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Muscle Tissue 1.Muscle tissue – organization, histogenesis and functions 2.Classification of muscle tissue 3.Smooth muscle tissue 4.Striated (skeletal) muscle tissue 5.Cardiac (heart) muscle tissue 6.Regeneration of muscle tissue Muscle tissue Textus muscularis: cells – myocytes extracellular matrix body movements digestion blood circulation respiratory movements other movement activities, incl. cellular contraction succession of relax and contraction: transformation of chemical into mechanical energy Prof. Dr. Nikolai Lazarov 2 Muscle fibers – myofibers Gr. sarkos, flesh muscle cells = myocytes (leiomyocytes, rhabdomyocytes, cardiomyocytes): elongated, cylindrical or fusiform = myofibers sarcolemma = plasmalemma sarcoplasm = cytoplasm sarcoplasmic reticulum = smooth endoplasmic reticulum sarcosomes = mitochondria myoglobin: oxygen-binding protein connective tissue components: endomysium (Gr. endon, within + mys, muscle) perimysium (Gr. peri, around, near + mys) epimysium (Gr. epi, upon + mys) myoepithelial cells pericytes myofibroblasts in healing wounds myoid cells of the testis Prof. Dr. Nikolai Lazarov 3 Myofibrils and myofilaments myofibrils: fill the muscle fibers separated by sarcoplasmic reticulum myofilaments: thick and thin filaments (contractile proteins) Prof. Dr. Nikolai Lazarov 4 Histogenesis embryonic origin: smooth muscle – mesenchyme striated – mesoblast myoepithelial cells – skin ectoblast skeletal muscle – mesoderm somites – skeletal muscles of the trunk general mesoderm – muscles of the head and limbs Prof. Dr. Nikolai Lazarov 5 Functions movements of the body as a whole body posture stabilization volume regulation of the internal organs: sphincters movement of substances within living organisms: blood, lymph, air, food and fluids, urine, sperm heat production: involuntary contractions of the skeletal muscles (trembling) Prof. Dr. Nikolai Lazarov 6 Properties of muscle tissue irritability the ability of a muscle to respond to a stimulus conductivity the ability of a muscle to conduct electrical impulses across the membrane contractility the ability of a muscle to shorten and to produce energy extensibility the ability of a muscle to lengthen beyond its resting length elasticity the ability of a muscle to return to its original length without damage Prof. Dr. Nikolai Lazarov NB: muscles can only pull or contract, not push! push! 7 Types of muscle tissue Prof. Dr. Nikolai Lazarov 8 Smooth muscle tissue Textus muscularis nonstriatus (glaber) Characteristics: origin: mesenchyme involuntary: ANS innervation tonus peristalsis nonstriated in the walls of hollow and tubular organs: blood vessels (with exception of capillaries) alimentary canal respiratory tract urogenital system associated with hair follicles in the skin (arrector pili muscles) Prof. Dr. Nikolai Lazarov 9 Smooth muscle tissue leiomyocyte (Gr. leios, smooth) shape: fusiform or “spindle shaped" length: 30-500 µm thickness: 5-10 µm Prof. Dr. Nikolai Lazarov 10 Ultrastructure dense bodies, corpora densa (contain α-actinin = similar to the Z line) caveolae (analogous to Т-tubule system) actin filaments (4.5 µm/7 nm): actin, tropomyosin, calmodulin – Ca2+ myosin (2.2 µm/17 nm): myosin II intermediate filaments (10 nm): desmin (skeletin), vimentin = non-contractile proteins Prof. Dr. Nikolai Lazarov 11 Smooth muscle types two types of smooth muscle: visceral (single-unit) smooth muscles in the walls of hollow organs small blood vessels • relatively poor nerve supply • abundant gap junctions function in syncytial fashion multi-unit smooth muscles large arteries upper respiratory tract muscles of hair follicles iris and ciliary body of the eye • rich nerve supply • innervate individual cells • allow for fine control • provide very precise and graded contractions Prof. Dr. Nikolai Lazarov 12 Regulation of contraction and relaxation Prof. Dr. Nikolai Lazarov 13 Skeletal muscle tissue Textus muscularis striatus (skeletalis) the most abundant tissue in the vertebrate body – 40% of the body mass origin: mesoblast (myotomes) voluntary: CNS innervation strong, quick voluntary control of contraction/relaxation cross-striated skeletal muscles initial and end parts of the digestive tract muscles of the head (incl. eye, ear) muscles of respiration Prof. Dr. Nikolai Lazarov 14 Skeletal muscle development 100 myoblasts (mononucleated) – 1 mature muscle cell (multinucleated): syncytium (symplast) Gr. syn, together + kytos, cell does not divide postnatally muscle