1. Copyright © John Wiley and Sons, Inc. All rights reserved. Chapter 10 Muscular Tissue Lecture slides prepared by Curtis DeFriez, Weber State University

2. Copyright © John Wiley and Sons, Inc. All rights reserved. Like nervous tissue, muscles are excitable or "irritable” they have the ability to respond to a stimulus Unlike nerves, however, muscles are also: Contractible (they can shorten in length) Extensible (they can extend or stretch) Elastic (they can return to their original shape) Functions of Muscular Tissue

3. Copyright © John Wiley and Sons, Inc. All rights reserved. Muscle makes up a large percentage of the body’s weight Their main functions are to: Create motion – muscles work with nerves, bones, and joints to produce body movements Stabilize body positions and maintain posture Store substances within the body using sphincters Move substances by peristaltic contractions Generate heat through thermogenesis Functions of Muscular Tissue

4. Copyright © John Wiley and Sons, Inc. All rights reserved. Three Types of Muscular Tissue

5. Copyright © John Wiley and Sons, Inc. All rights reserved. ( b) Cardiac muscle ( c) Visceral smooth muscle ( a) Skeletal muscle Three Types of Muscular Tissue

6. Copyright © John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle

7. Copyright © John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle

8. Copyright © John Wiley and Sons, Inc. All rights reserved. Skeletal muscle fibers are very long “cells” - next to neurons (which can be over a meter long), perhaps the longest in the body The Sartorious muscle contains single fibers that are at least 30 cm long A single sk eletal muscle fiber Skeletal Muscle

9. Copyright © John Wiley and Sons, Inc. All rights reserved. Sarcolemma Motor neuron Skeletal Muscle The terminal processes of a motor neuron in close proximity to the sarcolemma of a skeletal muscle fiber

10. Copyright © John Wiley and Sons, Inc. All rights reserved. The epimysium, perimysium, and endomysium all are continuous with the connective tissues that form tendons and ligaments (attach skeletal muscle to bone) and muscle fascia (connect muscles to other muscles to form groups of muscles) Organization of Muscle Tissue

11. Copyright © John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue Organization of a single muscle belly Epimysium Perimysium

12. Copyright © John Wiley and Sons, Inc. All rights reserved. Organization of a fasciculus Organization of Muscle Tissue

13. Copyright © John Wiley and Sons, Inc. All rights reserved. Organization of a muscle fiber Organization of Muscle Tissue

14. Copyright © John Wiley and Sons, Inc. All rights reserved. A muscle, a fasciculus, and a fiber all visualized Organization of Muscle Tissue

15. Copyright © John Wiley and Sons, Inc. All rights reserved. In groups of muscles the epimysium continues to become thicker, forming fascia which covers many muscles This graphic shows the fascia lata enveloping the entire group of quadriceps and hamstring muscles in the thing Organization of Muscle Tissue

16. Copyright © John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue Many large muscle groups are encased in both a superficial and a deep fascia Real Anatomy, John Wiley and Sons

17. Copyright © John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue An aponeurosis is essentially a thick fascia that connects two muscle bellies. This epicranial aponeurosis connects the muscle bellies of the occipitalis and the frontalis to form “one” muscle: The occipitofrontalis Epicranial aponeurosis Frontal belly of the occipitofrontalis m.

18. Copyright © John Wiley and Sons, Inc. All rights reserved. Veins, arteries, and nerves are located in the deep fascia between muscles of the thigh. Organization of Muscle Tissue

19. Copyright © John Wiley and Sons, Inc. All rights reserved. Beneath the connective tissue endomysium is found the plasma membrane (called the sarcolemma) of an individual skeletal muscle fiber The cytoplasm (sarcoplasm) of skeletal muscle fibers is chocked full of contractile proteins arranged in myofibrils The Skeletal Muscle Fiber

20. Copyright © John Wiley and Sons, Inc. All rights reserved. You should learn the names of the internal structures of the muscle fiber Sarcolemma Sarcoplasm Myofibril T-tubules Triad (with terminal cisterns Sarcoplasmic reticulum Sarcomere The Skeletal Muscle Fiber

