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Anatomy and Physiology 2e - Chapter 10: Muscle Tissue
- 1. Muscle Tissue OpenStax Anatomy Chapter 10
- 2. Overview of Muscle Tissues: Objectives Describe the different types of muscle Explain contractibility and extensibility
- 3. Muscle: An Overview • Three muscle tissue types • Skeletal • Smooth • Cardiac • Muscle tissue properties • Excitability • Elasticity • Extensibility • Contractility
- 4. Skeletal Muscle: Objectives Describe Describe excitation-contraction coupling Identify Identify areas of the skeletal muscle fibers Explain Explain how muscles work with tendons to move the body Describe Describe the layers of connective tissues packaging skeletal muscle
- 5. Connective Tissue Layers • Epimysium • Wraps entire muscle • Separates it from others • Allows contraction while maintaining stability • Perimysium • Surrounds Fascicles • Common in limbs • Allows movement of specific muscles • Endomysium • Contains extracellular fluid and nutrients • Aponeurosis • Fascia • Connective tissue between skin and bones
- 6. Skeletal Muscle Fibers • Sarcolemma • Plasma membrane • Sarcoplasm • Cytoplasm • Sarcoplasmic reticulum • Specialized ER • Calcium ions • Actin • Think filaments • Myosin • Thick filaments
- 7. The Sarcomere • Functional unit of a muscle fiber • Region of one Z-line to the next Z- line • 2 micrometers in length • Thin filaments • Action + troponin-tropomyosin • Thick filaments • Myosin
- 8. The Neuromuscular Junction • Site where motor neuron meets muscle fiber • Muscles first response is here • Excitation by Neuron is the only functional way to activate contraction • Excitation-Contraction Coupling • Skeletal muscles must be “excited” in order to contract • The excitation sweeps along the sarcolemma as a wave
- 9. Excitation-Contraction Coupling • Begins with signals from Somatic Nervous System • Excitation is always triggered by nervous system • Action potential travels Axon of motor neuron • Terminates at NMJ • Acetylcholine is released • Neurotransmitter • Crosses Synaptic cleft • Binds to receptors leading to depolarization
- 10. Excitation-Contraction Coupling • Voltage-Gated sodium channels • Open and Sodium enters Muscle fiber • Excess Ach degraded • Acetylcholinesterase • T-Tubules • Propagate signal • Allow action potential to reach membrane of SR • Carry action potential to interior of the cell • Triads surround Myofibrils
- 11. Muscle Fiber Contraction and Relaxation: Objectives Describe the components involved in a muscle contraction Describe Explain how muscles contract and relax Explain Describe the sliding filament model of muscle contraction Describe
- 12. Contraction of a Muscle Fiber • Lets walk through the steps…
- 13. Relaxation of a Muscle Fiber • Lets go through the steps…
- 14. Sliding Filament Model • Thin filaments are pulled • Slide past thick filaments • Only occurs when Myosin binding sites are exposed • Normally covered by Tropomyosin • Calcium binds to troponin • Causes tropomyosin to slide away • Myosin heads bind to form cross bridge
- 15. Sliding Filament Model • Z lines move together • I band comes smaller • A band stays the same • H zone shrinks This Photo by Unknown Author is licensed under CC BY-SA
- 16. ATP and Muscle Contraction • Active site is on actin is exposed • This happens as Calcium binds to troponin • Myosin head binds to actin and forms cross bridge • Phosphate is released during power stroke • Causes myosin head to pivot towards center of sarcomere • ADP and Phosphate are released
- 17. ATP and Muscle Contraction • New ATP attaches • Causes cross bridge to detach • Myosin hydrolyzes ATP • Forms ADP • Returns Myosin to cocked position
- 18. Muscle Metabolism • ATP is critical for: • Cross-bridge cycle • Active transport of Calcium • Creatine Phosphate • Stores energy in phosphate bonds • In resting muscle, excess ATP transfers energy to Creatine • Creatine Kinase breaks it down • 15 seconds worth of energy
- 19. Muscle Metabolism • Glycolysis is Next • Anaerobic process • Slower rate of ATP availability • Aerobic respiration • 95% of ATP required for resting or moderately active muscles • Oxygen Debt • Intense muscle activity • Amount of oxygen needed to compensate for ATP produced without oxygen • Needed to: restore ATP and Creating phosphate levels, Convert lactic acid to pyruvic acid or glucose/glycogen in liver
- 20. Relaxation and Strength • Relaxation begins with Motor neuron • ACh release stops • Muscle fiber repolarizes • Calcium gates close • Actin-binding sites are shielded • Muscle strength • Number of muscles fibers is genetically determined • Strength related to myofibrils and sarcomeres • Can increase as a result of hormones and stress This Photo by Unknown Author is licensed under CC BY-ND
- 21. Nervous System Control of Muscle Tension: Objectives Explain concentric, isotonic, and eccentric contractions Explain Describe the length-tension relationship Describe Describe the three phases of a muscle twitch Describe Define wave summation, tetanus, and treppe Define
- 22. Types of Muscle Contractions • Muscle tension • Force generated by contraction • Isotonic • Tension in muscle stays constant • Concentric Contraction • Muscle shortens to move load • Eccentric contraction • Muscle lengthens • Isometric • Muscle produces tension without changing angle
- 23. Motor Units • Group of muscle fibers innervated by a single motor neuron • Size depends on nature of muscle • Small motor units • Single motor neuron supplies small number of muscle fibers • Fine motor control • Eye muscles • Large Motor Unit • Single motor neuron supplies large number of muscle fibers • Gross movements • Recruitment • As more strength is needed, additional motor units are activated • Increases contraction force This Photo by Unknown Author is licensed under CC BY-SA