growth – augmentation of cell volume (hypertrophy) satellite (myosatellite) cells: retain their potential for the formation of new cells (stem cells) Prof. Dr. Nikolai Lazarov 15 Skeletal muscle tissue rhabdomyocyte (Gr. rhabdo, striped) shape: elongated, cylindrical length: 1-40 cm diameter: 10-100 µm numerous nuclei: 10-100/cell, located right up under the plasma membrane Prof. Dr. Nikolai Lazarov 16 Organization of skeletal muscle Skeletal muscle Muscle fasciculus Muscle fiber Myofibril Myofilaments Prof. Dr. Nikolai Lazarov 17 Myofibril 85-90% of the myofiber volume 2500-3500/rhabdomyofiber long cylindrical filamentous structure with a diameter of 0.5-2 µm system of transverse (T-) tubules – encircle the boundaries of the А-I bands “triad” = Т-tubule + 2 terminal cisternae: depot of Ca2+ Prof. Dr. Nikolai Lazarov 18 Ultrastructure Prof. Dr. Nikolai Lazarov 19 Sarcomere Sarcomere (Gr. sarkos + meros, part): length: 2-3 µm (~2.5 µm) – extends from Z line to Z line А band (anisotropic, i.e., birefringent in polarized light) H zone (from the German “Hell”, bright) М line (mesophragm, "Mittel", middle of the sarcomere): creatine kinase I band (isotropic, does not alter polarized light, monorefrigent) Z disk (“Zwischenscheibe”, the band in between the I bands) = telophragm: α-actinin Prof. Dr. Nikolai Lazarov 20 Sarcomere Prof. Dr. Nikolai Lazarov 21 Myofilaments thin (actin) filaments – 1 µm long/8 nm wide: actin – long filamentous polymers of F-actin; • 2 twisted strands of G-actin – globular monomer, 5.6 nm in diameter tropomyosin – 40 nm in length extending over 7 G-actin molecules • 2 polypeptide chains troponin – ТnT, TnI, TnC at intervals of 40 nm, attached to tropomyosin thick (myosin) filaments – 1.6 µm long/15 nm wide: head (ATPase activity) + proximal 60 nm of tail = heavy meromyosin distal 90 nm of the tail = light meromyosin 2 identical heavy chains and 2 pairs of light chains Prof. Dr. Nikolai Lazarov 22 Mechanism of contraction Prof. Dr. Nikolai Lazarov rigor mortis Sliding Filament Hypothesis: Huxley 23 Motor end plate myoneural junction – cholinergic (ACh) Prof. Dr. Nikolai Lazarov Myasthenia gravis 24 Neuromotor unit motor unit = an individual somatic motoneuron and all the skeletal muscle fibers (cells) it innervates a single nerve fiber (axon) can innervate up to 160 muscle fibers (cells), that all contract at the same time the number of motor units and the variable size of each unit can control the intensity (force) of a muscle contraction Prof. Dr. Nikolai Lazarov 25 Types of muscle fibers Red fibers (slow oxydative) – type I White fibers (fast glycolytic) – type IIb Intermediate (slow oxydative) – type IIa Prof. Dr. Nikolai Lazarov 26 Cardiac muscle tissue Textus muscularis striatus cardiacus origin: mesenchyme involuntary: ANS quick continuous automatic contraction: conduction system striated in the wall of the heart (myocardium) some large vessels Prof. Dr. Nikolai Lazarov 27 Cardiac muscle tissue cardiomyocyte (Gr. cardia, heart) three types of cardiac myocytes: contractile, conductive, secretory shape: cylindrical, bifurcated length: 85-100 µm diameter: 15-20 µm only 1 (or 2) centrally located pale-staining nuclei delicate sheath of endomysial connective tissue containing a rich capillary network Prof. Dr. Nikolai Lazarov 28 Cardiomyocyte Т-tubules: at the level of Z band “diad” = Т-tubule + one SR cistern Prof. Dr. Nikolai Lazarov 29 Ultrastructure mitochondria: 40% of the cytoplasmic volume atrial granules (ANF and BNF): 300-400 nm lipid droplets and lipofuscin glycogen granules intercalated discs: fascia adhaerens – in the transverse portion macula adhaerens (desmosomes) – in the vicinity, bind the cardiac cells together gap junction (nexus) – in the lateral portion, provides ionic continuity between cells Prof. Dr. Nikolai Lazarov 30 Myoepithelial cells basket cells: sweat gland mammary gland lacrimal gland salivary glands Prof. Dr. Nikolai Lazarov 31 Regeneration of muscle tissue Cardiac muscle has almost no regenerative capacity beyond early childhood: mature cardiac muscle cells do not divide proliferation of connective tissue myocardial scars Skeletal muscle can undergo limited regeneration source of regenerating cells is believed to be the satellite cell (stem cell) Smooth muscle is still capable of an active regenerative response (division) viable mononucleated smooth muscle cells and pericytes from blood vessels provide for the replacement of the damaged tissue Prof. Dr. Nikolai Lazarov 32 Thank you ... Prof. Dr. Nikolai Lazarov 33