribs, ribs812,donotattachdirectlyto the sternum. Ribs 810 attach to the sternum by a commoncartilage;ribs11and12donotattachatalltothesternumandarecalledfloating ribs.

SternumThe sternum (sternm), or breastbone (figure 6.21), is dividedinto three parts: themanubrium (m-nbr-m; handle), thebody,andthexiphoid(zifoyd,zfoyd;sword)process.Thester-numresemblesasword,withthemanubriumformingthehandle,thebodyformingtheblade,andthexiphoidprocessformingthetip. At the superior end of the sternum, a depression called thejugular notch is locatedbetweentheendsof theclavicleswherethey articulate with the sternum. A slight elevation, called thesternal angle, canbe felt at the junctionof themanubriumandthebodyofthesternum.Thisjunctionisanimportantlandmarkbecauseitidentifiesthelocationofthesecondrib.Thisidentifica-tionallowstheribstobecounted;forexample,itcanhelpahealthprofessionallocatetheapexoftheheart,whichisbetweenthefifthandsixthribs. The xiphoid process is another important landmark of thesternum.Duringcardiopulmonaryresuscitation(CPR), it isveryimportanttoplacethehandsoverthebodyofthesternumratherthan over the xiphoid process. Pressure applied to the xiphoidprocesscandriveitintoanunderlyingabdominalorgan,suchastheliver,causinginternalbleeding.

Clavicle

Jugular notch

Seventh cervical vertebra

First thoracic vertebra

True ribs(17)

Costal cartilage

False ribs(812)

Manubrium

Body

Xiphoid process

Sternum

Floating ribs

1

2

3

4

5

6

7

8

9

10

11

12

Anterior view

L1

T12

Sternal angle

Figure 6.21 Rib Cage



neck,locatedattheproximalendofthehumeralshaft.Lateraltotheheadaretwotubercles,agreater tubercleandalesser tubercle.Musclesoriginatingonthescapulaattachtothegreaterandlessertubercles and hold the humerus to the scapula. Approximatelyone-thirdofthewaydowntheshaftofthehumerus,onthelateralsurface,isthedeltoid tuberosity,wherethedeltoidmuscleattaches.Thesizeofthedeltoidtuberositycanincreaseastheresultoffre-quentandpowerfulpullsfromthedeltoidmuscle.Forexample,inbodybuilders,thedeltoidmuscleandthedeltoidtuberosityenlargesubstantially.Anthropologists,examiningancienthumanremains,canuse thepresenceofenlargeddeltoid tuberositiesasevidencethatapersonwasengagedinliftingheavyobjectsduringlife.Ifthehumerusofapersonexhibitsanunusuallylargedeltoidtuberosityforherage,itmayindicate,insomesocieties,thatshewasaslaveandwasrequiredtoliftheavyloads.Thedistalendofthehumerusismodified into specialized condyles that connect the humerusto the forearmbones.Epicondyles (epi-kondlz; epi, upon)onthedistalendofthehumerus,justlateraltothecondyles,provideattachmentsitesforforearmmuscles.

ForearmTheforearmhastwobones:theulna(ln)onthemedial(littlefinger)sideoftheforearmandtheradiusonthelateral(thumb)side(figure6.26).Theproximalendoftheulnaformsatrochlear notchthatfitstightlyovertheendofthehumerus,formingmostoftheelbowjoint.Justproximaltothetrochlearnotchisanextensionof theulna, called theolecranon (-lekr-non; elbow)process,whichcanbefeltasthepointoftheelbow(seefigure6.28).Justdistaltothetrochlearnotchisacoronoid(kr-noyd)process,whichhelpscompletethegripoftheulnaonthedistalendofthehumerus.Thedistalendoftheulnaformsahead,whicharticulateswiththebonesofthewrist,andastyloid processislocatedonitsmedialside.Theulnarheadcanbeseenasaprominentlumpontheposteriorulnarsideofthewrist.Theproximalendoftheradiushasaheadbywhichtheradiusarticulateswithboththehumerusandtheulna.Theradiusdoesnotattachasfirmlytothehumerusastheulnadoes.The radialhead rotates against thehumerus andulna.Just distal to the radial head is a radial tuberosity,where one ofthearmmuscles,thebicepsbrachii,attaches.Thedistalendoftheradiusarticulateswiththewristbones.Astyloidprocessislocatedonthelateralsideofthedistalendoftheradius.Theradialandulnarstyloidprocessesprovideattachmentsitesforligamentsofthewrist.

