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Chapter 10: Muscle Tissue A&P Biology 141 R.L. Brashear-Kaulfers

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1 Chapter 10: Muscle Tissue A&P Biology 141 R.L. Brashear-Kaulfers

2 Muscle Tissue One of 4 primary tissue types, divided into:
skeletal muscle cardiac muscle smooth muscle Without these muscles, nothing in the body would move and no body movement would occur

3 Skeletal Muscles- Organs of skeletal muscle tissue - are attached to the skeletal system and allow us to move Muscular System- Includes only skeletal muscles Skeletal Muscle Structures Muscle tissue (muscle cells or fibers) Connective tissues Nerves Blood vessels

4 6 Functions of Skeletal Muscles
Produce skeletal movement Maintain body position and posture Support soft tissues Guard body openings (entrance/exit) Maintain body temperature Store Nutrient reserves

5 How is muscle tissue organized at the tissue level
How is muscle tissue organized at the tissue level? Organization of Connective Tissues Figure 10–1

6 Organization of Connective Tissues
Muscles have 3 layers of connective tissues: 1. Epimysium-Exterior collagen layer Connected to deep fascia Separates muscle from surrounding tissue 2. perimysium- Surrounds muscle fiber bundles (fascicles) Contains blood vessel and nerve supply to fascicles 3. endomysium

7 3. Endomysium Surrounds individual muscle cells (muscle fibers)
Contains capillaries and nerve fibers contacting muscle cells Contains satellite cells (stem cells) that repair damage

8 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)

9 Nerves Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system
Blood Vessels Muscles have extensive vascular systems that: supply large amounts of oxygen supply nutrients carry away wastes

10 What are the characteristics of skeletal muscle fibers?
Skeletal muscle cells are called fibers Figure 10–2

11 Skeletal Muscle Fibers
Are very long Develop through fusion of mesodermal cells (myoblasts- embryonic cells)) Become very large Contain hundreds of nuclei –multinucleate Unfused cells are satellite cells- assist in repair after injury

12 Organization of Skeletal Muscle Fibers
Figure 10–3

13 The Sarcolemma The cell membrane of a muscle cell
Surrounds the sarcoplasm (cytoplasm of muscle fiber) A change in transmembrane potential begins contractions All regions of the cell must contract simultaneously

14 Transverse Tubules (T tubules)
Transmit action potential – impulses through cell Allow entire muscle fiber to contract simultaneously Have same properties as sarcolemma Filled with extracellular fluid

15 Myofibrils- 1-2um in diameter
Lengthwise subdivisions within muscle fiber Made up of bundles of protein filaments (myofilaments) Myofilaments - are responsible for muscle contraction 2 Types of Myofilaments Thin filaments: made of the protein actin Thick filaments: made of the protein myosin

16 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

17 A Triad Is formed by 1 T tubule and 2 terminal cisterna Cisternae
Concentrate Ca2+ (via ion pumps) Release Ca2+ into sarcomeres to begin muscle contraction

18 Structural components of the Sarcomeres
-The contractile units of muscle -Structural units of myofibrils -Form visible patterns within myofibrils Figure 10–4

19 Muscle Striations A striped or striated pattern within myofibrils:
alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

20 M Lines and Z Lines M line: Z lines: Zone of Overlap
the center of the A band at midline of sarcomere Z lines: the centers of the I bands at 2 ends of sarcomere Zone of Overlap The densest, darkest area on a light micrograph Where thick and thin filaments overlap

21 The H Zone The area around the M line
Has thick filaments but no thin filaments Titin Are strands of protein Reach from tips of thick filaments to the Z line Stabilize the filaments

22 Sarcomere Structure Figure 10–5

23 Sarcomere Function Transverse tubules encircle the sarcomere near zones of overlap Ca2+ released by SR causes thin and thick filaments to interact

24 Level 1: Skeletal Muscle
Level 2: Muscle Fascicle Figure 10–6 (1 of 5)

25 Level 3: Muscle Fiber Level 4: Myofibril Figure 10–6 (3 of 5)

26 Level 5: Sarcomere Figure 10–6 (5 of 5)

27 Muscle Contraction Is caused by interactions of thick and thin filaments Structures of protein molecules detemine interactions

28 A Thin Filament Figure 10–7a

29 4 Thin Filament Proteins
F actin: is 2 twisted rows of globular G actin the active sites on G actin strands bind to myosin Nebulin: holds F actin strands together Tropomyosin: is a double strand prevents actin–myosin interaction Troponin: - a globular protein binds tropomyosin to G actin controlled by Ca2+

30 Troponin and Tropomyosin
Initiating Contraction Ca2+ binds to receptor on troponin molecule Troponin–tropomyosin complex changes Exposes active site of F actin Figure 10–7b

31 A Thick Filament Contain twisted myosin subunits
Contain titin strands that recoil after stretching

32 The Mysosin Molecule Tail: Head: binds to other myosin molecules
made of 2 globular protein subunits reaches the nearest thin filament

33 Mysosin Action During contraction, myosin heads:
interact with actin filaments, forming cross-bridges pivot, producing motion

34 Skeletal Muscle Contraction
Sliding Filaments Sliding filament theory: thin filaments of sarcomere slide toward M line between thick filaments the width of A zone stays the same Z lines move closer together

35 What are the components of the neuromuscular junction, and the events involved in the neural control of skeletal muscles?

