1. Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College Chapter 6 The Muscular System © 2015 Pearson Education, Inc.

2. The Muscular System  Muscles are responsible for all types of body movement  Three basic muscle types are found in the body 1.Skeletal muscle 2.Cardiac muscle 3.Smooth muscle © 2015 Pearson Education, Inc.

3. Characteristics of Muscles  Skeletal and smooth muscle cells are elongated (muscle cell  muscle fiber)  Contraction and shortening of muscles is due to the movement of microfilaments  All muscles share some terminology  Prefixes myo and mys refer to “muscle”  Prefix sarco refers to “flesh” © 2015 Pearson Education, Inc.

4. Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (1 of 3)

5. © 2015 Pearson Education, Inc. Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (2 of 3)

6. © 2015 Pearson Education, Inc. Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (3 of 3)

7. Skeletal Muscle Characteristics  Most are attached by tendons to bones  Cells are multinucleate  Striated—have visible banding  Voluntary—subject to conscious control © 2015 Pearson Education, Inc.

8. Connective Tissue Wrappings of Skeletal Muscle  Cells are surrounded and bundled by connective tissue  Endomysium—encloses a single muscle fiber  Perimysium—wraps around a fascicle (bundle) of muscle fibers  Epimysium—covers the entire skeletal muscle  Fascia—on the outside of the epimysium © 2015 Pearson Education, Inc.

9. Figure 6.1 Connective tissue wrappings of skeletal muscle. Blood vessel Perimysium Muscle fiber (cell) Fascicle (wrapped by perimysium) Endomysium (between fibers) Tendon Bone Epimysium (wraps entire muscle)

10. Skeletal Muscle Attachments  Epimysium blends into a connective tissue attachment  Tendons—cordlike structures  Mostly collagen fibers  Often cross a joint because of their toughness and small size  Aponeuroses—sheetlike structures  Attach muscles indirectly to bones, cartilages, or connective tissue coverings © 2015 Pearson Education, Inc.

11. Skeletal Muscle Attachments  Sites of muscle attachment  Bones  Cartilages  Connective tissue coverings © 2015 Pearson Education, Inc.

12. Smooth Muscle Characteristics  Lacks striations  Spindle-shaped cells  Single nucleus  Involuntary—no conscious control  Found mainly in the walls of hollow visceral organs (such as stomach, urinary bladder, respiratory passages) © 2015 Pearson Education, Inc.

13. Figure 6.2a Arrangement of smooth and cardiac muscle cells. Mucosa Circular layer of smooth muscle (longitudinal view of cells) Submucosa (a) Longitudinal layer of smooth muscle (cross-sectional view of cells)

14. Cardiac Muscle Characteristics  Striations  Usually has a single nucleus  Branching cells  Joined to another muscle cell at an intercalated disc  Involuntary  Found only in the walls of the heart © 2015 Pearson Education, Inc.

15. Figure 6.2b Arrangement of smooth and cardiac muscle cells. Cardiac muscle bundles (b)

16. Skeletal Muscle Functions  Produce movement  Maintain posture  Stabilize joints  Generate heat © 2015 Pearson Education, Inc.

17. Microscopic Anatomy of Skeletal Muscle  Sarcolemma—specialized plasma membrane  Myofibrils—long organelles inside muscle cell  Light (I) bands and dark (A) bands give the muscle its striped appearance © 2015 Pearson Education, Inc.

18. Figure 6.3a Anatomy of a skeletal muscle fiber (cell). Sarcolemma Myofibril Nucleus Dark (A) band Light (I) band (a) Segment of a muscle fiber (cell)

19. Stimulation and Contraction of Single Skeletal Muscle Cells  Irritability (also called responsiveness)—ability to receive and respond to a stimulus  Contractility—ability to shorten when an adequate stimulus is received  Extensibility—ability of muscle cells to be stretched  Elasticity—ability to recoil and resume resting length after stretching © 2015 Pearson Education, Inc.

