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Joints

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http://classes.midlandstech.edu/carterp/Courses/bio210/chap08/lecture1.html

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Joints

  1. 1. Joints Siteswhere twoormore bonesmeetare calledjointsorarticulations. Two basicfunctionsof jointsare to give ourskeletonmobilityandholdittogether. ClassificationofJoints Structural classificationfocusesonthe material bindingthe bonestogetherandwhetherornota joint cavityis present. In fibrousjointsthe bonesare joinedtogetherbyfibroustissue andlackajointcavity. In cartilaginousjointsthe bonesare joinedtogetherbycartilage andtheylacka jointcavity. In synovial joints,the articulatingbonesare separatedbyafluid-containingjointcavity. Functional classificationisbasedonthe amountof movementallowedatthe joint. Synarthrosesare immovablejoints. Amphiarthrosesare slightlymovable joints. Diarthrosesare freelymovablejoints. FibrousJoints Sutures Suturesoccur betweenbonesof the skull anduse veryshortconnective tissuefiberstoholdthe bones together. Syndesmoses In syndesmoses,the bonesare connectedbyaligament,whichisacord or bandof fibroustissue.
  2. 2. Gomphoses A gomphosisisapeg-in-socketfibrousjoint. CartilaginousJoints Synchondroses Synchondrosesinvolveabar or plate of hyaline cartilage unitingthe bones,suchasthe epiphyseal plate. Symphyses In symphyses,suchasthe pubicsymphysis,the articularsurfacesare coveredwitharticularcartilage that isthenfusedtoan interveningpadorplate of fibrocartilage.
  3. 3. Synovial Joints General Structure The general structure of a synovial jointcontainsfivedistinguishing features. Articularcartilage coversthe endsof the articulatingbones. The joint(synovial)cavityisaspace that isfilledwithsynovial fluid. The two-layeredarticularcapsuleenclosesthe jointcavity. Synovial fluidisaviscous,slipperyfluidthatfillsall free space withinthe jointcavity. Reinforcingligamentscrosssynovial jointstostrengthenthe joint.
  4. 4. Bursae and Tendon Sheaths Bursae and tendonsheathsare bagsof lubricantthatreduce frictionatsynovial joints.
  5. 5. Factors Influencingthe Stability ofSynovial Joints ArticularSurfaces The shapesof the articularsurfacesof bonesfoundat a synovial jointdetermine the movementsthat occur at the joint,butplaya minimal role instabilizingthe joint. Ligaments Ligamentsata synovial jointpreventexcessiveorunwantedmovementsandhelptostabilizethe joint; the greaterthe numberof ligamentsatthe jointthe greaterthe stability. Muscle Tone Muscle tone keepstendonscrossingjointstaut,whichisthe mostimportantfactorstabilizingjoints. MovementsAllowedbySynovial Joints GlidingMovements In glidingmovementsone flat,ornearlyflat,bone surface glidesorslipsoveranother. AngularMovements Angularmovementsincrease ordecrease the angle betweentwobones. Flexiondecreasesthe angle of the jointandbringsthe articulatingbonesclosertogether. Extensionincreasesthe angle betweenthe articulatingbones. Dorsiflexiondecreasesthe angle betweenthe topof the foot(dorsal surface) andthe anteriorsurface of the tibia. Plantarflexiondecreasesthe angle betweenthe sole of the foot(plantarsurface) andthe posteriorside of the tibia. Abductionisthe movementof alimb(orfingers) awayfromthe midlinebody(orof the hand). Adductionisthe movementof alimb(orfingers) towardthe midline of the body(orthe hand). Circumductionismovingalimbsothat it describesacone inthe air. Rotation Rotationisthe turningof a bone alongitsownlongaxis. Special Movements Supinationisrotatingthe forearm laterallysothatthe palmfacesanteriorlyorsuperiorly.
