A and P Mod5

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A and P Mod5

  1. 1. Muscular System Muscle Tissue
  2. 2. 4 Functions:1. Produce skeletal movement and all types of movement2. Maintain posture and body position3. Guard the entrances and exits of the body4. Maintain body temperature
  3. 3. Characteristics of MusclesMuscle cells are elongatedMuscle cell are called musclefibersContractionof muscles isdue to the movement ofmicrofilaments in cell
  4. 4. 4 major functional characteristicsof muscle are:1. CONTRACTILITY – CAN SHORTEN FORCEFULLY2. EXCITABILITY – STIMULATED BY HORMONES AND NERVES
  5. 5. Four major functional characteristics of muscle are:1. CONTRACTILITY2. EXCITABILITY3. EXTENSIBILITY – CAN BE STRETCHED OUT4. ELASTICITY – EXTEND BEYOND NORMAL LENGTH AND RECOIL
  6. 6. 3 basic types of muscle are found in the body : 1. Cardiac muscle  found only in heart  Striated (striped in appearance)  single nucleus  involuntary
  7. 7. 3 basic types of muscle are found in the body : 2. Smooth muscle  found in organs  nonstriated  involuntary
  8. 8. 3 basic types of muscle are found in the body : 3. Skeletal  Striated  voluntary  multinucleated
  9. 9. Muscles can be also categorized bywhether they are: VOLUNTARY – CONSCIOUSLYCONTROLLED Or INVOLUTARY – NOTCONSCIOUSLY CONTROLLED
  10. 10. Muscles can be also categorized by whether they are:STRIATED – STRIPEDIN APPEARANCE orNONSTRIATED – NOT STRIPED IN APPEARANCE
  11. 11. Skeletal Muscle Characteristics multinucleate – Have morethan one nucleus per cell Nucleus is on the outside ofthe cell
  12. 12. Skeletal muscle characteristics continued:Muscle are attached tobone by tendons.tendons are denseregular connective tissue bellyMuscle itself iscalled the belly.
  13. 13. Skeletal muscle characteristics continued:The belly of the muscle is madeof bundles of muscle fibers (cells).Bundles of muscle fiberswrapped together arecalled fascicles.
  14. 14. Connective Tissue Wrappings of Skeletal Muscle 1. Endomysium – wraps a single muscle fiber 2. Perimysium – wraps a fascicle (bundle) of fibers 3. Epimysium– wraps entire muscle
  15. 15. Connective Tissue Wrappings of Skeletal MuscleThese three wrappings extend past the muscle to make the tendon and connect to bone.
  16. 16. Skeletal muscle characteristics continued:have nerves and blood vessels.controlled by nervous systemrequire lots of energy because ofcellular respirationtherefore need lotsof oxygen
  17. 17. Microscopic Anatomy of Skeletal MuscleSpecial terms for musclefiber organelles:Sarcosome =mitochondriaSarcoplasm = cytoplasm
  18. 18. Microscopic Anatomy of Skeletal MuscleSarcoplasmic reticulum =smooth endoplasmic reticulumSarcolemma = specialized plasma(cell) membrane
  19. 19. Microscopic Anatomy of Skeletal MuscleAlso has:T-tubules= tiny tubes sproutinginto the sarcolemma forming pits in thesarcolemma which allow signals totravel and stimulate movement.
