Muscle Tissue. PowerPoint Lecture Presentations prepared by Jason LaPres. Lone Star College North Harris Pearson Education, Inc.

Transcription

1 10 Muscle Tissue PowerPoint Lecture Presentations prepared by Jason LaPres Lone Star College North Harris

2 10-1 An Introduction to Muscle Tissue Learning Outcomes 10-1 Specify the functions of skeletal muscle tissue Describe the organization of muscle at the tissue level Explain the characteristics of skeletal muscle fibers, and identify the structural components of a sarcomere Identify the components of the neuromuscular junction, and summarize the events involved in the neural control of skeletal muscle contraction and relaxation.

3 10-1 An Introduction to Muscle Tissue Learning Outcomes 10-5 Describe the mechanism responsible for tension production in a muscle fiber, and compare the different types of muscle contraction Describe the mechanisms by which muscle fibers obtain the energy to power contractions Relate the types of muscle fibers to muscle performance, and distinguish between aerobic and anaerobic endurance.

4 10-1 An Introduction to Muscle Tissue Learning Outcomes 10-8 Identify the structural and functional differences between skeletal muscle fibers and cardiac muscle cells Identify the structural and functional differences between skeletal muscle fibers and smooth muscle cells, and discuss the roles of smooth muscle tissue in systems throughout the body.

5 An Introduction to Muscle Tissue Muscle Tissue A primary tissue type, divided into: Skeletal muscle tissue Cardiac muscle tissue Smooth muscle tissue

6 10-1 Functions of Skeletal Muscle Tissue Skeletal Muscles Are attached to the skeletal system Allow us to move The muscular system Includes only skeletal muscles

7 10-1 Functions of Skeletal Muscle Tissue Six Functions of Skeletal Muscle Tissue 1. Produce skeletal movement 2. Maintain posture and body position 3. Support soft tissues 4. Guard entrances and exits 5. Maintain body temperature 6. Store nutrient reserves

8 10-2 Organization of Muscle Skeletal Muscle Muscle tissue (muscle cells or fibers) Connective tissues Nerves Blood vessels

9 10-2 Organization of Muscle Organization of Connective Tissues Muscles have three layers of connective tissues 1. Epimysium 2. Perimysium 3. Endomysium

10 10-2 Organization of Muscle Epimysium Exterior collagen layer Connected to deep fascia Separates muscle from surrounding tissues

11 10-2 Organization of Muscle Perimysium Surrounds muscle fiber bundles (fascicles) Contains blood vessel and nerve supply to fascicles

12 10-2 Organization of Muscle Endomysium Surrounds individual muscle cells (muscle fibers) Contains capillaries and nerve fibers contacting muscle cells Contains myosatellite cells (stem cells) that repair damage

13 Figure 10-1 The Organization of Skeletal Muscles Skeletal Muscle (organ) Epimysium Perimysium Endomysium Nerve Muscle fascicle Muscle fibers Blood vessels Epimysium Blood vessels and nerves Tendon Endomysium Perimysium

14 Figure 10-1 The Organization of Skeletal Muscles Muscle Fascicle (bundle of fibers) Perimysium Epimysium Blood vessels and nerves Muscle fiber Endomysium Tendon Endomysium Perimysium

15 Figure 10-1 The Organization of Skeletal Muscles Tendon Epimysium Blood vessels and nerves Muscle Fiber (cell) Capillary Myofibril Axon of neuron Endomysium Sarcoplasm Mitochondrion Myosatellite cell Sarcolemma Nucleus Endomysium Perimysium

16 10-2 Organization of Muscle Organization of Connective Tissues Muscle Attachments Endomysium, perimysium, and epimysium come together: At ends of muscles To form connective tissue attachment to bone matrix I.e., tendon (bundle) or aponeurosis (sheet)

17 10-2 Organization of Muscle Blood Vessels and Nerves Muscles have extensive vascular systems that: Supply large amounts of oxygen Supply nutrients Carry away wastes Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)

18 10-3 Characteristics of Skeletal Muscle Fibers Skeletal Muscle Cells Are very long Develop through fusion of mesodermal cells (myoblasts) Become very large Contain hundreds of nuclei

19 Figure 10-2 The Formation of a Multinucleate Skeletal Muscle Fiber Myoblasts Muscle fibers develop through the fusion of mesodermal cells called myoblasts. A muscle fiber forms by the fusion of myoblasts. Muscle fiber LM 612 Sarcolemma Nuclei Nuclei Immature muscle fiber Myosatellite cell Myofibrils Mitochondria Myosatellite cell A diagrammatic view and a micrograph of one muscle fiber. Up to 30 cm in length Mature muscle fiber

20 Figure 10-2a The Formation of a Multinucleate Skeletal Muscle Fiber Myoblasts A muscle fiber forms by the fusion of myoblasts. Nuclei Immature muscle fiber Muscle fibers develop through the fusion of mesodermal cells called myoblasts. Myosatellite cell Myosatellite cell Up to 30 cm in length Mature muscle fiber

21 Figure 10-2b The Formation of a Multinucleate Skeletal Muscle Fiber Muscle fiber LM 612 Sarcolemma Nuclei Myofibrils Mitochondria A diagrammatic view and a micrograph of one muscle fiber.

