Muscle tissue 1) Striated skeletal muscle tissue. 2) Striated cardiac muscle tissue. 3) Smooth muscle tissue. anim_bicep_right anim_bicep_left muscleman2 General characteristic of muscle tissue * Origin: mesoderm and mesenchyme * Excitability * Contraction + relaxation Þ cause movement * Composition: muscle cells + connective tissue (+blood vessels + nerves) * contractile proteins in sarcoplasm – actin and myosin * Long axis of cells is usually oriented paralelly with direction of contraction Nomenclature • •mys/myos (muscle) •myocyte (muscle cell) • sarx/sarcós (meat): cell membrane = sarcolemma cytoplasm = sarcoplasm smooth ER = sarcoplasmic reticulum • Connective tissue of muscle * Endomysium – around each muscle cell (fiber) * Perimysium – around and among the primary bundles of muscle cells * Epimysium – connective tissue „capsule“ covering the surface of muscle • Image285 Connective tissue in skeletal muscle contains vessels and nerves rhabdomyocyte cardiomyocyte leiomyocyte Ø 25-100 µm Ø 15 µm Ø 3-10 µm MUSCLE CELLS 7 image002 Occurrence: Skeletal muscles Heart Inner organs (their wall Cross-striated skeletal muscle tissue * morphological and functional unit: muscle fiber (rhabdomyocyte) – elongated, cylindrical shape, multinucleated cell (=syncytium) – nuclei are located at the periphery (beneath sarcolemma), myofibrils show cross striation * diameter of muscle fiber: 25-100 mm * length: milimeters - centimeters (up 15) Skelmuscopy 99689 skeletal_muscle Structure of rhabdomyocyte * sarcolemma + T-tubules * nuclei (25-40 per 1mm of the length) * sarcoplasm: Ømyoglobin (protein with heme (iron-containing porphyrin) prostetic group, and is the primary oxygen-carrying pigment Ømyofibrils (cross-striated 1–2 µm thick fibrils) Øorganelles: mitochondria, Golgi apparatus, sarcoplasmic reticulum (Ca2+ depot , sarcotubules, terminal cisternae) Øinclusion (glycogen) * Rhabdomyocyte AP_I_7 9. D) SKeletal muscle 10. Peripheral nuclei SkMTHE40 005 Skeletal%20muscle%2003a 111sceletal musc Skeletal muscle cell (fiber) < rhabdomyocyte > •Used terms: •Muscle fiber = myofiber = syncitium = rhabdomyocyte •Muscle fiber – morphologic and functional unit of skeletal muscle [Ø 25 – 100 m] •Myofibrils – compartment of fiber sarcoplasm • [Ø 0.5 – 1.5 m] •Myofilaments – actin and myosin, are organized into sarcomeres (several in the length of myofibril) [Ø 8 and 15 nm] • •Sarcomere – the smallest contractile unit [2.5 mm in length] 019852403x Bundles of muscle fibrers Muscle fiber – morphologic and functional unit of skeletal muscle [Ø 25 – 100 m] Myofibrils – compartment of fiber sarcoplasm [Ø 0.5 – 1.5 m] Myofilaments – actin + myosin are organized into sarcomeres (several in the length of myofibril) [Ø 8 and 15 nm] actin + myosin sarcomere MuscleL1 Myofibril [Ø 0.5 – 1.5 m]: elongated structure in sarcoplasm, oriented paralelly to the length of cell, composed of 2 types of myofilaments – actin and myosin – arranged into: Sarcomere: the smallest contractile unit between Z-lines on myofibril (organization of myofilaments causes cross striation of myofibrils) Z-line Z-line Z-line Myofibril structure –izotropic parts (I-bands) – light, Z-line (telophragma) –anizotropic parts (A-bands) – dark, M-line (mesophragma), H-band •Myofilaments •Thick: only in A-band, myosin,15 nm thick, 1.6–1.8 µm long •Thin: in I-band and at periphery of A-band), F-actin and regulatory proteins (troponin, tropomyosin), 6 nm thick, 1.5 µm long • •Principle of myofibril shortening during muscle contraction: sliding mechanism mechanismu •the length of myofilaments does not change during contraction svaly1 svaly1 SARCOMERE I - band A – band I - band Z – line Z – line M – line H - zone MYOFIBRIL actin actin – myosin – actin actin Myofilaments: microfilaments 016 