36 Skeletal Muscle Contraction
Figure 10–9 (Navigator)

37 The Process of Contraction
Neural stimulation of sarcolemma: causes excitation–contraction coupling Cisternae of SR release Ca2+: which triggers interaction of thick and thin filaments consuming ATP and producing tension

38 Skeletal Muscle Innervation
Figure 10–10a, b (Navigator)

39 Skeletal Muscle Innervation
Figure 10–10c

40 The Neuromuscular Junction
Is the location of neural stimulation Action potential (electrical signal): travels along nerve axon ends at synaptic terminal Synaptic Terminal Releases neurotransmitter (acetylcholine or ACh) Into the synaptic cleft (gap between synaptic terminal and motor end plate)

41 The Neurotransmitter Acetylcholine or ACh:
travels across the synaptic cleft binds to membrane receptors on sarcolemma (motor end plate) causes sodium–ion rush into sarcoplasm is quickly broken down by enzyme (acetylcholinesterase or AChE)

42 Action Potential Generated by increase in sodium ions in sarcolemma
Travels along the T tubules Leads to excitation–contraction coupling

43 Excitation–Contraction Coupling
Action potential reaches a triad: releasing Ca2+ triggering contraction Requires myosin heads to be in “cocked” position: loaded by ATP energy

44 key steps involved in contraction of a skeletal muscle fiber Exposing the Active Site
Figure 10–11

45 The Contraction Cycle Figure 10–12 (1 of 4)

46 The Contraction Cycle Figure 10–12 (2 of 4)

47 The Contraction Cycle Figure 10–12 (3 of 4)

48 The Contraction Cycle Figure 10–12 (Navigator) (4 of 4)

49 5 Steps of the Contraction Cycle
Exposure of active sites Formation of cross-bridges Pivoting of myosin heads Detachment of cross-bridges Reactivation of myosin

50 Fiber Shortening As sarcomeres shorten, muscle pulls together, producing tension Figure 10–13

51 Contraction Duration Depends on: duration of neural stimulus
number of free calcium ions in sarcoplasm availability of ATP

52 Relaxation Ca2+ concentrations fall Ca2+ detaches from troponin
Active sites are recovered by tropomyosin Sarcomeres remain contracted

53 Rigor Mortis A fixed muscular contraction after death Caused when:
ion pumps cease to function calcium builds up in the sarcoplasm

54 A Review of Muscle Contraction
Table 10–1 (1 of 2)

55 A Review of Muscle Contraction
Table 10–1 (2 of 2)

56 KEY CONCEPT Skeletal muscle fibers shorten as thin filaments slide between thick filaments Free Ca2+ in the sarcoplasm triggers contraction SR releases Ca2+ when a motor neuron stimulates the muscle fiber Contraction is an active process Relaxation and return to resting length is passive

57 What is the mechanism responsible for tension production in a muscle fiber, and what factors determine the peak tension developed during a contraction?

58 Tension Production Tension of a Single Muscle Fiber
The all–or–none principal: as a whole, a muscle fiber is either contracted or relaxed Tension of a Single Muscle Fiber Depends on: the number of pivoting cross-bridges the fiber’s resting length at the time of stimulation the frequency of stimulation

59 Tension and Sarcomere Length
Figure 10–14

60 Length–Tension Relationship
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

61 Frequency of Stimulation
A single neural stimulation produces: a single contraction or twitch which lasts about 7–100 msec Sustained muscular contractions: require many repeated stimuli

62 Tension in a Twitch Length of twitch depends on type of muscle
Figure 10–15a (Navigator)

63 Myogram A graph of twitch tension development
Figure 10–15b (Navigator)

64 3 Phases of Twitch Latent period before contraction:
the action potential moves through sarcolemma causing Ca2+ release Contraction phase: calcium ions bind tension builds to peak Relaxation phase: Ca2+ levels fall active sites are covered tension falls to resting levels

65 Treppe A stair-step increase in twitch tension Figure 10–16a

66 Treppe Repeated stimulations immediately after relaxation phase:
stimulus frequency < 50/second Causes a series of contractions with increasing tension

67 Wave Summation Increasing tension or summation of twitches
Figure 10–16b

68 Wave Summation Repeated stimulations before the end of relaxation phase: stimulus frequency > 50/second Causes increasing tension or summation of twitches

69 Incomplete Tetanus Twitches reach maximum tension
If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension

70 Complete Tetanus If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction

71 What factors affect peak tension production during the contraction of an entire skeletal muscle, and what is the significance of the motor unit in this process?

