Muscle tissue Dept. Histology & Embryology Faculty of Medicine MU pvanhara@med.muni.cz Petr Vaňhara, PhD General characteristic of muscle tissue Hallmarks Unique cell architecture Excitability and contraction Mesodermal origin Muscle tissue Skeletal Cardiac Smooth − Composition: muscle cells + connective tissue, blood vessels − Unique cell architecture – long multinuclear cells – muscle fibers (rhabdomyocytes) − Long axis of cells is oriented parallel with direction of contraction − Specific terminology: • cell membrane = sarcolemma • cytoplasm = sarcoplasm • sER = sarcoplasmic reticulum • Muscle fiber – microscopic unit of skeletal muscle • Myofibril – LM unit – myofilaments – unit of muscle fibers • Myofilaments – filaments of actin and myosin (EM) Histology of skeletal muscle tissue Connective tissue of skeletal muscle − Endomysium – around each muscle cell (fiber) − Perimysium – around and among the primary bundles of muscle cells − Epimysium – dense irregular collagen c.t., continuous with tendons and fascia − Fascia – dense regular collagen c.t. − Containment − Limit of expansion of the muscle − Transmission of muscular forces Connective tissue of skeletal muscle Structure of skeletal muscle − morphological and functional unit: muscle fiber (rhabdomyocyte) – elongated, cylindrical-shaped, multinucleated cell (syncytium) − nuclei are located at the periphery (under sarcolemma) − myofibrils show cross striation − diameter of muscle fiber: 25-100 µm − length: millimeters - centimeters (up to 15) Structure of skeletal muscle • Myosin heavy chain (MHC) type I and II - distinct metabolic, contractile, and motor-unit properties - ATPase aktivity • Twitch type - Fast vs. slow • Fiber color - Red vs. white • Myoglobin content • Glycogen content • Energy metabolism • Endurance Classification of skeletal muscle fibers 1.Type I fibers "red" or "slow twitch", small diameter muscle fibers with high resistance to fatigue, higher concentration of ATPase, relatively low glycogen content and lower concentration of SDH (succinatdehydrogenase) as well as - besides the above mentioned high myoglobin content - a large number of mitochondria. They are mainly found in the "red" musculature and possess a good energy supply due to being well capillarized. They are employed in long-lasting movements with limited development of force. 2.Type II fibers "white" or "fast twitch", large diameter muscle fibers 1. Type IIA fibers: "fast" or "fast twitch" fibers with a high fatigue tendency, high content of glycolytic and oxidative enzymes that are needed with longer lasting contractions with relatively higher development of force. 2. Type IIB fibers: fast, easily fatigued fibers with high glycogen and low mitochondria content. Their energy supply occurs very rapidly, mainly via glycolysis, which is important for short or intermittent strain with a high amount of force development. 3. Type IIC fibers: so-called intermediary fibers, which can be ordered between types I and II and, depending on the training, develop more type I or more type II characteristics. Classification of skeletal muscle fibers Fast and slow twitch fibers Properties Type I fibers Type IIA fibers Type IIX fibers Motor Unit Type Slow Oxidative (SO) Fast Oxidative/Glycolytic (FOG) Fast Glycolytic (FG) Twitch Speed Slow Fast Fast Twitch Force Small Medium Large Resistance to fatigue High High Low Glycogen Content Low High High Capillary Supply Rich Rich Poor Myoglobin High High Low Red Color Dark Dark Pale Mitochondrial density High High Low Capillary density High Intermediate Low Oxidative Enzyme Capacity High Intermediate-high Low Z-Line Width Intermediate Wide Narrow Alkaline ATPase Activity Low High High Acidic ATPase Activity High Medium-high Low http://en.wikipedia.org/wiki/Skeletal_striated_muscle Muscle fiber = myofiber = syncitium = rhabdomyocyte Muscle fiber – morphologic and functional unit of skeletal muscle [Ø 25 – 100 µm] Myofibrils – compartment of fiber sarcoplasm [Ø 0.5 – 1.5 µm] Sarcomere – the smallest contractile unit [2.5 µm], serial arrangement in myofibrils Myofilaments – actin and myosin, are organized into sarcomeres [Ø 8 and 15 nm] Ultrastructure of rhabdomyocyte T-tubule terminal cisterna mitochondria myofibrils sarcolemma Ultrastructure of rhabdomyocyte Sarcolemme + t-tubules, Sarcoplasm: Nuclei, Mitochondria, Golgi apparatus, Glycogen (β granules) Sarcoplasmic reticulum (smooth ER) – reservoir of Ca2+ Myofibrils (parallel to the length of the muscle fiber) tubules + cisternae of sER Myofibrils − elongated structures [Ø 0.5 – 1.5 µ] in sarcoplasm of muscle fiber oriented in parallel to the length of the fiber, − Actin + myosin myofilaments − Sarcomere − Z-line − M-line and H-zone − I-band, A-band Sarcomere A–band I–band½ I-band H-zone Sarcomere