1. BIOLOGY 251 Human Anatomy & Physiology Chapter 10 Muscle Tissue Lecture Notes

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

3. Properties of Muscle Tissue Extensibility –ability to be stretched without damaging the tissue Elasticity –ability to return to original shape after being stretched Excitability –respond to chemicals released from nerve cells Conductivity –ability to propagate electrical signals over membrane Contractility –ability to shorten and generate force

4. 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

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. Three Types of Muscular Tissue

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

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

9. 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

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 a fasciculus Organization of Muscle Tissue

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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 Thin filaments

19. 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

20. 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

21. 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

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

23. 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

24. 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

25. 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

26. 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

27. 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

28. Copyright © John Wiley and Sons, Inc. All rights reserved. Structural proteins cont’d. Myomesin is the protein that forms the M line. The M line proteins bind to Titan and connect the adjacent thick filaments to one another and hold they in alignment at the M line. Nebulin is a long non-elastic protein wrapped around the entire length of each thin filament. It helps anchor the thin filaments to the Z disc. Muscle Proteins

29. 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

30. 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

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

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

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

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

35. 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

36. 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 Anaerobic glucose use 30-40 seconds Aerobic ATP production Minutes - hours

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

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

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

40. 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

41. 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

42. 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 (ACh) at the NM junction The enzyme acetylcholinesterase breaks down ACh after a short period of time Neuromuscular Junction

43. 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 ACh. Another way to say this: The receptors for ACh are on the ligand-gated sodium channels on the motor end plate Neuromuscular Junction

44. 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

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. Excitation-Contraction Coupling

49. 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)

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

51. 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

52. 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

53. 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

54. 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

55. 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

56. 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

57. 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

58. 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

59. 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

60. Copyright © John Wiley and Sons, Inc. All rights reserved. Figure 2.4