1. The Muscular System
Chapter 8

2. Types of muscle & function
Skeletal % of total body weight- voluntary
mostly movement of bone & body parts
Stabilizing body positions
Cardiac- only in heart- involuntary
Heart only
Develops pressure for arterial blood flow
Smooth- grouped in walls of hollow organs
Sphincters regulate flow in tubes
Maintain diameter of tubes
Move material in GI tract and reproductive organs

3. Muscle Functions Produce body movements Stabilize body positions
Regulate organ volume
Moving substances internally
Producing heat

4. Skeletal Muscle Tissue
Muscle includes: muscle fibers, connective tissue, nerves & blood vessels
Wrapped in Epimysium
Perimysium surrounds fiber bundles called fascicles
Endomysium surrounds each individual fiber

5. Skeletal Muscle Tissue
Well-supplied with blood vessels and nerves
Terminal of a neuron on each muscle fiber

6. Figure 8.1

7. Muscle Histology elongated cylindrical cells = muscle fibers
plasma membrane = sarcolemma
Transverse (T- tubules) tunnel from surface to center of each fiber
Multiple nuclei lie near surface
Cytoplasm = sarcoplasm

8. Figure 8.2a

9. Muscle histology (cont.)
Throughout sarcoplasm is sarcoplasmic reticulum
Stores Calcium ions
Sarcoplasm contains myoglobin
Red pigmented protein related to Hemoglobin that carries oxygen
Along entire length are myofibrils
Myofibrils made of protein filaments
Come in thick and thin filaments

10. Figure 8.2b

11. Sarcomere Filaments overlap in repeating patterns
Unit structure is called sarcomere
Separated by Z-discs
Darker area = A-band associated with thick filaments
H-zone has no thin filaments
I-band has thin filaments no thick filaments

12. Figure 8.2c

13. Figure 8.3a

14. Figure 8.3b

15. Functional Structure Thick filament (myosin) has moveable heads
Thin filaments (actin) are anchored to Z-discs
Contain myosin binding sites for myosin head
Also contain tropomyosin & troponin
Tropomyosin blocks myosin binding site at rest

16. Sliding Filament Mechanism
During contraction myosin heads bind actin sites
Pull and slide actin molecules (and Z-discs) toward H-zone
I-bands and H-zones narrow
Sliding generates force and shortens sarcomeres and thus fibers.

17. Figure 8.4

18. Neuromuscular Interaction
Nerve signal triggers muscle action potential
Delivered by motor neuron
One neuron can trigger 1 or more fibers at the same time
Neuron plus triggered fibers = motor unit

19. Neuromuscular Junction
neuronal ending to muscle fiber = Neuromuscular junction
Synaptic end bulbs (at neuron terminal)
Release neurotransmitter
Muscular area = Motor end plate
Between is synaptic cleft

20. Figure 8.5

21. Action at NMJ Release of acetylcholine (ACh)
Diffuses across cleft
2. Activation of ACh receptors
3. Generation of Muscle Action Potential
Repeats with each neuronal action potential
4. Breakdown of ACh

22. Contraction Trigger
Muscle action potential=> Ca2+ release from Sacroplasmic Reticulum (SR)
Ca2+ binds to troponin =>
Moves tropomyosin off actin sites =>
Myosin binds & starts cycle

23. Contraction Cycle
Myosin binds to actin & releases phosphate group (Forming crossbridges)
Crossbridge swivels releasing ADP & shortening sarcomere (Power stroke)
ATP binds to Myosin => release of myosin from actin
ATP broken down to ADP & Pi => activates myosin head to bind and start again
Repeats as long as Ca2+ concentration is high

24. Figure 8.6

25. Relaxation Breakdown of Ach to stop muscle Action potentials
Ca2+ ions transported back into SR lowering concentration=>
This takes ATP
tropomyosin covers actin binding sites

26. Figure 8.7

27. Muscle Tone
Even at rest some motor neuron activity occurs = Muscle Tone
If nerves are cut fiber becomes flaccid (very limp)

28. Metabolism
Rapid changes from very low ATP consumption to high levels of consumption
Creatine phosphate (high energy store)
Fast & good for ~ 15 sec

29. Figure 8.8a

30. Glycolysis Break down glucose to 2 pyruvates getting 2 ATPs
If insufficient mitochondria or oxygen pyruvate => lactic acid
Get about seconds more at max.

