Articulations or Joints

Transcription

1 Articulatins r Jints Bnes are cnnected t each ther by jints. The mst cmmn jint type is the diarthrsis f articulating jints, which has a fibrus cnnective tissue capsule (ligament), cntinuus with the peristeum f the tw bnes and which permits a degree f freedm f mvement between the tw bnes. The inner part f the capsule cnsists f the synvial membrane, which may extend as a fld (synvial fld). The synvial membrane is well vascularised with bth bld and lymph vessels. The main cell type present in the synvial membrane, are fibrblast-like cells, and invlved in the frmatin f the synvial fluid. This fluid is rich in hyalurnic acid and fills the jint cavity. Macrphage-like cells are als fund in the synvial membrane and are respnsible fr keeping the synvial fluid clean and free f cell fragments. The synvial fluid plays an imprtant rle in the lubricatin f the jint and in prviding nutritin fr the articular cartilage f the epiphyses. Fat depsits r pads, fund between the synvial membrane and the ligament, functin as mechanical shck absrbers. Aging changes t jints, in particular pathlgical changes f the articular cartilage (stearthritis), are very cmmn in the elderly. Functin Hld skeletn tgether

2 Prvide mbility Weakest part f the skeletn FIBROCARTILAGE Fibrcartilage is fund in areas f the bdy subject t high mechanical stress r weightbearing. It lacks the flexibility f the ther cartilage types. Fibrcartilage is present in: (a) intervertebral disks (b) pubic symphysis (c) tempr-mandibular jints (d) at sites f cnnectin f many ligaments t bnes (e.g. Ligamentum teres femris) (e) tendn insertins. Fibrcartilage is characterized by large numbers and cncentratins f cllagen fibers in the matrix. These cllagen fibers are the dminant feature f the matrix and with relatively little amrphus matrix. The large amunts f cllagen fibers result in the matrix appearing acidphilic in histlgical sectins after H&E staining. Fibrcartilage is nt surrunded by perichndrium. The intervertebral disks cnsist f fibrcartilage plates between the vertebrae and act as mechanical shck absrbers. In sectins they are seen t be frmed f tw cmpnents: (a) the annulus fibrsus, which is the uter regin cnsisting f rderly cncentric arrangements f cells and matrix dminated by type I cllagen (as in tendns) ( b) the nucleus pulpsus (large vaculated cells, that are vestiges f the embrynic ntchrd. Tw main functinal grups f jints synvial (NL; between val surfaces)= diarthrses (Gk. t fasten by a jint): extensive mvement at articular surfaces; maintained in appsitin by fibrus capsule and ligaments; surfaces lubricated by synvial fluid synvium: specialized layer f cllagenus tissue lining inner aspect f capsule; inner surface discntinuus layer cells up t fur synvial cells deep; n junctinal cmplexes

3 r basement membrane; mesenchymal rigin; type A synvcytes: plump, majrity; extensive Glgi cmplex, numerus lyssmes suggestive f macrphages; type B synvcytes: prfuse rer; represent fibrblasts; arelar synvium: synvium f lse CT fibrus synvium: denser cllagenus type; rich netwrk f capillaries and thick strands f cllagen adipse synvium: cmped f fat; intra-articular fat pads synvial fluid: fluid frm synvial extracellular matrix (nt a secretin); hyalurnic acid and assciated glycprteins secreted by type B synvcytes; transudate frm synvial capillaries; als small number f leuccytes, predminantly mncytes. articular cartilages: n perichndrium; cllagen f type I (in cntrast t type II cllagen f hyaline cartilage) bny end plate; lacks stens and canaliculi; stecytes ccupy large lacunae; thick layer f glycprtein-rich substance (resembles cement lines between stens) demarcates bny plate frm articulate surface. temprmandibular and knee jints: fibrcartilage cmpletely r partially interpsed btwn articular surfaces but unattached intervertebral jints: thick ligaments extending dwn anterir aspect f spinal clumn merges with anulus fibrsus; thinner ligament psterir; zygapphyseal jints: (zyg = yked) synvial jints btwn vertebral arches; stabilized by strng elastic ligaments cnnecting bny prcesses intervertebral disk = symphysial jints (i.e., fibrcartilage type); fibrcartilage arranged in cncentric rings - annulus fibrsus reinfrced peripherally by circumferential ligaments; central cavity cntaining viscus fluid = nucleus pulpsus cntaining physaliphrus cells (nucleus pulpsus remnant f ntchrd) slipped disk: fibrcartilage f annulus fibrsus thins and weakens; nucleus pulpsus extruded, particularly pster-lateral aspect. tendn: densest frm f cllagenus supprting tissue