WristThewrist is a relatively short region between the forearm andthe hand; it is composed of eight carpal (karpl; wrist) bones(figure6.27).Theseeightbonesarethescaphoid(skafoyd),lunate(lnt), triquetrum(tr-kwtrm),pisiform(pisi-frm), trape-zium(tra-pz-m),trapezoid(trap-zoyd),capitate(kapi-tt),andhamate(hamt).Thecarpalbonesarearrangedintworowsof four bones each and form a slight curvature that is concaveanteriorlyandconvexposteriorly.Anumberofmnemonicshavebeendevelopedtohelpstudentsrememberthecarpalbones.Thefollowing one allows students to remember them in order fromlateral tomedial for theproximal row (top) and frommedial tolateral(bythethumb)forthedistalrow:SoLongTopPart,HereComes The Thumbthat is, Scaphoid, Lunate, Triquetrum,Pisiform,Hamate,Capitate,Trapezoid,andTrapezium.

bonyattachmentofthescapulatotheremainderoftheskeleton.Theclavicleisthefirstbonetobeginossificationinthefetus.Thisrelatively brittle bone may be fractured in the newborn duringdelivery.Theboneremainsslenderinchildrenandmaybebrokenasachildattemptstotaketheimpactofafallonanoutstretchedhand.Theclavicleisthickerinadultsandislessvulnerabletofrac-ture.Eventhoughitisthefirstbonetobeginossification,itisthelast to completeossification.Thecoracoid (kr-koyd)processcurvesbelowtheclavicleandprovidesfortheattachmentofarmandchestmuscles.

upperlimbTheupper limbconsistsof thebonesof thearm, forearm,wrist,andhand(seefigure6.22).

ArmThe arm is the region between the shoulder and the elbow; itcontains the humerus (hmer-s; shoulder) (figure 6.25). Theproximalendofthehumerushasasmooth,roundedhead,whichattachesthehumerustothescapulaattheglenoidcavity.Aroundthe edgeof thehumeralhead is the anatomicalneck.When thejointneedstobesurgicallyreplaced,thisneckisnoteasilyacces-sible.Amoreaccessiblesiteforsurgicalremovalisatthesurgical

Upper limb

Pectoral girdle

Phalanges

Anterior view

Metacarpal bones

Clavicle

Scapula

Humerus

Radius

Ulna

Carpal bones

Figure 6.22 Bones of the Pectoral Girdle and Right Upper Limb



Spine of scapulaSupraspinous fossa of scapula

Acromion processof scapulaDistal end of clavicle

Coracoid processof scapulaBody of clavicle

Posterior

AnteriorDistal end

Proximal end

Posterior view

Acromion process

Glenoid cavity

Lateral border

Coracoid process

Subscapularfossa

Medial border

Viewin (d)

Inferior angle

Spine

Supraspinousfossa

Coracoid processAcromion process

Glenoid cavity

Infraspinous fossa

Lateral border

Anterior view

Superior viewSuperior view

Body of clavicle

Figure 6.23 Right Scapula and Clavicle(a)rightscapula,anteriorview.(b)rightscapula,posteriorview.(c)rightclavicle,superiorview.(d)Photographoftherightscapulaandclaviclefromasuperiorview,showingtherelationshipbetweenthedistalendoftheclavicleandtheacromionprocessofthescapula.

(a)

(c) (d)

(b)

Skeletal

the bones and ligaments ontheanteriorsideofthewristformacarpal tunnel, which does not havemuchgive.tendonsandnervespassfromtheforearmthroughthecarpaltunneltothehand.Fluidand connective tissue can accumulate inthe carpal tunnel as a result of inflamma-tionassociatedwithoveruseortrauma.theinflammationcanalsocausethetendonsin

the carpal tunnel to enlarge.the accumu-latedfluidandenlargedtendonscanapplypressuretoamajornervepassingthroughthe tunnel. the pressure on this nervecausescarpal tunnel syndrome,character-izedbytingling,burning,andnumbnessinthehand. treatments for carpal tunnel syndromevary, depending on the severity of the

syndrome.Mild cases can be treated non-surgically with either anti-inflammatorymedicationsorstretchingexercises.However,if symptoms have lasted for more than6months, surgery is recommended.Surgicaltechniques involve cutting the carpal liga-menttoenlargethecarpaltunnelandeasepressureonthenerve.

