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09 The Muscular System.pdf
- 1. MuscularSystem Principles of Anatomy and Physiology
- 2. Location Function Appearance Control Skeletal Skeletal Move bones Multinucleated and striated Voluntary Cardiac Heart Pump blood 1nucleus, striated, and intercalated discs Involuntary Visceral (smooth muscle) Various organs, example: GI tract Various functions, example: peristalsis 1nucleus and no striations Involuntary 3 Types of Muscular Tissue OpenStax College, Skeletal Smooth Cardiac, https://commons.wikimedia.org/wiki/File:414_Skeletal_Smooth_Cardiac.jpg, CC BY 3.0
- 3. Functions of Muscular Tissue Producing body movements Stabilizing body positions Generating heat Storing and mobilizing substances within the body
- 4. Electrical excitability Contractility Extensibility Elasticity Properties of Muscular Tissue
- 5. Levels of Organization within a Skeletal Muscle Skeletalmuscle Skeletal muscle Epimysium Muscle fascicle Organ made up of fascicles that contain muscle fibers (cells), blood vessels, and nerves; wrapped in epimysium Fascicle Muscle fascicle Perimysium Endomysium Muscle fiber Bundle of muscle fibers wrapped in perimysium
- 6. Levels of Organization within a Skeletal Muscle Muscle fiber (cell) Muscle fiber Sarcolemma Myofibrils • Long, cylindrical cell covered by endomysium and sarcolemma • Contains sarcoplasm, myofibrils, peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum, and terminal cisterns • Striated appearance Myofibril Sarcoplasmic Thin (actin) Sarcomere H zone Thick reticulum filament (myosin) filament I band A band Z disc M line • Threadlike contractile elements within the sarcoplasm of muscle fiber that extend for the entire length of the fiber • Composed of filaments
- 7. Filaments (myofilaments ) 2 types of contractile proteins within myofibrils are: • Thick filaments composed of myosin • Thin filaments composed of actin, tropomyosin and troponin • Sliding of thin filaments past thick filaments produces muscle shortening Levels of Organization within a Skeletal Muscle Myofibrils Portion of a thick filament Myosin head Portion of a thin filament Tropomyosin Actin Troponin
- 8. Muscle Myofibril fiber Microscopic Anatomy of a Muscle Fiber Sarcomere Thick (myosin) filament Thin (actin) filament I band A band M line Z disc H zone Sarcoplasmic reticulum
- 9. Muscle Myofibril fiber Microscopic Anatomy of a Muscle Fiber T erminal cisterna T tubule Triad Sarcoplasmic reticulum
- 10. Components of a Sarcomere Z discs Narrow, plate-shaped regions of dense material that separate one sarcomere from the next A band Dark, middle part of the sarcomere that extends for the entire length of the thick filaments and includes those parts of the thin filament that overlap them I band Lighter, less dense area of the sarcomere that contains the remainder of the thin filaments but no thick ones. A Z disc passes through the center of each I band. H zone Narrow region in the center of each A band that contains thick filaments but no thin filaments M line Region in the center of the H zone that contains proteins that hold thick filaments together at the center of the sarcomere
- 12. Muscle Proteins Regulatory Troponin Tropomyosin
- 13. Muscle Proteins Structural Alpha-actinin (structural protein of Z disc) Nebulin (anchors thin filaments to Z disc) Dystrophin (links thin filament to integral membrane proteins) Myomesin (forms M line proteins) Titin (connects Z disc to M line)
