Locomotion and Movement: Class 11 Biology Chapter 17 Hinglish mein

Match ke din ek fast bowler ko dekho. Run-up poore body ko pitch par bees-pachees metre aage le jaata hai. Crease par pair jam jaate hain aur bowling arm shoulder ke upar se tezi se ghoomta hai, aur is poore samay bowler palkein jhapka raha hai, saans le raha hai aur nigal raha hai. Inmein se har ek movement hai, phir bhi sirf run-up hi bowler ko ek nayi jagah le jaata hai.

Biologists is tarah ke movement ko alag naam dete hain. Jab koi animal apni khud ki koshish se apne poore body ko ek jagah se doosri jagah le jaata hai, to woh locomotion (गमन) dikhata hai. Chalna, daudna, chadhna, tairna aur udna, yeh sab locomotion hain. Bowler ka arm swing, mendhak ki jhapakti aankh aur tumhare heart ki dhadkan aise movements hain jo locomotion nahi hain.

Dhyaan se dekho to shayad hi koi zinda cheez bilkul sthir hoti hai. Tumhari palkein jhapakti hain, chabaate waqt jaw chalta hai, tumhari tongue har bole gaye word ko shape deti hai aur tumhara heart kabhi nahi rukta. Single cells mein, Amoeba aage ki taraf bane ek ubhaar mein apne cytoplasm ke behne se aage sarakta hai, aur bahut saare protists aur chhote animals baal jaise cilia hilate hain ya chaabuk jaise flagella lehraate hain, ya tentacles hilate hain, jaise Hydra karta hai.

Kya animals travel karne ke liye alag machinery rakhte hain? Aam taur par nahi. Tumhare pair tumhe school le jaate hain, phir bhi wahi pair tumhe kahin gaye bina baithne, ghutno ke bal aane ya panjon par khade hone dete hain. Hydra apne tentacles se prey pakadta hai aur unhi se surface par kalabaazi khaate hue aage bhi badhta hai. Paramoecium mein cilia ka ek hi set cell ko paani mein aage dhakelta hai aur food particles ko oral groove se cytopharynx mein bhi pahunchata hai. Kyunki ek hi equipment aksar dono kaam karta hai, isliye movement aur locomotion ko saath mein padhna hi sabse achha hai, aur locomotion ko movement ka ek special type maana jaata hai.

Kuch safar ke baare mein socho. Chital tiger ki aahat milte hi bhaag nikalta hai. Lakhon olive ridley turtles ande dene ke liye Odisha ke Gahirmatha mein kinaare par aate hain. Amur falcons eastern Asia se southern Africa ki lambi flight mein Nagaland mein rukte hain, northern winter se bachne ke liye. Aam taur par animals predators se bachne, breeding grounds tak pahunchne, behtar climate paane, aur food, shelter aur mates dhoondhne ke liye travel karte hain. Koi animal kaise travel karta hai, yeh is par depend karta hai ki woh kahan rehta hai aur us pal kya zaroorat hai.

17.1 Movement ke Types

Poore body se zoom karke single cells tak jao to pata chalta hai ki human cells teen basic tareekon se move karte hain: amoeboid, ciliary aur muscular (Fig. 17.1).

Amoeboid movement. Ghutne par kharonch lage to kuch hi ghanton mein white blood cells paas ki capillaries se nikal kar ghaav ke bacteria ki taraf rengne lagte hain. Yeh leucocytes, aur hamare tissues mein gasht lagane wale macrophages, Amoeba ki tarah travel karte hain. Cytoskeleton ke microfilaments cytoplasm ko aage dhakel kar ek temporary pair banate hain, pseudopodium, aur baaki cell uske peeche-peeche beh kar aa jaata hai.

