Muscle Tissue

1. Muscle Tissue MamounKremli Al-Maarefa College

2. Objectives • Identify basic structure of Muscles • Recognize types of muscular tissues and the difference between them • Recognize the relation between structure and function of various muscular tissues

3. Tissues • Four fundamental tissues are recognized: • Epithelial tissue • Connective tissue • Muscular tissue • Nervous tissue

4. Muscle Tissue - Characteristics • Cells are referred to as fibers because they are elongated • Contracts or shortens with force when stimulated • Contraction depends on myofilaments • Actin • Myosin • Plasma membrane is called sarcolemma • Sarcos = flesh • Lemma = sheath

5. Special functional characteristics • Contractility • Only one action: to shorten • Shortening generates pulling force • Excitability • Nerve fibers cause electrical impulse to travel • Extensibility • Stretch with contraction of an opposing muscle • Elasticity • Recoils passively after being stretched

6. Muscle Tissue Types • Skeletal: • attached to bones • Cardiac: • muscle of the heart • Smooth: • muscles associated with tubular structures and with the skin

7. Muscle Tissue Types Figure 10–1. Structure of the 3 muscle types. The drawings at right show these muscles in cross section. Skeletal muscle is composed of large, elongated, multinucleated fibers. Cardiac muscle is composed of irregular branched cells bound together longitudinally by intercalated disks. Smooth muscle is an agglomerate of fusiform cells. The density of the packing between the cells depends on the amount of extracellular connective tissue present.

8. Skeletal Muscle - Units Muscle Fascicle Fiber

9. Skeletal Muscle - Coverings Epimysium surrounds whole muscle Epimysium surrounds whole muscle

10. Skeletal Muscle - Coverings Perimysium Perimysium is around fascicle

11. Skeletal Muscle - Coverings Endomysium Endomysium is around each muscle fiber

12. Skeletal Muscle - Coverings • Epimysium, Perimysium, Endomysium Figure 10–2. Structure and function of skeletal muscle. The drawing at right shows the area of muscle detailed in the enlarged segment. Color highlights endomysium, perimysium, and epimysium.

13. Skeletal Muscle - Coverings

14. Skeletal Muscle – Blood Supply • Muscles must have plenty of blood supply • High demand for O2 and nutrients Figure 10–5. Longitudinal section of striated muscle fibers. The blood vessels were injected with a plastic material before the animal was killed. Note the extremely rich network of blood capillaries around the muscle fibers. Giemsa stain. Photomicrograph of low magnification made under polarized light. Vessels injected with plastic material

15. Skeletal Muscle • Voluntary movement • Long and cylindrical • Transverse striations • Each fiber is multi-nuclear (multinucleated cells – embryonic cells fuse) • 40% of body weight

16. Skeletal Muscle Figure 4.14a

17. Skeletal Muscle • Large, elongated, multinucleated fibers. • Nucleii are in periphery of cells, just under cell membrane Figure 10–6. Striated skeletal muscle in longitudinal section (lower) and in cross section (upper). The nuclei can be seen in the periphery of the cell, just under the cell membrane, particularly in the cross sections of these striated fibers. H&E stain. Medium magnification.

18. Skeletal Muscle • A band (dark-stained) • I band (light-stained) • Z line Figure 10–8. Longitudinal section of skeletal muscle fibers. Note the dark-stained A bands and the light-stained I bands, which are crossed by Z lines. Giemsa stain. High magnification. A band I band Z line Giemsa stain

19. Skeletal Muscle • A bands (dark-stained) • I bands (light-stained) • Z lines A bands I bands Z line Figure 10–8. Longitudinal section of skeletal muscle fibers. Note the dark-stained A bands and the light-stained I bands, which are crossed by Z lines. Giemsa stain. High magnification.