sarcomere-e redbutn redbutn redbutn sarcoplasm strips sarcoplasm Myofibrils - TEM sarcomere MuscleL1 Sarcomere Imag108 A–band I–band ½ I-band H-zone emmodel EM006b Skeletal muscle in EM image1 EM007b Sarcoplasmic reticulum, t-tubule 179 019852403x Terminal cisterna T-tubule Terminal cisterna TRIAD T-tubules are invaginations of sarcoplasm and leads action potential to terminal cisternae (it changes permeability of membrane for Ca ions) 019852403x I-band A-band I-band SR-Myofibrils T-tubule terminal cisterna mitochondria myofibrils tubules + cisternae of sER sarcolemma Characteristic of skeletal muscle fiber types Fibers: Red Intermediary White Colour Dark (red) Dark (red) Light (white) Content of myoglobin High Intermediate Low Number of mitochondria Many small Mi Many large Mi Little small Mi ATPase activity Low High High Type of metabolism Oxidative Aerobic and anaerobic Anaerobic Contraction Slow Quick Quick Defatigability Very small Small High Capilary density High High Low muscles5x Svalová tkáň - 7 Příčně pruhovaný sval Contraction * Propagation of action potential (depolarization) via T-tubule (= invagination of sarcolemma) * Change of terminal cisternae permeability – releasing of Ca+ ions increases their concentration in sarcoplasm * Myosin contacts actin and sarcomera shortens by sliding movement – contraction * Relaxation: repolarization, decreasing of Ca2+ ions concentration, inactivation of binding sites of actin for myosin * muscle1 A model of a sarcomere built of dinner forks humge006_img_0 SR-T-tubule Calsequestrin is to Ca2+ as haemoglobin is to O2 TRIAD Ca2+ Ca2+ The T-tubules have special Ca2+ channels termed 'dihydropyridine receptors'. Other Ca2+ channels ('ryanodine receptors') in the membrane of the SR cisternae. Opening of these channels causes Ca2+ to be dumped from the cisternae into the sarcoplasm. Muscleslidingfilament1 mandl-7no11anim Mechanism of muscle contraction * During contraction the thick /M/ and thin /A/ slide past each other /sliding filament theory/ and the Z-discs are brought near the ends of the thick filaments. Mus1ani Mechanism of muscle contraction actin players1 Players: Mechanism of contraction: sliding of myofilaments Imag110 myosin actin * musclecrossbridges2 Cardiac muscle - myocardium * is made up of long branched fibers, composed of cells – cardiomyocytes, * cardiomyocytes are cylindrical cells, which can be branched on one or both ends (Y, X shaped cells), * Sarkoplasm: 1 nucleus in the center of cell, striated myofibrils, numerous mitochondria, * cells are attached to one another by end-to-end junctions – intercalated discs. beating heart animation cardiac_muscle chains of cardiomyocytes blood capillary with erythrocytes pure23r pure23r pure23r pure23r Intercalated disc cardiacmuscle 111cardiac musc heartmuscle1 4 C) cardiac muscle; 5. E) striations, branched fibers, central nuclei heart2 06_21b image1 arm8 Diagram and electron micrograph of a part of cardiomyocyte DIFFERENCES BETWEEN CARDIAC AND SKELETAL MUSCLE TISSUES * * there are no triads, but diads: 1 t-tubule + 1 cisterna * t-tubules encircle the sarcomeres at the Z lines rather than at the zone of overlap. * sarcoplasmic reticulum via its tubules contact sarcolemma as well as the t-tubules * cardiac muscle cells are totally dependent on aerobic metabolism to obtain the energy needed to continue contracting. The sarcoplasm thus contains large numbers of mitochondria and abundant reserves of myoglobin (to store oxygen). Energy reserves are maintained in the form of glycogen and lipid inclusions. Intercalated disc * „scalariform“ shape of cell ends * fasciae adherentes (adhesion of cells) * Nexus (quick intercellular communication – transport of ions, electric impulses, informations) * Muscle7 