Ciliary movement. Dhool bhari sadak par saans lo to kuch dhool tumhari trachea tak pahunchti hai, lekin wahan rukti nahi. Trachea ki lining wale cells par cilia hote hain jo coordinated waves mein hilte hain, jaise stadium mein crowd wave karta hai, aur woh mucus ki ek patli layer ko gale ki taraf sarakate rehte hain; phansi hui dhool aur germs uske saath upar aate hain aur nigal liye jaate hain ya khaans kar bahar nikal jaate hain. Yahi lining, ciliated epithelium, kai tube jaise organs ke andar hoti hai. Oviduct mein iski beating ovum ko uterus ki taraf aage badhne mein madad karti hai.

Muscular movement. Teesra type, aur is chapter ka zyaadatar topic, muscle cells par depend karta hai jo force ke saath chhote hote hain. Haath modna, chabaana ya tongue hilana, sab mein iski zaroorat hoti hai, aur humans aur zyaadatar doosre multicellular animals locomotion ke liye bhi isi par nirbhar hain. Ek puppet show ke baare mein socho. Dhaage kheenchte hain, lakdi ka frame us kheench ko kisi sakht cheez par kaam karne deta hai, aur puppeteer decide karta hai ki kaun sa dhaaga kab kheenchna hai. Body mein muscles kheenchti hain, skeleton sakht levers deta hai aur nervous system orders deta hai, isliye locomotion ke liye teeno ka saath mein kaam karna zaroori hai. Hum pehle muscles dekhenge, phir skeleton aur uske joints.

17.2 Muscle

Muscle par aane se pehle flagella ke baare mein ek baat. Tum Chapter 8 mein inse mil chuke ho, cell membrane ke outgrowths ke roop mein, jo cilia jaise bane hote hain lekin lambe aur ginti mein kam. Euglena apna flagellum lehra kar tairta hai; sponge ke collar cells apne flagella hila kar uske canal system mein paani ko chalta rakhte hain; aur human sperm apne flagellum se aage badhta hai.

Tumhare body weight ka lagbhag aadha hissa, ek adult mein karib 40–50 per cent, muscle (पेशी) hai. Yeh tissue mesoderm se develop hota hai, jo embryo ki beech wali germ layer hai, aur yeh sirf ek kaam ke liye specialised hai, kheenchna. Chaar properties yeh mumkin banati hain:

• Excitability: yeh kisi stimulus par, aam taur par nerve impulse par, apni membrane mein electrical change ke saath respond karta hai.
• Contractility: yeh chhota ho sakta hai aur is tarah jis cheez se juda hai use kheench sakta hai.
• Extensibility: ise stretch kiya ja sakta hai, jaise toes chhoote waqt tumhari hamstrings stretch hoti hain.
• Elasticity: stretch ya contract hone ke baad yeh wapas apni resting length par aa jaata hai.

Teen sawaal muscles ko sort kar dete hain. Yeh kahan hai? Kya microscope mein yeh dhaaridaar dikhta hai? Kya tum ise apni marzi se control kar sakte ho? Pehla sawaal teen types deta hai, aur baaki do unhe describe karte hain (Fig. 17.2).

Location ke hisaab se. Skeletal muscles bones aur skeleton ke doosre parts se judi hoti hain. Visceral muscles hollow organs ki andar ki walls mein hoti hain, jaise alimentary canal aur reproductive tract. Cardiac muscle sirf heart mein milti hai, jahan iske cells branch karke aapas mein jud kar ek network banate hain.

Appearance ke hisaab se. Skeletal aur cardiac fibres mein regular cross stripes dikhti hain, isliye dono striated hain. Visceral muscle mein koi stripe nahi dikhti, isliye ise smooth (non-striated) muscle kehte hain. Control ke hisaab se. Sirf skeletal muscle tumhari marzi se chalti hai, isliye woh voluntary hai; visceral aur cardiac muscle involuntary hain. Nerves heart ko tez ya dheere dhadka sakti hain, lekin har beat ka order nahi deti.