4 nnsynvial: limited mvement; n free articular surfaces; jined by dense cllagenus tissue dense fibrus tissue: sutures btwn bnes f skull; syndesmses = fibrus tissue jints; synstses = after replacement by bne hyaline cartilage: synchndrsis r primary cartilaginus jint; unites first rib with sternum fibrcartilage: hyaline cartilage at ends f appsed bnes cnnected t each ther by plate f fibrcartilage; = symphyses r secndary cartilaginus jints; public symphysis (develps central cavity) and intervertebral disks (have fluidfilled central cavity) Jints are accrdingly classified 1. fibrus and cartilaginus jints where tw bnes are separated by a defrmable intermediate 2. synvial jints where ne surface slides freely ver anther. Fibrus jints. We have already mentined the jint between the bny shaft and cartilage at the ends f lng bnes. This is a synchndrsis, a cartilage sandwich with bne n either side: bne and cartilage fit tgether perfectly and the whle thing is cup shaped. If mvement ccurs the grwing bne will be damaged (slipped epiphysis) and this is cuntered by putting in a lng nail t fix it again. Sutures: are limited t the skull. They resemble a synchndrsis, but with fibrus tissue instead f cartilage between the bnes. Sutures are necessary fr skull grwth: cnsequently well marked in the yung less s in the adult. The nly mvement in sutures is at birth when the cranial bnes verlap t allw passage thrugh the maternal pelvis. After this mvement is discuraged by increasing cmplexity f the suture, which becmes serrated r denticulate. Later in life, when grwth is cmplete they fuse. gmphses: are peg and scket jints as seen between teeth and jaws. The jint is maintained by the peridntal ligament which gives nly a little t act as a shck absrber when we bite n a ball bearing. syndesmsis: nly ne f these in the bdy, the inferir tibi-fibular jint. In this type there is a little mvement, limited by a tight ligament. Since many jints are limited by ligaments this is prbably a special definitin we can d withut. symphysis: tw bnes united by cartilage, but designed t give a bit. The symphysis pubis with ligaments and fibrcartilage is nrmally clsed, but pens in childbirth due t hrmnal influences. Synvial jints have different parameters. Jint surfaces almst in cntact but discntinuus, as a great range f mvement is ften pssible, and the surfaces slide ver each ther. The sliding surfaces are cvered with a thin layer f cartilage. This gives a cefficient f frictin f < The jint cavity is sealed by a synvial membrane which secretes synvial fluid, a lubricant and nutrient. Arund this, in turn, is a tugh fibrus jint capsule which keeps the ends f the bnes in

5 prper rientatin. This is ften lcally thickened t frm jint ligaments. The synvial cavity is very small between articular surfaces but larger rund the edges where it may frm a bursa, a sack-like extensin which may be in cntact with the jint cavity. Varius inclusins may be present in the jint cavity: a tendn may pass thrugh, sheathed in synvial membrane. Fat pads may be present, packing the large gaps which ccur in sme jints between bne ends. Pieces f cartilage are als fund, in additin t articular cartilage. These may frm 1. a labrum r lip deepening a bny scket 2. menisci - incmplete discs r crescents increasing the size f articular surfaces 3. cmplete, r nearly cmplete articular discs f fibrcartilage. This will cnvert a jint int tw in parallel, which can then mve in independent directins. The temprmandibular jint f the jaw is a gd example f this. Limitatin f mvement is als imprtant. Usually achieved by 1. tensin in ligament, which have strain and pain receptrs 2. tensin f muscles arund a jint - passive resistance t stretch fllwed by reflex cntractin when stimuli frm mechanreceptrs becmes critical. These explain Hiltn's law: that jints and the muscles acting n them share a nerve supply. Paralysis f muscles thus affects jints. In spastic paralysis muscle tne is increased and mvement restricted. In ther paralyses jints becme lax, flail jints r actually disrupted. Charct elbw in syphilis. 3. Running ut f articular surface. 4. apprximatin f sft parts. Skeletal Articulatins: Jint Architecture Classificatin accrding t MOVEMENT: Synarthrsis - immvable, fibrus jints sutures - bne sheets mate clsely and held by fibers (skull) syndemsis - held by ligaments (mid-radiulnar, mid-tibifibular) Amphiarthrsis - slightly mvable, cartilaginus jint synchndrses - held by thin layer f hyaline cartilage (sterncstal, epiphyseal plate) symphyses - thin plate f hyaline cartilage separates disc f fibrcartilage frm bne (vertebral, pubic symphysis) Diarthrses - freely mvable, synvial jints Synvial jints (r diarthrses, r diarthridal jints) are the mst cmmn and mst mveable type f jints in the bdy. The whle f a diarthrsis is cntained by a ligamentus sac, the jint capsule r articular capsule.