20. The Nerve Stimulus and Action Potential  Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract  Motor unit—one motor neuron and all the skeletal muscle cells stimulated by that neuron © 2015 Pearson Education, Inc.

21. Figure 6.4a Motor units. Spinal cord Motor neuron cell bodies Muscle Muscle fibers (a) Axon terminals at neuromuscular junctions Motor unit 1 Motor unit 2 Nerve Axon of motor neuron

22. © 2015 Pearson Education, Inc. Figure 6.4b Motor units. Branching axon to motor unit (b) Axon terminals at neuromuscular junctions Muscle fibers

23. The Nerve Stimulus and Action Potential  Neuromuscular junction  Association site of axon terminal of the motor neuron and sarcolemma of a muscle  Neurotransmitter  Chemical released by nerve upon arrival of nerve impulse in the axon terminal  Acetylcholine (ACh) is the neurotransmitter that stimulates skeletal muscle © 2015 Pearson Education, Inc.

24. The Nerve Stimulus and Action Potential  Synaptic cleft  Gap between nerve and muscle  Nerve and muscle do not make contact  Filled with interstitial fluid © 2015 Pearson Education, Inc.

25. Transmission of Nerve Impulse to Muscle  When a nerve impulse reaches the axon terminal of the motor neuron, 1.Calcium channels open, and calcium ions enter the axon terminal 2.Calcium ion entry causes some synaptic vesicles to release acetylcholine (ACh) 3.ACh diffuses across the synaptic cleft and attaches to receptors on the sarcolemma of the muscle cell © 2015 Pearson Education, Inc.

26. Transmission of Nerve Impulse to Muscle 4.If enough ACh is released, the sarcolemma becomes temporarily more permeable to sodium (Na  )  Sodium rushes into the cell, and potassium leaves the cell 5.Depolarization opens more sodium channels that allow sodium ions to enter the cell  Once started, the action potential cannot be stopped, and contraction occurs © 2015 Pearson Education, Inc.

27. Transmission of Nerve Impulse to Muscle 6.Acetylcholinesterase (AChE) breaks down acetylcholine into acetic acid and choline  AChE ends muscle contraction © 2015 Pearson Education, Inc.

28. Transmission of Nerve Impulse to Muscle  Cell returns to its resting state when: 1.Potassium ions diffuse out of the cell 2.Sodium-potassium pump moves sodium and potassium ions back to their original positions © 2015 Pearson Education, Inc.

29. Figure 6.5 Events at the neuromuscular junction. Action potential reaches axon terminal of motor neuron. 1 Slide 2 Nerve impulse Nucleus Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Synaptic vesicle containing ACh Axon terminal of motor neuron Mitochondrion Sarcolemma Fusing synaptic vesicle Sarcoplasm of muscle fiber Folds of sarcolemma ACh receptor Ca 2+ Synaptic cleft ACh

30. © 2015 Pearson Education, Inc. Figure 6.5 Events at the neuromuscular junction.Slide 3 Action potential reaches axon terminal of motor neuron. 2 Calcium (Ca 2+ ) channels open, and Ca 2+ enters the axon terminal. 1 Synaptic vesicle containing ACh Axon terminal of motor neuron Mitochondrion Sarcolemma Fusing synaptic vesicle Sarcoplasm of muscle fiber Folds of sarcolemma ACh receptor Ca 2+ Synaptic cleft ACh

31. © 2015 Pearson Education, Inc. Figure 6.5 Events at the neuromuscular junction.Slide 4 Action potential reaches axon terminal of motor neuron. 2 Calcium (Ca 2+ ) channels open, and Ca 2+ enters the axon terminal. 3 Ca 2+ entry causes some synaptic vesicles to release their contents (acetylcholine, a neurotransmitter) by exocytosis. 1 Synaptic vesicle containing ACh Axon terminal of motor neuron Mitochondrion Sarcolemma Fusing synaptic vesicle Sarcoplasm of muscle fiber Folds of sarcolemma ACh receptor Ca 2+ Synaptic cleft ACh