Har type apne kaam ke liye fit hai. Skeletal muscles tumhara posture sambhalti hain aur locomotion ko power deti hain. Visceral muscle ki dheemi nichodne wali waves food ko gut mein aur gametes ko genital tract mein aage dhakelti hain. Cardiac muscle blood pump karne ke liye zindagi bhar rhythm mein contract hoti rehti hai.

Skeletal muscle ke andar

Tumhare biceps jaisi skeletal muscle levels mein bani hoti hai, jaise ek moti rassi patli rassiyon se banti hai (Fig. 17.3). Poori muscle collagen se bhare connective tissue ki ek sheet, fascia, ke andar hoti hai, jo uske andar ke bundles ko bhi baandh kar rakhti hai. Har bundle ek fascicle hai, aur har fascicle mein kai muscle fibres hote hain.

Muscle fibre ek single cell hai, lekin anokha: yeh kai centimetre lamba ho sakta hai aur ek continuous cytoplasm mein kai nuclei rakhta hai, jo ise syncytium banata hai. Iska zyaadatar volume lambe, parallel, banded dhaagon se bhara hota hai, jo myofibrils hain (NCERT inhe myofilaments bhi kehta hai). Inke chaaron taraf endoplasmic reticulum ka ek network lipta hota hai, jise yahan sarcoplasmic reticulum kehte hain, jo calcium ions store karta hai, yaani contraction ka switch. Fibre ki plasma membrane ka apna naam hai, sarcolemma, aur uske cytoplasm ka bhi, sarcoplasm.

Har myofibril mein do tarah ke protein filaments bhare hote hain jo ek doosre ke aur uski lambai ke parallel padte hain: actin ke patle thin filaments aur myosin ke chaude thick filaments. Inki arrangement se hi stripes banti hain. Jis hisse mein sirf thin filaments hote hain woh light dikhta hai; yeh I band hai, isotropic ka short form, kyunki yeh polarised light ko mushkil se badalta hai. Jis hisse mein thick filaments hote hain woh dark dikhta hai; yeh A band hai, anisotropic ke liye. Padosi myofibrils apne bands ek line mein rakhte hain, isliye poora fibre dhaaridaar dikhta hai.

Band pattern har kuch micrometres par repeat hota hai, aur har repeat ek sarcomere hai, woh unit jo asal mein contract hoti hai (Fig. 17.4). Sarcomere ke dono siron par ek dark Z line hoti hai, jo I band ke beech se guzarti hai aur thin filaments ko anchor karti hai. Iske centre mein ek patli fibrous M line A band ko cross karti hai aur thick filaments ko saath baandh kar rakhti hai. Is tarah ek myofibril sarcomeres ki ek lambi chain hai jo apni Z lines par end to end judi hoti hai.

Kya dono siron se aane wale thin filaments beech mein mil jaate hain? Resting sarcomere mein nahi. Woh bas itna andar khisakte hain ki thick filaments ke siron ko overlap kar sakein, aur A band ki ek central patti mein sirf thick filaments reh jaate hain. Yeh halki patti H zone hai, aur M line iske beech se guzarti hai.

17.2.1 Contractile Proteins ki Structure

Ek thin filament ko neeche se upar tak banao (Fig. 17.5). Chhoti, lagbhag gol protein units se shuru karo, G-actin (globular actin). Motiyon ki tarah ek saath piroye jaane par yeh F-actin (filamentous actin) ka ek strand banati hain, aur aise do strands ek doosre ke chaaron taraf do-ply rassi ki tarah lipat jaate hain. Is rassi ke grooves mein tropomyosin ke do patle dhaage poori lambai tak chalte hain. Aakhir mein, regular intervals par, ek complex protein, troponin, tropomyosin par laga hota hai.

Actin par active sites hoti hain jahan myosin head use pakad sakta hai. Resting muscle mein troponin ki ek subunit tropomyosin ko in sites ke upar rakhti hai aur unhe dhak kar rakhti hai, isliye thin filament taiyaar to hai lekin locked hai.