- 14. Skeletal Muscle Fiber Proteins Type Description Contractile proteins: Proteins that generate force during muscle contractions Myosin Contractile protein that makes up a thick filament; molecule consists of a tail and 2 myosin heads, which bind to myosin-binding sites on actin molecules of a thin filament during muscle contraction Actin Contractile protein that is the main component of a thin filament; each actin molecule has a myosin-binding site where the myosin head of a thick filament binds during muscle contraction Regulatory proteins: Proteins that help switch the muscle contraction process on and off Tropomyosin Regulatory protein that is a component of a thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin Troponin Regulatory protein that is a component of a thin filament; when calcium ions (Ca2+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin- binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin
- 15. Skeletal Muscle Fiber Proteins Type Description Structural proteins: Proteins that keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to the sarcolemma and the extracellular matrix Titin Structural protein that connects the Z disc to the M line of a sarcomere, thereby helping to stabilize the thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils -Actinin Structural protein of Z discs that attaches to actin molecules of a thin filament; helps anchor thin filaments to Z discs and regulates the length of thin filaments during development Myomesin Structural protein that wraps around the entire length of each thin filament; helps anchor thin filaments to Z discs and regulates the length of the thin filaments during development Nebulin Structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development Dystrophin Structural protein that links thin filaments of a sarcomere to integral membrane proteins in the sarcolemma, which are attached in turn to proteins in the connective tissue matrix that surrounds muscle fibers; thought to help reinforce the sarcolemma and help transmit tension generated by sarcomeres to tendons
- 16. The Sliding Filament Mechanism Myosin pulls on actin Thin filament slides inward Z discs move toward each other, and the sarcomere shortens Muscle contraction H H M M Z Z Z Z
- 17. Cocking of myosin head The Contraction Cycle Crossbridgedetachment Calcium Actin Thin filament Crossbridge Thick filament Myosin head ATP attaches and myosin head detaches Power stroke ADPand Pi released Thin filament Myosin head Thick filament Troponin Calcium binding ADPand Pi
- 18. Excitation-contraction Coupling Sarcoplasmic reticulum T tubule + + + + + Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) This concept connects the events of a muscle action potential with the sliding filament mechanism. Action potential (depolarization) Sarcoplasm Voltage-gated Ca2+ channel (open) Channel sensor Ca2+
- 19. Excitation-contraction Coupling This concept connects the events of a muscle action potential with the sliding filament mechanism. Sarcoplasm Sarcoplasmic reticulum + + + + T tubule + Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) Repolarization Channel sensor Ca2+ Voltage-gated Ca2+ channel (closed)
- 20. Length-tension Relationship %Sarcomere length Tension (%of maximum) The force of a muscle contraction depends on the length of the sarcomeresin a muscle before contraction. Optimal Too small Overstretched
- 21. What Starts the Excitation Process? Synaptic cleft Nerve impulse (action potential) Synaptic end bulb Motor end-plate Synaptic vesicle containingACh* Sarcolemma Neuromuscular junction Sarcolemma Myelin sheath surrounding axon of motor neuron muscle fiber Sarcoplasm Axon terminal Synaptic end bulb Myofibril of
- 22. What Starts the Excitation Process? Na+ Calcium Synaptic end bulb Nerve impulse (action potential) Voltage-gated calcium channels Synaptic vesicle containingACh* Synaptic cleft Ligand-gated sodium channel Motor end-plate Na+
- 23. Sarcoplasm Sarcoplasmic reticulum T tubule + + + + + Action potential (depolarization) Voltage-gated Ca2+ channel (open) Channel sensor Ca2+ What Starts the Excitation Process?