31. Figure 8.8b

32. Aerobic Cellular Respiration
Production of ATP in mitochondria
Requires oxygen and carbon substrate
Produces CO2 and H2O and heat.

33. Fatigue Inability to contract forcefully after prolonged activity
Limiting factors can include:
Ca2+
Creatine Phosphate
Oxygen
Build up of acid
Neuronal failure

34. Oxygen Use After Exercise
Convert lactic acid back to glucose in liver
Resynthesize Creatine Phosphate and ATP
Replace oxygen removed from myoglobin

35. Control of Muscle Contraction
Single Action Potential(AP) =>twitch
Smaller than maximum muscle force
Total tension of fiber depends on frequency of APs (number/second)
Require wave summation
Maximum = tetanus
Total tension of muscle depends on number of fibers contracting in unison
Increasing numbers = Motor unit recruitment

36. Figure 8.9

37. Figure 8.10

38. Fiber types Slow oxidative (SO)- small diameter & red
large amounts of myoglobin and mitochondria
ATP production primarily oxidative
Fatigue resistant-
Fast oxidative- glycolytic (FOG)
Large diameter = many myofibrils
Many mitochondria and high glycolytic capacity
Fast glycolytic fibers (FG)
white, fast & powerful and fast fatiguing
For strong, short term use

39. Recruitment
Muscle contractions only use the fibers required for the work
Recruited in order: SO=>FOG=>FG
if force is constant and the muscle shortens = Isotonic Contraction
If length is constant and the force varies = Isometric Contraction
The latter is often a postural muscle activity

40. Effects of Exercise SO/FG fiber ratio genetically determined
High FG => sprinters
High SO=> marathoners
Endurance exercise gives FG=> FOG
Increased diameter and numbers of mitochondria
Strength exercise increases size & strength of FG fibers

41. Cardiac Muscle Striated, short fibers and branched
Single central nucleus; Cells joined by gap junctions & desmosomes
Thickened joint area called intercalated discs
Some cardiac muscles generate own AP- autorhythmicity
Involuntary

42. Cardiac muscle No nerve- internal pacemaker
Ca2+- from S.R. and extracellular space
separate cells with gap junctions -> electrical connections

43. Figure 15.2b

44. Smooth muscle Involuntary In internal organs
Filaments not regular so not striated
Visceral (single unit) type or
Form sheets and are autorhythmic
Contract as a unit
Multi-unit type-
each has own nerve and can contract independently

45. Smooth Muscle Graded contractions and slow responses
Often sustain long term tone
Often triggered by autonomic nerves
modulated chemically, nerves, by mechanical events (stretching)

46. Figure 8.11

47. Aging
Like bone there is a slow progressive loss of skeletal muscle mass
Relative number of SO fibers tends to increase

48. Movement Move one bone relative to another
Origin => most stationary end
Location where the tendon attaches
Insertion => the most mobile end
Location where tendon inserts
Action => the motion or function of the muscle

49. Figure 8.12

50. Movement (cont.) Generally arranged in opposing pairs
Flexors- extensors; abductors- adductors
The major actor = Prime mover or agonist
The one with opposite effect = antagonist
Synergists- help prime mover
Fixators- stabilize origin of prime mover
Role of muscle varies with motion

51. Naming Terms-Table 8.2 Direction relative to body axes
e.g. Lateralis, medialis (medius), intermedius, rectus
Specific regions
e.g. abdominus, Brachialis, cleido, oculo-, uro-,
Origin
e.g. biceps, triceps, quadriceps
Shape
e.g. deltoid, orbicularis, serratus, trapezius

52. Names (Cont.) Other features Actions Specific references
e.g. alba, brevis, longus, magnus, vastus
Actions
e.g. abductor, adductor, flexor, extensor
Specific references
e.g. Buccinator (trumpeter), Sartorius (like a tailor)

53. Figure 8-13a

54. Figure 8-13b

55. Figure 8.14

56. Figure 8.15

57. Figure 8.16

58. Figure 8.17

59. Figure 8.18

60. Figure 8.19

61. Figure 8.20

62. Figure 8.21ab

63. Figure 8.21c

64. Figure 8.22

65. Figure 8.23a

66. Figure 8.23b

67. Figure 8.24ab

68. Figure 8.24cd