CLINICALIMPACT Carpal Tunnel Syndrome



Sternum

Clavicle

Distal end of clavicle

Acromionprocess

Jugular notch

Head

Anatomical neckLesser tubercle

Surgical neck

Olecranon fossa

Greater tubercle

Deltoid tuberosity

Lateral epicondyle

CondylesCapitulum

Trochlea

Medial epicondyle


Trochlea

Lateral epicondyle

Greater tubercle

Spinous process ofseventh cervical vertebra

Lumbar spinousprocesses

Superior borderof scapula

Scapula

Medial borderof scapula

Inferior angleof scapula

Spine of scapula

Figure 6.24 Surface Anatomy of the Pectoral Girdle and Thoracic Cage(a)Bonesofthepectoralgirdleandtheanteriorthorax.(b)Bonesofthescapulaandtheposteriorvertebralcolumn.

Figure 6.25 Right Humerus

(a)

(a)

(b)

(b)



Carpal bones(distalrow)

Radius

TrapezoidTrapezium

Proximalphalanx of thumb

Proximal phalanx of finger

Middle phalanx of finger

Distal phalanx of finger

Posterior view

Ulna

CapitateHamate

1

2345

Digits

Metacarpalbones

Distalphalanxof thumb

Carpalbones(proximalrow)

LunateScaphoid

TriquetrumPisiform

Heads ofmetacarpal

bones(knuckles)

Olecranonprocess

Headof ulna

Acromionprocess

Medial border of scapulaOlecranonprocess

HandFivemetacarpal(met-karpl)bonesareattachedtothecarpalbonesandformthebonyframeworkofthehand(figure6.27).Themetacarpalbonesarealignedwiththefivedigits:thethumbandfingers.They are numbered 1 to 5, from the thumb to the littlefinger.Theends,orheads,ofthefivemetacarpalbonesassociatedwiththethumbandfingersformtheknuckles(figure6.28).Eachfinger consistsof three smallbones calledphalanges (f-lanjz;sing.phalanx,flangks),namedaftertheGreekphalanx,awedgeof soldiers holding their spears, tips outward, in front of them.The phalanges of each finger are called proximal, middle, anddistal,accordingtotheirpositioninthedigit.Thethumbhastwophalanges,proximalanddistal.Thedigitsarealsonumbered1to5,startingfromthethumb.

PelvicGirdleThepelvic girdleistheplacewherethelowerlimbsattachtothebody(figure6.29).Therightandleftcoxal(koksul)bones,orhipbones, join each other anteriorly and the sacrum posteriorly toformaringofbonecalled thepelvic girdle.Thepelvis (pelvis;

Olecranon process

Head

Radial tuberosity

Radius(shaft)

Styloid process

Anterior view

Trochlear notchCoronoid process

Ulna(shaft)

HeadStyloid process

Superior view

Head of radius

Olecranonprocess

Coronoid process

Trochlearnotch

Figure 6.26 Right Ulna and Radius(a)anteriorviewoftherightulnaandradius.(b)Proximalendsoftherightulnaandradius.

(a)

(b)

Figure 6.27 Bones of the Right Wrist and Hand

Figure 6.28 Surface Anatomy Showing Bones of the Pectoral Girdle and Upper Limb



crest can be seen along the superiormargin of each ilium, andananterior superior iliac spine, an important hip landmark, islocatedattheanteriorendoftheiliaccrest.Thecoxalbonesjoineachotheranteriorlyatthepubic(pbik)symphysisandjointhesacrum posteriorly at the sacroiliac (s-kr-il-ak) joints (seefigure6.30).Theacetabulum(as--tab-lm;vinegarcup)isthesocketofthehipjoint.Theobturator(obtoo-r-tr)foramenisthelargeholeineachcoxalbonethatisclosedoffbymusclesandotherstructures. Themalepelviscanbedistinguishedfromthefemalepelvisbecauseitisusuallylargerandmoremassive,butthefemalepelvistendstobebroader(figure6.32;table6.3).Boththeinletandtheoutletofthefemalepelvisarelargerthanthoseofthemalepelvis,and the subpubic angle is greater in the female (figure 6.32a,b).Theincreasedsizeoftheseopeningshelpsaccommodatethefetus