- 24. What Starts the Excitation Process? Synaptic cleft Acetylcholinesterase • Breaks down ACh Na-
- 27. Muscle Metabolism Creation of creatine phosphate How do muscles derive the ATP necessary to power the contraction cycle? Anaerobic glycolysis Cellular respiration
- 28. Creation of Creatine Phosphate (CP) Creatine kinase catalyzes the transfer of a phosphate group from CP to ADP to rapidly yieldATP . Duration of energy provided: 15 seconds Creatine Creatine phosphate Creatine kinase + ADP Restingmuscle + ATP Energy for muscle contraction Active muscle ATP + Creatine
- 29. When CP stores are depleted, glucose is converted into pyruvic acid to generate ATP. Glycolysis Anaerobic Glycolysis Duration of energy provided: 2 minutes ATP ATP Pyruvate Pyruvate Lactic acid to blood No oxygen Blood glucose Muscle glycogen Glucose
- 30. Under aerobic conditions, pyruvic acid can enter the mitochondria and undergo a series of oxygen-requiring reactions to generate large amounts of ATP . Cellular Respiration
- 31. Cellular Respiration Duration of energy provided: minutes up to hours Pyruvic acid Fatty acids Heat CO2 H2O Pyruvic acid can enter the mitochondria and undergo a series of oxygen-requiring reactions to generate large amounts of ATP . O2 Blood glucose Cellular respiration in mitochondria 28 34 ATPmolecules
- 32. Muscle fatigueis the inability to maintain the force of contraction after prolonged activity. Muscle Fatigue
- 33. The onset of fatigue is due to: • Inadequate release of Ca2+ from SR • Depletion of CP , oxygen, and nutrients • Build-up of lactic acid and ADP • Insufficient release of ACh at the neuromuscular junction (NMJ) Muscle Fatigue
- 34. Central fatigue is the type of fatigue associated with the concentration of neurotransmitters within the central nervous system,which affects muscle function. Central Fatigue
- 35. oxygen debt Oxygen Consumption after Exercise Why do people continue to breathe heavily for a time after stopping exercise?
- 36. The extra oxygen goes toward: Oxygen Consumption after Exercise Replenishing CPstores Converting lactate into pyruvate Reloading O2 onto myoglobin
- 37. Control of Muscle Tension Somatic motor neuron Muscle fibers Spinal cord The strength of a muscle contraction depends on how many motor units are activated. Weak muscle contraction Activation of a few motor units Strong muscle contraction Activation of many motor units
- 39. Wave summation → results in a stronger contraction Frequency of Stimulation Unfused tetanus Fused tetanus Time Time Time T ension
- 40. Factors that Influence Tension 3. Sarcomere length 1. Size of motor unit 2. Recruitment of motor units 4. Frequency of stimulation
- 41. Even when at rest, a skeletal muscle exhibits a small amount of tension, called tone. Tone is established by the alternating, involuntary action of small groups of motor units in a muscle. Muscle Tone
- 42. Isotonic Isometric Tension is constant while muscle length changes. A muscle contracts but does not change in length. Isotonic vs. Isometric Contractions Concentric Eccentric
- 43. Structural Characteristics Structural characteristics Slow oxidative fibers (1) Fast oxidative- glycolytic fibers (2) Fast glycolytic fibers (3) Myoglobin content Large amount Large amount Small amount Mitochondria Many Many Few Capillaries Many Many Few Color Red Red-pink White (pale) 1 2 3 3 1 2
- 44. Functional Characteristics Functional characteristics Slow oxidativefibers Fast oxidative- glycolyticfibers Fast glycolyticfibers Capacity for generating ATP and method used High, by aerobic respiration Intermediate,by both aerobic respiration and anaerobic glycolysis Low, by anaerobic glycolysis Rate of ATP hydrolysis by myosin ATPase Slow Fast Fast Contraction velocity Slow Fast Fast Fatigue resistance High Intermediate Low Creatine kinase Lowest amount Intermediate amount Highest amount Glycogen stores Low Intermediate High Primaryfunction of fibers Maintaining posture and aerobic endurance activities Walking,sprinting Rapid,intense movements of short duration
- 45. Exercise and Skeletal Muscle Tissue What fiber type does a marathonermost heavily rely on? Slow oxidativefibers • Slow enough pace for cellular respiration to occur • Needs a lot of energy
- 46. Exercise and Skeletal Muscle Tissue What fiber type does a shot-putter most heavily rely on? Fast glycolyticfibers • Needs short bursts of energy
- 47. Exercise and Skeletal Muscle Tissue What fiber type does a soccer playermost heavily rely on? Fast oxidative-glycolyticfibers • Has periods where more energy and periods of rest are needed, with slower cellular respiration
