skeletal muscles functioning, Sintesi del corso di Fisiologia Umana

Scarica skeletal muscles functioning e più Sintesi del corso in PDF di Fisiologia Umana solo su Docsity! = Chapiet XIX £ 19.4 Skeletal murcles CELLULAR LEVEL + MUSCLE BODY = port È tha muacts kihak aqprroti forca. + Eeymisium = connecki ve issue that surrounds tha body + PERYMISIUM= donneckive. tisrue that extends into tha edu . It is divided into FAsticLES (bundies) af individua muacli CUS. + Each Pfascicle contalas muade cous coliedo NUscsLE riamRs becoune d Weir cdongated Napa. * ENDOMYSIUM = tinin sheath of conneckive tissue that encases tha moacle fibers which rua along thu full lengi È tha muoda. * Musche fibbers have many nuelei beccwae ga fiber is Por mid during embryonie Lift Prom tra pueion SL several cis. + The nuckei Rie below ue sarto emma T_T piaeme. mambrana aL mwacke Pibers * SARCOPLASM a semiPhuid mwaede fibet's cyto pioam. IE is packed, with mitochondria and Moribals bandsd buadde SELES die and +nin filodments made af voro d_ocktnal * SARCOPLASMIC RETI CULUM saclike mambranocus network tnod Surrunds each SY Ma muyofilris and is associok&gra with +he TEANSVERIE TUSUUES [T kuues) UL continuous uit Hus sarcolemma. anal qenekbrots. Into tha ceu's interior. (ui Ci A Tenittgmants of ine soncoplane rabicutum * TRIAD = ona T+tuovle + two Loti socs. + Sarcoplasmie retivslum £ T tubules halp transmitking signals dom tu aorcolemma. to Wu muofibuls. Tre sarcoploamie reticulum atotes Cat*ions Yak su released In response o eleciticol eignals. Abano nero udine ceto» MOLECULAR LEVEL * &keletal muadues su coed siviotzo. nucios becssvae sketetot nuecli cls have a atuped appeoranc. * Striations ona creatra. by tha oxrmangmant oi proteina Biba in tha myofbrits : TH FILAMENTS $ THIN FILA MENTE They ci AL Bas ma Us Bro oxis. They esist In 2:41 rosioÈ * SARCOMERE = Lundomientat mit thok composes muyofilril. Each sarcomui is borduned on citlmor end by 2 lines and thick Rloments sam connsckeal by VM lines. per____—-;- È n mM A 2 lisa con perpendiculoa tosta Tin oso) tem” zie Pong axis. A band sa XK striation due to Ha cwenlop ri n ria TER O Re ile 7 Righe equa no +hin filoments : i le ones. O Sam Bione Pilonments one presente T bands gin with only Ehin filoments, Ar its contr than is ® lina. Thin fament Overiap of Thick fiament lattice © thickandinin — latice (iband) | fiaments | (Hzone) {A band) []to pivot = ruotare CROSSBRIDGL CYCLE * Mechanism that dxives the aliding o thick and thin filormuents port me anethar duting muadi contradion. + Base af tha mechanism : roscillating motion of myoain ads poweredì bu ATP hydcobysis “ cyclic binding and. untindiing ct Hina crossbridops to tu tnin Liloments. + Myorin mdecules hove tuo energa Porms : -hiah energu form + myorin molecole atpres ersrqu (step 8) -l0w eneugy form: myonie molacula releozes Hna atbred 20py # to ldcive movemant A thin Filoments (stop 3). ATP is hydrolyzed Pa sese RR @cocting ot the PENN, 1 @ undinding ot myosin myosin head Aaa osi New ATP binds to myosin head @ainding ot ‘myosin 0 actin @ Rigor (myosin in low-energy lorm) Inorganic phosphate is released FA CSS "Se "= (o) ci @ Actin gets pulled toward middle of ‘sarcomere Myoain is in its enrgized form : ADP and Pi Mur bound. to Mine ATPone rive tha muyosin had. Myoein har high affinity for Ackin 20 Myoaina head, binds to an actin monomar in the adgacent thin filament. This: step con occut only in fire presence af Cart ® Power stroke The binding o) myoeir to actin triggers Ha releote cl Ha Pi Prom the ATPAse Gite. Tha huoain head pivots touard the middue tha soscomare pulling tha thin Pilament along with it. ADP is releonedì from the