basin)includesthepelvicgirdleandthecoccyx(figure6.30).Thesacrumandcoccyxformpartofthepelvisbutarealsopartoftheaxialskeleton.Eachcoxalboneisformedbythreebonesfusedtooneanotherto formasinglebone(figure6.31).The ilium (il-m) is themostsuperior, the ischium (isk-m) is inferiorandposterior,andthepubis(pbis)isinferiorandanterior.Aniliac

Coxal boneSacrum

Femur

Patella

Lower limb

Pelvic girdle

Tibia

Fibula

Tarsal bonesMetatarsalbonesPhalanges

Anterior view

Sacroiliac joint

Anterior superioriliac spine

Acetabulum

Coccyx

Iliac crest

Obturatorforamen

Subpubic angleAnterosuperior view

Ischium

Pubis

Ilium

Sacrum

Coxalbone

Pubic symphysis

Sacral promontory

Figure 6.29 Bones of the Pelvic Girdle and Right Lower Limb

Figure 6.30 Pelvis

TABle6.3 Differences Between Male and Female Pelvic GirdlesArea Description of DifferenceGeneral Femalepelvissomewhatlighterinweightand

widerlaterallybutshortersuperiorlyto inferiorlyandlessfunnel-shaped;lessobvious muscleattachmentpointsinfemalethaninmale

Sacrum Broaderinfemale,withtheinferiorportion directedmoreposteriorly;thesacralpromontory projectslessanteriorlyinfemale

Pelvicinlet Heart-shapedinmale;ovalinfemale

Pelvicoutlet Broaderandmoreshallowinfemale

Subpubicangle lessthan90degreesinmale;90degreesormore infemale

ilium Moreshallowandflaredlaterallyinfemale

ischialspines Fartherapartinfemale

ischialtuberosities turnedlaterallyinfemaleandmediallyinmale (notshowninfigure6.32)



Iliac crest

Greatersciatic notch

Ischial spine

Ischial tuberosityLateral view Medial view

Obturator foramen

Pubic symphysis

Acetabulum

Ilium

Pubis

Pelvic brim

Articular surface(area ofarticulationwith sacrum)

Greater sciatic notch

Ischium

Ischial spine

Ischium

Iliac fossa

Coccyx

Pubicsymphysis

Ischialspine

Sacral promontory

Subpubic angle

Pelvicbrim

Pelvicinlet(reddashedline)

Pubicsymphysis

Pelvicoutlet(bluedashedline)

Male Female

(a) Anterosuperior view (b) Anterosuperior view

Pelvic inletPelvicbrim

Coccyx

Sacral promontory

Pelvic outlet

(c) Medial view

Figure 6.31 Right Coxal Bone

Figure 6.32 Comparison of the Male Pelvis to the Female Pelvis(a)inamale,thepelvicinlet(red dashed line)andoutlet(blue dashed line)aresmall,andthesubpubicangleislessthan90degrees.(b)inafemale,thepelvicinlet(red dashed line)andoutlet(blue dashed line)arelarger,andthesubpubicangleis90degreesorgreater.(c)amidsagittalsectionthroughthepelvisshowsthepelvicinlet(red arrowandred dashed line)andthepelvicoutlet(blue arrowandblue dashed line).

(a) (b)



aredamaged.Ifthisoccurs,thefemoralheadmaydegeneratefromlackofnourishment.Thetrochantersarepointsofmuscleattach-ment.Thepatella(pa-tel),orkneecap(figure6.33b), is locatedwithinthemajortendonoftheanteriorthighmusclesandenablesthetendontobendovertheknee.

