Presentation is loading. Please wait.

Presentation is loading. Please wait.

Muscles and Muscle Tissue

Similar presentations


Presentation on theme: "Muscles and Muscle Tissue"— Presentation transcript:

1 Muscles and Muscle Tissue
Human Anatomy & Physiology Chapter 9 (Pages 275 – 319)

2 Three Types of Muscle Tissue
1. Skeletal muscle tissue: Attached to bones and skin Striated Voluntary (conscious control) Powerful 2. Cardiac muscle tissue: Only in the heart Involuntary 3. Smooth muscle tissue: In the walls of hollow organs (stomach, urinary bladder, airways) Not striated Skeletal muscle is the primary topic in this unit Longest muscle cells Skeletal, striated, voluntary Responsible for mobility, tires easily Cardiac Muscle Makes up heart walls Controlled by nervous system Cardiac, striated, involuntary Smooth Muscle Function = force fluids and other substances through internal body channels Visceral, nonstriated, involuntary Walls of hollow organs (digestive, urinary, reproductive tracts)

3 Skeletal – attached to skeleton
Cardiac – walls of the heart Smooth – walls of hollow organs, airway Table 9.3

4 Muscle Functions 1. Movement of bones or fluids (blood) 2. Maintaining posture and body position 3. Stabilizing joints 4. Heat generation (especially skeletal muscle)

5 Skeletal Muscle Each muscle is served by one artery, one nerve, and one or more veins Connective tissue sheaths of skeletal muscle: Epimysium: surrounds entire muscle Perimysium: surrounds fascicles (groups of muscle fibers) Endomysium: surrounds each muscle fiber

6 (wrapped by perimysium)
Epimysium Epimysium Bone Perimysium Tendon Endomysium Muscle fiber in middle of a fascicle Blood vessel Fascicle (wrapped by perimysium) Endomysium (between individual muscle fibers) Perimysium Fascicle Muscle fiber Figure 9.1

7 Table 9.1

8 Microscopic Anatomy of Skeletal Muscle Fiber
Cylindrical cell 10 to 100 m in diameter, up to 30 cm long Multiple nuclei Many mitochondria Glycosomes for glycogen storage, myoglobin for O2 storage Myofibrils – contractile filaments Sarcoplasmic reticulum – stores and releases Calcium when needed for contraction T tubules – conduct impulses deep into muscle

9 Diagram of part of a muscle fiber showing the myofibrils
Sarcolemma Mitochondrion Myofibril Nucleus Diagram of part of a muscle fiber showing the myofibrils (One myofibril is extended from the cut end of the fiber) Table 9.1

10 Sarcomere Smallest contractile unit (functional unit) of a muscle fiber Composed of thick and thin myofilaments made of contractile proteins

11 Thin (actin) filament Z disc Z disc Thick (myosin) filament Sarcomere Small part of one myofibril enlarged to show the myofilaments responsible for banding pattern. Each sarcomere extends from one Z disc to the next. Sarcomere Z disc Z disc Thin (actin) filament Elastic filaments Thick (myosin) filament Enlargement of one sarcomere (sectioned lengthwise) Notice the myosin heads on the thick filaments Figure 9.2 c, d

12 Longitudinal section of filaments within one sarcomere of a myofibril
Thick filament Thin filament Thick filament Thin filament Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament. A thin filament consists of two strands of actin subunits twisted into a helix plus two types of regulatory proteins (troponin and tropomyosin). Portion of a thick filament Portion of a thin filament Myosin head Tropomyosin Troponin Actin Actin-binding sites Heads Tail Active sites for myosin attachment ATP- binding site Actin subunits Myosin molecule Actin subunits Figure 9.3

13 Sliding Filament Model of Contraction
In the relaxed state, thin and thick filaments overlap only slightly During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments Sarcomeres shorten, muscle fibers shorten, whole muscle shortens

14 Fully relaxed sarcomere of a muscle fiber
1 Fully relaxed sarcomere of a muscle fiber 2 Fully contracted sarcomere of a muscle fiber Figure 9.6

15 Requirements for Skeletal Muscle Contraction
1. Activation: neural stimulation at neuromuscular junction 2. Excitation-contraction coupling: a. Generation and propagation of an action potential along the sarcolemma b. Final trigger: a brief rise in intracellular Ca2+ levels (Ca2+ released from the sarcoplasmic reticulum)