Ab thick filament. Socho ki kuch sau golf clubs ek saath bandhe hain, unke shafts agal-bagal hain aur unke heads poore bundle ke saath bahar nikle hue hain. Har club ek protein molecule hai jise meromyosin kehte hain. Iska lamba shaft, tail, light meromyosin (LMM) hai; short arm par laga iska head heavy meromyosin (HMM) hai. Tails aapas mein pack hokar filament banati hain, jabki heads aur arms uski surface se ek regular spacing aur angle par bahar nikalte hain. Har nikla hua head aur arm ek cross arm hai.

Head hi kaam karne wala part hai. Yeh ek ATPase hai, yaani ATP ko todne wala enzyme, aur ismein ek binding site ATP ke liye aur doosri, active site, actin ke liye hoti hai. Aisa part jo energy bhi release kare aur thin filament ko pakad bhi sake, theek wahi hai jo ek molecular motor ko chahiye.

17.2.2 Muscle Contraction ka Mechanism

Jab kisi bhi tarah ke filament ki lambai nahi badalti, to sarcomere chhota kaise ho sakta hai? Aaj maana jaane wala jawab sliding filament theory hai.

Brain se filaments tak ek command ko follow karo (Fig. 17.6). Central nervous system (CNS) ek motor neuron ke zariye impulse bhejta hai, jiska sira sarcolemma par ek neuromuscular junction par hota hai, jise motor end plate bhi kehte hain. Ek motor neuron branch karke kai fibres tak pahunchta hai; neuron aur woh saare fibres jinhe woh supply karta hai, milkar ek motor unit hain, aur woh fibres hamesha saath mein contract hote hain.

Junction par electrical message chemical tareeke se aage diya jaata hai. Nerve ending acetylcholine release karti hai, jo ek neurotransmitter hai, aur yeh sarcolemma mein ek action potential trigger karta hai, yaani aage badhta hua electrical signal. Jaise-jaise action potential fibre mein phailta hai, sarcoplasmic reticulum calcium ions ($\mathrm{C}\mathrm{a}{\phantom{X}}^{2+}$) ko sarcoplasm mein chhod deta hai.

Calcium is lock ki chaabi hai (Fig. 17.7). Yeh troponin ki ek subunit se bind hota hai, jo apna shape badalti hai aur tropomyosin ko ek taraf khisakne deti hai, jisse actin ki active sites khul jaati hain. Har myosin head pehle se taiyaar hai: usne ek ATP tod kar energy pakad rakhi hai. Ab woh ek khuli site ko pakad leta hai, aur thick aur thin filament ke beech ek cross bridge banata hai.

Iske baad head ek naav chalane wale ke chappu ki tarah ghoomta hai, aur thin filament ko A band ke centre ki taraf kheench leta hai. Yeh Z lines se anchored filaments ko kheench raha hai, isliye sarcomere ke dono halves mein Z lines andar ki taraf khinchti hain aur sarcomere chhota ho jaata hai: yahi contraction hai. Stroke ke dauraan head tooti ATP se bache ADP aur inorganic phosphate (${\mathrm{P}}_{\mathrm{i}}$) ko chhod deta hai aur apni relaxed position mein aa jaata hai, abhi bhi juda hua.

Chhodne ke liye ek naya ATP chahiye. Jab ek naya ATP bind hota hai, tabhi cross bridge tootta hai. Phir head us ATP ko todta hai, dobara cock hota hai, aur aage ki ek site pakad leta hai. Jaise ek team haath badal-badal kar rassi kheenchti hai, waise hi hazaaron heads ek doosre se alag timing par bind karte, kheenchte aur chhodte hain, isliye filaments smoothly slide karte hain. Jab tak calcium high rehta hai, yeh cycle chalti rehti hai.

