An Introduction to Muscle Tissue

1. An Introduction to Muscle Tissue • Muscle Tissue • A primary tissue type, divided into • Skeletal muscle • Cardiac muscle • Smooth muscle

2. An Introduction to Muscle Tissue • Skeletal Muscles • Are attached to the skeletal system • Allow us to move • The muscular system • Includes only skeletal muscles

3. Functions of Skeletal Muscles • Produce skeletal movement • Maintain body position • Support soft tissues • Guard openings • Maintain body temperature • Store nutrient reserves

4. Skeletal Muscle Structures • Muscle tissue (muscle cells or fibers) • Connective tissues • Nerves • Blood vessels

5. Skeletal Muscle Structures • Organization of Connective Tissues • Muscles have three layers of connective tissues • Epimysium: • exterior collagen layer • connected to deep fascia • Separates muscle from surrounding tissues • Perimysium: • surrounds muscle fiber bundles (fascicles) • contains blood vessel and nerve supply to fascicles • Endomysium: • surrounds individual muscle cells (muscle fibers) • contains capillaries and nerve fibers contacting muscle cells • contains myosatellite cells (stem cells) that repair damage

6. Skeletal Muscle Structures Figure 10–1 The Organization of Skeletal Muscles.

7. Skeletal Muscle Structures • Organization of Connective Tissues • Muscle attachments • Endomysium, perimysium, and epimysium come together: • at ends of muscles • to form connective tissue attachment to bone matrix • i.e., tendon (bundle) or aponeurosis (sheet)

8. Skeletal Muscle Structures • Nerves • Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord) • Blood Vessels • Muscles have extensive vascular systems that • Supply large amounts of oxygen • Supply nutrients • Carry away wastes

9. Skeletal Muscle Fibers • Are very long • Develop through fusion of mesodermal cells (myoblasts) • Become very large • Contain hundreds of nuclei

10. Skeletal Muscle Fibers Figure 10–2 The Formation of a Multinucleate Skeletal Muscle Fiber.

11. Skeletal Muscle Fibers Figure 10–2a The Formation of a Multinucleate Skeletal Muscle Fiber.

12. Skeletal Muscle Fibers Figure 10–2b The Formation of a Multinucleate Skeletal Muscle Fiber.

13. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • The sarcolemma • The cell membrane of a muscle fiber (cell) • Surrounds the sarcoplasm (cytoplasm of muscle fiber) • A change in transmembrane potential begins contractions

14. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Transverse tubules (T tubules) • Transmit action potential through cell • Allow entire muscle fiber to contract simultaneously • Have same properties as sarcolemma

15. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Myofibrils • Lengthwise subdivisions within muscle fiber • Made up of bundles of protein filaments (myofilaments) • Myofilaments are responsible for muscle contraction • Types of myofilaments: • thin filaments: • made of the protein actin • thick filaments: • made of the protein myosin

16. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Sarcoplasmic reticulum (SR) • A membranous structure surrounding each myofibril • Helps transmit action potential to myofibril • Similar in structure to smooth endoplasmic reticulum • Forms chambers (terminal cisternae) attached to T tubules

17. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Triad • Is formed by one T tubule and two terminal cisternae • Cisternae: • concentrate Ca2+ (via ion pumps) • release Ca2+ into sarcomeres to begin muscle contraction

18. Skeletal Muscle Fibers Figure 10–3 The Structure of a Skeletal Muscle Fiber.

19. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Sarcomeres • The contractile units of muscle • Structural units of myofibrils • Form visible patterns within myofibrils • Muscle striations • A striped or striated pattern within myofibrils: • alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

20. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Sarcomeres • M Lines and Z Lines: • M line: • the center of the A band • at midline of sarcomere • Z lines: • the centers of the I bands • at two ends of sarcomere

21. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Sarcomeres • Zone of overlap: • the densest, darkest area on a light micrograph • where thick and thin filaments overlap • The H Band: • the area around the M line • has thick filaments but no thin filaments

22. Skeletal Muscle Fibers • Internal Organization of Muscle Fibers • Sarcomeres • Titin: • are strands of protein • reach from tips of thick filaments to the Z line • stabilize the filaments

23. Skeletal Muscle Fibers Figure 10–4a Sarcomere Structure.

24. Skeletal Muscle Fibers Figure 10–4b Sarcomere Structure.

25. Skeletal Muscle Fibers Figure 10–5 Sarcomere Structure.

26. Skeletal Muscle Fibers Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.

27. Skeletal Muscle Fibers Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.

28. Skeletal Muscle Fibers • Sarcomere Function • Transverse tubules encircle the sarcomere near zones of overlap • Ca2+ released by SR causes thin and thick filaments to interact

29. Skeletal Muscle Fibers • Muscle Contraction • Is caused by interactions of thick and thin filaments • Structures of protein molecules determine interactions

30. Skeletal Muscle Fibers • Four Thin Filament Proteins • F-actin (Filamentous actin) • Is two twisted rows of globular G-actin • The active sites on G-actin strands bind to myosin • Nebulin • Holds F-actin strands together • Tropomyosin • Is a double strand • Prevents actin–myosin interaction • Troponin • A globular protein • Binds tropomyosin to G-actin • Controlled by Ca2+

31. Skeletal Muscle Fibers Figure 10–7a, b Thick and Thin Filaments.

32. Skeletal Muscle Fibers • Initiating Contraction • Ca2+ binds to receptor on troponin molecule • Troponin–tropomyosin complex changes • Exposes active site of F-actin

33. Skeletal Muscle Fibers • Thick Filaments • Contain twisted myosin subunits • Contain titin strands that recoil after stretching • The mysosin molecule • Tail: • binds to other myosin molecules • Head: • made of two globular protein subunits • reaches the nearest thin filament

34. Skeletal Muscle Fibers Figure 10–7c, d Thick and Thin Filaments.

35. Skeletal Muscle Fibers • Myosin Action • During contraction, myosin heads • Interact with actin filaments, forming cross-bridges • Pivot, producing motion