16 2. Excitation-Contraction (E-C) Coupling
Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments Latent period: Time when E-C coupling events occur Time between AP initiation and the beginning of contraction AP is propagated along sarcomere to T tubules Voltage-sensitive proteins stimulate Ca2+ release from SR Ca2+ is necessary for contraction

17 Terminal cisterna of SR
Setting the stage Axon terminal of motor neuron Synaptic cleft Action potential is generated ACh Sarcolemma Terminal cisterna of SR Muscle fiber Ca2+ One sarcomere Figure 9.11, step 1

18 Figure 9.11, step 2 Steps in E-C Coupling: The aftermath Sarcolemma
Voltage-sensitive tubule protein T tubule 1 Action potential is propagated along the sarcolemma and down the T tubules. Ca2+ release channel Calcium ions are released. 2 Terminal cisterna of SR Ca2+ Actin Troponin Tropomyosin blocking active sites Ca2+ Myosin Calcium binds to troponin and removes the blocking action of tropomyosin. 3 Active sites exposed and ready for myosin binding Contraction begins 4 Myosin cross bridge The aftermath Figure 9.11, step 2

19 3. Role of Calcium (Ca2+) in Contraction
3a. At low intracellular Ca2+ concentration: Tropomyosin blocks the active sites on actin Myosin heads cannot attach to actin Muscle fiber relaxes 3b. At higher intracellular Ca2+ concentrations: Ca2+ binds to troponin Troponin changes shape and moves tropomyosin away from active sites Events of the cross bridge cycle occur When nervous stimulation ceases, Ca2+ is pumped back into the SR and contraction ends

20 4. Cross Bridge Cycle Continues as long as the Ca2+ signal and adequate ATP are present Cross bridge formation—high-energy myosin head attaches to thin filament Working (power) stroke—myosin head pivots and pulls thin filament Cross bridge detachment —ATP attaches to myosin head and the cross bridge detaches “Cocking” of the myosin head—energy from hydrolysis of ATP cocks the myosin head into the high-energy state

21 Figure 9.12 Thin filament Actin Ca2+ Myosin cross bridge Thick
ADP Pi Thick filament Myosin 1 Cross bridge formation. ADP ADP Pi ATP hydrolysis Pi 4 Cocking of myosin head. 2 The power (working) stroke. ATP ATP 3 Cross bridge detachment. Figure 9.12

22 Motor Unit: The Nerve-Muscle Functional Unit
Motor unit = a motor neuron and all (four to several hundred) muscle fibers it supplies Small motor units in muscles that control fine movements (fingers, eyes) Large motor units in large weight-bearing muscles (thighs, hips)

23 neuromuscular junctions
Spinal cord Motor neuron cell body Muscle Nerve Motor unit 1 unit 2 fibers neuron axon Axon terminals at neuromuscular junctions Axons of motor neurons extend from the spinal cord to the muscle. There each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle. Figure 9.13a

24 Muscle Twitch Response of a muscle to a single, brief threshold stimulus Three phases of a twitch: Latent period: events of excitation-contraction coupling Period of contraction: cross bridge formation; tension increases Period of relaxation: Ca2+ reentry into the SR; tension declines to zero

25 Myogram showing the three phases of an isometric twitch
Latent period Single stimulus Period of contraction relaxation Myogram showing the three phases of an isometric twitch Figure 9.14a

26 Graded Muscle Responses
Variations in the degree of muscle contraction Required for proper control of skeletal movement Responses are graded by: Changing the frequency of stimulation A single stimulus results in a single contractile response—a muscle twitch If stimuli are given quickly enough, fused (complete) tetany results Changing the strength of the stimulus

27 A single stimulus is delivered. The muscle contracts and relaxes
Contraction Relaxation Stimulus Single stimulus single twitch A single stimulus is delivered. The muscle contracts and relaxes Figure 9.15a

28 Response to Change in Stimulus Strength
Threshold stimulus: stimulus strength at which the first observable muscle contraction occurs Muscle contracts more vigorously as stimulus strength is increased above threshold Contraction force is precisely controlled by recruitment (multiple motor unit summation), which brings more and more muscle fibers into action

29 Maximal stimulus Threshold
Stimulus strength Proportion of motor units excited Strength of muscle contraction Maximal contraction Maximal stimulus Threshold Figure 9.16