Heart%20muscle%2001a 034 intercalated discs – desmosomes, fasciae adherentes, nexuses striated cardiomyocytes A) Cardiac muscle arrobend arrobend arrobend arrobend arrobend arrobend pure23r pure23r pure23r pure23r pure23r pure23r pure23r nexus fascia adherens Cell 1 Cell 2 Intercalated disc: pure2 pure2 pure2 Actin myofilaments Myofibril of cardiomyocyte * Actin + myosin myofilaments * Sarcomere * Z-line * M-line and H-zone * I-band, A-band * T-tubule + 1 cisterna = diad (around Z-line) MuscleL1 abdelaziz_html_m5d945a9f Purkinje‘s fibers * are located in the inner layer of heart ventricle wall * are specialized cells fibers that conduct an electrical stimuli or impulses that enables the heart to contract in a coordinated fashion * numerous sodium ion channels and mitochondria, fewer myofibrils Image:Purkinje fibers.jpg gr84 Natriuretic hormone * in atrial granules in sarcoplasm of kardiomyocytes in ventricles * 300 – 400 nm Ø * this hormone is involved in regulation of volume of circulating blood * em2 Smooth muscle tissue * spindle shaped cells (leiomyocytes) with myofilaments not arranged into myofibrils (no striation), 1 nucleus in the centre of the cell * myofilaments form bands throughout the cell * actin filaments attach to the sarcolemma by focal adhesions or to the dense bodies substituing Z-lines in sarcoplasm * calmodulin (has function as troponin) * sarcoplasmic reticulum forms only tubules * Caveolae (have function as T-tubules) * zonulae occludentes and nexuses connect cells practi14 image006 Smooth muscle cmusmls cmusmts Caveolae Caveolae are equivalent to t-tubule and in their membrane ions channel are present to bring Ca needed fo Contraction. Caveolae are in contact with sarcoplasmic reticulum. image1 Leiomyocyte SmoothMuscle Smooth Muscle Leiomyocyte: contractile filaments + nexuses Myosin flaments Actin filaments Muscle tissue •Slides: * Skeletal muscle (2 – Apex linguae) * Heart muscle (64, 65 – Myocardium) * Smooth muscle (16 – Intestinum tenue) Smooth muscle int intestinum tenue int intestinum tenue – smooth muscle image006 Leiomyocytes are arranged into laeyers of wall of hollow (usually tubular) organs B) Smooth muscle smooth4 Cross section Longitudinal section muscle%20tissue%202 muscle%20tissue muscle%20tissue%203 cell%20types Structure_of_Myofibril muscle micriograph muscle%20cell-sarcomere sarcomere-e sarcomere-e SR-Myofibrils objct2 Development of rhabdomyocyte Ms_emb1 Msomi4 Origin of skeletal muscle: paraaxial mesoderm – somites – myotomes Fusion of myoblasts (primitive muscle cells in myotomes) into multinucleated muscle fiber Development of cardiomyocytes and leiomyocytes * Practice and Quiz muscle-spasm * Rhabdomyocyte * Endomysium * Sarcomere * T-tubule * Troponin * Myofilament * Myofibril * Sarcoplasmic reticulum * Actin * Sarcolemme * Perimysium * Leiomyocyte * Myosin * Epimysium * Triad * Intercalated disc * A-band * Cardiomyocyte * M-line * Myosin * Fascia adherens * Motor-end-plate * musclecardiacintercalated Muscle striated multinucleate skeletal skeletalmuscleEM Muscle smooth Muscle smooth uninucleate muscle cardiace intercalated disks cmustmlt2 cmustmlt3 File:Skeletal muscle - cross section, nerve bundle.jpg 062 351Blabeled_copy skin15 019852403x Naainn2ok Smooth muscle cell Basal lamina ??? 