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

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

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

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

8. 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

10. 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

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

12.  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

13. 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

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

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

20. 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

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

22. 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

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

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

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

27. 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

28. 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

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

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

32. 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

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

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

36. Intracellular proteins
 Actinin
 Titin
 Desmin

37.  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

38. 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

41. 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

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

44. 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

45. Effect of resting sarcomere length

46. 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

47. 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

49. 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

50. 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.

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

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

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

54. 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

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

56. 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

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

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

59. 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

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

61. 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

62. 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
EASILY FATIGUED MUSCLES FATIGUE RESISTANT

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

64. 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

65. 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)

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

67. Types
 Multiple fiber summation
 Frequency summation

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

69. (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

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

72. 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

73. Types of muscle contractions
 Isometric contractions
 Isotonic contractions

74. 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

75. 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

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

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