30 Response to Change in Stimulus Strength
Size principle: motor units with larger and larger fibers are recruited as stimulus intensity increases

31 Figure 9.18a

32 Figure 9.18b

33 Muscle Metabolism: Energy for Contraction
ATP is the only source used directly for contractile activities Available stores of ATP are depleted in 4–6 seconds ATP is regenerated by: Direct phosphorylation of ADP by creatine phosphate (CP) Anaerobic pathway (glycolysis) Aerobic respiration

34 Glucose (from glycogen breakdown or delivered from blood)
Energy source: glucose Glycolysis and lactic acid formation (b) Anaerobic pathway Oxygen use: None Products: 2 ATP per glucose, lactic acid Duration of energy provision: 60 seconds, or slightly more Glucose (from glycogen breakdown or delivered from blood) Glycolysis in cytosol Pyruvic acid Released to blood net gain 2 Lactic acid O2 ATP Figure 9.19b

35 Anaerobic Pathway No O2 used! At 70% of maximum contractile activity:
Bulging muscles compress blood vessels Oxygen delivery is impaired Pyruvic acid is converted into lactic acid Lactic acid: Diffuses into the bloodstream Used as fuel by the liver, kidneys, and heart Converted back into pyruvic acid by the liver

36 Glucose (from glycogen breakdown or delivered from blood)
Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism (c) Aerobic pathway Aerobic cellular respiration Oxygen use: Required Products: 32 ATP per glucose, CO2, H2O Duration of energy provision: Hours Glucose (from glycogen breakdown or delivered from blood) 32 O2 H2O CO2 Pyruvic acid Fatty acids Amino Aerobic respiration in mitochondria ATP net gain per glucose Figure 9.19c

37 Aerobic Pathway Requires O2
Produces 95% of ATP during rest and light to moderate exercise Fuels: stored glycogen, then blood borne glucose, pyruvic acid from glycolysis, and free fatty acids Glucose + O2  CO2 + H2O + ATP

38 Short-duration exercise
Prolonged-duration exercise ATP stored in muscles is used first. ATP is formed from creatine Phosphate and ADP. Glycogen stored in muscles is broken down to glucose, which is oxidized to generate ATP. ATP is generated by breakdown of several nutrient energy fuels by aerobic pathway. This pathway uses oxygen released from myoglobin or delivered in the blood by hemoglobin. When it ends, the oxygen deficit is paid back. Figure 9.20

39 Muscle Fatigue Physiological inability to contract Occurs when:
Ionic imbalances (K+, Ca2+, Pi) interfere with E-C coupling Prolonged exercise damages the SR and interferes with Ca2+ regulation and release Total lack of ATP occurs rarely, during states of continuous contraction, and causes contractures (continuous contractions)

40 Force of Muscle Contraction
The force of contraction is affected by: Number of muscle fibers stimulated (recruitment) Relative size of the fibers—hypertrophy of cells increases strength Frequency of stimulation— frequency allows time for more effective transfer of tension to noncontractile components Length-tension relationship—muscles contract most strongly when muscle fibers are 80–120% of their normal resting length

41 Large number of muscle fibers activated Muscle and sarcomere
stretched to slightly over 100% of resting length Large muscle fibers High frequency of stimulation Contractile force Figure 9.21

42 Sarcomeres excessively
greatly shortened Sarcomeres at resting length Sarcomeres excessively stretched 75% 100% 170% Optimal sarcomere operating length (80%–120% of resting length) Figure 9.22

43 Muscle Fiber Type Classified according to two characteristics:
Speed of contraction: slow or fast, according to: Speed at which myosin ATPases split ATP Pattern of electrical activity of the motor neurons Metabolic pathways for ATP synthesis: Oxidative fibers—use aerobic pathways Glycolytic fibers—use anaerobic glycolysis Three fiber types: Slow oxidative fibers (Type I) Fast oxidative fibers (Type IIa) Fast glycolytic fibers (Type IIb)

44 Maximum duration of use Mitochondrial density
Fiber Type Type I fibers Type II a fibers Type II x fibers Type II b fibers Contraction time Slow Moderately Fast Fast Very fast Size of motor neuron Small Medium Large Very large Resistance to fatigue High Fairly high Intermediate Low Activity Used for Aerobic Long-term anaerobic Short-term anaerobic Maximum duration of use Hours <30 minutes <5 minutes <1 minute Power produced Very high Mitochondrial density Capillary density Oxidative capacity Glycolytic capacity Major storage fuel Triglycerides Creatine phosphate, glycogen