Sarcomere Sarcoplasmic reticulum, t-tubule Terminal cisterna T-tubule Terminal cisterna TRIAD communicating intracellular cavities around myofibrils, separated from cytosol terminal cisternae (“junction”) and longitudinal tubules (“L” system). reservoir of Ca ions T-tubules (“T” system ) are invaginations of sarcoplasm and bring action potential to terminal cisternae change permeability of membrane for Ca ions Sarcoplasmic reticulum, t-tubule Thin myofilaments • Fibrilar actin (F-actin) • Tropomyosin – thin double helix in groove of actin double helix, spans 7 monomers of G-actin • Troponin – complex of 3 globular proteins • TnT (Troponin T) – binds tropomyosin • TnC (Troponin C) – binds calcium • TnI (Troponin I) inhibits interaction between thick and thin filaments Thick myofilaments • Myosin - Large polypeptide, golf stick shape - Bundles of myosin molecules form thick myofilament 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 binds actin - sarcomera then shortens by sliding movement – contraction − Relaxation: repolarization, decreasing of Ca2+ ions concentration, inactivation of binding sites of actin for myosin myosin actin Impulse along motor neuron axon Depolarization of presynpatic membrane (Na+ influx) Synaptic vesicle fuse with presynaptic membrane Acetylcholine exocyted to synaptic cleft Acetylcholine diffuse over synaptic cleft Acetylcholine bind to receptors in postsynaptic membrane Depolarization of postsynaptic membrane and sarcolemma (Na+ influx) T-tubules depolarization Depolarization of terminal cisternae of sER Depolarization of complete sER Release of CaII+ from sER to sarcoplasm CaII+ binds TnC Troponin complex changes configuration TnI removed from actin-myosin binding sites Globular parts of myosin bind to actin ATPase in globular parts of myosin activated Energy generated from ATP→ADP + Pi Movement of globular parts of myosin Actin myofilament drag to the center of sarcomere Sarcomere contracts (I-band shortens) Myofibrils contracted Muscle fiber contracted Contraction http://highered.mheducation.com/sites/0072495855/student_view0/chapter10/animati on__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html 1 2 3 4 Myelinated axons Neuromuscular junction Capillaries Muscle fiber nucleus Neuromuscular junction Costameres • Structural components linking myofibrils to sarcolemma • Circumferential alignment • dystrophin-associated glycoprotein (DAG) complex • links internal cytoskelet to ECM • Integrity of muscle fiber Duchenne muscular dystrophy BREAK made up of long branched fiber (cells) – cardiomyocytes, − cardiomyocytes are cylindrical cells, branched on one or both ends (Y, X shaped cells), − Sarcoplasm: single nucleus in the center of cell, striated myofibrils, numerous mitochondria, − cells are attached to one another by end-to-end junctions – intercalated discs. Histology of skeletal muscle tissue - myocardium chains of cardiomyocytes blood capillary with erythrocytes Intercalated disc CARDIAC MUSCLE TISSUES COMPARED TO SKELETAL − no triads, but diads: 1 t-tubule + 1 cisterna − t-tubules around 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 − large numbers of mitochondria in sarcoplasm and abundant reserves of myoglobin (to store oxygen) − abundant 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, information) nexus fascia adherensIntercalated disc: 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) Purkinje 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 Smooth muscle tissue 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 substituting Z-lines in sarcoplasm − calmodulin − sarcoplasmic reticulum forms only tubules, Ca ions are transported to the cell via pinocytic vesicles − zonulae occludentes and nexuses connect cells 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. Smooth muscle tissue + nexuses Smooth muscle tissue Leiomyocytes are arranged into layers in walls of hollow (usually tubular) organs Cross section Longitudinal section Hallmark Skeletal muscle Cardiac muscle Smooth muscle Cells Thick, long, cylindrical, non-branched Branched, cylindrical Small, spindle- shaped Nuclei Abundant, peripherally 1-2, centrally 1, centrally Filaments ratio (thin:thick) 6:1 6:1 12:1 sER and myofibrils Regular sER around myofibrils Less regular sER, myofibrils less apparent Less regular sER, myofibrils not developed T tubules Between A-I band, triads Z lines, diads Not developed Motor end plate Present Not present Not present Motor regulation Voluntary control No voluntary control No voluntary control Other Bundles, c.t. Intercalated discs Caveoli, overlapping cells Summary Embryonic development Regeneration Regeneration https://www.youtube.com/watch?v=b1WD564sjWw Tissue engineering Thank you for attention pvanhara@med.muni.cz http://www.med.muni.cz/histology