6 The surfaces f the tw bnes at the jint are cvered in cartilage. The thickness f the cartilage varies with each jint, and smetimes may be f uneven thickness. Articular cartilage is multilayered. A thin superficial layer prvides a smth surface fr the tw bnes t slide against each ther. Of all the layers, it has the highest cncentratin f cllagen and the lwest cncentratin f prteglycans, making it very resistant t shear stresses. Deeper than that is an intermediate layer, which is mechanically designed t absrb shcks and distribute the lad efficiently. The deepest layer is highly calcified, and anchrs the articular cartilage t the bne. In jints where the tw surfaces d nt fit snugly tgether, a meniscus r multiple flds f fibrcartilage within the jint crrect the fit, ensuring stability and the ptimal distributin f lad frces. The synvium is a membrane that cvers all the nn-cartilaginus surfaces within the jint capsule. It secretes synvial fluid int the jint, which nurishes and lubricates the articular cartilage. The synvium is separated frm the capsule by a layer f cellular tissue that cntains bld vessels and nerves.

7 Articular cartilage - prtective layer f dense white cnnective tissue cvering articulating bne surfaces that spreads lad ver wider are, therby reducing cntact stress Articular capsule - duble layered membrane that surrunds the jint Synvial fluid - clear, slightly yellw liquid that prvides lubricatin inside the articular capsule Bursae (and tendn sheath) - small capsules filled with synvial fluid that reduce frictin between tendn and bne Meniscus - articular fibrcartilage (sft tissue that intervenes between articulating bnes) that may 1. distribute lad ver wider area 2. imprve "fit" f articulating surfaces 3. limit translatin ("slip") f ne bne in relatin t anther 4. prtectin f periphery f jint 5. lubricatin 6. shck absrptin

8 1. Ball and scket 2. Cndylid (ellipsid) 3. Saddle 4. Hinge 5. Pivt Synvial jints can be further gruped by their shape, which cntrls the mvement they allw. 1. Ball and scket jints, such as the shulder and hip jints. These allw a wide range f mvement. 2. Cndylid jints (r ellipsid), such as the thumb. A cndylid jint is where tw bnes fit tgether with an dd shape (e.g. an ellipse), and ne bne is cncave, the ther cnvex. Sme classificatins make a distinctin between cndylid and ellipsid jints. 3. Saddle jints, such as at the thumb (between the metacarpal and carpal). Saddle jints, which resemble a saddle, permit the same mvements as the cndylid jints. 4. Hinge jints, such as the elbw (between the humerus and the ulna). These jints act like a dr hinge, allwing flexin and extensin in just ne plane. 5. Pivt jints, such as the elbw (between the radius and the ulna). This is where ne bne rtates abut anther. 6. Gliding jints, such as in the carpals f the wrist. These jints allw a wide variety f mvement, but nt much distance. 7. Plane jints, such as the synvial jint between the ribs and vertebrae at the intraarticular ligament. Tendns (muscle t bne) and Ligaments (bne t bne) Types include gliding (plane; arthrdial) - allws nn-axial gliding nly (intermetatarsal, intercarpal, facet jints f vertebrae) hinge (ginglymus) - cnvex vs. cncave (humerulnar, interphalangeal) pivt (screw; trchid) - allws rtatin arund ne axis (prximal and distal radiulnar, atlant-axial [between first and secnd cervical vertebrae])

9 cndylid (vid; ellipsidal) - mdified ball-and-scket (nt as deep) (radicarpal, 2-5 metacarpphalangeal) saddle (sellar) - shape f riding saddle (carpmetacarpal f thumb) ball and scket (spheridal) - reciprcally cnvex and cncave (hip and shulder)