22 10-3 Characteristics of Skeletal Muscle Fibers The Sarcolemma and Transverse Tubules The sarcolemma The cell membrane of a muscle fiber (cell) Surrounds the sarcoplasm (cytoplasm of muscle fiber) A change in transmembrane potential begins contractions

23 10-3 Characteristics of Skeletal Muscle Fibers The Sarcolemma and Transverse Tubules Transverse tubules (T tubules) Transmit action potential through cell Allow entire muscle fiber to contract simultaneously Have same properties as sarcolemma

24 10-3 Characteristics of Skeletal Muscle Fibers Myofibrils Lengthwise subdivisions within muscle fiber Made up of bundles of protein filaments (myofilaments) Myofilaments are responsible for muscle contraction Types of myofilaments: Thin filaments Made of the protein actin Thick filaments Made of the protein myosin

25 10-3 Characteristics of Skeletal Muscle Fibers The Sarcoplasmic Reticulum (SR) A membranous structure surrounding each myofibril Helps transmit action potential to myofibril Similar in structure to smooth endoplasmic reticulum Forms chambers (terminal cisternae) attached to T tubules

26 10-3 Characteristics of Skeletal Muscle Fibers The Sarcoplasmic Reticulum (SR) Triad Is formed by one T tubule and two terminal cisternae Cisternae Concentrate Ca 2+ (via ion pumps) Release Ca 2+ into sarcomeres to begin muscle contraction

27 Figure 10-3 The Structure of a Skeletal Muscle Fiber Myofibril Sarcolemma Nuclei Sarcoplasm MUSCLE FIBER Mitochondria Terminal cisterna Sarcolemma Sarcolemma Sarcoplasm Myofibril Myofibrils Thin filament Thick filament Triad Sarcoplasmic reticulum T tubules

28 Figure 10-3 The Structure of a Skeletal Muscle Fiber Myofibril Sarcolemma Nuclei Sarcoplasm MUSCLE FIBER

29 Figure 10-3 The Structure of a Skeletal Muscle Fiber Mitochondria Sarcolemma Terminal cisterna Sarcolemma Sarcoplasm Myofibril Myofibrils Thin filament Thick filament Triad Sarcoplasmic reticulum T tubules

30 Figure 10-3 The Structure of a Skeletal Muscle Fiber Mitochondria Sarcolemma Myofibril Thin filament Thick filament

31 Figure 10-3 The Structure of a Skeletal Muscle Fiber Terminal cisterna Sarcolemma Sarcoplasm Myofibrils Triad Sarcoplasmic reticulum T tubules

32 10-3 Structural Components of a Sarcomere Sarcomeres The contractile units of muscle Structural units of myofibrils Form visible patterns within myofibrils A striped or striated pattern within myofibrils Alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

33 10-3 Structural Components of a Sarcomere Sarcomeres The A Band M line The center of the A band At midline of sarcomere The H Band The area around the M line Has thick filaments but no thin filaments Zone of overlap The densest, darkest area on a light micrograph Where thick and thin filaments overlap

34 10-3 Structural Components of a Sarcomere Sarcomeres The I Band Z lines The centers of the I bands At two ends of sarcomere Titin Are strands of protein Reach from tips of thick filaments to the Z line Stabilize the filaments

35 Figure 10-4a Sarcomere Structure, Part I I band A band H band Z line Titin A longitudinal section of a sarcomere, showing bands Zone of overlap M line Sarcomere Thin Thick filament filament

36 Figure 10-4b Sarcomere Structure, Part I I band A band H band Z line A corresponding view of a sarcomere in a myofibril from a muscle fiber in the gastrocnemius muscle of the calf Myofibril TEM 64,000 Z line Zone of overlap M line Sarcomere

37 Figure 10-5 Sarcomere Structure, Part II Sarcomere Myofibril A superficial view of a sarcomere Thin filament Thick filament Actinin filaments Titin filament Attachment of titin Z line I band M line H band Zone of overlap Cross-sectional views of different portions of a sarcomere

38 Figure 10-6 Levels of Functional Organization in a Skeletal Muscle Skeletal Muscle Myofibril Epimysium Surrounded by: Epimysium Contains: Muscle fascicles Surrounded by: Sarcoplasmic reticulum Consists of: Sarcomeres (Z line to Z line) Sarcomere I band A band Muscle Fascicle Perimysium Surrounded by: Perimysium Contains: Muscle fibers Z line M line H band Titin Z line Contains: Thick filaments Thin filaments Muscle Fiber Endomysium Surrounded by: Endomysium Contains: Myofibrils