72 Tension Produced by Whole 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 InterActive Physiology: Contraction of Whole Muscle PLAY

73 Motor Units in a Skeletal Muscle
Figure 10–17

74 Motor Units in a Skeletal Muscle
Contain hundreds of muscle fibers That contract at the same time Controlled by a single motor neuron InterActive Physiology: Contraction of Motor Units PLAY

75 Recruitment (Multiple Motor Unit Summation)
In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulated

76 Maximum Tension Achieved when all motor units reach tetanus
Can be sustained only a very short time Sustained Tension Less than maximum tension Allows motor units to rest in rotation

77 KEY CONCEPT Voluntary muscle contractions involve sustained, tetanic contractions of skeletal muscle fibers Force is increased by increasing the number of stimulated motor units (recruitment)

78 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

79 What are the types of muscle contractions, and how do they differ?
2 Types of Skeletal Muscle Tension Isotonic contraction Isometric contraction

80 Isotonic Contraction Figure 10–18a, b

81 Isotonic Contraction Skeletal muscle changes length:
resulting in motion If muscle tension > resistance: muscle shortens (concentric contraction) If muscle tension < resistance: muscle lengthens (eccentric contraction)

82 Isometric Contraction
Figure 10–18c, d

83 Isometric Contraction
Skeletal muscle develops tension, but is prevented from changing length Note: Iso = same, metric = measure

84 Resistance and Speed of Contraction
Figure 10–19

85 Resistance and Speed of Contraction
Are inversely related The heavier the resistance on a muscle: the longer it takes for shortening to begin and the less the muscle will shorten

86 Muscle Relaxation After contraction, a muscle fiber returns to resting length by: elastic forces opposing muscle contractions gravity

87 Elastic Forces The pull of elastic elements (tendons and ligaments)
Expands the sarcomeres to resting length

88 Opposing Muscle Contractions
Reverse the direction of the original motion Are the work of opposing skeletal muscle pairs Gravity Can take the place of opposing muscle contraction to return a muscle to its resting state

89 What are the mechanisms by which muscle fibers obtain energy to power contractions?

90 ATP and 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

91 ATP and CP Reserves Adenosine triphosphate (ATP):
the active energy molecule Creatine phosphate (CP): the storage molecule for excess ATP energy in resting muscle

92 Recharging ATP Energy recharges ADP to ATP:
using the enzyme creatine phosphokinase (CPK) When CP is used up, other mechanisms generate ATP

93 Energy Storage in Muscle Fiber
Table 10–2

94 ATP Generation Cells produce ATP in 2 ways:
aerobic metabolism of fatty acids in the mitochondria anaerobic glycolysis in the cytoplasm

95 Aerobic Metabolism Is the primary energy source of resting muscles
Breaks down fatty acids Produces 34 ATP molecules per glucose molecule

96 Anaerobic Glycolysis Is the primary energy source for peak muscular activity Produces 2 ATP molecules per molecule of glucose Breaks down glucose from glycogen stored in skeletal muscles

97 Energy Use and Muscle Activity
At peak exertion: muscles lack oxygen to support mitochondria muscles rely on glycolysis for ATP pyruvic acid builds up, is converted to lactic acid

98 Muscle Metabolism InterActive Physiology: Muscle Metabolism PLAY
Figure 10–20a

99 Muscle Metabolism Figure 10–20c

100 What factors contribute to muscle fatigue, and what are the stages and mechanisms involved in muscle recovery?

101 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

102 The Recovery Period The time required after exertion for muscles to return to normal Oxygen becomes available Mitochondrial activity resumes

103 The Cori Cycle The removal and recycling of lactic acid by the liver
Liver converts lactic acid to pyruvic acid Glucose is released to recharge muscle glycogen reserves Oxygen Debt After exercise: the body needs more oxygen than usual to normalize metabolic activities resulting in heavy breathing

104 KEY CONCEPT 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

105 Heat Production and Loss
Active muscles produce heat Up to 70% of muscle energy can be lost as heat, raising body temperature Hormones and Muscle Metabolism Growth hormone Testosterone Thyroid hormones Epinephrine

