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Muscular System

Muscular System . Chapter 6. Muscle Cell Types . Skeletal (striated) Cardiac Smooth (non-striated). Similarities Among Muscle Cells. All elongated All called muscle fibers All have myofilaments ( muscle’s ability to contract) Prefixes- myo , mys , sarco ( all refer to muscle).

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Muscular System

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  1. Muscular System Chapter 6

  2. Muscle Cell Types • Skeletal (striated) • Cardiac • Smooth (non-striated)

  3. Similarities Among Muscle Cells • All elongated • All called muscle fibers • All have myofilaments ( muscle’s ability to contract) • Prefixes- myo, mys, sarco ( all refer to muscle)

  4. Skeletal Muscle

  5. Skeletal Muscle • Attach to the body’s skeleton • Help form smooth contours of the body • Cigar-shaped • Multinucleated (many nuclei) • Largest of all muscle fibers

  6. Skeletal Muscle • Also known as striated muscle (appear to be striped) • OR • Voluntary muscle: only muscle type to conscious control.

  7. Skeletal Muscle • Soft and fragile • But, can exert tremendous power • Fibers are bound together by connective tissue.

  8. Skeletal Muscle • Endomysium- connective tissue sheath that encloses muscle fibers. • Perimysium- coarse fibrous membrane that encloses several sheathed fibers. • Fascicle- bundle of fibers.

  9. Skeletal Muscle • Epimysium- tough overcoat of connective tissue around many fascicles. • Cover entire muscle • Tendons(cord-like)- attach muscles directly to bones. • Aponeuroses(sheet-like-) attach muscles directly to bones.

  10. Tendons • Attach muscle to bones. • Provide durability • Conserve space • Made of tough collagenic fibers

  11. Smooth muscle

  12. Smooth muscle • Contains no striations. • Involuntary muscle – we cannot consciously control it. • Found mainly in the walls of hollow visceral organs. • Stomach, bladder, respiratory passages

  13. Smooth Muscle • Propels substances along a definite track or pathway. • Using terms like visceral, nonstraited, involuntary • Spindle shaped • Single nuclei • Arranged in sheets or layers

  14. Smooth Muscle • Two layers- one running circularly and the other longitudionally • As the layers relax and contract they change the shape and size of the organ.

  15. Cardiac Muscle

  16. Cardiac muscle • Only found in the heart. • Striated, but involuntary • Cushioned by small amounts of soft connective tissue • Arranged in spiral/figure 8 bundles • Branching cells joined by junctions called intercalated discs

  17. Muscle Functions • 1. produce movement • 2. maintains posture • 3. stabilizes joints • 4. generates heat

  18. Muscle Functions- producing movement • Skeletal- mobility of the body • Cardiac- pump in heart to circulate blood • Smooth- push fluid and substances along their designated path.

  19. Muscle functions- maintains posture • Function continuously so we can maintain an erect or seated posture.

  20. Muscle functions- generating heat • Body heat is a by-product of muscle activity. • Heat is vital in maintaining normal body temperature.

  21. Muscle functions- stabilizing joints • As they pull on bones to cause movement they stabilize joints. • Tendons important in shoulder joint.

  22. Microscopic Anatomy of skeletal muscle

  23. anatomy • Sarcolemma – plasma membrane • Myofibrils- long ribbon-like organelles that push nuclei to sides and nearly fill the whole cytoplasm. • Chains of tiny contractile units called sarcomeres • Sarcomeres-aligned like boxcars in a train • Striped appearance comes from light (I) and dark (A) bands along the muscle. • Sarcoplasmic reticulum- specialized smooth ER • Stores calcium and releases it on demand

  24. 2 types of myofilaments • Thick filaments (made of protein myosin) • Cross bridges- link thick and thin filaments together during contraction. • Thin filaments (made of protein actin)

  25. Anatomy of skeletal muscle

  26. Skeletal muscle activity

  27. activity • Irritability- ability to receive and respond to stimulus • Contractibility- ability to shorten (forcibly) when adequate stimulus is received.

  28. Nerve stimulus and action potential • Skeletal muscle cells must be stimulated by nerve impulses. • One motor neuron can stimulate a few muscle cells or hundreds of muscle cells. • Motor unit- one motor neuron and all of the skeletal muscles it stimulates.