10 Majr jints in Human Bdy shulder (glenhumeral) - articulatin f glenid fssa and humerus (ball-and-scket) elbw (humerulnar) -articulatin f humerus and ulna (hinge) wrist (radicarpal) -articulatin f radius and carpals (cndylid) hip (acetabularfemral) -articulatin f acetabulum and femral head (ball-and-scket) knee (tibifemral) - articulatin f femur and tibia (hinge) ankle (talcrural) - articulatin f tibia and fibula with talus (hinge) spine (intervertebral) - intervertebral disc (symphysis - amphiarthrsis) frearm (prximal and distal radiulnar) - articulatin f heads f radius and ulna (pivt) neck (atlant-ccipital and atlant-axial) atlant-ccipital - articulatin f atlas (C1) and ccipital bne (skull) = cndylid jint atlant-axial - articulatin f atlas (C1) and axis (C2) = pivt jint Functinal Aspects f the Jint Jint Stability - ability t resist abnrmal displacement f articulating bnes prevents injuries t surrunding ligaments, muscles, and tendns high stability is desired Factrs affecting jint stability: Jint structure

11 reciprcally shaped = tend t fit tightly tgether Cntact area wide cntact area = high stability (shulder vs. hip) different amng jints and amng individuals change in jint angle --> change in cntact area --> change in stability maximal area f cntact at the clse-packed psitin Cnnective tissues weak and lax cnnective tissues = lw stability strengthening f tissues --> increase in stability muscle activity and fatigue --> decrease in stability Example: illitibial tract f fascia latae crsses lateral aspect f knee and cntributes t knee stability Jint Flexibility - range f mtin (ROM) allwed at a jint ROM - the angle thrugh which a jint mves frm anatmical psitin t the extreme limit f segment mtin is jint specific Factrs affecting jint flexibility: shapes f articulating bne surfaces intervening muscle r fatty tissue laxity extensibility f the cllagenus tissue and muscles fluid cntens in cartilagenus disc temperature f cllagenus tissues (warm-up?) stretching prgram Flexibility vs. injury surces f injury extremely lw flexibility = high chance f tear r rupture extremely high flexiblity = lw stability imbalance between dminant and nn-dminant sides injury preventin - high strength and flexibility desired stretching prgram Glgi Tendn Organs (GTO's) - sensry receptrs that sense tensin when activated cause antagnist t cntract and muscle being stretched t relax Muscle Spindles - sensry receptrs that mnitr changes in length f muscle when activated cause cntractin f muscle being stretched and inhibit tensin develpement in antagnist Gal f stretching prgram is t maximize GTO effect and minimize muscle spindle effect regular stretching --> flexibility increases

12 active (prduced by active tensin in antagnist muscle) vs. passive (prduced by frce ther than muscles) ballistic vs. static vs. prpriceptive neurmuscular facilitatin (PNF) stretching Cmmn jint Injuries and Pathlgies Sprains - stretching r tearing f cnnective tissue arund a jint Dislcatins - displacement f articulating bnes Bursitis - inflammatin f bursa sacs Arthritis -inflammatin f jint with pain and swelling rheumatid - mst debilitating and painful (immune system attacks healthy tissues) stearthritis - cartilage becmes rugh and wears away 1. A jint r articulatin r arthrsis is a pint f cntact between neighbring bnes, between cartilage and bnes, r between teeth and bnes. 2. Arthrlgy is the study f jints; kinesilgy is the study f mtin f the bdy. 3. Structural characteristics f a specific jint affect the strength, magnitude f mvement, and types f mvement that may ccur at a specific jint. B. Classificatin f Jints 1. Based n the presence r absence f a jint (synvial) cavity and the type f cnnective tissue that binds the bnes tgether, the structural classificatin f jints categrizes jints int three majr families: i. fibrus jints ii. cartilaginus jints iii. synvial jints 2. Based n the magnitude f mvement permitted, the functinal classificatin f jints categrizes jints int three majr grups: i. synarthrsis is an immvable jint ii. amphiarthrsis is a slightly mvable jint iii. diarthrsis is a freely mvable jint C. Fibrus Jints 1. Fibrus jints lack a synvial cavity, and the articulating bnes are held very clsely tgether by fibrus cnnective tissue; they permit little r n mvement. 2. There are three types f fibrus jints: i. Suture a. cnsists f a thin layer f dense fibrus cnnective tissue that strngly cnnects the bnes b. lcated exclusively between (mst) neighbring skull bnes (e.g., crnal suture) c. functinally classified as a synarthrsis d. a synstsis is a childhd suture that is replaced by bne in the adult ii. Syndesmsis a. cntains mre fibrus cnnective tissue than in a suture b. example is distal articulatin between tibia and fibula c. functinally is classified as an amphiarthrsis iii. Gmphsis a. jint in which a cne-shaped peg fits int a scket

