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Muscular System

Muscular System. Chapter 8. Functional Divisions of Muscle Control. Voluntary – Consciously controlled Involuntary – Automatically controlled. Structural Types of Muscles. Smooth. Skeletal. Cardiac. Skeletal Muscle. Move appendages Controls posture Controls GI tract openings

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Muscular System

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  1. Muscular System Chapter 8

  2. Functional Divisions of Muscle Control • Voluntary – • Consciously controlled • Involuntary – • Automatically controlled

  3. Structural Types of Muscles Smooth Skeletal Cardiac

  4. Skeletal Muscle • Move appendages • Controls posture • Controls GI tract openings • Generates body heat • Attached to skeleton • Voluntary movement • Striated • Long fibers • Many nuclei • Strongest contractions

  5. Cardiac Muscle • Found in the walls of the heart • Involuntary Movement • Roughly rectangular with branches that contact adjacent cells • Striated • Intercalated Discs = branching fibers that interconnect • Allow cardiac cells to function as a unit • Does not fatigue or develop oxygen debt

  6. Smooth Muscle • In walls of hollow organs (GI tract and blood vessels) • Dilates pupils • Involuntary movement • Spindle-shaped • Not striated • Slowest and weakest contractions • No oxygen debt

  7. Tissue Characteristics • Excitability • Can receive and respond to stimuli • Contractility • Can shorten and thicken • Extensibility • Can stretch • Elasticity • Can return to original shape

  8. Gross Anatomy of Muscles • Muscle Belly/Body • Medial section • Fascicle • Group of muscle fibers • Muscle Fiber • 1 individual cell • Up to 12 inches

  9. Connective Tissues

  10. Gross Anatomy of Muscles • Fascia • Sheet or broad band of dense connective tissue • Surrounds space between skin and muscles • Deep fascia surrounds muscle • Supports muscles and hold them together as single units • Serves as route for passage of blood vessels and nerves

  11. 3 Types of Connective Tissue • Epimysium • Outermost covering around entire muscle • Perimysium • Surrounds fascicles • Endomysium • Surrounds each individual fiber • Each of these types of connective tissue transmit blood vessels and nerves to muscle components

  12. Tendons • Near bone the three layers of connective tissues converge to form a thick band of dense connective tissue that extends from muscle to attach to bone.

  13. Aponeurosis • Broad sheet of dense connective tissue • May attach muscle to bone or muscle to another muscle

  14. Naming Muscles • Direction of muscle fibers: • Rectus (straight) : parallel to body midline, or long bone • Rectus abdominis • Oblique: run slanted • External obliques

  15. Naming Muscles • Muscle Size: • Maximus: largest • Gluteus maximus • Minimus: smallest • Gluteus minimus • Longus: long • Adductor longus

  16. Naming Muscles • Location: • Bone association • Frontalis, Temporalis • Number of Origins: • Biceps: • 2 • Triceps: • 3 • Quadriceps: • 4

  17. Naming Muscles • Location of Origin and Insertion: • Sternocleidomastoid • Origin = sternum and clavicle • Insertion = mastoid process • Shape: Deltoid = triangle • Muscle Action Adductors, abductors, flexors, extensors

  18. Fiber Organization • Parallel: (biceps brachii) • Found in most skeletal muscles • Fasicles are parallel to long axis • Fxn of muscle is parallel to individual cells • Entire muscle shortens by same % • Maximum shortening = 30%

  19. Fiber Organization • Convergent: (pectoralis group) • Fibers are fanned, come together at a central point to pull on a tendon, tendonous sheet, or seam of collagen fibers • Versatile contraction direction • Stimulation of one group of fibers can determine direction of pull

  20. Fiber Organization • Pennate: • All fasicles form a common angle with the tendon • Contain more muscle cells than a parallel muscle • Pull at an angle – tendon movement is shorter than parallel • Generates more tension

  21. Fiber Organization • Pennate: • Unipennate: • Muscle cells on one side only • Extensor digitorum longus • Bipennate: • Fiber extends on both sides of tendon • Rectus femoris • Multipennate: • Tendon brances within the muscle • deltoids

  22. Fiber Organization • Circular or Sphincter: (Pyloric Sphincter) • Concentrically arranged cells around an opening • Contraction produces a decrease in the diameter of an opening • Found at entrances and exits in digestive and urinary tracts

  23. Large  Small Muscle Fiber Myofibrils Myofilaments (Arranged in Repeating units called Sarcomeres)

  24. Microscopic Anatomy • Sarcolemma • Plasma membrane of each fiber • Sarcoplasm • Cytoplasm • Contains myoglobin (protein – binds oxygengenerates ATP; energy source)

  25. Microscopic Anatomy • Myofibril • specialized cylindrical organelle made of myofilament bundles • 1-2 um diameter • up to several thousand in 1 fiber • covered by sarcoplasmic reticulum: specialized smooth ER, stores calcium ions • connects to other SR and to sarcolemma by T tubules