21. Copyright © John Wiley and Sons, Inc. All rights reserved. The Skeletal Muscle Fiber Increasing the level of magnification, the myofibrils are seen to be composed of filaments Thick filaments Thing filaments

22. Copyright © John Wiley and Sons, Inc. All rights reserved. A scanning electron micrograph of a sarcomere The basic functional unit of skeletal muscle fibers is the sarcomere: An arrangement of thick and thin filaments sandwiched between two Z discs The Skeletal Muscle Fiber

23. Copyright © John Wiley and Sons, Inc. All rights reserved. The “Z line” is really a Z disc when considered in 3 dimensions. A sarcomere extends from Z disc to Z disc. Muscle contraction occurs in the sarcomeres The Skeletal Muscle Fiber

24. Copyright © John Wiley and Sons, Inc. All rights reserved. Myofibrils are built from three groups of proteins Contractile proteins generate force during contraction Regulatory proteins help switch the contraction process on and off Structural proteins keep the thick and thin filaments in proper alignment and link the myofibrils to the sarcolemma and extracellular matrix Muscle Proteins

25. Copyright © John Wiley and Sons, Inc. All rights reserved. The thin filaments are comprised mostly of the structural protein actin, and the thick filaments are comprised mostly of the structural protein myosin However, in both types of filaments, there are also other structural and regulatory proteins Muscle Proteins

26. Copyright © John Wiley and Sons, Inc. All rights reserved. In the thin filaments actin proteins are strung together like a bead of pearls In the thick filaments myosin proteins look like golf clubs bound together Muscle Proteins

27. Copyright © John Wiley and Sons, Inc. All rights reserved. In this first graphic, the myosin binding sites on the actin proteins are readily visible. The regulatory proteins troponin and tropomyosin have been added to the bottom graphic: The myosin binding sites have been covered Muscle Proteins

28. Copyright © John Wiley and Sons, Inc. All rights reserved. In this graphic the troponin-tropomyosin complex has slid down into the “gutters” of the actin molecule unblocking the myosin binding site The troponin-tropomyosin complex can slide back and forth depending on the presence of Ca 2+ Myosin binding site exposed Muscle Proteins

29. Copyright © John Wiley and Sons, Inc. All rights reserved. Ca 2+ binds to troponin which changes the shape of the troponin-tropomyosin complex and uncovers the myosin binding sites on actin Muscle Proteins

30. Copyright © John Wiley and Sons, Inc. All rights reserved. Besides contractile and regulatory proteins, muscle contains about a dozen structural proteins which contribute to the alignment, stability, elasticity, and extensibility of myofibrils Titan is the third most plentiful protein in muscle, after actin and myosin - it extends from the Z disc and accounts for much of the elasticity of myofibrils Dystrophin is discussed later as it relates to the disease of muscular dystrophy Muscle Proteins

31. Copyright © John Wiley and Sons, Inc. All rights reserved. With exposure of the myosin binding sites on actin (the thin filaments)—in the presence of Ca 2+ and ATP—the thick and thin filaments “slide” on one another and the sarcomere is shortened The Sliding-Filament Mechanism

32. Copyright © John Wiley and Sons, Inc. All rights reserved. The “sliding” of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 step process The Sliding-Filament Mechanism

33. Copyright © John Wiley and Sons, Inc. All rights reserved. Step 1: ATP hydrolysis Step 2: Attachment

34. Copyright © John Wiley and Sons, Inc. All rights reserved. Step 3: Power Stroke Step 4: Detachment

35. Copyright © John Wiley and Sons, Inc. All rights reserved. The Sliding-Filament Mechanism

36. Copyright © John Wiley and Sons, Inc. All rights reserved. Contraction and Movement Overview Interactions Animation Contraction and Movement You must be connected to the internet to run this animation.

