Flashcards in L14 Musc Deck (9)
LO2: expl mech contin of musc fibres, musc sheath, tendon and bone.
LO3: expl heir composit of typ skel musc, outl princip compons at molec, organellar, cellul, histol and reg anat lev.
-skel musc fibre- up to 400mm long. 35+nuc per MM. Cylind 10-60um diam. Tapered, round or notched ends esp tend juncs. Fibres shorter than length musc insert to CT.
-pow outp dep on no fibres not growth in length. Exerc incr musc vol by fibre hypert. NOT by div of musc cells which are termin diff.
-struc- musc sheat/epimysium thick CT outs. Thinner CT perimysium surr fasciculi. perimysium carry nerves and BVIndiv musc fib surr by endomysium. BVs also. Dark longit streaks= sarcosomes (mito) in sarcoplasm.
-var arts skel musc- convergent eg pectoral is maj. Circ eg orbicularis oris- not att to bone or cartil. Multipennate eg deltoid. Fusiform eg biceps branchi. Bipennate eg rectus femoris. Unipennate eg extensor digitarum longus. Paral eg sartorius.
-skel musc fibres ineterdig with tend Coll bundles and musc fibres myofilams. Extrinsic musc eg tongue and some suprahyoid musc of throat each have insertions in bone or cartil. Ext musc protrude and retract tongue and move Lat. intrinsic musc within tongue not att bone, allow change shape and posit. Skel musc of tongue often termin by ineterdig with Coll and ECM of surr CT. plasticity and str of CT and multidirectional orient of musc fibs= v mob.
-striated musc cell=musc fibre- packed with paral cols myofibrils- each with banding, 1um diam. Lip drops and glycog for energ. Periph nuc just under endomysium.
-M line in H band in A dark band. Z line in light I band. Each myofibrils has thin actin and thick myosin filams. Sarcomere=Z-Z. Contrac= decr gap btw A and Z, with A constant.
-illus of cent nuc if blade pass just deep of sarcolemma. Capill netw surr skel musc fibres. Not always active blood supp, capill sphincters.
LO4: desc ultra struc app skel musc and state which bands cont actin, myosin or both.
-ultra struc-periph nuc. Myofibrils in fascicles. Mito lot in rows btw myofibrils in sarcoplasm.
MHAZI- M band dark within lighter H band within A band of thick myosin overlap actin. Z band within I band mainly actin. H band var thicken-just myosin. Z holds actin filams. M line X link in TS.
LO5: outl mech of slid filam mod of striated musc contrac.
-H and I shrink as contrac. A band myosin constant. Myofilams not Change length just rel posit. Ends of actin extend furth into A. Narr I event oblits H. Actin att to Z, Z drawn togeth. Shorten sarcomeres= shorten myofibril.
-actin, tropomysoin and troponin complex=thin filam of skel and cardiac musc. Actin bi str helix pos and neg ends. Tropomysoin lines groove of helix (coil rnd and reinforce) and is assoc with a troponin complex- TnI+C+T. I+T are diag of MI, rel by isch card musc in 1 HR, need meas 20hr. Quant trop not propor to amnt card dam. Heavy myosin heads need grip actin. 1 myosin rod like with 2 heads protruding. Each thick filam=lot myosin. Heads protrus at opp ends filam. In cent sarcomeres thick filams no heads. Myosin heads ext tow actin filams in regs of poten overlap. Need expos BS under tropomysoin. Heads bind, move, rel.
-X bridges- HMM is only X bridge (heavy myosin). Filam displ 300nm. HMM bridge displ under 10nm. So must be repet action. HMM head provs contrac by breakd ATP by myosin ATPase.
-coupling excit and contrac- contrac occs in many sarcomeres synch. Stim cert areas of fib surf (AI junc)= extensive contrac. AI junc is invag of sarcolemma as TTs.
-role Ca- incr Ca binds TnC=conf change=tropomysoin ways from actin BS for myosin. So myosin heads bind actin=contrac. Tropomysoin slips into groove allow myosin bind. Ca under contr of TT mem depol, triggs contrac via troponin. Innervat 1 Ca req to trig contrac. In vivo aid relax by rem Ca.
-seq events in sliding thin filam-
Myosin head low energ config, ATP assoc. ATP split=cocking myosin head. Myosin X bridge atts actin=high energ config, ADP and PI assoc. ADP and PI rel=working stroke-myosin head pivots and bends as pulls actin filam=slid tow M line.
Rigormortis config- myosin head tight bound to actin as death no ATP.
Norm ATP to myosin head=uncoup from actin. ATP hydrolases= myosin head bend and adv 5nm. Myosin head weak binds actin, rels PI=str binding and =pow stroke when head returns. ATP to head=detatch. Rep. Indiv heads att and flex diff times=movem.
LO6: desc mech of innerv of musc and excit at contrac coup.
-Ach rel at NMJ=depol, along cell surf and down TTs around ev myofibril. TT at ev AI junc. Lot SR either side-Ca reserv. Depol-alt conf of var Ca gates in SR=rel Ca= bind troponin bound to tropomysoin. Triad=closely associated TT and SR either side. SR termin cist.
-NMJ-small termin swells of axon cont vesics of Ach. Nerve imp=rel to AchR on sarcolemma=AP propag along musc. Ev cell at least 1 motor end pl. motor axon from CNS, br. As get stronger incr nerve fibre grow and bind musc. Schwann cells on nerve fib. Junc folds in sarcolemma= incr AchRs. Folds= su neural clefts.
-contrac actin by nerves ent epimysium. Att musc at motor end pl. 1 per fibre. Plate like or arborised with termin portion part buried on sarcoplasm, they rel Ach.
Sensory nerve endings- NM spindles occ in mus and tend prov info on state of musc contrac.