  20. 20. Also has:Myofibril – threadlike structuresin muscle fiber
  21. 21. Myofibril made of two types offilaments:1.Myosin protein is a thick filament2. Actin protein is aThin filament
  22. 22. Also have:Sarcomeres• smaller sections of a myofilament•around 2 µm in length•functional unit ofthe skeletal muscle
  23. 23. Also have: Sarcomeres• Sarcomere is the repeating units of the myofibrils• Sarcomeres give skeletal muscle its striated appearance
  24. 24. Skeletal muscle
  25. 25. Also have: SarcomeresStructures of the Sarcomere: A bands – dark thick bands made from myosin protein I bands – lighter bands made from actin protein
  26. 26. H zone – area between theends of the actin myofilamentswhich point to one another fromopposite ends of the sarcomere
  27. 27. heads actin myosin H zoneZ disk– where the actin or thinfilaments attach at one end-Z disk are made out of protein
  28. 28. The myosin proteins havehead-like structures on them
  29. 29. Sliding-Filament ModelIs the model explaining how amuscle cell or fiber is believedto contract
  30. 30. Sliding Filament ModelActin is surrounded by two otherproteins: 1. tropomyosin which winds around the actin blocking active sites 2. troponin which lies across the tropomyosin and keeps it in place
  31. 31. Sliding filament modelNerve impulse by neurotransmitteracetylcholine stimulates thesarcoplasmic reticulum to release Ca2+into the sarcoplasmCa2+ bind to the troponin and causethe position of the tropomyosin tochange exposing the active sites onthe actin filament
  32. 32. Sliding filament modelThe heads of the myosin filamentthen bind to the active site of the actinfilament forming a cross bridge
  33. 33. Sliding filament modelThe Ca2+ ions are then releasedOnce cross bridges are formed themyosin filament heads will shift calleda power stroke pulling the actinfilaments closer together;
  34. 34. Sliding filament modelThis happens simultaneously in allthe sacromeres and muscle fiberscausing the muscle to contract.
  35. 35. During sarcomere contraction:Reduced are the : H zone (shortens) I band (shortens) Overall length of sarcomere (reduced) I
  36. 36. During sarcomere contraction:Stays same: actin filament myosin filament A band (made by myosin)
  37. 37. Energy Requirements•Muscle contraction requires lotsof energy provided in the form ofATP (adenosine triphosphate).•When the first phosphate bond inATP is broken large amounts ofenergy is released.•ATP becomes ADP and Pmolecule.
  38. 38. ATP related to sliding filament model:•ATP bonds to head of myosinfilament•ATP ADP + P energybecomes available to the myosinhead to move.•P released from myosin, myosinthen binds to the actin strongly andpower stroke occurs
  39. 39. ATP related to sliding filament model:•ADP falls off and is recycled•New ATP can attach to providemore energy•New ATP attached, crossbridgeis broken
  40. 40. What stops the contraction?Same thing that started it – Ca ions 2+When nerve impulse stops, sarcoplasmicreticulum stops releasing Ca2+ ions whichno longer binds with troponin, and the activesites are no longer available.
  41. 41. Quiz
  42. 42. Motor Units Motor unit is  One motor neuron (nerve cell) and all the  Muscle cells stimulated by that neuron
  43. 43. Parts of the motor neuron Axon – process that extends from the cell body and carries signal away Note: may branchPresynaptic terminal –very end of the axon neurotransmitter containing vesicles are found
  44. 44. Parts of the motor neuronNeuromuscular junction – where thenerve and muscle fiber meet (don’t touch). Parts of the neuromuscular junctionSynapse – interface between a nerve celland another cell (muscle cell)Synaptic cleft – gap between nerve andmuscle cells that is filled with interstitialfluid
  45. 45. Postsynaptic membrane –membrane of the muscle fiber in theregion of the synapseAcetylcholine (ACh)– Most commonneurotransmitter (chemical) released byneuron traveling across the cleftinteracting with the postsynapticmembrane of muscle cell stimulating it tocontract.
  46. 46. Synaptic vesicles – found inside thepresynaptic terminal containingneurotransmitters.Acetylcholinesterase – enzyme thatinactivates ACh to stop musclecontraction.
  47. 47. How the motor neuron stimulates muscle contraction:1.Action potential (electricalsignal) travels down axon2. Vesicles in the presynapticterminal release ACh.3. ACh travels across the synapticcleft.
