1. Chapter 9 Muscular System
Three Types of Muscle Tissues
Skeletal Muscle
usually attached to bones
under conscious control
striated
Cardiac Muscle
wall of heart
not under conscious control
striated
Smooth Muscle
walls of most viscera, blood vessels, skin
not under conscious control
not striated

2. Muscle Tissues
Skeletal Muscle
Smooth Muscle
Cardiac Muscle

3. Major Skeletal Muscles

4. Major Skeletal Muscles

5. Structure of a Skeletal Muscle
organ of the muscular system
- skeletal muscle tissue
- nervous tissue
- blood
- connective tissues
fascia
tendons
aponeuroses

6. Connective tissue coverings
Fascia (dense connective tissue) covers each skeletal muscle.
- may project beyond end of muscle to form a cordlike tendon (muscle to bone)
Other connective tissues form broad fibrous sheets (aponeuroses) which may attach to coverings of adjacent muscles.
Epimysium - layer that closely surrounds skeletal muscle

7. Perimysium - layer that extends inward and separates muscle tissue into small sections
Fascicles - bundles of skeletal muscle fiber in the small sections
Endomysium - thin covering than surrounds each muscle fiber within a fascicle
Layers of connective tissue enclose and separate all parts of skeletal muscle allowing somewhat independent movement.

8. Fascia is a complex network that extends throughout the body
Deep fascia - surrounds each muscle
Subcutaneous fascia - lies just beneath skin
Subserous fascia - covers serous membranes

9. Connective Tissue Coverings

10. Skeletal Muscle Fibers

11. Skeletal muscle fibers
Each skeletal muscle fiber is a single muscle cell.
Fibers are cylindrical with rounded ends that are attached to connective tissues
Each cell has many nuclei
Muscle cell membrane - sarcolemma

12. Cytoplasm = sarcoplasm
The sarcoplasm contains:
nuclei - control center
mitochondria - site of cellular respiration
sarcoplasmic reticulum - membraneous channels that activate muscle contraction when stimulated

13. cisternae - enlarged portion of sarcoplasmic reticulum
transverse tubules - membraneous channels that activate myofibrils (threadlike protein filaments)
actin -thin filaments
myosin - thick filaments

14. Actin and Myosin arrangement of the filaments causes striations:
I bands(light) - thin actin
Z lines - I bands attach to it
A bands( dark) - thick myosin overlapping thin actin
myosin attached to Z lines by titin (protein)
H zone - central region of only thick filaments (myosin)
M line - thickening area on H zone
Sarcomere - extends from one Z line to the next Z line

15. Sarcomere
I bands
A bands
H zone
Z lines
M line

16. Myofilaments

17. Neuromuscular Junction
Each muscle fiber is connected to an extension of a motor neuron
extends from the brain or spinal cord
Motor neurons stimulate muscle fibers to contract
Nerve fiber and muscle fiber meet at the neuromuscular junction
The motor end plate lies on one side of a neuromuscular junction

18. Synaptic cleft separates the nerve fiber and muscle fiber
In response to a nerve impulse, the end of a motor nerve fiber secretes a neurotransmitter which diffuses across the junction and stimulates the muscle fiber to contract.

19. Neuromuscular Junction

20. Motor units
Made of one motor neuron and the muscle fibers associated with it
Number of muscle fibers varies
Fewer muscle fibers = finer movements
Ex: eyes
More muscle fibers = coarse movements Ex: large muscle in the back

21. Motor Unit single motor neuron
all muscle fibers controlled by motor neuron

22. Role of myosin and actin
Muscle fiber contraction results from a sliding movement of actin and myosin filaments.
About 2/3 of protein in skeletal muscle is myosin
Myosin consists of 2 twisted protein strands with globular cross bridges projecting outward

23. If Ca2+ present cross-bridges of myosin filaments form linkages with actin filaments.
Actin - myosin interactions provides the basis for contraction in all 3
muscle types.
Actin is about 1/4 of the protein in skeletal muscle
Many actin molecules aggregate into double twisted strand

24. When a fiber is at rest, proteins troponin and tropomyosin molecules interfere with linkage formation.
Ca ions remove the inhibition, binding to troponin and altering the position of tropomyosin exposing the binding sites on actin.

25. Sliding filament theory
When stimulated to contract the head of a myosin cross bridge attaches to actin binding site, pulling the actin filament toward the center of the sarcomere, shortening the muscle
ATP converted to ADP releasing energy

26. Stimulus for contraction
Muscle fiber is usually stimulated by acetylcholine (ACh)
released from the end of a motor nerve fiber.
Ach is synthesized in cytoplasm of a motor neuron
ACh combines with receptors in the sarcolemma and stimulates it

27. A muscle impulse travels through the transverse tubules to the sarcoplasmic reticulum (SR) which has a high concentration of Ca2+
cisternae membranes become more permeable to Ca2+ diffuse out of cisternae into the sarcoplasm causing linkages to form between actin and myosin which leads to muscle contraction

28. Contraction continues as long as ATP and ACh are present
Cessation of nerve impulse leads to muscle relaxation
ACh is decomposed by acetylcholinesterase
Stimulus to sarcolemma ceases, Ca2+ goes back into SR - Cross bridge linkages break and recock
Muscle relaxes

29. Stimulus for Contraction

31. Sliding Filament Model of Muscle Contraction

32. myosin cross-bridge pulls thin filament

33. Major Events of Muscle Contraction and Relaxation

34. Energy sources for contraction
• ATP supplies the energy for muscle fiber contraction
Muscles only have enough ATP to contract briefly
ATP must be regenerated
creatine phosphate stores energy that can be used to synthesize ATP as it is decomposed