39 Figure 10-6 Levels of Functional Organization in a Skeletal Muscle Skeletal Muscle Epimysium Surrounded by: Epimysium Contains: Muscle fascicles

40 Figure 10-6 Levels of Functional Organization in a Skeletal Muscle Muscle Fascicle Perimysium Surrounded by: Perimysium Contains: Muscle fibers

41 Figure 10-6 Levels of Functional Organization in a Skeletal Muscle Muscle Fiber Endomysium Surrounded by: Endomysium Contains: Myofibrils

42 Figure 10-6 Levels of Functional Organization in a Skeletal Muscle Myofibril Surrounded by: Sarcoplasmic reticulum Consists of: Sarcomeres (Z line to Z line)

43 Figure 10-6 Levels of Functional Organization in a Skeletal Muscle Sarcomere I band A band Contains: Thick filaments Thin filaments Z line M line Titin Z line H band

44 10-3 Structural Components of a Sarcomere Thin Filaments F-actin (filamentous actin) Is two twisted rows of globular G-actin The active sites on G-actin strands bind to myosin Nebulin Holds F-actin strands together

45 10-3 Structural Components of a Sarcomere Thin Filaments Tropomyosin Is a double strand Prevents actin myosin interaction Troponin A globular protein Binds tropomyosin to G-actin Controlled by Ca 2+

46 Figure 10-7ab Thick and Thin Filaments Sarcomere H band Actinin Z line Titin Myofibril Z line M line The gross structure of a thin filament, showing the attachment at the Z line Troponin Active site Nebulin Tropomyosin G-actin molecules The organization of G-actin subunits in an F-actin strand, and the position of the troponin tropomyosin complex F-actin strand

47 Figure 10-7a Thick and Thin Filaments Actinin Z line Titin The gross structure of a thin filament, showing the attachment at the Z line

48 Figure 10-7b Thick and Thin Filaments Troponin Active site Nebulin Tropomyosin G-actin molecules The organization of G-actin subunits in an F-actin strand, and the position of the troponin tropomyosin complex F-actin strand

49 10-3 Structural Components of a Sarcomere Initiating Contraction Ca 2+ binds to receptor on troponin molecule Troponin tropomyosin complex changes Exposes active site of F-actin

50 10-3 Structural Components of a Sarcomere Thick Filaments Contain about 300 twisted myosin subunits Contain titin strands that recoil after stretching The mysosin molecule Tail Binds to other myosin molecules Head Made of two globular protein subunits Reaches the nearest thin filament

51 Figure 10-7cd Thick and Thin Filaments Titin The structure of thick filaments, showing the orientation of the myosin molecules M line Myosin tail Hinge The structure of a myosin molecule Myosin head

52 10-3 Structural Components of a Sarcomere Myosin Action During contraction, myosin heads: Interact with actin filaments, forming crossbridges Pivot, producing motion

53 10-3 Structural Components of a Sarcomere Sliding Filaments and Muscle Contraction Sliding filament theory Thin filaments of sarcomere slide toward M line, alongside thick filaments The width of A zone stays the same Z lines move closer together

54 Figure 10-8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber I band A band Z line H band Z line A relaxed sarcomere showing location of the A band, Z lines, and I band.

55 Figure 10-8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber I band A band Z line H band Z line During a contraction, the A band stays the same width, but the Z lines move closer together and the I band gets smaller. When the ends of a myofibril are free to move, the sarcomeres shorten simultaneously and the ends of the myofibril are pulled toward its center.

56 10-3 Structural Components of a Sarcomere Skeletal Muscle Contraction The process of contraction Neural stimulation of sarcolemma Causes excitation contraction coupling Muscle fiber contraction Interaction of thick and thin filaments Tension production

57 Figure 10-9 An Overview of Skeletal Muscle Contraction Neural control Excitation contraction coupling Excitation Calcium release triggers ATP Thick-thin filament interaction Muscle fiber contraction leads to Tension production

58 Figure 10-9 An Overview of Skeletal Muscle Contraction Neural control

59 Figure 10-9 An Overview of Skeletal Muscle Contraction Excitation Calcium release triggers ATP Thick-thin filament interaction

60 Figure 10-9 An Overview of Skeletal Muscle Contraction Muscle fiber contraction leads to Tension production

61 10-4 Components of the Neuromuscular Junction The Control of Skeletal Muscle Activity The neuromuscular junction (NMJ) Special intercellular connection between the nervous system and skeletal muscle fiber Controls calcium ion release into the sarcoplasm A&P FLIX Events at the Neuromuscular Junction

