1587411978-skeletal-muscle.pptx

Myology
Skeletal muscles anatomy
Anatomy & physiology of skeletal muscles

1. Skeletal muscles DR MEMOONA KHALID

2. Physiologic anatomy 40% of the body skeletal muscles 10% of the body smooth and cardiac muscles

3. Myofilaments ( about 1500 myosin and 3000 actin filaments) Myofibrils(about 100-1000) Muscle fibre Muscle fasiculus Skeletal muscle

4. Structure of muscle fibre Diameter is from 10-80 micrometers Sarcolemma Each muscle fibres contain myofibrils  sarcoplasm  sarcoplasmic reticulum T-tubules

5. Sarcolemma Consists of plasma membrane outer coat— a thin layer of polysaccharide material containing collagen fibrils

6. Sarcoplasm The spaces between myofibrils are filled with intracellular fluid called sarcoplasm It contains potassium ,magnesium ,phosphate ions protein enzymes large number of mitochondria

7. Sarcoplasmic reticulum Runs parallel to myofibrils in muscle fibres Consists of terminal cisternae – triade arrangement long longitudnal tubules Calcium ATPase pump Calcium releasing channels calsequestrin

8. T –Tubules(transverse) Extensive tubular network which runs transverse to the myofibrils They form a plane of T-tubules Contain extracellular fluid in their lumen Contain dihydropyridine receptors---voltage gated calcium channels

9. Structure of myofibrils Each myofibril contains about 1500 myosin and 3000 actin filaments

10. Striated appearance because of alternate light and dark bands Light bands also called I-bands---contain actin filaments Dark bands also called A-bands---contain myosin and ends of actin filaments H-bands---contain only myosin filaments

11. Z-Disc(Z-line) Composed of filamentous proteins It passes crosswise across the myofibrils ,attaching them to one another all the way across the muscle fibre Ends of actin filaments are attached to Z-disc

12. Sarcomere Structural and functional unit of skeletal muscle Between two successive Z-Discs It is 2 micrometer

13. Structure of myofilaments Myosin filament(myosin II) ---composed of multiple myosin molecules(200 or more) Actin filament

14. Myosin molecule Molecular weight of about 480,000 Composed of six polypeptide chains -two heavy chains -four light chains Tail of myosine molecule Head of myosine molecule

15. TAIL OF MYOSINE MOLECULE two heavy chains wrap spirally around each other to form a double helix

16. HEAD OF MYOSINE MOLECULE One end of each of the two heavy chains is folded bilaterally into a globular polypeptide structure Two free heads Four light chains are also part of myosin head

17. Functions of myosin head 1- ATPase activity 2-actin binding site

18. Myosin filament Made up of 200 or more individual myosine molecules Total length is 1.6 micrometer Consists of body arms cross bridges

19. BODY OF THE FILAMENT tails of myosin molecules bundles together to form body of filament

20. ARMS OF THE FILAMENT A part of the body of each myosin molecule hangs to the side along with the head Arms extend the heads outward from the body

21. CROSS –BRIDGES OF THE FILAMENT The protruding arms and heads are called cross bridges Each cross bridge is flexible at two points called Hinges No cross bridges at center of filament

22. Actin filament Composed of three protein components 1-actin G- actin F- actin 2-troponin troponin T troponin I troponin C 3-tropomyosin

23. ACTIN MOLECULE G- actin one molecule of ADP is attached active sites on the actin filament F- actin

24. Actin filament G- actin molecule polymerizes to form F- actin Two strands of F- actin filaments spiral around each other to form a double helix Back bone of actin filament Length is about 1micrometer

25. TROPOMYOSIN MOLECULE Molecular wht . Is 70,000 Length is 40 nanometer Wrap spirally around F- actin double helix

26. TROPONIN Complex of three loosely bound protein subunits Attached intermittently along the sides of tropomyosin molecule

27. Intracellular proteins Actinin Titin Desmin

28. Actinin binds actin to Z-lines Titin – is a filamentous protein,so very springy acts as framework that holds actin and myosin filaments in place Desmin binds Z-lines to plasma membrane

29. Skeletal muscle contraction MUSCLE TWITCH a single action potential causes a brief contraction followed by relaxation LATENT PERIOD the twitch starts about 2 m sec. after the application of stimulus

30. Walk along theory Also called Ratchet theory Activation of actin and myosin filaments Changes in intra molecular forces btw. The head and arm Tilt of head of myosin—power stroke The binding of new ATP causes detachment of the head from actin

31. FENN EFFECT Greater the amount of work performed by the muscle ,the greater the amount of ATP that is cleaved

32. Factors affecting force of contraction 1-effect of resting sarcomere length on force of contraction(tension)—in individual muscle fibre 2-effect of muscle length on force of contraction in the whole intact muscle 3-relation of velocity of contraction to load

33. Effect of resting sarcomere length

34. Effect of muscle length (whole muscle) on force of contraction The whole muscle has a lot of connective tissue in it The sarcomeres in different parts of the muscle do not always contract the same amount Active tension—the tension in the muscle that occur during contraction Passive tension or tone –tension before contraction

35. Relation of velocity of contraction to load Pre-load resistance applied before contraction of muscle After loadresistance during the contraction of muscle Velocity of contraction becomes progressively less as the load increases Application of the load causes stretching of resting muscle fibre

36. Energetics of muscle contraction WORK when a muscle contracts against a load ,it performs work W = L X D L =load D = distance of movement

37. SOURCES OF ENERGY ATP Main source of energy ATP ADP + 7.3 kcal About 4 millimole of ATP is sufficient to maintain full contraction for 1-2 sec.