20. Skeletal Muscle • A-band (actin & myosin ) • I-band( actin only) • Z lines(attachment of actin) • H-band(myosin only) • M-line (Myomesin, creatine kinase)

21. Skeletal Muscle Structure • Invaginations of the T system at transition between A and I bands (twice in every sarcomere) • They associate with terminal cisternae of the sarcoplasmic reticulum (SR)(which is the specialized calcium-storing smooth endoplasmic reticulum). • Abundant mitochondria is present between myofibrils. Figure 10–17. Segment of mammalian skeletal muscle. The sarcolemma and muscle fibrils are partially cut, showing the following components: The invaginations of the T system occur at the level of transition between the A and I bands twice in every sarcomere. They associate with terminal cisternae of the sarcoplasmic reticulum (SR), forming triads. Abundant mitochondria lie between the myofibrils. The cut surface of the myofibrils shows the thin and thick filaments. Surrounding the sarcolemma are a basal lamina and reticular fibers. (Reproduced, with permission, from Krstíc RV: Ultrastructure of the Mammalian Cell. Springer-Verlag, 1979.)

22. Skeletal Muscle Structure Figure 10–11. Structure and position of the thick and thin filaments in the sarcomere. The molecular structure of these components is shown at right. (Drawing by Sylvia Colard Keene. Reproduced, with permission, from Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders, 1968.) Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders

23. Skeletal Muscle – Sarcomere structure Figure 10–11. Structure and position of the thick and thin filaments in the sarcomere. The molecular structure of these components is shown at right. (Drawing by Sylvia Colard Keene. Reproduced, with permission, from Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders, 1968.) Bloom W, Fawcett DW: A Textbook of Histology, 9th ed, Saunders

24. The Thin Filament - Actin Figure 10–13. Schematic representation of the thin filament, showing the spatial configuration of 3 major protein components—actin, tropomyosin, and troponin. The individual components in the upper part of the drawing are shown in polymerized form in the lower part. The globular actin molecules are polarized and polymerize in one direction. Note that each tropomyosin molecule extends over 7 actin molecules. TnI, TnC, and TnT are troponin subunits.

25. Skeletal muscle • Fibers have striations • Myofibrils are organelles of the cell: these are made up of filaments • Sarcomere • Basic unit of contraction • Myofibrils are long rows of repeating sarcomeres • Boundaries: Z discs (or lines) -an organelle

26. Myofibrils • Made of three types of filaments (or myofilaments): • Thick (myosin) • Thin (actin) • Elastic (titin) ______actin _____________myosin titin_____

27. Sliding Filament Model __relaxed sarcomere__ _partly contracted_ fully contracted Sarcomere shortens because actin pulled towards its middle by myosin cross bridges “A” band constant because it is caused by myosin, which doesn’t change length Titin resists overstretching

28. Sliding Filament Model

30. Sarcoplasmic reticulum is smooth ER • Tubules surround myofibrils • Cross-channels called “terminal cisternae” • Store Ca++ and release when muscle stimulated to contract • Two thin filaments triggering sliding filament mechanism of contraction • T tubules are continuous with sarcolemma, therefore whole muscle (deep parts as well) contracts simultaneously

31. Neuromuscular Junction • Motor neurons innervate muscle fibers • Motor end plate is where they meet • Neurotransmitters are released by nerve signal: this initiates calcium ion release and muscle contraction

32. Neuromuscular Junction • Motor Unit: a motor neuron and all the muscle fibers it innervates (these all contract together)

33. Motor Unit

34. Motor Unit

35. Motor End-plate Figure 10–18.Ultrastructure of the motor end-plate and the mechanism of muscle contraction. The drawing at the upper right shows branching of a small nerve with a motor end-plate for each muscle fiber. The structure of one of the bulbs of an end-plate is highly enlarged in the center drawing. Note that the axon terminal bud contains synaptic vesicles. The region of the muscle cell membrane covered by the terminal bud has clefts and ridges called junctional folds. The axon loses its myelin sheath and dilates, establishing close, irregular contact with the muscle fiber. Muscle contraction begins with the release of acetylcholine from the synaptic vesicles of the end-plate. This neurotransmitter causes a local increase in the permeability of the sarcolemma. The process is propagated to the rest of the sarcolemma, including its invaginations (all of which constitute the T system), and is transferred to the sarcoplasmic reticulum (SR). The increase of permeability in this organelle liberates calcium ions (drawing at upper left) that trigger the sliding filament mechanism of muscle contraction. Thin filaments slide between the thick filaments and reduce the distance between the Z lines, thereby reducing the size of all bands except the A band. H, H band; S, sarcomere.