Ab dekho ki sliding se bands par kya asar hota hai (Fig. 17.8). Thick filaments move nahi karte, isliye A band ki lambai same rehti hai. Thin filaments A band mein aur gehre slide karte hain, isliye har I band chhota hota hai aur H zone patla hota hai; jab thin filaments ke sire M line par milte hain to H zone gayab ho jaata hai. Koi bhi filament chhota nahi hua. Sirf unka overlap badha hai.

Relaxation matlab switch ka off hona. Jaise hi nerve impulses rukte hain, sarcoplasmic reticulum $\mathrm{C}\mathrm{a}{\phantom{X}}^{2+}$ ko wapas apni cisternae mein pump kar leta hai. Calcium ke bina troponin tropomyosin ko phir se active sites dhakne deta hai, isliye naye cross bridges nahi ban paate. Thin filaments wapas bahar slide karte hain aur Z lines apni shuruaati jagah par laut aati hain.

Muscles is baat mein alag hoti hain ki woh kitni jaldi respond karti hain: tumhari aankhein ghumane wali chhoti muscles calf ki badi muscles se kahin zyada tezi se contract aur relax hoti hain. Jab kisi muscle se baar-baar zor ka kaam liya jaata hai, jaise sprint ke finish mein, to uske fibres ko oxygen jaldi nahi mil paati aur woh glycogen ko anaerobically todte hain. Tab lactic acid jama hota hai aur muscle thak jaati hai, is condition ko fatigue kehte hain.

Muscle fibres kaam ke do styles mein bhi aate hain. Endurance ke liye bane fibres mitochondria se bhare hote hain aur myoglobin se bharpoor hote hain, jo ek red pigment hai aur un mitochondria ke liye oxygen store karta hai taaki woh ATP bana sakein. Yeh pigment unhe rang deta hai, isliye yeh red fibres hain; kyunki yeh oxygen par chalte hain, inhe aerobic muscles bhi kehte hain. Chhote bursts ke liye bane fibres mein myoglobin kam hota hai aur woh pale dikhte hain, isliye yeh white fibres hain. Inmein mitochondria kam lekin sarcoplasmic reticulum zyada hota hai, aur yeh apni energy mainly anaerobic breakdown se lete hain. Long-distance runners ki leg muscles mein aksar red fibres ka hissa zyada hota hai, aur sprinters mein white ka.

17.3 Skeletal System

Muscle sirf kheench sakti hai, aur kheenchne se kuch nahi hota jab tak kheenchne ke liye koi sakht cheez na ho. Skeleton yahi sakht parts deta hai: muscles ke move karne ke liye levers, body ka shape banaye rakhne wala frame, aur brain, spinal cord, heart aur lungs ke chaaron taraf sakht cover.

Apni naak ki nok dabao, phir apna maatha. Naak thodi mud jaati hai kyunki woh cartilage hai; maatha nahi mudta kyunki woh bone hai. Dono specialised connective tissues hain, aur fark unke matrix mein hai: calcium salts bone ko sakht banate hain, jabki chondroitin salts cartilage ko mazboot lekin lachila rakhte hain. Ek adult human skeleton mein 206 bones aur kuch cartilages hote hain, do divisions mein (Fig. 17.10): body ke main axis ke saath 80 bones ka axial skeleton, aur limbs aur girdles mein 126 bones ka appendicular skeleton.

Axial skeleton

Axial skeleton body ka central column hai aur woh sab kuch jo usse juda hai: skull, vertebral column, sternum aur ribs.

Skull ki 22 bones mein se zyaadatar do sets mein fit hoti hain (Table 17.2): 8 cranial bones cranium banati hain, yaani brain ke chaaron taraf ka case, aur 14 facial bones chehra banati hain, jaws aur gaalon se lekar naak aur eye sockets tak. Skull region mein do surprises bhi hain. U-shaped hyoid, buccal cavity (munh ke floor) ke base par, body ki akeli bone hai jo kisi doosri bone ke saath joint nahi banati; muscles aur ligaments ise apni jagah latka kar rakhte hain, aur yeh tongue ko anchor karti hai. Har middle ear mein teen ear ossicles hote hain, malleus, incus aur stapes; stapes body ki sabse chhoti bone hai.

