1. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Human Anatomy & Physiology SEVENTH EDITION Elaine N. Marieb Katja Hoehn PowerPoint ® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community College C H A P T E R 9 Muscles and Muscle Tissue P A R T A

2. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Overview  The three types of muscle tissue are cardiac, smooth and skeletal  These types differ in structure, location, function, and means of activation PLAY InterActive Physiology ®: Anatomy Review: Skeletal Muscle Tissue, page 3

3. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Function  Skeletal muscles are responsible for all locomotion, plus to maintain posture, stabilize joints, and generate heat.  Cardiac muscle is responsible for pushing the blood through the body  Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs

4. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Similarities  Skeletal and smooth muscle cells are elongated and are called muscle fibers  Muscle contraction depends on two kinds of myofilaments – actin and myosin  Muscle terminology is similar  Sarcolemma – muscle plasma membrane  Sarcoplasm – cytoplasm of a muscle cell  Prefixes – myo, mys, and sarco all refer to muscle

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cardiac Muscle Tissue  Occurs only in the heart  Is striated like skeletal muscle but is not voluntary  Contracts at a fairly steady rate set by the heart’s pacemaker  Neural controls allow the heart to respond to changes in bodily needs

6. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Smooth Muscle Tissue  Found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages  Forces food and other substances through internal body channels  It is not striated and is not voluntary

7. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle  Each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue

8. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle Tissue  Is controlled voluntarily (by conscious control)  Contracts rapidly but tires easily  Is responsible for overall body motility  Is extremely adaptable and can exert forces ranging from a fraction of an ounce to over 70 pounds

9. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Contracted vs, not contracted

10. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functional Characteristics of Muscle Tissue  Excitability, or irritability – the ability to receive and respond to stimuli  Contractility – the ability to shorten forcibly  Extensibility – the ability to be stretched or extended  Elasticity – the ability to recoil and resume the original resting length

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure and Organization of Skeletal Muscle Table 9.1a

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure and Organization of Skeletal Muscle Table 9.1b

13. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle  The three connective tissue sheaths are:  Endomysium –areolar and reticular fibers surrounding each muscle fiber  Perimysium – fibrous connective tissue that surrounds groups of muscle fibers (cells) called fascicles  Epimysium –dense irregular connective tissue that surrounds the entire muscle

14. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle: Nerve and Blood Supply  Each muscle is served by one nerve, an artery, and one or more veins  Each skeletal muscle fiber is supplied with a nerve ending that controls contraction  Contracting fibers require continuous delivery of oxygen and nutrients via arteries  Wastes must be removed via veins

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

16. Skeletal Muscle: Attachments  Most skeletal muscles span joints and are attached to bone in at least two places  When muscles contract, the movable bone (insertion) moves toward the immovable bone (origin)

17. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle: Attachments  Muscles attach:  Directly – epimysium of the muscle is fused to the periosteum of a bone  Indirectly – connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis

18. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of a Skeletal Muscle Fiber  Each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma  Fibers are 10 to 100  m in diameter, and up to 30 centimeters long

19. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of a Skeletal Muscle Fiber  Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin  Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules

20. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myofibrils  Myofibrils are densely packed, rodlike contractile elements  They make up most of the muscle volume  The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident Cell Myofibril

21. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myofibrils Figure 9.3b

22. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sarcomeres  The smallest contractile unit of a muscle  The region of a myofibril between two successive Z discs  Composed of myofilaments made up of contractile proteins  Myofilaments are of two types – thick and thin

23. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sarcomeres Figure 9.3c

24. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myofilaments: Banding Pattern  Thick filaments – extend the entire length of an A band  Thin filaments – extend across the I band and partway into the A band  Z-disc – coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another

25. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myofilaments: Banding Pattern Figure 9.3c,d

26. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Ultrastructure of Myofilaments: Thick Filaments  Thick filaments are composed of the protein myosin  Each myosin molecule has a rod-like tail and two globular heads

27. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Ultrastructure of Myofilaments: Thin Filaments  Thin filaments are chiefly composed of the protein actin  Contain sites to which myosin heads attach during contraction  Tropomyosin and troponin are regulatory subunits bound to actin

28. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Arrangement of the Filaments in a Sarcomere  Longitudinal section within one sarcomere Figure 9.4d

29. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sarcoplasmic Reticulum (SR)  SR is endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril  Terminal cisternae form perpendicular cross channels  Functions in the regulation of intracellular calcium levels

30. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sarcoplasmic Reticulum (SR)  T tubules penetrate into the cell’s interior at each A band–I band junction  T tubules associate with the paired terminal cisternae to form triads

31. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings T Tubules  T tubules are continuous with the sarcolemma  They conduct impulses to the deepest regions of the muscle  These impulses signal for the release of Ca 2+ from adjacent terminal cisternae

32. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sliding Filament Model of Contraction  Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree  In the relaxed state, thin and thick filaments overlap only slightly  Upon stimulation, myosin heads bind to actin and sliding begins

33. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sliding Filament Model of Contraction  Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere  As this event occurs throughout the sarcomeres, the muscle shortens

34. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle Contraction  In order to contract, a skeletal muscle must:  Be stimulated by a nerve ending  Propagate an electrical current, or action potential, along its sarcolemma  Have a rise in intracellular Ca 2+ levels, the final trigger for contraction

35. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Stimulus of Skeletal Muscle  Skeletal muscles are stimulated by motor neurons of the somatic nervous system  Axons of these neurons travel in nerves to muscle cells  Axons of motor neurons branch profusely as they enter muscles  Each axonal branch forms a neuromuscular junction with a single muscle fiber

36. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction  The neuromuscular junction is formed from:  Axonal endings, have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh)  The motor end plate of a muscle is a specific part of the sarcolemma that contains ACh receptors and helps form the neuromuscular junction  Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft

37. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction Figure 9.7 (a-c)

38. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction  When a nerve impulse reaches the end of an axon at the neuromuscular junction:  Voltage-regulated calcium channels open and allow Ca 2+ to enter the axon  Ca 2+ inside the axon terminal causes axonal vesicles to fuse with the axonal membrane

39. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction  This fusion releases ACh into the synaptic cleft via exocytosis  ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma  Binding of ACh to its receptors initiates an action potential in the muscle

40. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Destruction of Acetylcholine  ACh bound to ACh receptors is quickly destroyed by the enzyme acetylcholinesterase  This destruction prevents continued muscle fiber contraction in the absence of additional stimuli  Events at the neuromuscular junction Events at the neuromuscular junction  Generation of an action potential

41. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Excitation-Contraction Coupling  Excitation-Contraction Coupling Excitation-Contraction Coupling

42. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 ADP PiPi Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca 2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites on actin; contraction ends and muscle fiber relaxes. Ca 2+ 1 2 3 4 5 6

43. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma.

44. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. 1

45. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. SR Ca 2+ 1 2

46. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. SR Ca 2+ 1 2 3

47. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. SR Ca 2+ 1 2 3 4

48. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca 2+ by active transport into the SR after the action potential ends. SR Ca 2+ 1 2 3 4 5

49. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 ADP PiPi Net entry of Na + Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synaptic vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca 2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca 2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites on actin; contraction ends and muscle fiber relaxes. Ca 2+ 1 2 3 4 5 6

50. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sequential Events of Contraction  Cross bridge formation – myosin cross bridge attaches to actin filament Cross bridge formation  Working (power) stroke – myosin head pivots and pulls actin filament toward M line  Cross bridge detachment – ATP attaches to myosin head and the cross bridge detaches  “Cocking” of the myosin head – energy from hydrolysis of ATP cocks the myosin head into the high-energy state PLAY InterActive Physiology ®: Sliding Filament Theory, pages 3-29

51. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ATP ADP ATP hydrolysis ADP ATP PiPi PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and P i, the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) As new ATP attaches to the myosin head, the link between myosin and actin weakens, and the cross bridge detaches. Thick filament 1 4 2 3

52. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ADP PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. 1

53. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ADP PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. 1 2

54. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ADP ATP PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. 1 2 Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released.

55. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ATP ADP ATP PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Myosin head (low-energy configuration) As new ATP attaches to the myosin head, the link between myosin and actin weakens, and the cross bridge detaches. 1 2 3 Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released.

56. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ATP ADP ATP hydrolysis ADP ATP PiPi PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and P i, the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) As new ATP attaches to the myosin head, the link between myosin and actin weakens, and the cross bridge detaches. Thick filament 1 4 2 3

57. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ATP ADP ATP hydrolysis ADP ATP PiPi PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and P i, the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) As new ATP attaches to the myosin head, the link between myosin and actin weakens, and the cross bridge detaches. Thick filament 1 4 2 3

58. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Contraction of Skeletal Muscle Fibers  Contraction – refers to the activation of myosin’s cross bridges (force-generating sites)  Shortening occurs when the tension generated by the cross bridge exceeds forces opposing shortening  Contraction ends when cross bridges become inactive, the tension generated declines, and relaxation is induced

59. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Overview – Contraction of a Skeletal Muscle  Principles of muscle mechanics:  Force exerted by a contracting muscle on an object is muscle tension.  Opposing force on the muscle by the weight of the object is called the load.  A contracting muscle does not always shorted and move the load.  Isometric vs. Isotonic  A muscle contracts with varying force and for different periods of time in response to stimuli

60. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Motor Unit  Each muscle is served by at least one motor nerve  Contains axons of up to hundreds of motor neurons.

61. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Motor Unit  A motor unit = motor neuron and all the muscle fibers it supplies.motor unit  Motor neuron fires - all of the fibers it innervates contract  May have as many as several hundred or as few as four  Fine control vs. gross (large) movements  Muscle fibers are spread out within a unit  Stimulation of a single motor unit causes a weak contraction of the entire muscle.

62. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Muscle Twitch  Muscle twitch = the response of the motor unit to a single action potential  The muscle fibers contract quickly and then relax 1.Latent: excitation- contraction coupling is occurring 2.Contraction: cross bridges are active 3.Relaxation: initiated by reentry of Ca 2+ into the SR

63. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Developmental Aspects  All muscle tissues develop from embryonic mesoderm cells called myoblasts  Skeletal muscle myoblasts fuse (multiple nuclei)  Cardiac and Smooth develop gap junctions  Smooth muscle has good ability to regenerate throughout life  Muscle mass differs between sexes due to testosterone  Muscle is highly vascularized – resistant to infection