LegThelegistheregionbetweenthekneeandtheankle(figure6.34).Itcontainstwobones,calledthetibia(tib-;shinbone)andthefibula(fib-l).Thetibiaisthelargerofthetwoandisthemajorweight-bearingboneoftheleg.Theroundedcondylesofthefemurrestontheflatcondylesontheproximalendofthetibia.Justdis-taltothecondylesofthetibia,onitsanteriorsurface,isthetibial tuberosity, where themuscles of the anterior thigh attach. Thefibuladoesnotarticulatewiththefemur,butitsheadisattachedtotheproximalendofthetibia.Thedistalendsofthetibiaandfibula form a partial socket that articulates with a bone of theankle(thetalus).Aprominencecanbeseenoneachsideoftheankle(figure6.34).Thesearethemedial malleolus(mal--ls)ofthetibiaandthelateral malleolusofthefibula.

during childbirth.Thepelvic inlet is formedby thepelvicbrimand the sacralpromontory.Thepelvic outlet isboundedby theischialspines,thepubicsymphysis,andthecoccyx(figure6.32c).

lowerlimbThelowerlimbconsistsofthebonesofthethigh,leg,ankle,andfoot(seefigure6.29).

ThighThethighistheregionbetweenthehipandtheknee(figure6.33a).Itcontainsasinglebonecalledthefemur.Theheadofthefemurarticulateswiththeacetabulumofthecoxalbone.Atthedistalendofthefemur,thecondylesarticulatewiththetibia.Epicondyles,locatedmedialandlateraltothecondyles,arepointsofligamentattachment. The femur can be distinguished from the humerusby its long neck, located between the head and the trochanters(trkan-terz). A broken hip is usually a break of the femoralneck.Abrokenhipisdifficulttorepairandoftenrequirespinningtoholdthefemoralheadtotheshaft.Amajorcomplicationcanoccurifthebloodvesselsbetweenthefemoralheadandtheacetabulum

Head

Neck

Greater trochanter

Lateral epicondyleLateral condyle

Body (shaft) of femur

Head

Neck

Medialepicondyle

Greater trochanter

Lateral epicondyle

Medialcondyle

Patellar groove

Linea aspera

Intercondylar fossa

Lesser trochanter

Anteriorsurface

Anterior view

Anterior view

Posterior view

Figure 6.33 Bones of the Thigh(a)rightfemur.(b)Patella.

(a)

(b)



AnkleThe ankle consists of seven tarsal (tarsl; the sole of the foot)bones (figure6.35).The tarsal bones are the talus (tls; anklebone), calcaneus (kal-kn-s; heel), cuboid (kboyd), andnavicular(n-viky-lr),andthemedial,intermediate,andlateralcuneiforms (kn-i-frmz). The talus articulates with the tibiaand fibula to form the ankle joint, and the calcaneus forms theheel(figure6.36).AmnemonicforthedistalrowisMILCthatis,Medial,Intermediate,andLateralcuneiformsandtheCuboid.AmnemonicfortheproximalthreebonesisNoThanksCowthatis,Navicular,Talus,andCalcaneus.

FootThemetatarsal (met-tarsl)bones andphalanges of the footarearrangedandnumberedinamannerverysimilartothemeta-carpal bones and phalanges of the hand (see figure 6.35). Themetatarsalbonesaresomewhatlongerthanthemetacarpalbones,whereas the phalanges of the foot are considerably shorter thanthoseofthehand. There are three primary arches in the foot, formed by thepositions of the tarsal bones andmetatarsal bones, and held inplacebyligaments.Twolongitudinalarchesextendfromtheheeltotheballofthefoot,andatransversearchextendsacrossthefoot.Thearchesfunctionsimilarlytothespringsofacar,allowingthefoottogiveandspringback.

Lateral condyle

Head

Medial condyleTibial tuberosity

TibiaFibula

Lateral malleolus

Anterior view

Medial malleolus

Cuboid

Lateral cuneiformMetatarsalbones

Proximal phalanx

Middle phalanxDistal phalanx

Calcaneus

Talus

Navicular

Intermediate cuneiformMedial cuneiform

Proximal phalanxof great toe

1234

5

Tarsal bones

Digits

Navicular

Cuboid

Fibula

Talus

Calcaneus

Tarsal bones

Tibia

Metatarsal bonesDistal phalanxof great toe

Superior view Medial view

Phalanges

Figure 6.34 Bones of the Legtherighttibiaandfibulaareshown.