- 24. Sarcomere Length-Tension Range • Maximal tension occurs at 80-120% of a sarcomeres resting length • Longer=thick and thin filaments don’t overlap • Shorter=Zone of overlap is reduced , thin filaments can’t go anywhere
- 25. Frequency of Motor Neuron Stimulation • Single stimulus produce single contraction • Called a twitch • A few to 100 milliseconds • Tension measure with myogram • Latent period • Action potential propagates • Contraction phase • Calcium binds troponin • Cross bridges form • Relaxation phase • Contraction stops • Muscle fibers return to rest
- 26. Wave Summation and Tetanus • Wave summation • Fibers stimulated while previous twitch is still occurring • Excitation-contraction coupling affects are added together • Occurs because second stimulus causes more calcium to be released • Tetanus • Continuous contraction • Calcium allows all sarcomeres to form cross-bridges
- 27. Treppe • Muscle tension increases in graded manner • Muscles dormant for extended periods • Muscle contractions become more efficient • Only maintained with steady ATP
- 28. Muscle Tone • Muscles are contracted small amounts • Few motor units are activated at any given time • Prevents fatigue • Hypotonia • Flaccid muscles • Functional impairments • Hypertonia • Muscle rigidity • Excessive reflex responses This Photo by Unknown Author is licensed under CC BY
- 29. Types of Muscle Fibers: Objectives Describe the types of skeletal muscle fibers Explain fast and slow muscle fibers
- 30. Types of Muscle Fibers • Slow oxidative • Contract slowly • Use aerobic respiration • Fast oxidative • Fast contraction • Aerobic respiration • Can switch to anaerobic • Fast glycolytic • Fast contraction • Anaerobic glycolysis • Fatigue more quickly This Photo by Unknown Author is licensed under CC BY-SA
- 31. Exercise and Muscle Performance: Objectives Describe hypertrophy and atrophy Describe Explain how resistance exercise builds muscle Explain Explain how performance-enhancing substances affect muscle Explain
- 32. Endurance Exercise • Predominately slow fibers • Little force but numerous repetitions • Training makes fibers more efficient • More mitochondria produced • Myoglobin increases (Oxygen storage) • Angiogenesis to supply more oxygen and remove waste
- 33. Resistance Exercise • Fast glycolytic fibers • Short, powerful movements • Muscles have higher ratio of FG to SO/FO • Increases myofibril formation • Increases thickness of muscle • Leads to hypertrophy • No increased mitochondria or angiogenesis
- 34. Performance Enhancing Substitutes • Anabolic steroids • Stimulate muscle formation • Oxygen availability • Erythropoietin • Human Growth Hormone • Promotes muscle healing • Faster recovery • Creatine • Provides quick bursts of ATP This Photo by Unknown Author is licensed under CC BY-NC-ND
- 35. Cardiac Muscle Tissue: Objectives Describe intercalated discs and gap junctions Describe a desmosome
- 36. Cardiac Muscle • Found only in Heart • Striated • Sarcomeres • Intercalated disc • Allows cardiac muscle cells to contract in wave like pattern • Desmosomes • Anchors the ends of cardiac muscle fibers together • Autorhythmicity • Pacemaker cells control contraction of the heart
- 37. Smooth Muscle: Objectives Describe a dense body Describe Explain how smooth muscle works with internal organs and passageways through the body Explain Explain how smooth muscles differ from skeletal and cardiac muscle Explain Explain the difference between single-unit and multi-unit smooth muscle Explain
- 38. Smooth Muscle • Found in walls of hollow organs • Spindle shaped fibers • 30 to 200 micrometers in length • No striations • Do contain thick and thin filaments • Dense body • Analogous to the Z-disc • Anchors thin filaments • Calmodulin • Regulates cross bridges • Calcium binds, activates myosin kinase • Activates myosin heads
- 39. Smooth Muscle Contraction • Once myosin is activated: • Myosin attaches to Actin • Pulls on thin filaments • Dense bodies are pulled on • Ends of muscle pull towards center • T-tubules are not required • Smaller diameter muscles • Long function periods mean: • Power output is low • Contractions continue without using lots of energy • Latch bridges • Smooth muscles can maintain contraction when Calcium is removed
- 40. Involuntary Control • NMJs are not as organized as skeletal muscle • Varicosity • Series of neurotransmitter- filled bulges • Release neurotransmitters into synaptic cleft • Pacesetter cell • Spontaneously trigger action potentials and contractions
- 41. Involuntary Control • Single-Unit smooth muscle • More common • Muscle fibers joined by gap junctions • Muscle contracts as single unit • Visceral muscle • Stress-relaxation response • Stretching triggers contraction • Multi-unit smooth muscle • Not electrically coupled • Large blood vessels
- 42. Development and Regeneration of Muscle Tissue: Objectives Describe the function of satellite cells Describe Define fibrosis Define Explain why muscle has the greatest regeneration ability Explain
- 43. Muscle Development and Regeneration • Embryonic Mesoderm • Skeletal muscle develops from Mesodermal somites • Skeletal muscle in head and limbs develop from General mesoderm • Somites • Give rise to myoblasts • Myoblast • Muscle forming stem cell • Migrates and fuse to form Myotube This Photo by Unknown Author is licensed under CC BY-SA
- 44. Muscle Development and Regeneration • Satellite cell • Similar to Myoblast • Incorporated into muscle cells • Facilitate protein synthesis • Repair and growth • Fibrosis • Muscle fibers replaced by scar tissue • Pericyte • Stem cell that regenerates smooth muscle This Photo by Unknown Author is licensed under CC BY-SA