111sceletal musc 111cardiac musc 50310876 * image1 image1A EM image1B skeletalmuscleEM Muscle_Cell_Close-up_1 Structure or rhabdomyocyte Sarcomere Sarcolemme + t-tubules, In sarcoplasm: Nuclei, Mitochondria, Golgi apparatus, Glycogen (beta granules) (sarcoplasm with organelles forms columns among myofibrils) Sarcoplasmic reticulum (smooth ER) – reservoir of Ca2+ Myofibrils (parallel to the length of the muscle fiber) tubule cmumep Mechanism of contraction: •The chemical players in muscle contraction are: * 1. myosin (protein) * 2. actin (protein) * 3. tropomyosin (protein) * 4. troponin (protein) * 5. ATP (nucleotide) * 6. calcium ions * - There are two binding sites on each myosin head, one for ATP and one for actin. ATP is hydrolyzed into ADP + phosphate and energy is transferd into the head of myosin. * - Thin filaments are made of these three protein molecules: 1. actin, 2. tropomyosin, * 3. troponin. - The major component of the thin filament, actin is composed of a double strand of * actin subunits each of which contain myosin binding sites. - The regulatory protein tropomyosin twists around the actin. When the sarcomere * is not shortening, the position of the tropomyosin covers the binding sites on the * actin subunits and prevents myosin cross bridge binding. - Troponin, which is found periodically along the tropomyosin strand, functions to * move the tropomyosin aside, exposing the myosin binding sites. - Role of calcium in muscle contraction: action potential occurs - calcium ions are * released from the terminal cisternae - calcium ions then bind to troponin – * tropomyosin moves away from the myosin binding sites on actin. Review of participants in the Cross Bridge Cycle: * * Participant Will bind to: * 1. Myosin ATP, Actin * 2. Actin Myosin, Troponin * 3. Tropomyosin Troponin * 4. Troponin Calcium, Actin, • Tropomyosin * 5. ATP Myosin * 6. Calcium ions Troponin Detail of steps required to expose the binding sites on actin: * Presence of an action potential in the muscle cell membrane. * Release of calcium ions from the terminal cisternae. * Calcium ions rush into the cytosol and bind to the troponin. * There is a change in the conformation of the troponin-tropomyosin complex. * This tropomyosin slides over, exposing the binding sites on actin. Summary of the role that ATP plays in the contraction of muscle: * 1. ATP transfers its energy to the myosin cross bridge, which in turn energizes the power stroke. * 2. ATP disconnects the myosin cross bridge from the binding site on actin. * 3. ATP fuels the pump that actively transports calcium ions back into the sarcoplasmic reticulum. ATP is required to cleave the avidly formed bond between actin and myosin. In the absence of ATP the cross linking becomes fixed, and the muscle becomes rigid and inextensible. This condition is seen shortly after death when the muscles' energy supply is used up, and is known as rigor mortis. ChemCrossBridgeCycle The thin actin filament is a dimeric polymer of G-actin sub-units arranged like two strings of beads twisted together. Attached to the actin chain of the thin filament, are the proteins troponin (Tn) and tropomyosin. A tropomyosin molecule runs along each actin chain, bound to the actin. Each tropomyosin sub-unit covers about 7 G-actin sub-units. The troponin molecule has three sub-units: TnT that binds to tropomyosin near the ends of the tropomyosin sub-units; TnI that binds to the actin; and TnC that binds to the TnI and TnT sub-units, and which also has a strong affinity for Ca2+ at four binding sites. The thick filaments, at either end, have sticking off at regular intervals, the fibrillar necks and globular, ATPase heads of the myosin subunits - the polymerized tails of which make the backbone of the filament. The heads at the opposite ends of the thick filament stick off in opposite directions leaving a bare middle region (pseudo H-zone) on the filament. Each successive myosin head is staggered so that six rows of heads stick off in six directions (60o intervals) around the filament. Each myosin filament is surrounded by six actin filaments and each actin filament by three myosins. Each myosin filament is surrounded by six actin filaments and each actin filament by three myosins. SarcomereStructure