38. ATP is used for Walk along mechanism Pumping calcium from sarcoplasm into sarcoplasmic reticulum Pumping sodium and potassium ions through the muscle fibre membrane

39. SOURCES OF ATP( rephosphorylation ) 1-lipid breakdown 2-phosphocreatine 3-carbohydrate breakdown

40. Lipid breakdown At rest and during light exercise Utilizes lipid in the form of free fatty acids

41. Phosphocreatin As exercise increases ,it is the first source to reconstitute ATP It is energy rich phosphate compound present in muscles Very little in muscle fibres ,so supply energy for short period

42. Carbohydrate breakdown 1-Blood glucose 2-Glycogen (in liver and skeletal muscles)

43. BLOOD GLUCOSE As exercise increases ,glucose from blood stream enters into muscle fibres In presence of oxygen, glucose  pyruvate citric acid cycle  carbondioxide +water +40 ATP

44. In absence of oxygen glucose  pyruvate lactic acid +4 ATP

45. GLYCOGEN With glycolysis ,rate of formation of ATP is about 2.5 times more rapid Aerobic glycolysis Anaerobic glycolysis

46. Oxidative metabolism It means combining oxygen with products of glycolysis and with various other cellular food stuffs to liberate ATP, such as ATP liberated by lipid breakdown , phosphocreatine All reactions take place by oxidative metabolism in mitochondria

47. Types of muscle fibres 1-fast twitch fibres or white fibres 2-slow twitch fibres or red fibres

48. FAST TWITCH FIBRES SLOW TWITCH FIBRES 1- REACT RAPIDLY TO STIMULUS RESPOND SLOWLY BUT WITH PROLONGED CONTRACTION 2- ARE LARGE FIBRES FOR GREAT STRENGTH OF CONTRACTION ARE SMALL FIBRES 3- HAVE EXTENSIVE SARCOPLASMIC RETICULUM FOR RAPID RELEASE OF CALCIUM TO INITIATE CONTRACTION LESS EXTENSIVE SARCOPLASMIC RETICULUM 4- LARGE AMOUNT OF GLYCOLYTIC ENZYMES FOR RAPID RELEASE OF ENERGY BY GLYCOLYTIC PROCESS

49. FAST FIBRES SLOW FIBRES 5- LESS EXTENSIVE BLOOD SUPPLY BEC. OXIDATIVE METABOLISM IS OF SECONDARY IMPORTANCE MORE EXTENSIVE BLOOD SUPPLY 6- FEWER MITOCHONDRIA BEC. OXIDATIVE METABOLISM IS OF SECONDARY IMPORTANCE INCREASE NO. OF MITOCHONDRIA BEC. OF HIGH LEVEL OF OXIDATIVE METABOLISM 7- MYOGLOBIN IS LESS EXTENSIVE(WHITE FIBRE ) MYOGLOBIN IS MORE EXTENSIVE(RED FIBRES) 8- INNERVATED BY LARGE NERVE FIBRES INNERVATED BY SMAL NERVE FIBRES 9- EASILY FATIGUED MUSCLES FATIGUE RESISTANT

50. Motor unit The apparatus comprising of a single motor neuron and the muscle fibres innervated by it

51. Size of motor units Small motor units  only 5-10 muscle fibres per motor unit  small muscles concerned with fine movements Large motor units 1500 muscle fibres per motor unit  large muscles concerned with posture and power

52. Types of motor unit(according to type of muscle fibres ) 1- S (slow ) 2- F R (fast resistance to fatigue) 3- F F (fast fatiguable )

53. Summation Adding together of individual twitch contractions to increase the intensity of overall muscle contraction

54. Types Multiple fiber summation Frequency summation

55. Multiple fiber summation Increasing number of motor units contracting simultaneously example  standing and then walking

56. ( size principle) When CNS sends weak signals small motor units are stimulated first  as the strength of the signal increases larger motor units are also excited Cause is that small motor neurons in the spinal cord are more excitable than the larger ones

57. Frequency summation In this there are summation of contractions because second contraction falls in relaxation period of first twitch

58. Staircase effect ( treppe ) When a muscle begins to contract after a long period of rest , its initial force of contraction will be little but it will increase progressively Cause is increasing calcium ions in sarcoplasm

59. Types of muscle contractions Isometric contractions Isotonic contractions

60. Isometric contractions Once a muscle contracts , its length will remain constant but tension may increase Postural muscles of body  erector spinae muscles of spines during sitting and standing

61. Isotonic contractions Once a muscle contracts ,its tension remains same but length changes during contraction Movement of arms and fingers during typing and waving for a friend

62. Skeletal muscle tone When muscles are at rest ,a certain amount of tautness usually remains It is function of muscle spindle

63. Applied physiology Muscle hypertrophy Muscle atrophy Muscle fiber hyperplasia Macro motor units when some motor nerve fibers to a muscle are destroyed –in poliomyelitis