Exercise 14

1. Exercise 14 Microscopic Anatomy, Organization, and Classification of Skeletal Muscle

3. SKELETAL MUSCLE • Voluntary or involuntary? • Striated or not? • Multinucleate or uninucleate?

4. Terminology • “Myo-” or “-Mys-” = muscle • “Sarco-” = flesh

5. Figure 12.1a Microscopic anatomy of skeletal muscle. Microscopic Anatomy • Muscle Fiber • Nuclei Dark A band Light I band Nuclei Fiber

6. Figure 12.1b Microscopic anatomy of skeletal muscle. Muscle Fiber Anatomy • Sarcolemma • Sarcoplasm Sarcolemma Mitochondrion Myofibril Nucleus Dark A band Light I band

7. Figure 12.1c Microscopic anatomy of skeletal muscle. • Myofibrils • Composed of myofilaments • Actin (thin filaments) & myosin (thick filaments) Z disc H zone Z disc Thin (actin) filament Thick (myosin) filament I band I band A band M line

8. Transverse tubules • Sarcoplasmic Reticulum (SR) • Smooth ER • Terminal cisternae: enlarged portion of SR on either side of T tubule • Triad = T tubule + 2 terminal cisternae Fig. 10-3

9. Fig. 10-6

10. Figure 12.3 Photomicrograph of muscle fibers, longitudinal and cross sections (800). Nuclei of muscle fibers Muscle fibers, longitudinal view Muscle fibers, cross-sectional view

11. Figure 12.1d Microscopic anatomy of skeletal muscle. • Sarcomeres • Organized group of myofilaments • Contractile units, smallest functional unit of muscle fiber • Z-line to Z-line M line Z disc Z disc Thin (actin) filament Elastic (titin) filaments Thick (myosin) filament I band: LIGHT • midline is Z line/disc • Thin only A band: DARK • Thick and thin • M line in middle

12. Myofilaments • Thick filaments: myosin • “cross-bridges” Contraction: myosin head changes shape & will grab onto actin…and pull it toward M-line Fig. 10-7

13. Myofilaments • Thin filaments: 3 types of protein molecules • actin • Tropomyosin • Troponin

14. Connective Tissue Wrappings:3 Layers • Epimysium = outer • Perimysium = central • Endomysium = inner

15. Connective Tissue Wrappings • Epimysium • Epi = on (outside layer) • Surrounds entire muscle

16. Connective Tissue Wrappings • Perimysium • Peri = around (central layer) • Divides muscle into compartments: • Fascicle = bundle of muscle fibers (cells) Fig. 10-1

17. Connective Tissue Wrappings • Endomysium • Endo = inside (inner layer) • Surrounds individual skeletal muscle cells (fibers) Fig. 10-1

18. Connective Tissues, cont. • Layers continuous & interwoven – blend into one another • Muscle’s ends: layers unite to form • Bundle: TENDON • Attach skeletal muscles to bones • Contraction pulls the bone(s) • Broad sheet: APONEUROSIS • Attach skeletal muscles to bones or other muscles

19. Connective tissue layers! • Muscle—covered by epimysium • Fascicles—covered by perimysium • Fiber (cell)—covered by endomysium • Myofibril—covered by sarcoplasmic reticulum • Sarcomere—contains thick and thin filaments

20. Figure 12.4 Connective tissue coverings of skeletal muscle. Epimysium Perimysium Epimysium Bone Endomysium Tendon Muscle fiber within a fascicle Blood vessel Perimysium wrapping a fascicle Endomysium (between individual muscle fibers) Muscle fiber Fascicle Perimysium

25. Blood & Nerve Supply • Muscles need lots of energy, lots of oxygen • Blood vessels supply these • Each fiber (cell) has capillary blood supply • Contraction stimulated by nerve impulses • Axons (nerve fibers) penetrate connective tissue layers, & innervate individual muscle fibers (cells)

26. How Muscles Contract: DVD

27. Neuromuscular Junction • Junction of motor neuron & a muscle fiber • MOTOR Neuron —elongated portion = axon • synaptic terminals • synaptic cleft

28. Neuromuscular Junction • Synaptic terminals • synaptic vesicles • Filled with acetylcholine (ACh) • Neurotransmitter • Release triggers muscle contraction • motor end plate • Sarcolemma, has receptors to bind ACh

29. Neuromuscular Junction “Action Potential” Fig. 10-10

30. Neuromuscular Junction • Motor unit = A single motor neuron & ALL the muscle fibers it controls Fig. 10-17

31. Figure 12.5 The neuromuscular junction. Synaptic vesicle containing ACh Sarcolemma Mitochondrion Synaptic cleft Axon terminal of motor neuron Fusing synaptic vesicles ACh Junctional folds of sarcolemma Sarcoplasm of muscle fiber ACh receptors

32. Figure 12.6 Photomicrograph of neuromuscular junctions (750). Terminal branch of an axon Axon terminal at neuromuscular junction Muscle fibers

33. Fig. 10-10

34. Fig. 10-10

36. Figure 12.6 Photomicrograph of neuromuscular junctions (750). Terminal branch of an axon Axon terminal at neuromuscular junction Muscle fibers

37. Review Figure 12.1

38. Review Figure 12.2

39. Review Figure 12.3 Action potential Nucleus Junctional folds of the sarcolemma Part of a myofibril