37. Copyright © John Wiley and Sons, Inc. All rights reserved. Limited contact between actin and myosin Compressed thick filaments Length-Tension Relationship Sarcomere shortening produces tension within a muscle

38. Copyright © John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling We will come back to the term excitation-contraction coupling in a little bit Before we can describe the entire process, from thinking of moving a muscle to actual contraction of sarcomeres, we must first explore the processes that occur at the neuromuscular junction

39. Copyright © John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction coupling (EC coupling) involves events at the junction between a motor neuron and a skeletal muscle fiber Neuromuscular Junction

40. Copyright © John Wiley and Sons, Inc. All rights reserved. An enlarged view of the neuromuscular junction The presynaptic membrane is on the neuron while the postsynaptic membrane is the motor end plate on the muscle cell. The two membranes are separated by a space, or “cleft” Neuromuscular Junction

41. Copyright © John Wiley and Sons, Inc. All rights reserved. Conscious thought (to move a muscle) results in activation of a motor neuron, and release of the neurotransmitter acetylcholine (AcCh) at the NM junction The enzyme acetylcholinesterase breaks down AcCh after a short period of time Neuromuscular Junction

42. Copyright © John Wiley and Sons, Inc. All rights reserved. The plasma membrane on the “far side” of the NMJ belongs to the muscle cell and is called the motor end plate The motor end plate is rich in chemical (ligand) - gated sodium channels that respond to AcCh. Another way to say this: The receptors for AcCh are on the ligand-gated sodium channels on the motor end plate Neuromuscular Junction

43. Copyright © John Wiley and Sons, Inc. All rights reserved. The chemical events at the NMJ transmit the electrical events of a neuronal action potential into the electrical events of a muscle action potential Neuromuscular Junction

44. Copyright © John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction Interactions Animation Neuromuscular Junctions You must be connected to the internet to run this animation.

45. Copyright © John Wiley and Sons, Inc. All rights reserved. The muscle AP is propagated over the surface of the muscle cell membrane (sarcolemma) via voltage (electrical)-gated Na + and K + channels Muscle Action Potential

46. Copyright © John Wiley and Sons, Inc. All rights reserved. By placing a micropipette inside a muscle cell, and then measuring the electrical potential across the cell membrane, the phases of an action potential (AP) can be graphed (as in this figure) Muscle Action Potential

47. Copyright © John Wiley and Sons, Inc. All rights reserved. The behavior of the Na + and K + channels, at various points in the AP, are seen in this graphic Na + gates open during the depolarization phase K + gates open during the repolarization phase Muscle Action Potential

48. Copyright © John Wiley and Sons, Inc. All rights reserved. Generating An Action Potential The flow of ions through cell a membrane looks a lot like a "piece" of electricity flowing through a wire (but not as fast) Generating an AP on the muscle membrane involves the transfer of information from an electrical signal (down the neuron), to a chemical signal (at the NMJ), back to an electrical signal (depolarization of the sarcolemma) This added complexity (changing from electrical to chemical back to electrical signals) provides necessary control of the process

49. Copyright © John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling

50. Copyright © John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling EC coupling involves putting it all together The thought process going on in the brain The AP arriving at the neuromuscular junction The regeneration of an AP on the muscle membrane Release of Ca 2+ from the sarcoplasmic reticulum Sliding of thick on thin filaments in sarcomeres Generation of muscle tension (work)

51. Copyright © John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling

52. Copyright © John Wiley and Sons, Inc. All rights reserved. The brain The motor neuron Acetylcholine (ACh) Acetylcholinesterase enzyme Ach receptors on the motor endplate Na + -K + channels on the sarcolemma Na + flow K + flow Regenerate AP The T-tubules The SR Ca 2+ release Troponin/Tropomyosin ATP Myosin binding Filaments slide Muscles contract Role Players in E-C coupling Excitation-Contraction Coupling

53. Copyright © John Wiley and Sons, Inc. All rights reserved. Contraction of Sarcomere Interactions Animation Contraction of a Sarcomere You must be connected to the internet to run this animation.