13 b. nly example is rt f tth cnnected by peridntal ligament t alvelus f mandible r maxilla c. functinally is classified as a synarthrsis D. Cartilaginus Jints 1. Cartilaginus jints lack a synvial cavity, and the articulating bnes are tightly cnnected by cartilage; they permit little r n mvement. 2. There are tw types f cartilaginus jints: i. Synchndrsis a. the cnnecting tissue is hyaline cartilage b. an example is an epiphyseal plate c. functinally is classified as a synarthrsis ii. Symphysis a. the cnnecting tissue is a disc f fibrcartilage b. an example is the pubic symphysis c. functinally is classified as an amphiarthrsis E. Synvial Jints 1. Synvial jints are characterized by the presence f a synvial (jint) cavity; they are functinally classified as diarthrses. 2. Additinal imprtant characteristics include: i. articular cartilage ii. articular capsule cmpsed f tw layers: a. uter fibrus capsule that may have ligaments b. inner synvial membrane which secretes lubricating synvial fluid that fills the synvial cavity iii. many synvial jints als cntain: a. accessry ligaments, including extracapsular ligaments and intracapsular ligaments b. articular discs r menisci iv. rich bld and nerve supply 3. Fluid-filled sacs called bursae as well as tubelike bursae called tendn sheaths reduce frictin at sme jints during mvements. 4. Types f synvial jints include: i. planar jint at which gliding mvements may ccur a. articulating surfaces are usually flat r slightly curved b. nly side-t-side and back-and-frth mvements are permitted withut mvement arund any axis; it is a nnaxial jint c. example is jint between clavicle and sternum ii. hinge jint a. mnaxial r uniaxial jint at which cnvex surface f ne bne fits int cncave surface f anther bne b. flexin and extensin (and smetimes hyperextensin) may ccur c. examples include knee jint, elbw jint, and ankle jint iii. pivt jint a. mnaxial jint at which runded r pinted surface f ne bne articulates within a ring frmed partly by anther bne and partly by a ligament b. rtatin may ccur

14 c. example is rtatin f atlas arund dens f axis when turning the head iv. cndylid r ellipsidal jint a. biaxial jint at which an val-shaped cndyle f ne bne rests against an elliptical cavity f anther bne b. the fur angular mvements (and circumductin) may ccur c. example is the wrist jint v. saddle jint a. biaxial jint at which articular surface f ne bne is saddle-shaped and the articular surface f the ther bne resembles the legs f a rider sitting in a saddle b. is technically a mdified ellipsidal jint in which mvement is smewhat freer c. example is jint between trapezium and base f the first metacarpal vi. ball-and-scket jint a. multiaxial (r plyaxial) jint at which ball-like surface f ne bne rests against cuplike depressin f anther bne b. the fur angular mvements and rtatin may ccur c. the nly examples are the shulder and hip jints F. Types f Mvements at Synvial Jints 1. The general kinds f mtin that ccur at synvial jints include: i. gliding mtin in which articulating surfaces slide acrss each ther ii. angular mvements in which there is a change in the angle between articulating bnes iii. rtatin mvement in which a bne turns arund its wn lngitudinal axis iv. special mvements which ccur nly at certain jints 2. Specific types f mvements that may ccur at synvial jints include i. gliding mvements ccur at planar jints a. ne surface mves back-and-frth and frm side-t-side ver anther surface withut changing the angle between the bnes b. examples include jints between neighbring carpals ii. angular mvements change the angle between bnes; there are several types including: a. flexin decreases the angle (e.g., bending the elbw jint) - lateral flexin is bending f the spine in the frntal plane b. extensin increases the angle (e.g., straightening the knee jint); - hyperextensin is extensin beynd the anatmical psitin (e.g., bending the head psterirly) c. abductin is mvement f a bne away frm the midline f the bdy (e.g., mving the humerus laterally) - fr fingers a line drawn thrugh the middle finger is used, and fr tes a line drawn thrugh the secnd te is used, as the line f reference d. adductin is mvement f a bne tward the midline f the bdy (e.g., returning the humerus t the anatmical psitin after previus abductin) - fr fingers and tes, the lines f reference described abve are used e. circumductin is a mvement in which the distal end f a bne mves in a circle while the prximal end remains stable (e.g., winding up t