Figure 6.35 Bones of the Right Foot

(a) (b)



(font-nelz),orsoftspots(figure6.37).Theyallowflexibilityinthe skullduring thebirthprocess, aswell asgrowthof theheadafter birth. Syndesmoses (sindez-msz) are fibrous joints inwhichthebonesareseparatedbysomedistanceandheldtogetherby ligaments. An example is the fibrous membrane connectingmostofthedistalpartsoftheradiusandulna.Gomphoses(gom-fsz)consistofpegsfittedintosocketsandheldinplacebyliga-ments.Thejointbetweenatoothanditssocketisagomphosis.

cartilaginousJointsCartilaginous joints unite two bones bymeans of cartilage.Onlyslightmovementcanoccuratthesejoints.Examplesarethecartilageintheepiphysealplatesofgrowinglongbonesandthecartilages

6.8 JointSLearning Outcomes After reading this section, you should be able to

A. Describethetwosystemsforclassifyingjoints.B. Explainthestructureofafibrousjoint,listthethreetypes,and

giveexamplesofeachtype.C. Giveexamplesofcartilaginousjoints.D. illustratethestructureofasynovialjointandexplaintheroles

ofthecomponentsofasynovialjoint.e. classifysynovialjointsbasedontheshapeofthebonesinthe

jointandgiveanexampleofeachtype.F. Demonstratethedifferencebetweenthefollowingpairs

ofmovements:flexionandextension;plantarflexionanddorsiflexion;abductionandadduction;supinationandpronation;elevationanddepression;protractionandretraction;oppositionandreposition;inversionandeversion.

A joint, or an articulation, is a place where two bones cometogether. A joint is usually considered movable, but that is notalwaysthecase.Manyjointsexhibitlimitedmovement,andothersarecompletely,oralmostcompletely,immovable. Onemethodofclassifyingjointsisafunctionalclassification.Basedonthedegreeofmotion,ajointmaybecalledasynarthrosis(sinar-thrsis;nonmovablejoint),anamphiarthrosis(amfi-ar-thrsis; slightlymovable joint), or adiarthrosis (d-ar-thrsis;freelymovable joint).However, functionalclassificationissome-what restrictive and is not used in this text. Instead, we use astructuralclassificationwherebyjointsareclassifiedaccordingtothe type of connective tissue that binds the bones together andwhetherthereisafluid-filledjointcapsule.Thethreemajorstruc-turalclassesofjointsarefibrous,cartilaginous,andsynovial.

FibrousJointsFibrous joints consist of two bones that are united by fibroustissueandthatexhibitlittleornomovement.Jointsinthisgroupare further subdivided on the basis of structure as sutures, syn-desmoses,orgomphoses.Sutures (soochoorz)arefibrous jointsbetween the bones of the skull (see figure 6.11). In a newborn,somepartsofthesuturesarequitewideandarecalledfontanels

Lateralmalleolus

PatellaTibial tuberosity

Anterior crestof tibia

Medial malleolus

Head of fibula

Calcaneus

Medial epicondyle of femur

Lateral epicondyleof femur

Parietalbone

Occipitalbone

Mastoid (posterolateral) fontanel

Lateral view

Superior view

Frontalbone

Sphenoidal(anterolateral)fontanel

Temporal bone

Squamoussuture

Lambdoidsuture

Coronalsuture

Frontal bones(not yet fusedinto a single bone)

Frontal(anterior)fontanel

Parietalbone

Occipital(posterior)fontanelOccipital

bone

Sagittalsuture

Figure 6.36 Surface Anatomy Showing Bones of the Lower Limb

Figure 6.37 Fetal Skull Showing Fontanels and Sutures

(a)

(b)



(bers; pocket). Bursae are located between structures that rubtogether,suchaswhereatendoncrossesabone;theyreducefric-tion,whichcoulddamagethestructuresinvolved.Inflammationofabursa,oftenresultingfromabrasion,iscalledbursitis.Asynovialmembranemay extend as a tendon sheath along some tendonsassociatedwithjoints(figure6.38).