62 Figure Skeletal Muscle Innervation Motor neuron Path of electrical impulse (action potential) Axon Neuromuscular junction SEE BELOW Synaptic terminal Sarcoplasmic reticulum Motor end plate Myofibril Motor end plate

63 Figure Skeletal Muscle Innervation The cytoplasm of the synaptic terminal contains vesicles filled with molecules of acetylcholine, or ACh. Acetylcholine is a neurotransmitter, a chemical released by a neuron to change the permeability or other properties of another cell s plasma membrane. The synaptic cleft and the motor end plate contain molecules of the enzyme acetylcholinesterase (AChE), which breaks down ACh. Vesicles ACh The synaptic cleft, a narrow space, separates the synaptic terminal of the neuron from the opposing motor end plate. Junctional AChE fold of motor end plate

64 Figure Skeletal Muscle Innervation The stimulus for ACh release is the arrival of an electrical impulse, or action potential, at the synaptic terminal. An action potential is a sudden change in the transmembrane potential that travels along the length of the axon. Arriving action potential

65 Figure Skeletal Muscle Innervation When the action potential reaches the neuron s synaptic terminal, permeability changes in the membrane trigger the exocytosis of ACh into the synaptic cleft. Exocytosis occurs as vesicles fuse with the neuron s plasma membrane. Motor end plate

66 Figure Skeletal Muscle Innervation ACh molecules diffuse across the synatpic cleft and bind to ACh receptors on the surface of the motor end plate. ACh binding alters the membrane s permeability to sodium ions. Because the extracellular fluid contains a high concentration of sodium ions, and sodium ion concentration inside the cell is very low, sodium ions rush into the sarcoplasm. ACh receptor site

67 Figure Skeletal Muscle Innervation The sudden inrush of sodium ions results in the generation of an action potential in the sarcolemma. AChE quickly breaks down the ACh on the motor end plate and in the synaptic cleft, thus inactivating the ACh receptor sites. Action potential AChE

68 10-4 Components of the Neuromuscular Junction Excitation Contraction Coupling Action potential reaches a triad Releasing Ca 2+ Triggering contraction Requires myosin heads to be in cocked position Loaded by ATP energy A&P FLIX Excitation-Contraction Coupling

69 Figure The Exposure of Active Sites SARCOPLASMIC RETICULUM Calcium channels open Myosin tail (thick filament) Tropomyosin strand G-actin (thin filament) Active site Troponin Nebulin In a resting sarcomere, the tropomyosin strands cover the active sites on the thin filaments, preventing cross-bridge formation. When calcium ions enter the sarcomere, they bind to troponin, which rotates and swings the tropomyosin away from the active sites. Cross-bridge formation then occurs, and the contraction cycle begins.

70 10-4 Skeletal Muscle Contraction The Contraction Cycle 1. Contraction Cycle Begins 2. Active-Site Exposure 3. Cross-Bridge Formation 4. Myosin Head Pivoting 5. Cross-Bridge Detachment 6. Myosin Reactivation A&P FLIX The Cross Bridge Cycle

71 Figure The Contraction Cycle Contraction Cycle Begins The contraction cycle, which involves a series of interrelated steps, begins with the arrival of calcium ions within the zone of overlap. Myosin head Troponin Tropomyosin Actin

72 Figure The Contraction Cycle Active-Site Exposure Calcium ions bind to troponin, weakening the bond between actin and the troponin tropomyosin complex. The troponin molecule then changes position, rolling the tropomyosin molecule away from the active sites on actin and allowing interaction with the energized myosin heads. Sarcoplasm Active site

73 Figure The Contraction Cycle Cross-Bridge Formation Once the active sites are exposed, the energized myosin heads bind to them, forming cross-bridges.

74 Figure The Contraction Cycle Myosin Head Pivoting After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots toward the M line. This action is called the power stroke; when it occurs, the bound ADP and phosphate group are released.

75 Figure The Contraction Cycle Cross-Bridge Detachment When another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken. The active site is now exposed and able to form another cross-bridge.

76 Figure The Contraction Cycle Myosin Reactivation Myosin reactivation occurs when the free myosin head splits ATP into ADP and P. The energy released is used to recock the myosin head.

77 Figure The Contraction Cycle Resting Sarcomere Zone of overlap (shown in sequence above)

78 Figure The Contraction Cycle Contracted Sarcomere

79 10-4 Skeletal Muscle Contraction Fiber Shortening As sarcomeres shorten, muscle pulls together, producing tension Muscle shortening can occur at both ends of the muscle, or at only one end of the muscle This depends on the way the muscle is attached at the ends

80 Figure Shortening during a Contraction When both ends are free to move, the ends of a contracting muscle fiber move toward the center of the muscle fiber. When one end of a myofibril is fixed in position, and the other end free to move, the free end is pulled toward the fixed end.