  48. 48. How the motor neuron stimulates muscle contraction:4. ACh stimulates a new action potential in the sarcolemma through the T-tubules5. T-tubules stimulate the sarcoplasmic reticulum to release Ca+2 ions by diffusion.
  49. 49. How the motor neuron stimulates muscle contraction:6. We know Ca+2 ions attach to troponin changing arrangement of tropomyosin exposing sites on actin- crossbridges-powerstroke- contraction
  50. 50. How motor neuron is responsible for stopping contraction:1.Action potential stops2.ACh is no longer released and isbroken down by acetylcholinesterase.3. Calcium is no longer released but ispumped back into sarcoplasmicreticulum.
  51. 51. How motor neuron is responsible for stopping contraction:5.Troponin releases Ca ions and +2tropomyosin rearranges covering theactin active sites again.6.Crossbridges of myosin/actin arebroken7.Muscle is relaxed!!
  52. 52. All-or-none law of skeletal muscle contractionIndividual muscle fiberscontract with equal force inresponse to each actionpotentialEither a fiber is contracted orrelaxed no inbetween.
  53. 53. How do you get degrees of muscle movement? Slight, fine movement(thread a needle) compared tocoarse, extreme movements(pick up a 100 lb weight).
  54. 54. How do you get degrees of muscle movement?1. By the size of the motor unit oramount of axon branching A. Large motor unit – axonbranches hundreds of times stimulatinghundreds of muscle fibers at the sametime resulting in coarse movement withless control or
  55. 55. How do you get degrees of muscle movement?Two ways:1. The size of the motor unit or amount of axon branching A. Large motor unit – axon branches hundreds of times stimulatinghundreds of muscle fibers at the same time resulting in coarse movement with less control orB. Small motor unit – axonbranches only a few timesstimulating only a few musclefibers or just one at the timeresulting in fine movement withmore control.
  56. 56. How do you get degrees of muscle movement?2.Frequency of the action potentialcan affect muscle contraction Stronger the stimulus the higher the frequency of action potentials that travel down motor neuron
  57. 57. There are 4 levels of frequency:A.Subthreshold stimulus – toosmall to create an action potentialB.Threshold stimulus – strongenough to create an actionpotential
  58. 58. B. Threshold stimulus -stimulus is strong enough to create an action potentialC. Submaximal stimuli – stimuliof increasing strength that createmore action potentials alongmore neurons
  59. 59. C. Submaximal stimuli – stimuli of increasing strength that create moreaction potentials along more neuronsD.Maximal stimulus – a stimuluswhich is strong enough to createaction potentials in all theneurons innervating a wholenerveInnervating = controlling
  60. 60. Nerve stimulates several motorunits together.The more motor units (multiplemotor unit summation) activated themore muscle fibers contract thegreater the force of the musclecontraction.If motor unit is stimulated it hasbeen recruited.
  61. 61. •Muscle tone – the state of partialcontraction of the muscle, evenwhen not being used.•Less muscle tone when asleep,than when awake.•Motor units will take turnscontracting and relaxing to havemuscle tone.
  62. 62. Energy for muscle fibers comes from one of three ways:1.Aerobic respiration glucose synthesized into ATP most efficient; 36 ATP – 1Glucose slow and requires oxygen
  63. 63. 2. Creatine phosphate• gives up a phosphate to ADP converting it to ATP• stored in the muscle cells in only small amounts• 1 ATP for each creatine phosphate stored, less efficient than aerobic
  64. 64. 3. Anaerobic respiration• Glucose broken down to pyruvic acid to ATP• No oxygen required• Produces lactic acid toxic to muscles causes burning• Not very efficient, 1 pyruvic acid yields 2 ATP
  65. 65. If anaerobic is less efficient than aerobic why use it?Sometimes body cannot keep themuscle supplied with oxygen at afast enough rate.Myoglobin molecule stores oxygen inmuscle cell but sometimes notenough.

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