The document discusses the structure and function of the three main types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscle is striated and voluntary. It contains long, cylindrical muscle fibers (myocytes) with many nuclei. Cardiac muscle is also striated but involuntary. It forms the walls of the heart and has intercalated discs joining cells end to end. Smooth muscle is not striated and involuntary. It is found in organs and has spindle-shaped cells that appear as discs in cross section.

3. Skeletal muscle giant multinucleated cylindrical cell s referred as = muscle fibers or rhabdomyocytes ( gr. rhabdos = rod) the length - mm to cm, thickness varies from 10 to 100  m

5. sarkotubules terminal cisternae an organelle of great importance is the sarcoplasmic reticulum , a special type of sER i t consists of longitudinal sarcotubules that are confluent with transversally oriented channels called terminal cisternae p airs of parallel terminal cisternae run transversally across the myofibrils in close apposition to the T tubule T tubule is an invagination of the sarcolemma and is not part of the sarcoplasmic reticulum t wo terminal cisternae and T tubule constitute structure called as triad of skeletal muscle t riads usually occur in sites where the dark and light bands meet

8. sarcomere . . . . m yofibrils - contractile fibrils resolvable with the LM that are mostly randomly dispersed within the sarcoplasm t heir diameter is about 1 -2  m (in cross sections, the myofibrils appear as dots, in longitudinal sections, they show a conspicuous cross banding ) t he dark band is called the anisotropic , or A band , because it is doubly refractive to polarized light and appers dark in the fresh state t he light isotropic , or I band , is single refractive to polarized light and is pale in the fresh e ach I band is intersected by a thin dark line - the Z line , likewise, the dark A band is bisected by a thin, light-staining band, called H band , within it M-line is seen t he segment of myofibril extending between two Z lines is a sarcomere , its length varies from 3.5 to 4  m

14. Thin myofilament - from F-actin + protein complex composed of troponin and tropomyosin t ropomyosin runs around F-actin in 40 nm distances troponin: of 3 proteins Troponin I, C and T

18. Muscles - structure

21. cardiomyocytes: contracting and non contracting Contracting (working) cardiomyocytes cells are of cylindrical form, 20  m in diameter and 50 to 200  m in length at specialized junctional zones called intercalated discs , cardiac muscle cells are joined end to end and form a linear unit - cardiac muscle fiber intercalated discs - sites of intercellular contacts

23. the cardiomyocyte is enveloped by a thin sarcolemma and contains one elongated nucleus situated centrally between diverging myofibrils , in its vicinity a small Golgi apparatus, lipid droplets and deposits of lipofuscin pigment are found myofibrils are oriented parallel and run from one end to another and show the cross banding, the sarcomeres are composed of the same parts as in skeletal muscle (A, I bands, Z, M lines, H zone) n umerous mitochondria arranged in rows and sarcoplasmic reticulum are seen among the myofibrils

24. T he intercalated discs are areas of extensive cell contact a t the sites of intercalated discs, special adhering and communicating junctions are fascia adherens (corresponds to the zonula adherens,belt desmozone.), macula adherens (spot desmosome) and nexus (gap junction) Non-contracting cardiomyocytes (subendocardial layer, develops from cardiac jelly) i n addition to the cardiomyocytes whose primary function is contraction, there are specialized cells whose function is to generate the stimuli for the heart beat cells are located just beneath the endocardium,subendocardial layer.) and in a whole represent impuls conducting system of the heart (sinoatrial node - node of Keith-Flack, atrio- ventricular node - node of Tawara, atrioventricular bundle - bundle of Hiss) b y light microscopy, cells of the conducting system are larger, thicker and more palely stained, with abundant central sarcoplasm and relatively few myofibrils, located usually in a peripheral position t he cells contain also large quantities of glycogen noncontracting cells form similar to contractile cardiac muscle cells fibers called Purkinje fibers

26. c ell nuclei have a cigar shaped form in dilated cells, but are of corkscrew appearance in cells which are contracted cells vary greatly in length, from 20  m (in the walls of small ducts and blood vessels) to 500  m (in the pregnant human uterus) t he cytoplasm - called sarcoplasm - appears rather homogeneous and is filled with fine contractile filaments (myofilaments) that are hardly seen R emember : the spindle-shaped form is imperceptible only in the longitudinal sections of smooth muscle i n the transverse section the smooth muscle cells appear as homogenous discs of various diameters - t he largest of the discs are cut through the middle of the cells and usually contain the nucleus

28. the bulk of the cytoplasm is occupied by two sets of myofilaments : actin filaments are dominant myosin filaments occur only in a small amount myofilaments do not exhibit the paracrystalline organization that is seen in the skeletal or cardiac muscle Physiology: smooth mucle cells contract slowly and have low force of contraction t hey are innervated with adrenergic and cholinergic nerve fibers that act antagonistically nucleus thick filament thin filaments dense body intermediate filament