81 10-4 Skeletal Muscle Relaxation Relaxation Contraction Duration Depends on: Duration of neural stimulus Number of free calcium ions in sarcoplasm Availability of ATP

82 10-4 Skeletal Muscle Relaxation Relaxation Ca 2+ concentrations fall Ca 2+ detaches from troponin Active sites are re-covered by tropomyosin Rigor Mortis A fixed muscular contraction after death Caused when: Ion pumps cease to function; ran out of ATP Calcium builds up in the sarcoplasm

83 10-4 Skeletal Muscle Contraction and Relaxation Summary Skeletal muscle fibers shorten as thin filaments slide between thick filaments Free Ca 2+ in the sarcoplasm triggers contraction SR releases Ca 2+ when a motor neuron stimulates the muscle fiber Contraction is an active process Relaxation and return to resting length are passive

84 Table 10-1 Steps Involved in Skeletal Muscle Contraction and Relaxation Steps in Initiating Muscle Contraction Steps in Muscle Relaxation Synaptic terminal Motor end plate T tubule Sarcolemma ACh released, binding to receptors Sarcoplasmic reticulum releases Ca 2+ Active site exposure, cross-bridge formation Ca 2+ Actin Myosin Action potential reaches T tubule ACh broken down by AChE Sarcoplasmic reticulum recaptures Ca 2+ Active sites covered, no cross-bridge interaction Contraction begins Contraction ends Relaxation occurs, passive return to resting length

85 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers As a whole, a muscle fiber is either contracted or relaxed Depends on: The number of pivoting cross-bridges The fiber s resting length at the time of stimulation The frequency of stimulation

86 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers Length Tension Relationships Number of pivoting cross-bridges depends on: Amount of overlap between thick and thin fibers Optimum overlap produces greatest amount of tension Too much or too little reduces efficiency Normal resting sarcomere length Is 75% to 130% of optimal length

87 Figure The Effect of Sarcomere Length on Active Tension Tension (percent of maximum) Normal range Decreased length Optimal resting length: The normal range of sarcomere lengths in the body is 75 to 130 percent of the optimal length. Increased sarcomere length

88 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers The Frequency of Stimulation A single neural stimulation produces: A single contraction or twitch Which lasts about msec. Sustained muscular contractions Require many repeated stimuli

89 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers Twitches 1. Latent period The action potential moves through sarcolemma Causing Ca 2+ release 2. Contraction phase Calcium ions bind Tension builds to peak 3. Relaxation phase Ca 2+ levels fall Active sites are covered and tension falls to resting levels

90 Figure 10-15a The Development of Tension in a Twitch Eye muscle Gastrocnemius Soleus Tension Time (msec) Stimulus A myogram showing differences in tension over time for a twitch in different skeletal muscles.

91 Figure 10-15b The Development of Tension in a Twitch Maximum tension development Tension Stimulus Resting phase Latent Contraction period phase Relaxation phase The details of tension over time for a single twitch in the gastrocnemius muscle. Notice the presence of a latent period, which corresponds to the time needed for the conduction of an action potential and the subsequent release of calcium ions by the sarcoplasmic reticulum.

92 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers Treppe A stair-step increase in twitch tension Repeated stimulations immediately after relaxation phase Stimulus frequency <50/second Causes a series of contractions with increasing tension

93 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers Wave summation Increasing tension or summation of twitches Repeated stimulations before the end of relaxation phase Stimulus frequency >50/second Causes increasing tension or summation of twitches

94 Figure 10-16ab Effects of Repeated Stimulations Maximum tension (in tetanus) = Stimulus Tension Maximum tension (in treppe) Time Treppe. Treppe is an increase in peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch. Time Wave summation. Wave summation occurs when successive stimuli arrive before the relaxation phase has been completed.

95 10-5 Tension Production and Contraction Types Tension Production by Muscles Fibers Incomplete tetanus Twitches reach maximum tension If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension Complete tetanus If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction

96 Figure 10-16cd Effects of Repeated Stimulations Maximum tension (in tetanus) Tension Time Incomplete tetanus. Incomplete tetanus occurs if the stimulus frequency increases further. Tension production rises to a peak, and the periods of relaxation are very brief. Time Complete tetanus. During complete tetanus, the stimulus frequency is so high that the relaxation phase is eliminated; tension plateaus at maximal levels.