45 Table 9.2

46 Predominance of fast glycolytic (fatigable) fibers Small load
of slow oxidative (fatigue-resistant) fibers Contractile velocity Contractile duration Figure 9.23

47 FO SO FG Figure 9.24

48

49 The greater the load, the less the muscle contraction
Light load Intermediate load Heavy load Stimulus The greater the load, the less the muscle shortens and the shorter the duration of contraction The greater the load, the slower the contraction Figure 9.25

50 Effects of Exercise Aerobic (endurance) exercise: Leads to increased:
Muscle capillaries Number of mitochondria Myoglobin synthesis Results in greater endurance, strength, and resistance to fatigue May convert fast glycolytic fibers into fast oxidative fibers

51 Effects of Resistance Exercise
Resistance exercise (typically anaerobic) results in: Muscle hypertrophy (due to increase in fiber size) Increased mitochondria, myofilaments, glycogen stores, and connective tissue

52 The Overload Principle
Forcing a muscle to work hard promotes increased muscle strength and endurance Muscles adapt to increased demands Muscles must be overloaded to produce further gains

53 Why Warm up? Treppe - muscles increase strength of contraction due to:
increased availability of Ca2+ Increased warmth due to activity causes an increase in the efficiency of muscle enzymes

54 Smooth Muscle Longitudinal layer of smooth muscle (shows smooth
muscle fibers in cross section) Small intestine Mucosa Cross section of the intestine showing the smooth muscle layers (one circular and the other longitudinal) running at right angles to each other. Circular layer of smooth muscle (shows longitudinal views of smooth muscle fibers) Figure 9.26

55 Peristalsis Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs Longitudinal layer contracts; organ dilates and shortens Circular layer contracts; organ constricts and elongates

56 Table 9.3

57 Table 9.3

58 Myofilaments in Smooth Muscle
Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2) Thick filaments have heads along their entire length No troponin complex; protein calmodulin binds Ca2+ Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner

59 Figure 9.28a

60 Figure 9.28b

61 Contraction of Smooth Muscle
Slow, synchronized contractions Cells are electrically coupled by gap junctions Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for sheets of muscle Rate and intensity of contraction may be modified by neural and chemical stimuli Sliding filament mechanism Final trigger is  intracellular Ca2+ Ca2+ is obtained from the SR and extracellular space

62 Table 9.3

63 Special Features of Smooth Muscle Contraction
Stress-relaxation response: Responds to stretch only briefly, then adapts to new length Retains ability to contract on demand Enables organs such as the stomach and bladder to temporarily store contents Length and tension changes: Can contract when between half and twice its resting length Hyperplasia Muscle cells divide to multiply numbers EX: response of uterus to estrogen

64 Table 9.3

65 Types of Smooth Muscle Single-unit (visceral) smooth muscle:
Sheets contract rhythmically as a unit (gap junctions) Arranged in opposing sheets and exhibit stress-relaxation response Multiunit smooth muscle: Located in large airways, large arteries, arrector pili muscles, and iris of eye Gap junctions are rare Arranged in motor units Graded contractions occur in response to neural stimuli

66 Developmental Aspects
Cardiac and skeletal muscle become amitotic, but can lengthen and thicken Skeletal muscle cells have limited regenerative ability Injured heart muscle is mostly replaced by connective tissue Smooth muscle regenerates throughout life Athletics and training can improve neuromuscular control

67 Developmental Aspects
Female skeletal muscle makes up 36% of body mass Male skeletal muscle makes up 42% of body mass, primarily due to testosterone Body strength per unit muscle mass is the same in both sexes With age, connective tissue increases and muscle fibers decrease By age 30, loss of muscle mass (sarcopenia) begins Regular exercise reverses sarcopenia

68 Muscular Dystrophy Group of inherited muscle-destroying diseases
Muscles enlarge due to fat and connective tissue deposits Muscle fibers atrophy Duchenne muscular dystrophy (DMD): Most common and severe type Inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin Victims become clumsy and fall frequently; usually die of respiratory failure in their 20s No cure, but viral gene therapy or infusion of stem cells with correct dystrophin genes show promise


Download ppt "Muscles and Muscle Tissue"

Similar presentations


Ads by Google