Skull ke base par do gol ubhaar hote hain, occipital condyles, jo vertebral column ke upar tike hote hain. Do condyles wale skull ko dicondylic kehte hain; human skull aisa hi hai.

Backbone ek thos rod ke bajaye 26 tukdon ki chain kyun hai? Chain mud sakti hai aur phir bhi spinal cord ki hifaazat kar sakti hai. Vertebral column dorsal side par skull ke base se hips tak chalta hai, aur trunk ka main frame banata hai (Fig. 17.11). Har vertebra ke beech se ek khokhli jagah, neural canal, guzarti hai, aur yeh canals ek line mein milkar ek tunnel banati hain jismein spinal cord rehti hai.

Skull se ginna shuru karo to gardan mein 7 cervical vertebrae, chest mein 12 thoracic aur lower back mein 5 lumbar hain, phir ek sacral aur ek coccygeal piece, dono fused vertebrae se bane. Sabse upar wali vertebra, atlas, occipital condyles ke saath joint banati hai aur skull ko uthaye rakhti hai. Giraffe ki lambi gardan mein bhi tumhare jaisi saat cervical vertebrae hoti hain, kyunki lagbhag sabhi mammals mein saat hoti hain; bas uski vertebrae bahut lambi hoti hain.

Column spinal cord ki hifaazat karta hai aur head ko sambhalta hai, aur ribs aur back muscles dono isse jude hote hain. Saamne, sternum (breastbone) thorax ki ventral midline mein ek flat bone hai.

Barah jode patli, flat, mudi hui bones, ribs, chest ko gherti hain. Rib ke peeche wale sire par vertebral column ke saath joints ke liye do surfaces hoti hain, isliye rib ko bicephalic (do sir wali) kehte hain. Saamne, ribs is baat mein alag hoti hain ki woh sternum tak kaise pahunchti hain (Fig. 17.12):

• True ribs, jode 1–7: peeche thoracic vertebrae se aur saamne sternum se judi, har ek apni hyaline cartilage ki patti ke zariye.
• False (vertebrochondral) ribs, jode 8–10: inki cartilage sternum tak nahi pahunchti balki saatvi rib ki cartilage se jud jaati hai.
• Floating ribs, jode 11–12: sirf peeche judi, saamne free.

Thoracic vertebrae, ribs aur sternum milkar rib cage banate hain, heart aur lungs ke chaaron taraf ek lachila ghera jo saans lene par hilta bhi hai (Chapter 14).

Appendicular skeleton

Appendicular skeleton limbs aur un do girdles se milkar bana hai jo unhe axial skeleton se jodte hain. Har limb mein 30 bones hain, aur forelimb aur hindlimb ek hi plan follow karte hain (Fig. 17.13).

Forelimb mein, shoulder se ungli ke sire tak, aate hain upper arm ki humerus, forearm ki radius aur ulna, wrist mein 8 carpals, hatheli mein 5 metacarpals aur ungliyon mein 14 phalanges: angoothe mein do aur har ungli mein teen.

Hindlimb mein thigh mein femur hai, jo body ki sabse lambi bone hai, lower leg mein tibia aur fibula, ankle mein 7 tarsals, talwe mein 5 metatarsals aur toes mein 14 phalanges. Ek aur bone tees poore karti hai: cup-shaped patella (kneecap), jo saamne se knee ko dhakti hai.

Girdles limbs ko axial skeleton se jodti hain: upper limbs ke liye pectoral girdle aur lower limbs ke liye pelvic girdle (Fig. 17.14). Har girdle ke do halves hote hain, har taraf ek.