- 48. Cardiac muscle has the same arrangement as skeletal muscle, but also has intercalateddiscs. Cardiac Muscle Intercalated discs Cardiac muscle fiber Desmosome Gap junction Mitochondria Nucleus
- 49. Cardiac muscle cells have more mitochondria, and their contractions last 10 15 times longer than skeletal muscle contractions. Cardiac Muscle
- 50. Smooth muscle Smooth Muscle Skeletal muscle Cardiac muscle
- 51. Smooth Muscle Skeletal muscle Cardiac muscle Smooth muscle • Found in most visceral organs (e.g., intestines, stomach) • Work automatically without you being aware of them • Involved in many 'housekeeping' functions
- 52. Smooth Muscle Single-unit fibers Multi-unit fibers Muscle fibers Autonomic neurons Gap junction Nucleus
- 53. • Can shorten/stretch more than skeletal and cardiac muscle • Fibers shorten in response to stretch! Smooth Muscle Relaxed muscle cell • Contracts slower and for longer than skeletal and cardiac muscle • No sarcomeres, troponin, or tropomyosin • Proteins contract like a corkscrew, using calmodulin and myosin light chain kinase Contracted muscle cell
- 54. Major Features of the 3 Types of Muscle Tissue Characteristic Skeletal muscle Cardiac muscle Smooth muscle Microscopic appearance and features Long, cylindrical fiber with many peripherally located nuclei; unbranched; striated Branched cylindrical fiber with 1 centrally located nucleus; intercalated discs join neighboring fibers; striated Fiber thickest in the middle, tapered at each end, and with 1centrally positioned nucleus; not striated Location Most commonly attached by tendon to bones Heart Walls of hollow viscera, airways, blood vessels, iris and ciliary body of eye, arrector pili muscles of hair follicles Fiber diameter Very large (10 100 m) Large (19 20 m) Small (3 8 m) Connective tissue components Endomysium, perimysium, and epimysium Endomysium and perimysium Endomysium Contractile proteins organized into sarcomeres Yes Yes No Transverse tubules present Yes, aligned with each Yes, aligned with each Z disc No
- 55. Major Features of the 3 Types of Muscle Tissue Characteristic Skeletal muscle Cardiac muscle Smooth muscle Sarcoplasmic reticulum Abundant Some Very little Junctions between fibers None Intercalated discs contain gap junctions and desmosomes Gap junctions in visceral smooth muscle; none in multi-unit smooth muscle Source of Ca2+ for contraction Sarcoplasmic reticulum Sarcoplasmic reticulum and interstitial fluid Sarcoplasmic reticulum and interstitial fluid Regulator proteins for contraction Troponin and tropomyosin Troponin and tropomyosin Calmodulin and myosin light-chain kinase Speed of contraction Fast Moderate Slow Nervouscontrol Voluntary (somatic nervous system) Involuntary (autonomic nervous system) Involuntary (autonomic nervous system) Contraction regulation Acetylcholine released by somatic motor neurons Acetylcholine and norepinephrine released by autonomic motor neurons, several hormones Acetylcholine and norepinephrine released by autonomic motor neurons; several hormones; local chemical change; stretching Capacity for regeneration Limited, via satellite cells Limited, under certain conditions Considerable (compared with other muscle tissues, but limited compared with epithelium), via pericytes
- 56. Mature skeletal muscle fibers cannot undergo mitosis. Regeneration of Muscle Tissue Hypertrophy Hyperplasia Increase in cell size Increase in cell number
- 57. In a Nutshell ✓ The muscular system is made up of 3 types of muscles: skeletal, cardiac, and smooth. ✓ Skeletal muscle cells are referred to as muscle fibers and are multinucleated and striated. ✓ Major functional properties of skeletal muscle fibers include electrical excitability, contractility, extensibility, and elasticity. ✓ The contractility of muscle fibers involves the sliding of microfilaments in the skeletal muscle fiber. ✓ Contraction is coupled with electrical excitation of the skeletal muscle fiber.
- 58. In a Nutshell ✓ Impulses come from the nervous system to the muscular system at the neuromuscular junction (NMJ). ✓ Cardiac muscles differ from the skeletal muscles because they are involuntary. Although there are many similarities, cardiac muscles also exhibit differences in structure and function. ✓ Smooth muscles also differ from skeletal muscles. They are also involuntary, and they use different regulatory proteins during their contractions.
- 59. End…