32. © 2015 Pearson Education, Inc. Figure 6.5 Events at the neuromuscular junction.Slide 5 Action potential reaches axon terminal of motor neuron. 2 Calcium (Ca 2+ ) channels open, and Ca 2+ enters the axon terminal. 4 3 Ca 2+ entry causes some synaptic vesicles to release their contents (acetylcholine, a neurotransmitter) by exocytosis. Acetylcholine diffuses across the synaptic cleft and binds to receptors in the sarcolemma. 1 Synaptic vesicle containing ACh Axon terminal of motor neuron Mitochondrion Sarcolemma Fusing synaptic vesicle Sarcoplasm of muscle fiber Folds of sarcolemma ACh receptor Ca 2+ Synaptic cleft ACh

33. © 2015 Pearson Education, Inc. Figure 6.5 Events at the neuromuscular junction.Slide 6 Ion channel in sarcolemma opens; ions pass. Na + K+K+ 5 ACh binds and channels open that allow simultaneous passage of Na + into the muscle fiber and K + out of the muscle fiber. More Na + ions enter than K + ions leave, producing a local change in the electrical conditions of the membrane (depolarization). This eventually leads to an action potential.

34. © 2015 Pearson Education, Inc. Figure 6.5 Events at the neuromuscular junction.Slide 7 Ion channel closed; ions cannot pass. Degraded ACh K+K+ Na + ACh Acetylcholine- sterase The enzyme acetylcholinesterase breaks down ACh in the synaptic cleft, ending the process. 6

35. Contraction of Skeletal Muscle  Muscle fiber contraction is “all or none”  Within a skeletal muscle, not all fibers may be stimulated during the same interval  Different combinations of muscle fiber contractions may give differing responses  Graded responses—different degrees of skeletal muscle shortening © 2015 Pearson Education, Inc.

36. Contraction of Skeletal Muscle  Graded responses can be produced by changing:  The frequency of muscle stimulation  The number of muscle cells being stimulated at one time © 2015 Pearson Education, Inc.

37. Types of Graded Responses  Twitch  Single, brief contraction  Not a normal muscle function © 2015 Pearson Education, Inc.

38. Figure 6.9a A whole muscle’s response to different rates of stimulation. (a) Twitch (Stimuli) Tension (g)

39. Types of Graded Responses  Summing of contractions  One contraction is immediately followed by another  Because stimulations are more frequent, the muscle does not completely return to a resting state  The effects are “summed” (added) © 2015 Pearson Education, Inc.

40. Figure 6.9b A whole muscle’s response to different rates of stimulation. (Stimuli) Tension (g) (b) Summing of contractions

41. Types of Graded Responses  Unfused (incomplete) tetanus  Some relaxation occurs between contractions, but nerve stimuli arrive at an even faster rate than during summing of contractions  Unless the muscle contraction is smooth and sustained, it is said to be in unfused tetanus © 2015 Pearson Education, Inc.

42. Figure 6.9c A whole muscle’s response to different rates of stimulation. (Stimuli) Tension (g) (c) Unfused (incomplete) tetanus

43. Types of Graded Responses  Fused (complete) tetanus  No evidence of relaxation before the following contractions  Frequency of stimulations does not allow for relaxation between contractions  The result is a smooth and sustained muscle contraction © 2015 Pearson Education, Inc.

44. Figure 6.9d A whole muscle’s response to different rates of stimulation. (Stimuli) Tension (g) (d) Fused (complete) tetanus

45. Muscle Response to Strong Stimuli  Muscle force depends upon the number of fibers stimulated  Contraction of more fibers results in greater muscle tension  Muscles can continue to contract unless they run out of energy © 2015 Pearson Education, Inc.

46. Energy for Muscle Contraction  ATP  Immediate source of energy for muscle contraction  Stored in muscle fibers in small amounts that are quickly used up  After this initial time, other pathways must be utilized to produce ATP © 2015 Pearson Education, Inc.