36. Types of Skeletal Muscle: • Type I fibres (red fibres). • Red muscles (large amounts of myoglobin and mitochondria). • Type II fibres(white fibers). • White muscles (less amounts of myoglobin and mitochondria). • Type III Fibres (Intermediate). • Have characteristics between type I & II In humans, skeletal muscles are composed of mixtures of these 3 types of fibres.

37. Red muscles are used when sustained production of force is necessary, e.g. in the control of posture. • White muscles are for rapid accelerations and short lasting maximal contraction e.g. extraocularmuscles of the human eye)

38. Cardiac Muscle • Striations • Involuntary • One nucleus • Deep center • Heart muscle

39. Cardiac muscle • Bundles form thick myocardium • Cardiac muscle cells are single cells (not called fibers) • Cells branch • Cells join at intercalated discs • 1-2 nuclei in center • Here “fiber” = long row of joined cardiac muscle cells • Rhythmicity: • More T-Tubules

40. Cardiac Muscle Figure 4.14b

41. Cardiac Muscle Figure 10–22. Drawing of a section of heart muscle, showing central nuclei, cross-striation, and intercalated disks.

42. Cardiac Muscle Figure 10–23. Photomicrograph of cardiac muscle. Note the cross-striation and the intercalated disks (arrowheads). Pararosaniline–toluidine blue (PT) stain. High magnification.

43. Cardiac Muscle

44. Cardiac Muscle Figure 10–26.Junctional specializations making up the intercalated disk. Fasciae (or zonulae) adherentes (A) in the transverse portions of the disk anchor actin filaments of the terminal sarcomeres to the plasmalemma. Maculae adherentes, or desmosomes (B), found primarily in the transverse portions of the disk, bind cells together, preventing their separation during contraction cycles. Gap junctions (C), restricted to longitudinal portions of the disk—the area subjected to the least stress—ionically couple cells and provide for the spread of contractile depolarization.

45. Smooth muscle • Muscles are spindle-shaped cells • One central nucleus • Grouped into sheets: often running perpendicular to each other • Peristalsis • No striations (no sarcomeres) • Contractions are slow, sustained and resistant to fatigue • Does not always require a nervous signal: can be stimulated by stretching or hormones • 6 major locations: • inside the eye 2. walls of vessels 3. respiratory tubes • 4. digestive tubes 5. urinary organs 6. reproductive organs

46. Smooth Muscle • Spindle shaped • Not striated • Single nucleus • Involuntary movement • Internal organs

47. Smooth Muscle

48. Smooth Muscle • Centrally located nucleii Figure 10–29. Photomicrographs of smooth muscle cells in cross section (upper) and in longitudinal section (lower). Note the centrally located nuclei. In many cells the nuclei were not included in the section. PT stain. Medium magnification.

49. Smooth Muscle • Cells are surrounded by a net of reticular fibers Figure 10–30. Drawing of a segment of smooth muscle. All cells are surrounded by a net of reticular fibers. In cross section, these cells show various diameters.

50. Smooth Muscle • Cytoplasmic filaments insert on dense bodies located in the cell membrane and deep in the cytoplasm. • Contraction of these filaments decreases the size of the cell and promotes the contraction of the whole muscle. • During the contraction the cell nucleus is deformed. Figure 10–33. Smooth muscle cells relaxed and contracted. Cytoplasmic filaments insert on dense bodies located in the cell membrane and deep in the cytoplasm. Contraction of these filaments decreases the size of the cell and promotes the contraction of the whole muscle. During the contraction the cell nucleus is deformed.