1. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 11 Physiology of the Muscular System

2. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 2 Introduction Muscular system is responsible for moving the framework of the body Muscular system is responsible for moving the framework of the body In addition to movement, muscle tissue performs various other functions In addition to movement, muscle tissue performs various other functions

3. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 3 General Functions Movement of the body as a whole or of its parts Movement of the body as a whole or of its parts Heat production Heat production Posture Posture

4. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 4 Function of Skeletal Muscle Tissue Characteristics of skeletal muscle cells Characteristics of skeletal muscle cells  Excitability (irritability)—ability to be stimulated  Contractility—ability to contract, or shorten, and produce body movement  Extensibility—ability to extend, or stretch, allowing muscles to return to their resting length

5. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 5 Function of Skeletal Muscle Tissue Overview of the muscle cell (Figures 11-1 and 11-2) Overview of the muscle cell (Figures 11-1 and 11-2)  Muscle cells are called fibers because of their threadlike shape  Sarcolemma—plasma membrane of muscle fibers  Sarcoplasmic reticulum (SR) Network of tubules and sacs found within muscle fibers Network of tubules and sacs found within muscle fibers Membrane of the sarcoplasmic reticulum continually pumps calcium ions from the sarcoplasm and stores the ions within its sacs for later release (Figure 11-3) Membrane of the sarcoplasmic reticulum continually pumps calcium ions from the sarcoplasm and stores the ions within its sacs for later release (Figure 11-3)

6. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 6 Function of Skeletal Muscle Tissue Overview of the muscle cell (cont.) Overview of the muscle cell (cont.)  Muscle fibers contain many mitochondria and several nuclei  Myofibrils—numerous fine fibers packed close together in sarcoplasm  Sarcomere Segment of myofibril between two successive Z lines Segment of myofibril between two successive Z lines Each myofibril consists of many sarcomeres Each myofibril consists of many sarcomeres Contractile unit of muscle fibers Contractile unit of muscle fibers

7. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 7 Function of Skeletal Muscle Tissue Overview of the muscle cell (cont.) Overview of the muscle cell (cont.)  Striated muscle (Figure 11-4) Dark stripes called A bands; light H zone runs across midsection of each dark A band Dark stripes called A bands; light H zone runs across midsection of each dark A band Light stripes called I bands; dark Z line extends across center of each light I band Light stripes called I bands; dark Z line extends across center of each light I band

8. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 8 Function of Skeletal Muscle Tissue Overview of the muscle cell (cont.) Overview of the muscle cell (cont.)  T tubules Transverse tubules extend across sarcoplasm at right angles to long axis of muscle fiber Transverse tubules extend across sarcoplasm at right angles to long axis of muscle fiber Formed by inward extensions of sarcolemma Formed by inward extensions of sarcolemma Membrane has ion pumps that continually transport Ca++ ions inward from sarcoplasm Membrane has ion pumps that continually transport Ca++ ions inward from sarcoplasm Allow electrical impulses traveling along sarcolemma to move deeper into cell Allow electrical impulses traveling along sarcolemma to move deeper into cell

9. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 9 Function of Skeletal Muscle Tissue Overview of the muscle cell (cont.) Overview of the muscle cell (cont.)  Triad Triplet of tubules; a T tubule sandwiched between two sacs of sarcoplasmic reticulum; allows an electrical impulse traveling along a T tubule to stimulate the membranes of adjacent sacs of the sarcoplasmic reticulum Triplet of tubules; a T tubule sandwiched between two sacs of sarcoplasmic reticulum; allows an electrical impulse traveling along a T tubule to stimulate the membranes of adjacent sacs of the sarcoplasmic reticulum

10. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 10 Function of Skeletal Muscle Tissue Myofilaments (Figures 11-5 and 11-6) Myofilaments (Figures 11-5 and 11-6)  Each myofibril contains thousands of thick and thin myofilaments

11. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 11 Function of Skeletal Muscle Tissue Myofilaments (cont.) Myofilaments (cont.)  Four different kinds of protein molecules make up myofilaments Myosin Myosin  Makes up almost all the thick filament  Myosin “heads” are chemically attracted to actin molecules  Myosin “heads” are known as cross bridges when attached to actin Actin—globular protein that forms two fibrous strands that twist around each other to form bulk of thin filament Actin—globular protein that forms two fibrous strands that twist around each other to form bulk of thin filament Tropomyosin—protein that blocks the active sites on actin molecules Tropomyosin—protein that blocks the active sites on actin molecules Troponin—protein that holds tropomyosin molecules in place Troponin—protein that holds tropomyosin molecules in place

12. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 12 Function of Skeletal Muscle Tissue Myofilaments (cont.) Myofilaments (cont.)  Thin filaments attach to both Z lines (Z disks) of a sarcomere and extend partway toward the center  Thick myosin filaments do not attach to the Z lines

13. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 13 Function of Skeletal Muscle Tissue The mechanism of contraction The mechanism of contraction  Excitation and contraction (Figures 11-7 through 11-12; Table 11-1) A skeletal muscle fiber remains at rest until stimulated by a motor neuron A skeletal muscle fiber remains at rest until stimulated by a motor neuron Neuromuscular junction—motor neurons connect to sarcolemma at motor endplate (Figure 11-7) Neuromuscular junction—motor neurons connect to sarcolemma at motor endplate (Figure 11-7) Neuromuscular junction is a synapse where neurotransmitter molecules transmit signals Neuromuscular junction is a synapse where neurotransmitter molecules transmit signals

14. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 14 Function of Skeletal Muscle Tissue  Excitation and contraction (cont.) Acetylcholine—neurotransmitter released into synaptic cleft that diffuses across gap, stimulates receptors, and initiates impulse in sarcolemma Acetylcholine—neurotransmitter released into synaptic cleft that diffuses across gap, stimulates receptors, and initiates impulse in sarcolemma Nerve impulse travels over sarcolemma and inward along T tubules, which triggers release of calcium ions Nerve impulse travels over sarcolemma and inward along T tubules, which triggers release of calcium ions Calcium binds to troponin, causing tropomyosin to shift and expose active sites on actin Calcium binds to troponin, causing tropomyosin to shift and expose active sites on actin

15. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 15 Function of Skeletal Muscle Tissue  Excitation and contraction (cont.) Sliding filament model (Figures 11-11 and 11-12) Sliding filament model (Figures 11-11 and 11-12)  When active sites on actin are exposed, myosin heads bind to them  Myosin heads bend, pulling the thin filaments past them  Each head releases, binds to next active site, and pulls again  Entire myofibril shortens

16. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 16 Function of Skeletal Muscle Tissue The mechanism of contraction (cont.) The mechanism of contraction (cont.)  Relaxation Immediately after Ca ++ ions are released, sarcoplasmic reticulum begins actively pumping them back into sacs (Figure 11-3) Immediately after Ca ++ ions are released, sarcoplasmic reticulum begins actively pumping them back into sacs (Figure 11-3) Ca ++ ions are removed from troponin molecules, shutting down contraction Ca ++ ions are removed from troponin molecules, shutting down contraction

17. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 17 Function of Skeletal Muscle Tissue The mechanism of contraction (cont.) The mechanism of contraction (cont.)  Energy sources for muscle contraction (Figure 11-13) Hydrolysis of ATP yields energy required for muscular contraction Hydrolysis of ATP yields energy required for muscular contraction Adenosine triphosphate (ATP) binds to myosin head and then transfers its energy to myosin head to perform work of pulling thin filament during contraction Adenosine triphosphate (ATP) binds to myosin head and then transfers its energy to myosin head to perform work of pulling thin filament during contraction Muscle fibers continually resynthesize ATP from breakdown of creatine phosphate (CP) Muscle fibers continually resynthesize ATP from breakdown of creatine phosphate (CP)

18. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 18 Function of Skeletal Muscle Tissue  Energy sources for muscle contraction (cont.) Catabolism by muscle fibers requires glucose and oxygen Catabolism by muscle fibers requires glucose and oxygen At rest, excess O 2 in the sarcoplasm is bound to myoglobin (Box 11-4) At rest, excess O 2 in the sarcoplasm is bound to myoglobin (Box 11-4)  Red fibers—muscle fibers with high levels of myoglobin  White fibers—muscle fibers with little myoglobin Aerobic respiration occurs when adequate O 2 is available Aerobic respiration occurs when adequate O 2 is available

19. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 19 Function of Skeletal Muscle Tissue The mechanism of contraction (cont.) The mechanism of contraction (cont.)  Energy sources for muscle contraction (cont.) Anaerobic respiration occurs when low levels of O 2 are available and results in formation of lactic acid Anaerobic respiration occurs when low levels of O 2 are available and results in formation of lactic acid Glucose and oxygen supplied to muscle fibers by blood capillaries (Figure 11-14) Glucose and oxygen supplied to muscle fibers by blood capillaries (Figure 11-14) Skeletal muscle contraction produces waste heat that can be used to help maintain set point body temperature (Figure 11- 15) Skeletal muscle contraction produces waste heat that can be used to help maintain set point body temperature (Figure 11- 15)

20. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 20 Function of Skeletal Muscle Organs Muscles are composed of bundles of muscle fibers that are held together by fibrous connective tissue Muscles are composed of bundles of muscle fibers that are held together by fibrous connective tissue Motor unit (Figure 11-16) Motor unit (Figure 11-16)  Motor unit—motor neuron plus the muscle fibers to which it attaches  Some motor units consist of only a few muscle fibers, whereas others consist of numerous fibers  Generally, the smaller the number of fibers in a motor unit, the more precise the movement available; the larger the number of fibers in a motor unit, the more powerful the contraction available Myography—method of graphing the changing tension of a muscle as it contracts (Figure 11-17) Myography—method of graphing the changing tension of a muscle as it contracts (Figure 11-17)

21. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 21 Function of Skeletal Muscle Organs Twitch contraction (Figure 11-18) Twitch contraction (Figure 11-18)  A quick jerk of a muscle that is produced as a result of a single, brief threshold stimulus (generally occurs only in experimental situations)  The twitch contraction has three phases Latent phase—nerve impulse travels to the sarcoplasmic reticulum to trigger release of Ca ++ Latent phase—nerve impulse travels to the sarcoplasmic reticulum to trigger release of Ca ++ Contraction phase—Ca ++ binds to troponin and sliding of filaments occurs Contraction phase—Ca ++ binds to troponin and sliding of filaments occurs Relaxation phase—sliding of filaments ceases Relaxation phase—sliding of filaments ceases

22. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 22 Function of Skeletal Muscle Organs Treppe—the staircase phenomenon (Figure 11-19, B) Treppe—the staircase phenomenon (Figure 11-19, B)  Gradual, steplike increase in the strength of contractions seen in a series of twitch contractions that occur 1 second apart  Eventually, the muscle responds with less forceful contractions, and relaxation phase becomes shorter  If relaxation phase disappears completely, a contracture occurs

23. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 23 Function of Skeletal Muscle Organs Tetanus—smooth, sustained contractions Tetanus—smooth, sustained contractions  Multiple wave summation—multiple twitch waves are added together to sustain muscle tension for a longer time  Incomplete tetanus—very short periods of relaxation occur between peaks of tension (Figure 11-19, C)  Complete tetanus—the stimulation is such that twitch waves fuse into a single, sustained peak (Figure 11-19, D)

24. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 24 Function of Skeletal Muscle Organs Muscle tone Muscle tone  Tonic contraction—continual, partial contraction of a muscle  At any one time, a small number of muscle fibers within a muscle contract, producing a tightness or muscle tone  Muscles with less tone than normal are flaccid  Muscles with more tone than normal are spastic  Muscle tone is maintained by negative feedback mechanisms

25. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 25 Function of Skeletal Muscle Organs Graded strength principle Graded strength principle  Skeletal muscles contract with varying degrees of strength at different times  Factors that contribute to the phenomenon of graded strength (Figure 11-23) Metabolic condition of individual fibers Metabolic condition of individual fibers Number of muscle fibers contracting simultaneously; the greater the number of fibers contracting, the stronger the contraction Number of muscle fibers contracting simultaneously; the greater the number of fibers contracting, the stronger the contraction Number of motor units recruited Number of motor units recruited

26. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 26 Function of Skeletal Muscle Organs Factors that contribute to the phenomenon of graded strength (cont.) Factors that contribute to the phenomenon of graded strength (cont.) Intensity and frequency of stimulation (Figure 11-20) Intensity and frequency of stimulation (Figure 11-20) Length-tension relationship (Figure 11-21) Length-tension relationship (Figure 11-21)  Maximal strength that a muscle can develop bears a direct relationship to the initial length of its fibers  A shortened muscle’s sarcomeres are compressed; therefore, the muscle cannot develop much tension  An overstretched muscle cannot develop much tension because the thick myofilaments are too far from the thin myofilaments  Strongest maximal contraction is possible only when the skeletal muscle has been stretched to its optimal length

27. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 27 Function of Skeletal Muscle Organs  Factors that contribute to the phenomenon of graded strength (cont.) Stretch reflex (Figure 11-22) Stretch reflex (Figure 11-22)  The load imposed on a muscle influences the strength of a skeletal contraction  Stretch reflex—the body tries to maintain a constancy of muscle length in response to increased load  Maintains a relatively constant length as load is increased up to a maximum sustainable level

28. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 28 Function of Skeletal Muscle Organs Isotonic and isometric contractions (Figure 11-24) Isotonic and isometric contractions (Figure 11-24)  Isotonic contraction Contraction in which the tone or tension within a muscle remains the same as the length of the muscle changes Contraction in which the tone or tension within a muscle remains the same as the length of the muscle changes  Concentric—muscle shortens as it contracts  Eccentric—muscle lengthens while contracting Isotonic—literally means “same tension” Isotonic—literally means “same tension” All of the energy of contraction is used to pull on thin myofilaments and thereby change the length of a fiber’s sarcomeres All of the energy of contraction is used to pull on thin myofilaments and thereby change the length of a fiber’s sarcomeres

29. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 29 Function of Skeletal Muscle Organs Isotonic and isometric contractions (cont.) Isotonic and isometric contractions (cont.)  Isometric contraction Contraction in which muscle length remains the same while the muscle tension increases Contraction in which muscle length remains the same while the muscle tension increases Isometric—literally means “same length” Isometric—literally means “same length”  Most body movements occur as a result of both types of contractions

30. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 30 Function of Cardiac and Smooth Muscle Tissue Cardiac muscle (Figure 11-25) Cardiac muscle (Figure 11-25)  Found only in the heart, forming the bulk of the wall of each chamber  Also known as striated involuntary muscle  Contracts rhythmically and continuously to provide the pumping action needed to maintain a constant blood flow

31. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 31 Function of Cardiac and Smooth Muscle Tissue  Cardiac muscle resembles skeletal muscle but has specialized features related to its role in continuously pumping blood Each cardiac muscle contains parallel myofibrils (Figure 11-25) Each cardiac muscle contains parallel myofibrils (Figure 11-25) Cardiac muscle fibers form strong, electrically coupled junctions (intercalated disks) with other fibers; individual cells also exhibit branching Cardiac muscle fibers form strong, electrically coupled junctions (intercalated disks) with other fibers; individual cells also exhibit branching Syncytium—continuous, electrically coupled mass Syncytium—continuous, electrically coupled mass Cardiac muscle fibers form a continuous, contractile band around the heart chambers that conducts a single impulse across a virtually continuous sarcolemma Cardiac muscle fibers form a continuous, contractile band around the heart chambers that conducts a single impulse across a virtually continuous sarcolemma

32. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 32 Function of Cardiac and Smooth Muscle Tissue Cardiac muscle (cont.) Cardiac muscle (cont.) T tubules are larger and form diads with a rather sparse sarcoplasmic reticulum T tubules are larger and form diads with a rather sparse sarcoplasmic reticulum Cardiac muscle sustains each impulse longer than in skeletal muscle; therefore, impulses cannot come rapidly enough to produce tetanus (Figure 11-26) Cardiac muscle sustains each impulse longer than in skeletal muscle; therefore, impulses cannot come rapidly enough to produce tetanus (Figure 11-26) Cardiac muscle does not run low on ATP and does not experience fatigue Cardiac muscle does not run low on ATP and does not experience fatigue Cardiac muscle is self-stimulating Cardiac muscle is self-stimulating

33. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 33 Function of Cardiac and Smooth Muscle Tissue Smooth muscle Smooth muscle  Smooth muscle is composed of small, tapered cells with single nuclei (Figure 11-27)  No T tubules are present, and only a loosely organized sarcoplasmic reticulum is present  Ca ++ comes from outside the cell and binds to calmodulin instead of troponin to trigger a contraction  No striations, because thick and thin myofilaments are arranged differently than in skeletal or cardiac muscle fibers; myofilaments are not organized into sarcomeres

34. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 34 Function of Cardiac and Smooth Muscle Tissue Smooth muscle (cont.) Smooth muscle (cont.)  Two types of smooth muscle tissue (Figure 11-28): Single-unit (visceral) Single-unit (visceral)  Gap junctions join smooth muscle fibers into large, continuous sheets  Most common type; forms a muscular layer in the walls of hollow structures such as the digestive, urinary, and reproductive tracts  Exhibits autorhythmicity, producing peristalsis Multiunit Multiunit  Does not act as a single unit but is composed of many independent cell units  Each fiber responds only to nervous input

35. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 35 The Big Picture: Muscle Tissue and the Whole Body Function of all three major types of muscle is integral to the function of the entire body Function of all three major types of muscle is integral to the function of the entire body All three types of muscle tissue provide the movement necessary for survival All three types of muscle tissue provide the movement necessary for survival Relative constancy of the body’s internal temperature is maintained by “waste” heat generated by muscle tissue Relative constancy of the body’s internal temperature is maintained by “waste” heat generated by muscle tissue Maintains the body in a relatively stable position Maintains the body in a relatively stable position