47. Energy for Muscle Contraction  Three ways to generate ATP 1.Direct phosphorylation of ADP by creatine phosphate 2.Aerobic respiration 3.Anaerobic glycolysis and lactic acid formation © 2015 Pearson Education, Inc.

48. Energy for Muscle Contraction  Direct phosphorylation of ADP by creatine phosphate (CP)—fastest  Muscle cells store CP, a high-energy molecule  After ATP is depleted, ADP remains  CP transfers a phosphate group to ADP to regenerate ATP  CP supplies are exhausted in less than 15 seconds  About 1 ATP is created per CP molecule © 2015 Pearson Education, Inc.

49. Figure 6.10a Methods of regenerating ATP during muscle activity. (a) Direct phosphorylation CP ADP ATP Creatine Coupled reaction of creatine phosphate (CP) and ADP Energy source: Oxygen use: Products: None 1 ATP per CP, creatine 15 seconds Duration of energy provision:

50. Energy for Muscle Contraction  Aerobic respiration  Glucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP)  A series of metabolic pathways occurs in the mitochondria  This is a slower reaction that requires continuous oxygen  Carbon dioxide and water are produced © 2015 Pearson Education, Inc.

51. Figure 6.10c Methods of regenerating ATP during muscle activity. Aerobic respiration in mitochondria (c) Aerobic pathway Energy source: Aerobic cellular respiration glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism CO 2 H2OH2O O2O2 O2O2 Oxygen use: Required 32 ATP per glucose, CO 2, H 2 O Hours Glucose (from glycogen breakdown or delivered from blood) Pyruvic acid Fatty acids Amino acids net gain per glucose ATP 32 Products: Duration of energy provision: Aerobic respiration in mitochondria

52. Energy for Muscle Contraction  Anaerobic glycolysis and lactic acid formation  Reaction that breaks down glucose without oxygen  Glucose is broken down to pyruvic acid to produce about 2 ATP  Pyruvic acid is converted to lactic acid  This reaction is not as efficient, but is fast  Huge amounts of glucose are needed  Lactic acid produces muscle fatigue © 2015 Pearson Education, Inc.

53. Figure 6.10b Methods of regenerating ATP during muscle activity. glucose Energy source: Glycolysis and lactic acid formation (b) Anaerobic pathway ATP 2 O2O2 O2O2 Oxygen use: Products: Duration of energy provision: None 2 ATP per glucose, lactic acid 40 seconds, or slightly more net gain Released to blood Glucose (from glycogen breakdown or delivered from blood) Pyruvic acid Lactic acid Glycolysis in cytosol

54. Muscle Fatigue and Oxygen Deficit  If muscle activity is strenuous and prolonged, muscle fatigue occurs because:  Ionic imbalances occur  Lactic acid accumulates in the muscle  Energy (ATP) supply decreases  After exercise, the oxygen deficit is repaid by rapid, deep breathing © 2015 Pearson Education, Inc.

55. Types of Muscle Contractions  Isotonic contractions  Myofilaments are able to slide past each other during contractions  The muscle shortens, and movement occurs  Example: bending the knee; rotating the arm  Isometric contractions  Tension in the muscles increases  The muscle is unable to shorten or produce movement  Example: pushing against a wall with bent elbows © 2015 Pearson Education, Inc.

56. Muscle Tone  Muscle tone keeps muscles healthy and ready to react  Result of a staggered series of nerve impulses delivered to different cells within the muscle  If the nerve supply is destroyed, the muscle loses tone, becomes paralyzed, and atrophies © 2015 Pearson Education, Inc.

57. Effect of Exercise on Muscles  Exercise increases muscle size, strength, and endurance  Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue  Makes body metabolism more efficient  Improves digestion, coordination  Resistance (isometric) exercise (weight lifting) increases muscle size and strength © 2015 Pearson Education, Inc.

58. Figure 6.11 The effects of aerobic training versus strength training. (a)(b)

59. © 2015 Pearson Education, Inc. Table 6.2 The Five Golden Rules of Skeletal Muscle Activity.