15 pitch a ball); it is typically a cmbinatin f the fur angular mvements and rtatin iii. rtatin is mvement f a bne arund its wn lngitudinal axis; there are tw types: a. medial (r internal) rtatin b. lateral (r external) rtatin iv. special mvements ccur nly at certain jints: a. elevatin and depressin are, respectively, an upward mvement f a part f the bdy (e.g., elevating the mandible t clse the muth), and a dwnward mvement f a part f the bdy (e.g., depressing the mandible t pen the muth) b. prtractin and retractin are mvements f the mandible r shulder girdle frward r backward, respectively, n a plane parallel t the grund c. inversin and eversin are mvements f the sle f the ft medially r laterally, respectively d. drsiflexin and plantar flexin are bending f the ankle jint s that the ft mves in a drsal r plantar (sle) directin, respectively e. supinatin and prnatin are mvements f the frearm in which the palm turns anterirly/superirly r psterirly/inferirly, respectively f. ppsitin is mvement f a thumb acrss the palm t tuch the fingertips n the same hand. G. Selected Jints f the Bdy 1. Selected jints are characterized by the fllwing: i. definitin, i.e., descriptin f the type f jint and the bnes that frm the jint ii. anatmical cmpnents iii. mvements that may ccur 2. The selected jints that are described in detail include: i. temprmandibular jint (TMJ) ii. shulder (humerscapular r glenhumeral) jint iii. elbw jint iv. hip (cxal) jint v. knee (tibifemral) jint vi. ankle (talcrural) jint 3. The imprtant characteristics f ther majr jints are als described H. Factrs Affecting Cntact and Range f Mtin at Synvial Jints 1. Factrs which cntribute t keeping the articular surfaces in cntact and, therefre, determine the type and range f mtin (ROM) pssible, include: i. structure r shape f the articulating bnes ii. strength and tensin (tautness) f the jint ligaments iii. arrangement and tensin f muscles arund the jint iv. appsitin f neighbring sft parts v. effect f hrmnes (e.g., relaxin relaxes pelvic jints tward the end f pregnancy) vi. disuse f a jint

16 I. Aging and Jints 1. The effects f aging n jints are variable amng individuals and are affected by genetic factrs and wear and tear; the aging prcess usually results in: i. decreased prductin f synvial fluid ii. thinning f articular cartilage iii. shrtening f ligaments and a decrease in their flexibility iv. degenerative changes in the knees, elbws, hips and shulders J. Arthrplasty 1. Severely damaged jints may be replaced surgically with artificial jints in a prcedure called arthrplasty. 2. The mst cmmnly replaced jints are the hips, knees, and shulders. K. Key Medical Terms Assciated with Jints 1. Students shuld familiarize themselves with the glssary f key medical terms. Key Terms: active stretching articular capsule articular cartilage articular fibrcartilage ballistic stretching clse-packed psitin Glgi tendn rgan jint flexibility jint stability lse-packed psitin muscle spindle passive stretching prpriceptive neurmuscular facilitatin range f mtin reciprcal inhibitin static stretching stretch reflex the stretching f muscles, tendns, and ligaments prduced by active develpment f tensin in the antagnist muscles duble layered membrane that surrunds every synvial jint prtective layer f dense white cnnective tissue cvering the articulating bne surfaces at diarthrdial jints sft tissue discs r menisci that intervene between articulating bnes a series f quick, buncing-type stretches jint rientatin fr which the cntact between the articulating bne surfaces is maximum sensry receptr that inhibits tensin develpment in a muscle a term indicating the relative ranges f mtin allwed at a jint the ability f a jint t resist abnrmal displacement f the articulating bnes any jint rientatin ther than the clse-packed psitin sensry receptr that prvkes reflex cntractin in a stretched muscle and inhibits tensin develpment in antagnist muscles the stretching f muscles, tendns, and ligaments prduced by a stretching frce ther than tensin in the antagnist muscles a grup f stretching prcedures invlving alternating cntractin and relaxatin f the muscles being stretched the angle thrugh which a jint mves frm anatmical psitin t the extreme limit f segment mtin in a particular directin the inhibitin f the antagnist muscles resulting frm activatin f muscle spindles maintaining a slw, cntrlled, sustained stretch ver time, usually abut 30 secnds a mnsynaptic reflex initiated by stretching f muscle spindles and

17 synvial fluid resulting in immediate develpment f muscle tensin clear, slightly yellw liquid that prvides lubricatin inside the articular capsule at synvial jints