97 10-5 Tension Production and Contraction Types Tension Production by Skeletal Muscles Depends on: Internal tension produced by muscle fibers External tension exerted by muscle fibers on elastic extracellular fibers Total number of muscle fibers stimulated

98 10-5 Tension Production and Contraction Types Motor Units and Tension Production Motor units in a skeletal muscle: Contain hundreds of muscle fibers That contract at the same time Controlled by a single motor neuron

99 10-5 Tension Production and Contraction Types Motor Units and Tension Production Recruitment (multiple motor unit summation) In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated Maximum tension Achieved when all motor units reach tetanus Can be sustained only a very short time

100 Figure 10-17a The Arrangement and Activity of Motor Units in a Skeletal Muscle Axons of motor neurons Motor nerve SPINAL CORD KEY Motor unit 1 Muscle fibers Motor unit 2 Motor unit 3 Muscle fibers of different motor units are intermingled, so the forces applied to the tendon remain roughly balanced regardless of which motor units are stimulated.

101 Figure 10-17b The Arrangement and Activity of Motor Units in a Skeletal Muscle Tension in tendon Tension Motor unit 1 Motor unit 2 Motor unit 3 Time The tension applied to the tendon remains relatively constant, even though individual motor units cycle between contraction and relaxation.

102 10-5 Tension Production and Contraction Types Motor Units and Tension Production Sustained tension Less than maximum tension Allows motor units rest in rotation Muscle tone The normal tension and firmness of a muscle at rest Muscle units actively maintain body position, without motion Increasing muscle tone increases metabolic energy used, even at rest

103 10-5 Tension Production and Contraction Types Motor Units and Tension Production Contraction are classified based on pattern of tension production Isotonic contraction Isometric contraction

104 10-5 Tension Production and Contraction Types Isotonic Contraction Skeletal muscle changes length Resulting in motion If muscle tension > load (resistance): Muscle shortens (concentric contraction) If muscle tension < load (resistance): Muscle lengthens (eccentric contraction)

105 Figure 10-18a Concentric, Eccentric, and Isometric Contractions Tendon Muscle contracts (concentric contraction) 2 kg 2 kg Muscle tension (kg) Amount of load Peak tension production Muscle relaxes Contraction begins Resting length Time Muscle length (percent of resting length)

106 Figure 10-18b Concentric, Eccentric, and Isometric Contractions 6 kg Support removed when contraction begins (eccentric contraction) Muscle tension (kg) Support removed, contraction begins Peak tension production Resting length Muscle length (percent of resting length) 6 kg Time

107 10-5 Tension Production and Contraction Types Isometric Contraction Skeletal muscle develops tension, but is prevented from changing length iso- = same, metric = measure

108 Figure 10-18c Concentric, Eccentric, and Isometric Contractions Muscle contracts (isometric contraction) Muscle tension (kg) Amount of load Peak tension production Muscle relaxes Contraction begins Length unchanged 6 kg 6 kg Time Muscle length (percent of resting length)

109 10-5 Tension Production and Contraction Types Load and Speed of Contraction Are inversely related The heavier the load (resistance) on a muscle The longer it takes for shortening to begin And the less the muscle will shorten

110 Figure Load and Speed of Contraction Distance shortened Small load Intermediate load Large load Stimulus Time (msec)

111 10-5 Tension Production and Contraction Types Muscle Relaxation and the Return to Resting Length Elastic Forces The pull of elastic elements (tendons and ligaments) Expands the sarcomeres to resting length Opposing Muscle Contractions Reverse the direction of the original motion Are the work of opposing skeletal muscle pairs

112 10-5 Tension Production and Contraction Types Muscle Relaxation and the Return to Resting Length Gravity Can take the place of opposing muscle contraction to return a muscle to its resting state

113 10-6 Energy to Power Contractions ATP Provides Energy For Muscle Contraction Sustained muscle contraction uses a lot of ATP energy Muscles store enough energy to start contraction Muscle fibers must manufacture more ATP as needed

114 10-6 Energy to Power Contractions ATP and CP Reserves Adenosine triphosphate (ATP) The active energy molecule Creatine phosphate (CP) The storage molecule for excess ATP energy in resting muscle Energy recharges ADP to ATP Using the enzyme creatine kinase (CK) When CP is used up, other mechanisms generate ATP

115 10-6 Energy to Power Contractions ATP Generation Cells produce ATP in two ways 1. Aerobic metabolism of fatty acids in the mitochondria 2. Anaerobic glycolysis in the cytoplasm

116 10-6 Energy to Power Contractions Aerobic Metabolism Is the primary energy source of resting muscles Breaks down fatty acids Produces 34 ATP molecules per glucose molecule Glycolysis Is the primary energy source for peak muscular activity Produces two ATP molecules per molecule of glucose Breaks down glucose from glycogen stored in skeletal muscles

117 Table 10-2 Sources of Energy in a Typical Muscle Fiber

118 10-6 Energy to Power Contractions Energy Use and the Level of Muscular Activity Skeletal muscles at rest metabolize fatty acids and store glycogen During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct

119 Figure Muscle Metabolism Fatty acids Fatty acids Blood vessels Glucose Glycogen Glucose Glycogen Pyruvate Mitochondria Creatine Resting muscle: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen. To myofibrils to support muscle contraction Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction. Lactate Glucose Glycogen Pyruvate Creatine Lactate To myofibrils to support muscle contraction Peak activity: Most ATP is produced through glycolysis, with lactate as a by-product. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed.