Types of Synovial JointsSynovialjointsareclassifiedaccordingtotheshapeoftheadjoiningarticularsurfaces(figure6.39).Plane joints,orgliding joints,consistof twoopposed flat surfaces that glide over eachother. Examplesof these joints are the articular facets between vertebrae. Saddle joints consist of two saddle-shaped articulating surfaces orientedatrightanglestoeachother.Movementinthesejointscanoccurintwoplanes.Thejointbetweenthemetacarpalboneandthecarpalbone(trapezium)ofthethumbisasaddlejoint.Hinge jointspermitmovementinoneplaneonly.Theyconsistofaconvexcylinderofoneboneapplied toacorrespondingconcavityof theotherbone.Examples are the elbow and knee joints (figure 6.40a,b). The flatcondylarsurfaceofthekneejointismodifiedintoaconcavesurfacebyshock-absorbing fibrocartilagepadscalledmenisci (m-niss).Pivot jointsrestrictmovementtorotationaroundasingleaxis.Eachpivotjointconsistsofacylindricalbonyprocessthatrotateswithinaringcomposedpartlyofboneandpartlyofligament.Therotationthatoccursbetweentheaxisandatlaswhenshakingtheheadnoisanexample.Thearticulationbetweentheproximalendsoftheulnaandradiusisalsoapivotjoint.

betweentheribsandthesternum.Thecartilageofsomecartilaginousjoints,wheremuchstrainisplacedonthejoint,maybereinforcedbyadditionalcollagenfibers.Thistypeofcartilage,calledfibrocartilage(seechapter4),formsjointssuchastheintervertebraldisks.

SynovialJointsSynovial(si-nv-l)jointsarefreelymovablejointsthatcontainfluidinacavitysurroundingtheendsofarticulatingbones.Mostjointsthatunitethebonesoftheappendicularskeletonaresyno-vialjoints,whereasmanyofthejointsthatunitethebonesoftheaxialskeletonarenot.Thispatternreflectsthegreatermobilityoftheappendicularskeletoncomparedtothatoftheaxialskeleton. Severalfeaturesofsynovialjointsareimportanttotheirfunc-tion(figure6.38).Thearticularsurfacesofboneswithinsynovialjointsarecoveredwitha thin layerofarticular cartilage,whichprovidesasmoothsurfacewherethebonesmeet.Thejoint cavityisfilledwithfluid.Thecavityisenclosedbyajoint capsule,whichhelpsholdthebonestogetherandallowsformovement.Portionsofthefibrouspartofthejointcapsulemaybethickenedtoformligaments. In addition, ligaments and tendons outside the jointcapsulecontributetothestrengthofthejoint. A synovial membrane lines the joint cavity everywhereexcept over the articular cartilage. The membrane producessynovial fluid, which is a complex mixture of polysaccharides,proteins,lipids,andcells.Synovialfluidformsathin,lubricatingfilmcovering the surfaces of the joint. In certain synovial joints, thesynovialmembranemayextendasapocket,orsac,calledabursa

Bursa

Joint cavity (filledwith synovial fluid)

Articularcartilage

Tendonsheath

Tendon

Bone

Bone

Blood vesselNerve

Synovial membraneFibrous part of joint capsule

Jointcapsule

Outer layer

Inner layerPeriosteum

Figure 6.38 Structure of a Synovial Joint



Class and Example of JointPlane

SlightAcromion process of scapula and clavicleCarpals and metacarpals 25Ribs and vertebraeBetween carpal bonesBetween metatarsal bonesBetween tarsal bonesBetween articular processes of adjacent vertebrae

(complex joint with several planes and synchondroses)

Acromioclavicular

Two axes

SlightSlight

Carpometacarpal

CostovertebralIntercarpalIntermetatarsalIntertarsalIntervertebral

Sacroiliac

Tarsometatarsal

Multiple axes as a groupSlightSlightSlightSlightSlight

Slight

Slight

SaddleCarpometacarpal pollicisIntercarpalSternoclavicular

Carpal and metacarpal of thumbBetween carpal bonesManubrium of sternum and clavicle

HingeCubital (elbow)KneeInterphalangealTalocrural (ankle)

Humerus, ulna, and radiusFemur and tibiaBetween phalangesTalus, tibia, and fibula

One axisOne axisOne axisMultiple axes; one predominates

PivotMedial atlantoaxialProximal radioulnarDistal radioulnar

Atlas and axisRadius and ulnaRadius and ulna

RotationRotationRotation

Ball-and-SocketCoxal (hip)Humeral (shoulder)