  26. Microscopic Anatomy • Myofilament • Structural protein strands in myofibril • Made up of mainly actin and myosin • Sarcomere • Basic unit of contraction

  27. Sarcomere Anatomy • A Band = area where thick and thin filaments overlap, dark striations • I Band = area where only thin filaments occur, light striations • Z Line = dense protein (connectin) extending perpendicular to length of myofibril • lies in the middle of each I-band • connect thin filaments and individual myofibrils to each other

  28. Sarcomere Anatomy • Sarcomere = area between two Z lines • H Zone = area in middle of A bands where there is no overlap of thin filaments • Only visible in relaxed muscles • M Line = fine (desmin) proteins • Connects middles of thick filaments • Found in middle of H Zone

  29. Thick Myofilaments • Myosin • golf club shaped proteins with long tails and "fat" heads • filament consists of staggered myosin macromolecules • have actin binding sites and ATP binding sites with ATPase

  30. Thin Myofilaments • Actin • anchored to Z lines • kidney bean shaped monomers; polymerized into long chains • tropomyosin coils around actin • troponin binds to tropomyosin and to actin • Tropomyosin/Troponin Complex blocks active sites on actin chains 6 thin filaments are arranged as a hexagon around each thick filament

  31. Sliding Filament Theory • Thin filaments slide over thick filaments • Z lines pull together • I band and H zone shorten • A band stays same length

  32. Resting Muscle • Calcium ions are stored in SR • ATP is bound on thick filaments • Troponin is blocking myosin binding site on actin

  33. Sliding Filament Theory • Impulse arrives at neuromuscular junction • Ach reaches receptors in muscle cell, signals ion channels to open • Sodium flows into cell • Action potential travels down T-tubules • Signals SR to release calcium

  34. Sliding Filament Theory • Ca2+ binds to troponin molecules in the thin filaments (actin) • Troponin moves laterally to uncover binding site for myosin • Cross bridge attachment • Myosin binds to actin • Ca2+ also activates splitting of ATP • Leaves ADP and PO4 hanging on myosin

  35. Sliding Filament Theory • Power stroke • Energy released from splitting ATP is used to tilt myosin head • Tilting heads pull actin forward • Much energy is lost as heat • ADP and PO4 are released from head

  36. Sliding Filament Theory • Rigor Complex • Myosin head remains attached to actin • More ATP binds to myosin causing detachment • Cycle repeats, shortening sarcomeres

  37. Sliding Filament Theory

  38. Sliding Filament Theory SDSU Biology 590 - Actin Myosin Crossbridge 3D Animation

  39. Returning to Rest • Cholinesterase inactivates acetylcholine • Calcium ions return to sarcoplasmic reticulum by active transport • All cross bridges are broken and thin filaments are allowed to slide back to original positions

  40. Skeletal Muscle Contraction Physiology • Motor unit • Motor neuron and all of the muscle fibers it stimulates • Motor neuron • Nerve cells that carry action potentials to skeletal muscle fibers • Neuromuscular junction • Specialized site where neuron and muscle come together

  41. Muscle Metabolism • Stored ATP is energy source • ATP generated by • Phosphorylation of ADP • Anaerobic Fermentation • Aerobic Respiration (Most ATP generated)

  42. Phosphorylation of ADP • Once contraction begins stored ATP is used up in a matter of seconds • ADP and creatine phosphate stored in muscles • High energy molecule • Creatine phosphate is broken down • Energy released is used to regenerate ATP

  43. Anaerobic Cycles • Oxygen is not required • Use stored glycogen • Lactic acid formed • Produces ATP quickly in small amounts • Short-term vigorous exercise • Used up within minutes

  44. Aerobic Respiration • Requires oxygen • Produces most ATP over long period of time • Mitochondria • Energy for hours • Prolonged activities where endurance is important

  45. Muscle Fatigue • Physiological inability of muscle to contract • Build up of lactic acid lowers cell’s pH • Cell becomes unresponsive to stimulation • Relative deficiency of ATP • Accumulation of lactic acid • Cramps: inability to relax • Lack of ATP stops active transport of Ca++ into SR

  46. Oxygen Debt • Temporary lack of oxygen availability • Causes accumulation of lactic acid • Muscles feel sore • Repaid when additional oxygen is taken in after exercise (heavy breathing) • Lactic acid converted to pyruvic acid • Synthesize ATP and creatine phosphate • Slow process (hours)

  47. Stimuli All or none law • When muscle fiber is stimulated it will contract fully or not at all • Threshold stimulus = weakest stimulus that can initiate a contraction • Subthreshold stimulus = too weak to cause a contraction

  48. Motor Units Motor Unit: one motor neuron + muscle fibers it stimulates - avg. = 150 Contraction Strength - how many - how frequently Recruitment: Stronger stimuli increases # of motor units activated

  49. Types of Muscle Contraction • Twitch • Rapid response to a single stimulus that is slightly over the threshold • 1/10th of a second Myograph

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