myoein had, myosia molecola is in its Lou eno atote. Myoein and actin or tioht bound together : riocc. (ricor MORTIS is tha stifgning ci tie body that occurs afia dat. lt occuts becaure tha ossbrido cycle gets stuck at step 8). A new ATP enters tha ATPase aite trigggiing x” conformartianal change in the had, which decreass tha affiattu o muosia Por actin and thay seporadte. ATP is split into ADP& Pi releasino enna. Soma ©) this euro is taken bu tha muosia molecole Gs it pe into its high-enarogu Porn. Tha ADP4 Pi remaia bound to Ha ATPase site, ip Colt is prernt the cycle uil. continue restosurinp Fiom step 1. TA muscle cel ggrarates force continvaluy Adboring contraction becawae many crossbridaes ep through the cucle simoltanasutiy DUE cut LL phase with each othwu. * Tha crossbridge cycle could continue indefinitely 20 tha Troponin and tropomyortn interack usitn Catt regulating tha cudla. LXCITA FICII-COI! FRAC FICN COUPLING * Sequence of events thok links tha AP to contraction. * Muscle cells mus excitabie, +nay ou able of gensating APs ip Aneîr plasma mambranes out }_ do prsrne. 6 6 A A A Ap b_ b b è gone È E NEUROMUSCU AR IUNCTION NEUROMUSQULARI FINCTION Connection between a motornevton and a muacka cell. Terminal boobons (axon terminals af +ha motor neon) stre and releare ACh which binds to specific receptors. Each muadie Piber receives input from only ona motor nuston. Opporite +ha boutons is the motor end pote (specialized region A Ka sarcdamma) which is highlu Adua and contains high dentitu Ach receptors. When a motornevton is ackhivotidi APs propaggti to Hana terminal boutons of ali fibers in Hu motor uit. Tlu depplarizatiion covses voltage. gold. Cat*+ channels o open attowming Ca't to enter the cutosol and triggnar the celeone of Ach by exocytovis(step 1) Sarcolemma Ryanodine. receptors © ‘SR membrane Tiubule ‘OH receptors iù e Sarcopiasmio È IP ‘DHP recepior potential » Tiubule membrane + Ttubules and SR membranss ore Linked boy tuo proteins: fa AN A. A. A. A. A. fa A PESEEECE 4 ACK binds to nicotinie choLine rgie receptori alb Ha motor end. pilota cowalng cotton channets to cpen. Na* enters the fiber and produas a depolorizastion: Mau end plote potentio LUPA), EPP is much lonpa than orcinoxy postsynbptie potential, infock it is always above threshold and trigogrs AP în the musce cell. IP an AP occues in a mer navton it is aluays PoUOWEd bu An AP in +ht nuscle cell (stepi2) Once an AP is initiated in a mad ceri, it propoagata through tne entire sacrolemma. and down Hus T iuagles. AP Buiggexs tha releme PB Cat* from Hne Latera sac (ep 3). ROLE of CALCIUM, TROPONIN È TROPOMYOSIN * Muscle cell relaxed : -[cot+] is low n - troponia is in normal confarmation SENTI ASTRI -troponutorin blocks actins myoein binding aites. + Tx cytosolic Cat* level is low because tha membrane DR the SR (sarcoplasmic reticulom) has Cat* punge thok transport. Cat ions Prom cytorol to SR. SR can store Ca*+. ‘ Voltage. gated Ca** channels in tha SR ore normally cioied to prevent Ca** Prom Aeaking cu. Whan AP occors, it vavraes tha Catt channels to pen increoring tha cutosslie Coft level. - dinyAropyfidine receptors (> Pound. in +e T tubole Membrane. Fonckion ar voltage nensorcs. - rganocdinga receptors 4 Lovnd. in the SR mambrane. Tiuy sue Ca** channels gated by the DHP rece ptofs. AP in the Tibbolas — DHP reaplors underoo a comPormattional change le signat is transmitted to tha ruanodina receptor covaing Cat*t channels open Calcium. indoceri colcium releose : phenomanon in which He initial releme of Cat+ buiggas tha relleane i mote Cat*Prom SR. Relaxed muscle Contracted muscle Rigida d spot S Time (mese) * Force = Sa È transducer