54. Copyright © John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy Stored ATP 3 seconds Energy transferred from stored creatine phosphate 12 seconds Aerobic ATP production Anaerobic glucose use 30-40 seconds

55. Copyright © John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy

56. Copyright © John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy

57. Copyright © John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy

58. Copyright © John Wiley and Sons, Inc. All rights reserved. In a state of homeostasis, muscle use of O 2 and nutrients is balanced by the production of manageable levels of waste products like CO 2 Heat - 70-80% of the energy used by muscles is lost as heat - muscle activity is important for maintaining body temperature Lactic acid (anaerobic) Skeletal Muscle Metabolism

59. Copyright © John Wiley and Sons, Inc. All rights reserved. Oxygen Debt, or "Excess Post-Exercise Oxygen Consumption" (EPOC) is the amount of O 2 repayment required after exercise in skeletal muscle to: Replenish ATP stores Replenish creatine phosphate and myoglobin stores Convert lactic acid back into pyruvate so it can be used in the Krebs cycle to replenish ATP Skeletal Muscle Metabolism

60. Copyright © John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Metabolism

61. Copyright © John Wiley and Sons, Inc. All rights reserved. Muscle Metabolism You must be connected to the internet to run this animation.

62. Copyright © John Wiley and Sons, Inc. All rights reserved. Cardiac and Smooth Muscle Metabolism In response to a single AP, cardiac muscle contracts 10-15 times longer than skeletal muscle, and must continue to do so, without rest, for the life of the individual To meet this constant demand, cardiac muscle generally uses the rich supply of O 2 delivered by the extensive coronary circulation to generate ATP through aerobic respiration

63. Copyright © John Wiley and Sons, Inc. All rights reserved. Cardiac and Smooth Muscle Metabolism Like cardiac muscle, smooth muscle (in your deep organs) is autorhythmic and is not under voluntary control (your heart beats and your stomach digests without you thinking about it). Unlike cardiac (and skeletal muscle) however, smooth muscle has a low capacity for generating ATP and does so only through anaerobic respiration (glycolysis)

64. Copyright © John Wiley and Sons, Inc. All rights reserved. Motor Unit is composed of a motor neuron plus all of the muscle cells it innervates  High precision Fewer muscle fibers per neuron Laryngeal and extraocular muscles (2-20)  Low precision Many muscle fibers per neuron Thigh muscles (2,000-3,000) The Motor Unit

65. Copyright © John Wiley and Sons, Inc. All rights reserved. Florescent dye is used to show the terminal processes of a single neuron which terminate on a few muscle fibers The Motor Unit

66. Copyright © John Wiley and Sons, Inc. All rights reserved. Activities requiring extreme precision (like the subtle and rapid movements of the eye) involve muscles with very small motor units (1-4 muscle fibers/neuron) The Motor Unit

67. Copyright © John Wiley and Sons, Inc. All rights reserved. All-or-none principle of muscle contraction When an individual muscle fiber is stimulated to depolarization, and an action potential is propagated along its sarcolemma, it must contract to it’s full force— it can’t partially contract Also, when a single motor unit is recruited to contract, all the muscle fibers in that motor unit must all contract at the same time The Motor Unit

68. Copyright © John Wiley and Sons, Inc. All rights reserved. Skeletal muscle fibers are not all alike in appearance or function. By appearance: Red muscle fibers (the dark meat in chicken legs) have a high myoglobin content, more mitochondria, more energy stores, and a greater blood supply White muscle fibers (the white meat in chicken breasts) have less myoglobin, mitochondria, and blood supply Skeletal Muscle Fiber Types

69. Copyright © John Wiley and Sons, Inc. All rights reserved. Slow oxidative fibers (SO) are small, appear dark red, are the least powerful type. They are very fatigue resistant Used for endurance like running a marathon Fast oxidative-glycolytic fibers (FOG) are intermediate in size, appear dark red, and are moderately resistant to fatigue. Used for walking Fast glycolytic fibers (FG) are large, white, and powerful Suited to intense anaerobic activity of short duration Skeletal Muscle Fiber Types