  29. Nerve stimulus and action potential • Axon (long threadlike extension of neuron) reaches the muscle. • Branches into a number of axonal terminals (each forms junctions with sarcolemma of a different muscle cell) • Called neuromuscular junctions • Nerve endings and muscle cells never touch- space between them is called the synaptic cleft.

  30. Nerve stimulus and action potential Neurotransmitter- Ach (acetylcholine) -stimulates skeletal muscle Action potential- electrical current

  31. Acetylcholine

  32. Muscle response to increasingly rapid stimulation • Muscle twitching- single, brief, jerky contractions. • Not the way our muscles normally operate • Most types of muscular activity- nerve impulses are delivered to the muscle so rapidly that the cells do not get a chance to relax completely.

  33. Muscle response to stronger stimuli • Only a few cells stimulated- contraction of muscle is slight. • All muscle cells stimulated- contraction of muscle is as strong as it can get.

  34. Providing energy for muscle contraction • As muscle contracts, the bonds of ATP molecules are broken. • Muscles store limited amount of ATP (only enough to get you going) • ATP must be regenerated continuously

  35. 3 pathways for ATP regeneration • 1. Direct phosphorylation of ADP by creatine phosphate • 2. Aerobic respiration • 3. Anaerobic glycolysis and lactic acid fermentation

  36. Direct phosphorylation • Creatine phosphate- high-energy molecule • Only found in muscle fibers • CP donates a high energy phosphate group to ADP regenerating ATP.

  37. Aerobic respiration • Occurs in mitochondria • Glucose is broken down completely to carbon dioxide and water. • Requires a lot of oxygen

  38. Anaerobic Glycolysis and lactic acid fermentation • Glycolysis: biochemical pathway in which one six-carbon molecule of glucose is oxidized to produce two 3-C molecules of pyruvic acid.

  39. Muscle Fatigue and Oxygen Debt • Muscle fatigue: occurs if we exercise our muscles strenuously for a long time. • Unable to contract even if it is being stimulated. • Believed to be a result from oxygen debt • Oxygen debt occurs during prolonged muscle activity. • When muscles lack oxygen- lactic acid builds up in muscles

  40. Types of Muscle Contractions- Isotonic Myofiliments successful in their sliding movements Muscle shortens Movement occurs Bending the knee Rotating arms Smiling

  41. Types of Muscle Contractions- Isometric • Myosin filaments are “skidding their wheels” • Tension of the muscle keeps increasing • Trying to slide but cannot • Like when you try to pick up a 400 pound object

  42. Muscle tone • Even when muscle is voluntarily relaxed- some fibers are contracting • Muscle remains firm, healthy , and constantly ready for action. • Muscle tone- state of continuous partial contraction

  43. Effect of Exercise on Muscles • If you don’t use muscle, you lose it. • Regular exercise increases muscle size, strength, and endurance. • Aerobic- (endurance)- jogging, biking, aerobics class • Result in stronger, more flexible muscle • Makes overall body metabolism more efficient • Improves digestion • Enhances neuromuscular coordination • Makes skeleton stronger

  44. Types of Body Movements • 600 skeletal muscles- attached to a bone or other connective tissue structure. • Origin- attached to the immovable or less movable bone. • Insertion- attached to the movable bone • When the muscle contracts the insertion moves toward the origin.

  45. Types of Body Movements • Flexion- saggital plane- decreased angle- brings two bones together. • Bending knee • Bending elbow • Bending forward at the hip

  46. Types of Body Movements • Extension- opposite of flexion- increases the angle or distance between two bones. • straightening knee/ straightening elbow • If angle is over 180 degrees- hyperextension • Tip head posteriorly so chin points to ceiling.

  47. Types of Body Movements • Rotation- movement of a bone over its longitudinal axis. • Common in ball-and-socket joints • Shaking your head no

  48. Types of Body Movements • Abduction- moving a limb away from the midline of the body.

  49. Types of Body Movements • Adduction- opposite of abduction- movement of limb toward the body midline.

  50. Types of Body Movements • Circumduction- combination of flexion, extension, abduction, and adduction • Commonly ball-and-socket joint (shoulder) • Proximal end is stationary and distal end moves in a circle

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