Apni ungliyon se pectoral girdle ke ek half ko trace karo. Gardan ke base se shoulder tak jaane wali bony patti clavicle (collar bone) hai, do curves wali ek lambi, patli bone. Shoulder par yeh acromion se milti hai, jo ek flat, phaila hua ubhaar hai aur spine ke sire par hota hai; spine scapula (shoulder blade) ke peeche aar-paar jaane wali ek uthi hui ridge hai. Scapula khud ek badi, flat, triangular bone hai jo thorax ke peeche doosri se saatvi ribs ke upar hoti hai. Acromion ke theek neeche ismein ek uthla cup hota hai, glenoid cavity, jismein humerus apna gol head fit karti hai; cup mein yeh ball hi shoulder joint hai.

Pelvic girdle mein hip socket se shuru karo. Femur ka head ek gehre cup, acetabulum, mein baitha hota hai, jo theek wahan hai jahan teen bones, ilium, ischium aur pubis, fuse hokar ek coxal bone (hip bone) banati hain. Pelvic girdle do coxal bones se bani hai, aur saamne yeh pubic symphysis par milti hain, jo fibrous cartilage wala ek joint hai.

17.4 Joints

Elbow mod kar ek school bag uthao. Biceps forearm ko kheenchta hai, aur forearm elbow par ghoomta hai, jo is lever ka fulcrum hai. Joint woh koi bhi point hai jahan bones milti hain, ya jahan ek bone ek cartilage se milti hai, aur joints par hi muscle ka force movement banta hai. Kuch joints mushkil se hilte hain aur kuch khul kar ghoomte hain, yeh is par depend karta hai ki bones aapas mein kaise bandhi hain. Isi aadhar par teen structural types hain (Fig. 17.15).

Fibrous joints bilkul nahi hilte. Cranium ki flat bones lehardaar seams, sutures, ke saath dense fibrous connective tissue se kinaare se kinaare tak lock hoti hain. Newborn baby mein yeh seams abhi band nahi hue hote, isiliye baby ke sir mein naram jagahein hoti hain.

Cartilaginous joints mein bones cartilage se judi hoti hain, jo thoda sa movement hone deti hai. Padosi vertebrae ki bodies isi tarah judi hoti hain, cartilage ke pads ke zariye jinhe intervertebral discs kehte hain: koi akela joint zyada nahi mudta, lekin milkar yeh tumhari peeth ko mudne aur ghoomne dete hain.

Synovial joints mein fluid se bhari ek synovial cavity dono bones ki surfaces ko alag rakhti hai, isliye woh ek doosre par aasani se move kar sakti hain. Yeh joints locomotion aur zyaadatar doosre movements ko mumkin banate hain, aur inke shapes tay karte hain ki har joint kaun se movements hone deta hai (Fig. 17.16).

17.5 Muscular aur Skeletal System ke Disorders

Kisi bhi machine ki tarah, muscle aur bone system alag-alag jagah fail ho sakta hai: jahan nerve muscle se milti hai, muscle fibres mein, bones mein ya joints mein (Fig. 17.17).

Inmein se do seedhe us mechanism se jude hain jo tumne padha. Myasthenia gravis mein body ki apni antibodies motor end plate par acetylcholine receptors ko damage kar deti hain, isliye impulses ab bharose se fibres mein action potentials shuru nahi kar paate. Tetany yaad dilata hai ki calcium cell ke bahar bhi maayne rakhta hai: jab blood aur tissue fluid mein $\mathrm{C}\mathrm{a}{\phantom{X}}^{2+}$ bahut gir jaata hai, to nerves aur muscles zaroorat se zyada excitable ho jaati hain aur apne aap fire karne lagti hain.

Osteoporosis menopause ke baad women mein sabse common hai, jab estrogen ka level girta hai, jo bone ko mazboot rakhne mein madad karta hai. Gout tab hota hai jab uric acid, ek nitrogenous waste (Chapter 16), itna jama ho jaata hai ki joints mein crystals ban jaate hain, khaas kar pair ke bade angoothe ke base wale joint mein.