In] Tension (9) Stimutator Strip chert record * Isomatiio tuwitoh is an al - or- none eyent. «The controctile componont LC (Sarcomares) doesn't extend Ehe entire Length op each nuaede fiber and doesn't Aransmit force uoureckiy to tha ends o Ma cell as Tha Sarcomores shortens even though tha vuole muacta doesn't. [Series elastie componsat 939) ps. tha ports 9 a made that don't ackvelu qpnerate. force but Muay passi velu transmit it to nwade's ends. * Whan a nvacle contracts isomatricatty tha cc shortens and stretches tha SEC pulling it on Ihr ends & the nuade. SEC Lengehens as +ha CC Ghortens giving an ovali Length change PL zero. ISOTONIC. TWITCHES + Thu muacie generates a constant tension greater than anu forces Opposing iL and. the muacie Length changes. * Thrane one timo types of isotonie contractions : - CONCENTRIC CONTRACTION : tha muade shoctens ECCENTRICO CONTRACTION: tha made Rengtheas . * To meanure an isstonie twitch +he Lower end op the muadie is attached to a movabie Load. audn +ha muacte is oble to shorten whan it contracks. Rrlexed muscle Gontracted muscle / N Lengih transgucer Movable rese i tr \ 2 U i PLATEAL dì x ) 2a Si ) Ct Time (maso) transducer Degree of shortening (mm) Tension (9) su Strip chart recorder +In the pateco phase tha muacie shortens and the Loodi moves. Before tha piotecu phose +ha Porce increases, laut the nuveale doeen't shorten until the force eguels tte Load. * Isofpnie twitch isn'£ an alt-or- nona event : its size and shape depend on tha size cf +ha Aood. Whan tu. Load. is increased greater tension is needed to overcome it so thare is tha platea. When the Load exceed tha amount o Porce tha muacie can gpraroke, the muade can't move it and corìmracks iseme:tricoliy. Isotonic Isotonic Isotonic Isometric contraction contraction contraction contraction ; = È } » - KE" i $ 0 dl Load — a i f no I A 7 nil È Li id 209ì e sr n= none Isometric contraction Latent period to start of shortening 17 grams Shortening - begins Ends Tension (9) o stimuti È 4 4 i Time (msec) FACTORS AFFECTING the FORCE * Tha force Apaated in individual muacdie fibers depends on: = numiberl of nuca. Linding aites on ackin tinat as expased = number Sd ackive ctosbridges = frequency Ist atimolotion = files | dulamatber -“nanggs.IN Fiber Length FREQUENCY of STIMULATION * As tha atimulation Prequency increases nuactes move prom twitch contractions bo : <TREPPE occors at a freguency a stimuialion here indipendent twitches follow ona another closely such that +e peak tension rises in a atepwise way with cachtwitoh. Pagare Tension (9) Q i Time (msec) 253UMMATION is tha process Au ring uhich amvaede is stimulated repetitively auch that additional APs osvive before twitches can be completed 20 the iwitchas become auparimporoì on ona AnoThar Yelding a greater Porce. Summazion happens whanuwen tuitches occue at a frequency such that Catt can't be removedì Pron Ma cutosol Gs capidly as it ìs releasedì from Has SR. Tension (9) Stimuli @ Twitch @ Summation TIFTANUS occurs ak highar freguencizs of stinulation. UNFUSED ITETANUS SU ti force shows small Catt levels ou great enouph osciltattions with brief to continually aatorote pariodis of relaxation Eroponin so AU muprin- binding between peaks. sites on ackina cus contincally feaks ona reached when expored resulting in a platea. Ca** levels qu. greal encuph to saburati troponin, expoting AU nuorin- Binding eies n ackin. - Average tension (constant) “Tension @ incomplete tetanus @ Complete tetanus (unfused) (fused) Time (msec) * Tetanic tension increares up to a poink, Porthar increates in Prequency yetd no more inereazes in force + nosinun ddtanie Tengion FIBER DIAMETER * Ti greater tu filber dliomuetter, the greater its cross. sectionai pura and tha moce force it con grate. 