120 Figure 10-20a Muscle Metabolism Fatty acids Blood vessels Glucose Glycogen Mitochondria Creatine Resting muscle: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen.

121 Figure 10-20b Muscle Metabolism Fatty acids Glucose Glycogen Pyruvate Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction. To myofibrils to support muscle contraction

122 Figure 10-20c Muscle Metabolism Lactate Glucose Glycogen Pyruvate Creatine Lactate To myofibrils to support muscle contraction Peak activity: Most ATP is produced through glycolysis, with lactate as a by-product. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed.

123 10-6 Energy to Power Contractions Muscle Fatigue When muscles can no longer perform a required activity, they are fatigued Results of Muscle Fatigue Depletion of metabolic reserves Damage to sarcolemma and sarcoplasmic reticulum Low ph (lactic acid) Muscle exhaustion and pain

124 10-6 Energy to Power Contractions The Recovery Period The time required after exertion for muscles to return to normal Oxygen becomes available Mitochondrial activity resumes

125 10-6 Energy to Power Contractions Lactic Acid Removal and Recycling The Cori Cycle The removal and recycling of lactic acid by the liver Liver converts lactate to pyruvate Glucose is released to recharge muscle glycogen reserves

126 10-6 Energy to Power Contractions The Oxygen Debt After exercise or other exertion: The body needs more oxygen than usual to normalize metabolic activities Resulting in heavy breathing Also called excess postexercise oxygen consumption (EPOC)

127 10-6 Energy to Power Contractions Heat Production and Loss Active muscles produce heat Up to 70% of muscle energy can be lost as heat, raising body temperature

128 10-6 Energy to Power Contractions Hormones and Muscle Metabolism Growth hormone Testosterone Thyroid hormones Epinephrine

129 10-7 Types of Muscles Fibers and Endurance Muscle Performance Force The maximum amount of tension produced Endurance The amount of time an activity can be sustained Force and endurance depend on: The types of muscle fibers Physical conditioning

130 10-7 Types of Muscles Fibers and Endurance Three Major Types of Skeletal Muscle Fibers 1. Fast fibers 2. Slow fibers 3. Intermediate fibers

131 10-7 Types of Muscles Fibers and Endurance Fast Fibers Contract very quickly Have large diameter, large glycogen reserves, few mitochondria Have strong contractions, fatigue quickly

132 10-7 Types of Muscles Fibers and Endurance Slow Fibers Are slow to contract, slow to fatigue Have small diameter, more mitochondria Have high oxygen supply Contain myoglobin (red pigment, binds oxygen)

133 10-7 Types of Muscles Fibers and Endurance Intermediate Fibers Are mid-sized Have low myoglobin Have more capillaries than fast fibers, slower to fatigue

134 Figure Fast versus Slow Fibers Slow fibers Smaller diameter, darker color due to myoglobin; fatigue resistant LM 170 Fast fibers Larger diameter, paler color; easily fatigued LM 170 LM 783

135 Table 10-3 Properties of Skeletal Muscle Fiber Types

136 10-7 Types of Muscles Fibers and Endurance Muscle Performance and the Distribution of Muscle Fibers White muscles Mostly fast fibers Pale (e.g., chicken breast) Red muscles Mostly slow fibers Dark (e.g., chicken legs) Most human muscles Mixed fibers Pink

137 10-7 Types of Muscles Fibers and Endurance Muscle Hypertrophy Muscle growth from heavy training Increases diameter of muscle fibers Increases number of myofibrils Increases mitochondria, glycogen reserves Muscle Atrophy Lack of muscle activity Reduces muscle size, tone, and power

138 10-7 Types of Muscles Fibers and Endurance Physical Conditioning Improves both power and endurance Anaerobic activities (e.g., 50-meter dash, weightlifting) Use fast fibers Fatigue quickly with strenuous activity Improved by: Frequent, brief, intensive workouts Causes hypertrophy

139 10-7 Types of Muscles Fibers and Endurance Physical Conditioning Improves both power and endurance Aerobic activities (prolonged activity) Supported by mitochondria Require oxygen and nutrients Improves: Endurance by training fast fibers to be more like intermediate fibers Cardiovascular performance

140 10-7 Types of Muscles Fibers and Endurance Importance of Exercise What you don t use, you lose Muscle tone indicates base activity in motor units of skeletal muscles Muscles become flaccid when inactive for days or weeks Muscle fibers break down proteins, become smaller and weaker With prolonged inactivity, fibrous tissue may replace muscle fibers