  6. 6. Pronationisrotatingthe arm mediallysothatthe palmfacesposteriorlyorinferiorly. Inversionturnsthe sole of the footsothat it facesmedially. Eversionturnsthe sole of the footso that it faceslaterally. Protractionmovesthe mandible anteriorly,jutsthe jaw forward. Retractionreturnsthe mandible toitsoriginal position. Elevationmeansliftingabodypartsuperiorly. Depressionmeanstomove anelevatedbodypartinferiorly. Oppositionoccurswhenyoutouchyourthumbto the fingersonthe same hand. Types ofSynovial Joints Plane jointshave flatarticularsurfacesandallow glidingandtransitionalmovements. Hinge jointsconsistof a cylindrical projectionthatnestsinatrough-shapedstructure,andallow movementalongasingle plane. Pivotjointsconsistof aroundedstructure that protrudesintoasleeve orring,andallow uniaxial rotationof a bone aroundthe longaxis. Condyloid,orellipsoid,jointsconsistof anoval articularsurface that nestsina complementary depression,andpermitall angularmovements. Saddle jointsconsistof eacharticularsurface bearingcomplementaryconcave andconvex areas,and allowmore freedomof movementthancondyloidjoints. Ball-and-socketjointsconsistof aspherical orhemispherical structure thatarticulateswithacuplike structure.Theyare the mostfreelymovingjointsandallow multiaxial movements.
  7. 7. SelectedSynovial Joints Knee Joint Enclosedinone jointcavity,the knee jointisactuallythree jointsinone:the femoropatellarjoint,the lateral andmedial jointsbetweenthe femoral condyles,andthe menisci of the tibia,knowncollectively as the tibiofemoraljoint. Many differenttypesof ligamentsstabilizeandstrengthen the capsuleof the knee joint. The knee capsule isreinforcedbymuscle tendonssuchasthe strong tendonsof the quadricepsmuscles and the tendonof the semimembranosus.
  8. 8. Shoulder(Glenohumeral) Joint
  9. 9. Stabilityhasbeensacrificedtoprovide the mostfreelymovingjointinthe body. The ligamentsthathelptoreinforce the shoulderjointare the coracohumeral ligamentandthe three glenohumeral ligaments. The tendonsthat crossthe shoulderjointandprovide the moststabilizingeffectonthe jointare the tendonof the longheadof the bicepsbrachii andthe four tendonsthatmake upthe rotator cuff.
  10. 10. ElbowJoint The elbowjointprovidesastable andsmoothlyoperatinghingejointthatallowsflexionandextension only. The ligamentsinvolved inprovidingstabilitytothe elbow jointare the annularligament,the ulnar collateral ligament,andthe radial collateral ligament. Tendonsof several armmuscles,the bicepsandthe triceps,alsoprovide additional stabilitybycrossing the elbowjoint. Hip (Coxal) Joint The hip jointisa ball-and-socketjointthatprovidesagoodrange of motion. Several strongligamentsreinforce the capsule of the hipjoint.
  11. 11. The muscle tendonsthatcross the jointcontribute tothe stabilityandstrengthof the joint,butthe majorityof the stabilityof the hipjointisdue tothe deepsocketof the acetabulumandthe ligaments. TemporomandibularJoint The temporomandibularjointallowsbothhinge-like movementandside-to-sidelateral excursion. The jointcontainsan articulardiscthat dividesthe synovial cavityintocompartmentsthatsupporteach type of movement. The lateral aspectof the fibrouscapsule containsalateral ligamentthatreinforcesthe joint.
  12. 12. Homeostatic Imbalancesof Joints Common JointInjuries Cartilage Tears
  13. 13. Sprains Dislocations Inflammatory and Degenerative Conditions BursitisandTendonitis Bursitis,aninflammationof the bursa,isusuallycausedbya blow or friction;tendonitisisinflammation of the tendons,andisusuallycaused byoveruse. Arthritis Arthritisdescribesmanyinflammatoryordegenerativediseasesthatdamage the joints,resultingin pain,stiffness,andswellingof the joint. Osteoarthritisisthe mostcommonchronicarthritis.Itisthe resultof breakdownof articularcartilage and subsequentthickeningof bone tissue,whichmayrestrictjointmovement. Rheumatoidarthritisisachronicinflammatorydisorderthatisan autoimmune disease. Gouty arthritisresultswhenuricacidisdepositedinthe softtissues of the joints.
  14. 14. Lyme Disease Lyme disease isabacterial disease transmittedbyticksthatnormallylive onmice anddeer.Itcausesa charachteristic"bulls-eye rash,flu-like symptoms,andmaybe accompaniedbydisruptionsincognition and jointpainandarthritis. Withouttreatment(antibiotics) itcanprogressto neurological disordersandirregularheartbeat. Developmental AspectsofJoints Jointsdevelopatthe same time asbones,resemblingadultformbyeightweeksgestation. At late middle age and beyond,ligamentsandtendonsshortenandweaken,intervertebral discsbecome more likelytoherniate,andthere isonsetof osteoarthritis.

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