Coxal bone and femurScapula and humerus

Multiple axesMultiple axes

EllipsoidAtlantooccipitalMetacarpopha- langeal (knuckles)Metatarsopha- langeal (ball of foot)Radiocarpal (wrist)Temporomandibular

Atlas and occipital boneMetacarpal bones and phalangesMetatarsal bones and phalangesRadius and carpal bonesMandible and temporal bone

Two axesTwo axes

Two axes

Multiple axesMultiple axes; one predominates

Ball-and-socket

Ellipsoid

Plane

Saddle

Hinge

Pivot

Structures Joined Movement

Between sacrum and coxal bone

Tarsal bones and metatarsal bones

Figure 6.39 Types of Synovial Joints



type ofmovement,whereas others permitmovement in severaldirections.All themovementsaredescribedrelative to theana-tomicalposition.Becausemostmovementsareaccompaniedbymovementsintheoppositedirection,theyareoftenillustratedinpairs(figure6.41). Flexion and extension are common opposing movementsthatmaybedefinedinanumberofways,althougheachdefinitionhasanexception.Theliteraldefinitionsaretobend(flex)andtostraighten (extend). But we have chosen to use definitions withmoreutilityandfewerexceptions.Thus,wesaythatflexionmovesapartofthebodyintheanteriordirectionfromthefrontalplane,whereas extensionmoves a part in the posterior direction fromthefrontalplane(figure6.41a,b).Anexceptionistheknee,whereflexionmovestheleginaposteriordirectionandextensionmovesitinananteriordirection.

Ball-and-socket joints consistofaball (head)at theendofoneboneandasocket inanadjacentbone intowhichaportionof the ball fits. This type of joint allows awide range ofmove-mentinalmostanydirection.Examplesaretheshoulderandhipjoints (figure6.40c,d).Ellipsoid (-lipsoyd) joints, orcondyloid(kondi-loyd) joints, are elongated ball-and-socket joints. Theshapeofthejointlimitsitsrangeofmovementnearlytothatofahingemotion,but intwoplanes.Examplesofellipsoid jointsarethejointbetweentheoccipitalcondylesoftheskullandtheatlasofthevertebralcolumnandthejointsbetweenthemetacarpalbonesandphalanges.

typesofMovementThetypesofmovementoccurringatagiven jointarerelated tothe structure of that joint. Some joints are limited to only one

Elbow

Humerus

Fat pad

Olecranon bursa

Trochlea

Articular cartilage of the trochlear notch

Joint capsule

Joint cavity

Synovial membrane

Articular cartilage

Coronoid process

Ulna

Femur

ArticularcartilageMeniscus

Tibia

QuadricepsfemoristendonSuprapatellarbursaSubcutaneousprepatellarbursaPatella

Fat padPatellarligamentDeepinfrapatellarbursa

Knee

Pelvic boneArticular cartilage

Joint cavityLigamentum teresHead of femur

Neck of femur

Joint capsule

Greatertrochanter

Lessertrochanter

Femur

Hip

Subacromial bursaJoint cavity

Acromion process (articular surface)

Articular cartilage over head of humerus

Scapula (cut surface)

Joint capsule

Articular cartilageover glenoid cavity

Shoulder

Tendon sheath on tendon of long head of biceps brachii

Biceps brachiitendon

Humerus

Biceps brachiimuscle

Sagittal sectionSagittal section

Frontal section Frontal section

Figure 6.40 Examples of Synovial Joints(a)Elbow.(b)Knee.(c)Shoulder.(d)Hip.

(a)

(c)

(b)

(d)



Flexion

Extension

Pronation

Supination

Medial rotation Lateral rotation

Circumduction

Anterior tofrontal plane

Posterior tofrontal plane

Flexion Extension

Frontal plane

Abduction

Abduction

Adduction

(a)

(d)

(e) (f)

(b) (c)

Figure 6.41 Types of Movement(a)Flexionandextensionoftheelbow.(b)Flexionandextensionoftheneck.(c)abductionandadductionofthefingers.(d)Pronationandsupinationofthehand.(e)Medialandlateralrotationofthearm.(f )circumductionofthearm.



Depressionismovementofastructureinaninferiordirection.Openingthemouthinvolvesdepressionofthemandible.

Excursionismovementofastr

see 78267 chapter 06

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