141 10-8 Cardiac Muscle Tissue Cardiac Muscle Tissue Cardiac muscle cells are striated and found only in the heart Striations are similar to that of skeletal muscle because the internal arrangement of myofilaments is similar

142 10-8 Cardiac Muscle Tissue Structural Characteristics of Cardiac Muscle Tissue Unlike skeletal muscle, cardiac muscle cells (cardiocytes): Are small Have a single nucleus Have short, wide T tubules Have no triads Have SR with no terminal cisternae Are aerobic (high in myoglobin, mitochondria) Have intercalated discs

143 10-8 Cardiac Muscle Tissue Intercalated Discs Are specialized contact points between cardiocytes Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes) Functions of intercalated discs: Maintain structure Enhance molecular and electrical connections Conduct action potentials

144 10-8 Cardiac Muscle Tissue Intercalated Discs Coordination of cardiocytes Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

145 Figure 10-22a Cardiac Muscle Tissue Cardiac muscle cell Intercalated discs Nucleus Cardiac muscle tissue LM 575 A light micrograph of cardiac muscle tissue.

146 Figure 10-22b Cardiac Muscle Tissue Cardiac muscle cell (intact) Intercalated disc (sectioned) A diagrammatic view of cardiac muscle. Note the striations and intercalated discs. Mitochondria Nucleus Myofibrils Cardiac muscle cell (sectioned) Intercalated disc

147 Figure 10-22c Cardiac Muscle Tissue Entrance to T tubule Mitochondrion Sarcolemma Myofibrils Contact of sarcoplasmic reticulum with T tubule Sarcoplasmic reticulum Cardiac muscle tissue showing short, broad T-tubules and SR that lacks terminal cisternae.

148 10-8 Cardiac Muscle Tissue Functional Characteristics of Cardiac Muscle Tissue Automaticity Contraction without neural stimulation Controlled by pacemaker cells Variable contraction tension Controlled by nervous system Extended contraction time Ten times as long as skeletal muscle Prevention of wave summation and tetanic contractions by cell membranes Long refractory period

149 10-9 Smooth Muscle Tissue Smooth Muscle in Body Systems Forms around other tissues In integumentary system Arrector pili muscles cause goose bumps In blood vessels and airways Regulates blood pressure and airflow In reproductive and glandular systems Produces movements In digestive and urinary systems Forms sphincters Produces contractions

150 10-9 Smooth Muscle Tissue Structural Characteristics of Smooth Muscle Tissue Nonstriated tissue Different internal organization of actin and myosin Different functional characteristics

151 Figure 10-23a Smooth Muscle Tissue Circular muscle layer Longitudinal muscle layer Smooth muscle tissue LM 100 Many visceral organs contain several layers of smooth muscle tissue oriented in different directions. Here, a single sectional view shows smooth muscle cells in both longitudinal (L) and transverse (T) sections.

152 Figure 10-23b Smooth Muscle Tissue Relaxed (sectional view) Dense body Actin Myosin Relaxed (superficial view) Intermediate filaments (desmin) Adjacent smooth muscle cells are bound together at dense bodies, transmitting the contractile forces from cell to cell throughout the tissue. Contracted (superficial view) A single relaxed smooth muscle cell is spindle shaped and has no striations. Note the changes in cell shape as contraction occurs.

153 10-9 Smooth Muscle Tissue Characteristics of Smooth Muscle Cells Long, slender, and spindle shaped Have a single, central nucleus Have no T tubules, myofibrils, or sarcomeres Have no tendons or aponeuroses Have scattered myosin fibers Myosin fibers have more heads per thick filament Have thin filaments attached to dense bodies Dense bodies transmit contractions from cell to cell

154 10-9 Smooth Muscle Tissue Functional Characteristics of Smooth Muscle Tissue 1. Excitation contraction coupling 2. Length tension relationships 3. Control of contractions 4. Smooth muscle tone

155 10-9 Smooth Muscle Tissue Excitation Contraction Coupling Free Ca 2+ in cytoplasm triggers contraction Ca 2+ binds with calmodulin In the sarcoplasm Activates myosin light chain kinase Enzyme breaks down ATP, initiates contraction

156 10-9 Smooth Muscle Tissue Length Tension Relationships Thick and thin filaments are scattered Resting length not related to tension development Functions over a wide range of lengths (plasticity)

157 10-9 Smooth Muscle Tissue Control of Contractions Multiunit smooth muscle cells Connected to motor neurons Visceral smooth muscle cells Not connected to motor neurons Rhythmic cycles of activity controlled by pacesetter cells

158 10-9 Smooth Muscle Tissue Smooth Muscle Tone Maintains normal levels of activity Modified by neural, hormonal, or chemical factors

159 Table 10-4 A Comparison of Skeletal, Cardiac, and Smooth Muscle Tissues