106 How do the types of muscle fibers relate to muscle performance?

107 Muscle Performance Power: Endurance: Power and endurance depend on:
the maximum amount of tension produced Endurance: the amount of time an activity can be sustained Power and endurance depend on: the types of muscle fibers physical conditioning

108 3 Types of Skeletal Muscle Fibers
1. Fast fibers- Contract very quickly Have large diameter, large glycogen reserves, few mitochondria Have strong contractions, fatigue quickly 2. Slow fibers-Are slow to contract, slow to fatigue Have small diameter, more mitochondria Have high oxygen supply Contain myoglobin (red pigment, binds oxygen) 3. Intermediate fibers-Are mid-sized Have low myoglobin Have more capillaries than fast fiber, slower to fatigue

109 Fast versus Slow Fibers
Figure 10–21

110 Comparing Skeletal Muscle Fibers
Table 10–3

111 Muscles and Fiber Types
White muscle: mostly fast fibers pale (e.g., chicken breast) Red muscle: mostly slow fibers dark (e.g., chicken legs) Most human muscles: mixed fibers pink

112 Muscle Hypertrophy Muscle Atrophy 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

113 What is the difference between aerobic and anaerobic endurance, and their effects on muscular performance? Physical Conditioning – Improves both power and endurance

114 Anaerobic Endurance Anaerobic activities (e.g., 50-meter dash, weightlifting): use fast fibers fatigue quickly with strenuous activity Improved by: frequent, brief, intensive workouts hypertrophy

115 Aerobic Endurance Aerobic activities (prolonged activity):
supported by mitochondria require oxygen and nutrients Improved by: repetitive training (neural responses) cardiovascular training

116 KEY CONCEPT What you don’t use, you loose
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

117 What are the structural and functional differences between skeletal muscle fibers and cardiac muscle cells?

118 Structure of Cardiac Tissue
Cardiac muscle is striated, found only in the heart Figure 10–22

119 7 Characteristics of Cardiocytes
Unlike skeletal muscle, cardiac muscle cells (cardiocytes): are small have a single nucleus have short, wide T tubules

120 7 Characteristics of Cardiocytes
have no triads have SR with no terminal cisternae are aerobic (high in myoglobin, mitochondria) have intercalated discs

121 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

122 Coordination of Cardiocytes
Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

123 4 Functions of Cardiac Tissue
Automaticity: contraction without neural stimulation controlled by pacemaker cells Variable contraction tension: controlled by nervous system Extended contraction time Prevention of wave summation and tetanic contractions by cell membranes

124 Role of Smooth Muscle in Body Systems
Forms around other tissues In blood vessels: regulates blood pressure and flow In reproductive and glandular systems: produces movements In digestive and urinary systems: forms sphincters produces contractions In integumentary system: arrector pili muscles cause goose bumps

125 What are the structural and functional differences between skeletal muscle fibers and smooth muscle cells?

126 Structure of Smooth Muscle
Nonstriated tissue Figure 10–23

127 Comparing Smooth and Striated Muscle
Different internal organization of actin and myosin Different functional characteristics

128 8 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

129 8 Characteristics of Smooth Muscle Cells
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

130 Functional Characteristics of Smooth Muscle
Excitation–contraction coupling Length–tension relationships Control of contractions Smooth muscle tone

131 Excitation–Contraction Coupling
Free Ca2+ in cytoplasm triggers contraction Ca2+ binds with calmodulin: in the sarcoplasm activates myosin light chain kinase Enzyme breaks down ATP, initiates contraction

132 Length–Tension Relationships
Thick and thin filaments are scattered Resting length not related to tension development Functions over a wide range of lengths (plasticity)

133 Control of Contractions
Subdivisions: 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

134 Smooth Muscle Tone Maintains normal levels of activity
Modified by neural, hormonal, or chemical factors

135 Characteristics of Skeletal, Cardiac, and Smooth Muscle
Table 10–4

136 SUMMARY (1 of 3) 3 types of muscle tissue:
skeletal cardiac smooth Functions of skeletal muscles Structure of skeletal muscle cells: endomysium perimysium epimysium Functional anatomy of skeletal muscle fiber: actin and myosin

137 SUMMARY (2 of 3) Nervous control of skeletal muscle fibers:
neuromuscular junctions action potentials Tension production in skeletal muscle fibers: twitch, treppe, tetanus Tension production by skeletal muscles: motor units and contractions Skeletal muscle activity and energy: ATP and CP aerobic and anaerobic energy

138 SUMMARY (3 of 3) Skeletal muscle fatigue and recovery
3 types of skeletal muscle fibers: fast, slow, and intermediate Skeletal muscle performance: white and red muscles physical conditioning Structures and functions of: cardiac muscle tissue smooth muscle tissue

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