Skel musc can regen somewhat. Gross dam rep by CT=scar. If nerve/BS interp, fibres degen and repl by fib tiss.
-skel musc contrac-
Init- nerve imp along MN axon to NMJ. Rel Ach to cleft=loc depol sarcolemma=Na in gen depol spreads to TT. Volt sensor prots of TT mem change conf. Gated Ca rel channs of adjac termin cist of SR are activ. Ca rap rel to sarcoplasm. Ca to TnC=contrac. Ca return to termin cist by AT after AP ends= tropomysoin blocks again.
LO7: desc histol of cardiac and smooth musc rel to struc and func.
-cardiac musc- invol but striated. Rhyth and auton. Only in heart and walls of adjoining great vess. 1/2 cent nuc per cell. Intercal discs for elec and mech coup with adj cells. Branching. Endomysium rich capill supp. Elong nuc deep in fibre. Fibres can bifurcate=complex 3D netw. Fibres are only func syncitia. Cells joined end to end by intercal discs. Cells 100x15um Sep Lat by fine CT of endomysium. Brown atrophy die to lipofusion pigm. Fibres cont lot sarcosomes with lot cristae. Less conspicuous striation. Less well enclosed in SR. TTs in Z band.
-intercal discs- spec juncs. Apposed facing mems have recip pits and grooves. Intercal discs are strng horiz compactions occ at Z band. Weaker vertic compon cont gap juncs.
-ultra struc- actin and myosin contin masses in cytop. NOT distinct myofibrils. Mito and SR penet through cytop btw myofibrils.
-intercal discs of as substits for Z bands where cells meet end to end. Have gap juncs with plane for elec coupling. And adherens juncs to anchor cells and actin, Ag plane.
-TTs lie in register with Z band not AI junc. Less SR- diads NOT triads. Diad close assoc permits rel Ca into sarcoplasm and subseq contrac.
LO8: outl struc and func of purkinje fibres.
-all cardiac musc cells spont intrinsic rhyth contrac. AP from SAN to AVN to ventricles. Impulses carried by spec myocardial cells of which distal conducting cells carrying imp to ventricle musc. Are purkinje fibres- fast conduc. Tracts of PK fibres transm AP from AVN to ventric.
-PK fibres are large cells with lot glycog, sparse A and M myofilams. Extens gap juncs where join. Fewer fibrils and less intercal discs. Under endocardium. Comm fnd along inter ventric septum. Conduct AP 3-4m/s comp to card musc fibre 0.5m/s so rap spread of imp X whole heart. Ventric contrac synch.
-regen- more resis to inj but not regen. Dam cont by format fibrio connective scar tiss.
LO7: smooth musc.
-smooth musc- long fusif spind cells, cent nuc. NOT striated, NO sarcomeres, NO TT. Contrac still relies on A and M interac but slight diff mech. Contrac slower, more sust, req less ATP. Latch mech. Can stay contract for HR/days. Can be stretched. Resp to sim of nerve sigs, horms, drugs, loc conc blood gases. Form sheets, bundles or lays cont 1000s cells.
-often form walls of passage or cav (modif vol). Eg vasc strucs, GIT, RT, GUT. Contractile part GIT mid oesoph to anus. Resp walls trach to alv ducts. Wall of ducts and glands, ruin and genet ducts. Musc of iris. Arrector pili part of areolar tiss.
-clinic sig eg BP, dysmenorrhea, asthma, atherosclerosis, abn gut Mobil.
-tiss organisation- scatt singly, small grps, or large sheets. Assoc with CT.
-modif smooth musc cells can app singly as:
Myoepith cells- stellate form netw arnd sec units of some exoc gls eg sweat, saliv, mamm. Contrac AIDS sec to ducts. Myoepith in ocular iris contrac=pupil dilat.
Myofibroblast- at sites of wound heal. Prod T1 Coll ma, also contrac (lot A and M)- help draw wound edge togeth. Also tooth loss.
-comm arrangements- indiv cells embedd in elastic tiss. Bundles of fibres env in sheaths of fibro elastic tiss.in paired sheets with long axes paral within sheets. Orthogonal btw sheets esp duct walls. Within sheets cells are stagg.
-most smooth musc cells innerv by ANS fibres rel nt from varicosities into wide cleft. Plexi of nerves in nearby CT partic submuc and outs ME. Have swells rel Ach stim adj cells. NOT ev cell innerv. Abund gap juncs transfer deeper. Adj cells may have gap junc contact. Contrac slower then skel. Less ordered interac A and M.
-relaxed smooth musc- long thin cells and nuc. Nuc NOT in rows like tendon.
Contracted- fusif shape more obv. Twisted nuc.
-smooth musc filams- thin:thick 12:1 vs 5/6:1 in skel. Oval dense areas contact myofilams and sarcolemma. Ultrastruc simil to the mater of Z band of striated musc. May have simil func of att for myofilams.
-func props- changes in smooth musc by: endog, horm, nerves, innerv by unmyel post gang nerves of ANS.
-smooth musc thick and thin filam arr diag in cell ,spiral down long axis=twisting contrac. Intermed filam bundles att dense bods scatt through sarcoplasm and occas anch to sarcolemma. Caveoli= TT. Intermed vimentin and desmin spiral down in contact edge. All filam contact dark dense bods=anast netw, pull on=shorten and twist cell as A and M slide by diff mech. Ca req for contrac.
LO9: desc lim nat of rep in mat musc.
-skel- can't di but tiss can regen by mito to activ of sat cells. So hyperplasia folls musc inj. Sat cells can also fuse exist musc=incr mass=hypert.
-cardiac- incapable of regen, dam, fibrob invade, div, lay scar tiss.
-smooth- retain mito to activ, can form new cells. Eg preg uterus wall hypert and hyperplasia.