19.5 Skeletal murcle metabolism, X,Y,2 sus controUed bu excitatoug inpot. Prom. a nuursa (W) in tha CNS. $ small motor Unit As +he AP_in W increarses tha motor ni become active in order DL lnereosing size. VELOCITY of SHORTENING SO ear Tin made is atinvtated +0 Pot controck isotonico Us and bt distano it shortens is pilota cer tima while different Loods sous poca. on ua mura de. Zero load Intermediate load Distance shortened o 20 40 60 80 100 120 Time (msec) 3 Res: 1.The Lotent psrod cf shortening increases with increoniag L00ad. 2.Tha duration dd shoctenino Aeccreases with increasing Load. 3.The velocity of Ahortening decrears wi increaaiao Load. Maximum velocity LOAD-VELOCITY CURVE (zero load) Shortening velocity Load is greater than ‘or equal to maximum tension (force) of muscle Load CREATINE PHOSPHATE SISTEM * han a murcle filcer is resting its alemand for ATP is smali but vien it contracks tha demand. oi ATP sooxs. + ATP is produca Gy oxidative phrosphoulotion and sulostratn-Level phosphoti Lazion. Tha creatina phosphata gives its P bo ADP in order to Porm AP and creoaaL. + Whan a muacle is exercisedi continuovatu at a Uant to modarote intentitu most 0} Hr needledìi ATP is supplied bu oxidative prosphotilation -Creatine phosphate Anaerobic giycolysis Oridative phosphorylation Energy used per source Time (mn) * In heavy exercise ATP is prodwcedì by substrate - level phosphotilation. Greatine prosphate Enrgy usi par source “Timo in) GLYCOLYTIC FIBERS * They have high cytosolic concentrations of glycolytie enzymes — thay con gensruote ATP via qluco Qysis + They have Low capacitu for generating ATP via oxidokive phosphori Lation becouse thuy Contaia Pe mitochondeia.. «Thy Lock in mioglobina. ao tray sans cosued white muscis reddish mobi + Tiuy or better able to produce ATP when oxyqra avoifobilityà is Lov because glucslyais doesn't require oxjgen. *TASTELICOLITE Fibcas contoins fast monia and ave high Aycolyfic capacity, They rr Bound. in tha Longare motor units. Tiuy tend to produce Lackie acia during high intenutu giercite. During Lou- intensity exercise Pew qUicoQUtic. fibers our recitedì ao Les Lactie acid ia professa. OXIDA TIVE FIDERS Thu ove rich in mitochondtia and have high capacit for prodlucing ATA. via oxidlative. phosphocila.tion. * They vor Small and well abppiea with copiUaries. « They contain myoglobin . #30) DXIDATIVE FIBERS contain elow moria and have high oxidative copacitu. Tina one Rocokra in ina amalder motor vis. LTAST_ONIDATIVNE FIBERS contain fast muoain and have high pxidative copaciy Thy Jour foonol in tha iatermidiote matr units. TALIGUE = dedine in a muacle's abi Lily tw maintain a constant force ok contraction in respect with Ha Long-ker mo, ripetitive stimu oddion. Stimulation ak a low 4 frequency prodces Like orany fatigre. Stimolodtion at his atiguo - RENE REA fotine Thu end LUN e or ina record. ef Stimuo Ration ok a high enouph to yeld maximum paio > tetanie tenzion Potiues omette tnsion (6) more rapid. AFC tha cost pertodi tension Sam a IONE returns to previ Ur lauets en but Fabigge aets in more rapidi. LONG-TERM RESPONSES to EXERCISE 1 Aerdoie exercise increases the oxidative capacita di mac Ciloess increasing their resistance to fatigre, so some qcolutie ficers lai converted. to fast oxidative Uber. + High- intensity exercise decieaores tha oxidative capaci A nuede fibers and increases rar quucolutie capacita conventinp roma af tha fart oxidodive {vers into fast guicolutic ficers. 