70. Copyright © John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Fiber Types

71. Copyright © John Wiley and Sons, Inc. All rights reserved. Most skeletal muscles are a mixture of all three types of skeletal muscle fibers; about half the fibers in a typical skeletal muscle are slow oxidative (SO) fibers Within a particular motor unit all the skeletal muscle fibers are the same type The different motor units in a muscle are recruited in a specific order depending on the task being performed (fast anaerobic activity for maximal force, etc.) Skeletal Muscle Fiber Types

72. Copyright © John Wiley and Sons, Inc. All rights reserved. There is a brief delay called the latent period as the AP sweeps over the sarcolemma and Ca 2+ ions are released from the sarcoplasmic reticulum (SR) During the next phase the fiber is actively contracting This is followed by relaxation as the Ca 2+ ions are re- sequestered into the SR and myosin binding sites are covered by tropomyosin Temporary loss of excitability is call the refractory period – All muscle fibers in a motor unit will not respond to a stimulus during this short time Tension in a Muscle

73. Copyright © John Wiley and Sons, Inc. All rights reserved. A twitch is recorded when a stimulus that results in contraction (force) of a single muscle fiber is measured over a very brief millisecond time frame Tension in a Muscle

74. Copyright © John Wiley and Sons, Inc. All rights reserved. Applying increased numbers of action potentials to a muscle fiber (or a fascicle, a muscle, or a muscle group) results in fusion of contractions (tetanus) and the performance of useful work Tension in a Muscle

75. Copyright © John Wiley and Sons, Inc. All rights reserved. Two motor units, one in green, the other in purple, demonstrate the concept of progressive activation of a muscle known as recruitment Recruitment allows a muscle to accomplish increasing gradations of contractile strength Tension in a Muscle

76. Copyright © John Wiley and Sons, Inc. All rights reserved. Muscle Tension Interactions Animation Control of Muscle Tension You must be connected to the internet to run this animation.

77. Copyright © John Wiley and Sons, Inc. All rights reserved. Muscle Contraction Isotonic contractions results in movement Concentric isotonic is a type of muscle contraction in which the muscle shorten while generating force Eccentric isotonic is a contraction in which muscle tension is less than the resistance (the muscle lengthens) Isometric contractions results in no movement Muscle force and resistance are equal Supporting objects in a fixed position and posture

78. Copyright © John Wiley and Sons, Inc. All rights reserved. Muscle Contraction

79. Copyright © John Wiley and Sons, Inc. All rights reserved. Exercise-induced muscle damage After intense exercise electron micrographs reveal considerable muscle damage including torn sarcolemmas and disrupted Z-discs Blood levels of proteins normally confined only to muscle (including myoglobin and the enzyme creatine kinase) increase as they are released from damaged muscle Imbalances of Homeostasis

80. Copyright © John Wiley and Sons, Inc. All rights reserved. Spasm A sudden involuntary contraction of a single muscle within a large group of muscles – usually painless Cramp Involuntary and often painful muscle contractions Caused by inadequate blood flow to muscles (such as in dehydration), overuse and injury, and abnormal blood electrolyte levels Imbalances of Homeostasis

81. Copyright © John Wiley and Sons, Inc. All rights reserved. Disease States and Disorders Fibrosis (myofibrosis)  Replacement of muscle fibers by excessive amounts of connective tissues (fibrous scar tissue) Myosclerosis  Hardening of the muscle caused by calcification Both myosclerosis and muscle fibrosis occur as a result of trauma and various metabolic disorders Imbalances of Homeostasis

82. Copyright © John Wiley and Sons, Inc. All rights reserved. Aging In part due to decreased levels of physical activity, with aging humans undergo a slow, progressive loss of skeletal muscle mass that is replaced largely by fibrous connective tissue and adipose tissue Muscle strength at 85 is about half that at age 25 Compared to the other two fiber types, the relative number of slow oxidative fibers appears to increase Imbalances of Homeostasis