19.6 Smooth £, conolioe MVLATKE Noncyckng gta. mmemmeiccceion Acea aper E Mora SÈ cronica rt n dop P, ARP 2 ds SMOO TH MUSCLES + Thy lack +ha afriastions and an found in interna agans, blood vessels and unvolantasti aockores. * Thy have thick and 4a filaments uhich ant asangea in Sorncomares, bot in porodtet with each stia. + Thy qgeamote force through tha cross bridge cucke. * DENSE BODIEI = points aioachment between Piloments and conneckive tissue in tha cell, they Transmit contracitie facce fo Ke coll's exterior. corsair a <= V Thin Denso bodies flamont Contraction L «gg eresia ae | EXCITATION- CONTRACTION COLP LING * Emockhu muacle contractione on repulattedì by intra cellulosi Cot*. Gybosolic Ca'* activatres Ha crossbridge aycie but smostt made don't contain tTromyoin so Cat binds to calmoduNin reversilole, A conformational change occutrs which enaleies Hu Cat. cotmodulin comptex to bind to tru moria Light cain Kinase (MLCKR), which cotatizes Ma phosphoci Lazica = masala ocossbricpes. Thu cycle stops when phosphatarss (enzumes +hak remove phosphate proupî which Las bEvAdi to myosin) inackivade. IAYOAO. Actnation f n4oaia can occuTt cnlu la presents af Co becauee phosphodtases. Compete usim Mute. NEURAL REGULATION * In smooth muedles, nevtotransmitters pu reiecsed from, voxicotities and diffoee over a Rong alistonce to ott celas. Near cells ou eunchronized als thanks to gap qUACHons. + Tit smocth muacle membrane is depolonizea i Mus input is excitatory , and nyperpolazzal ip tha input is innictno.. + Some amastin muraclies don't have APs, i? thy have Ina AP is Polowed by greater tention. * MULD- UNIT SMODTH Muster smocth muadu tuee in Lohicn fa ces sua Langely aeporated and. auppled usithi eutens. * SINGUE TUNIT SMOOTH, Motu. SÙuiootn mvaeclhe Ate a unica Ma ces ae separated bu Ap Fancions. SPONTANEOUS CHANGES in MEMBRANE POTENTIAL + Two types of spontanzcos depollorizartions : + PACE MAKER POTENTIALS + slow depoforizotione covred by ont or more O these permeabiLitu Changes : -increases in Naf rincreases in Cort - decreases in kt *SLONCMAVE POTENTIALS + eyclicot depoloauizatione ano repolanizations caused by Piuctvarticas in No permaobility . -50 Membrane potential (mV) (a) Pacomakor potential NANNA Time (sec) (0) Stow-wave potential CARDIAC MUSCLE * I is striakted with sorcommaes, has conttactions repuloted by ha firoponin - trofonugo rin syatem + Condiac muecls cells Jona connected bu gap punctionS 0 AP once initiatert travels +hroughout tha entire cel astaprie. + Candiac AP Rast Lor hundreds SÌ ms ao aummation can't ocout. * Cardiac muscle cells aren't cilindrie they have a = ahape. + Unvoluntory muade Branched structure of cardiac muscle Intercalated disk and ib ca da Ziine ‘In tha intercalated disks there ate gap qunetionse, which allows th. electrical coupling, and desmossmes, which allows mechanical unit of + otgan. * Certain heont muacia cells exhibit pacempier activity « - Sincatioi nodla Ces - sioventricolor node cris. TABLE 12.2 Comparison of Skeletal, Smooth, and Cardiac Muscle Property, Speleta] |_Smootti (sigta-unt; | Smbott matin 2 Gandia Strations (sarcomeres) Yes No No ves Actin and myosin ves | es Yes ves Level of control Voluntary Involuntary Involuntary Involuntary e O A LES OI Ge Neuroetfectorunetion Neuromuscular Varicosities—diffuse Varicosities—diffuse Varicosities—diffuse junction—specific Hormonal control None Several, depending on Several, depending on Epinephrine location location Source of calcium |_SR ‘5R and ECF SR and ECF SR and ECF Reguiatory protein that Troponin Calmodulin Calmodulin Troponin binds calcium | | Gap junetions No Yes No (or few) Nes Pacemaker activity No Yes No Nes Myosin ATPase activity Fastest Slowest Siowest Intermediate Recruitment Yes No Nes No