35. The amount of ATP and creatine phosphate in a muscle can sustain contraction for only a few seconds
Active muscles depend upon cellular respiration of glucose for energy
Muscles store glucose in the form of glycogen

36. Oxygen Supply and Cellular Respiration

37. Anaerobic respiration yields few ATP molecules (2), whereas aerobic respiration provides many ATP's (34)
Hemoglobin in red blood cells carries oxygen from the lungs to body cells

38. Myoglobin(pigment) in muscle cells stores some oxygen temporarily reducing a the need for a continuous blood supply during contraction
Contracting muscle fibers may compress blood vessels

39. Oxygen debt
During rest or moderate exercise, oxygen is sufficient to support aerobic respiration
During strenuous exercise, an oxygen deficiency may develop, and lactic acid may accumulate as a result of anaerobic respiration
Lactic acid is carried by blood to the liver where it can be converted to glucose

40. The amount of oxygen needed to convert accumulated lactic acid to glucose and to restore supplies of ATP and creatine phosphate is called oxygen debt
Several hours may be needed to repay an oxygen debt after strenuous exercise

41. Oxygen Debt

42. Muscle fatigue A fatigued muscle loses its ability to contract
Usually due to the effects of accumulation of lactic acid
Lactic acid lowers the pH and prevents muscle fibers from responding to stimulation

43. Muscle cramps are due to a lack of ATP
ATP moves Ca2+ into SR and breaks the linkages between actin and myosin so the muscle fibers can relax
In a cramp part of the muscle may contract uncontrollably and other parts may be rigid

44. Physical training promotes new capillary growth and more mitochondria within muscles
Athletes usually produce less lactic acid than nonathletes because of their increased ability to supply oxygen and nutrients to muscles

45. Fast and slow muscles
The speed of contraction is related to a muscle's specific function
Slow-contracting(slow twitch) muscles contain oxygen storing myoglobin (red pigment) and many mitochondria
- can generate ATP fast enough to keep up with ATP breakdown and can contract for long periods Ex: long back muscles

46. Fast-contracting(fast twitch) muscles have less myoglobin, a poorer blood supply and fewer mitochondria
- have reduced ability to carry on aerobic respiration and tend to fatigue relatively rapidly Ex: hand and eye muscles
Most skeletal muscles have both types

47. Heat production By-product of cellular respiration
Active muscles release large amounts of heat
Blood transports heat throughout the body

48. Muscular Responses Threshold stimulus
Minimal strength of stimulation needed to cause a muscular contraction .
All-or-none response
A muscle fiber does not partially contract
If a muscle fiber contracts at all, it will contract completely.

49. Recording a muscle contraction
A myogram is a recording of an electrically stimulated isolated muscle pulling a lever.

50. A twitch is a single contraction lasting a fraction of a second
The latent period is the time between stimulus and responding muscle contraction (0.01 second in a frog)
The refractory period immediately follows a contraction - a muscle cannot respond (very brief)

51. Muscular Responses

52. Staircase effect
An inactive muscle undergoes a series of contractions of increasing strength when subjected to a series of stimuli
The staircase effect seems to be due to failure to remove calcium ions from the SR rapidly enough
A muscle fiber contraction is otherwise an all-or-none response

53. Summation
A muscle fiber exposed to a series of increasing stimuli reaches a point where it can't completely relax before the next stimuli
Force of individual twitches combines and the contraction is sustained
• Forceful, sustained contraction without relaxation is a tetanic contraction (tetanus)

54. Summation process by which individual twitches combine
produces sustained contractions
can lead to tetanic contractions

55. Recruitment of motor units
Each motor unit is controlled by a single motor neuron
all muscle fibers in a motor unit are stimulated at the same time (all-or-none)
A whole muscle is made of many motor units controlled by different motor neurons

56. At low intensity of stimulation, relatively small numbers of motor units contract
At increasing intensities of stimulation, other motor units are recruited until the muscle contracts with maximal tension
(recruitment)

57. Sustained contractions
Smaller motor units (finer fibers) respond earlier to stimuli
Larger units ( thicker fibers) respond later and more forcefully
Product of small and larger motor units is a sustained contraction of increasing strength (multiple motor unit summation)

58. Tetanic contractions occur in skeletal muscles
Muscle tone is a continuous state of partial contraction even when the muscle appears to be at rest - nerve impulse goes to a few muscle fibers
Ex: Maintaining posture

59. Types of contractions
Isotonic - a muscle contracts and its ends are pulled closer together
Ex: lifting objects
Isometric - a muscle contracts but its attachments do not move and it does not shorten.
Ex: push against a wall

60. Isokinetic - the force a muscle generates is less than that required to move or lift an object, lengthening the muscle
Ex: laying an object down on a table
Most body movements involve both isometric and isotonic contractions.

61. Smooth Muscles
The contractile mechanisms of smooth and cardiac muscles are similar to those of skeletal muscle.
• Shorter than the fibers of skeletal muscle and have single centrally located nuclei
Cells are elongated with tapering ends and contain thinner filaments of actin and myosin - lack striations

62. They lack transverse tubules, and the SR is not well developed.
• Two major types
multiunit smooth muscle: fibers occur separate rather than in sheets
- contraction occurs after stimulation by motor nerve impulses or certain hormones
Ex: Iris and walls of blood vessels

63. visceral smooth muscle: sheets of spindle shaped cells - most common
- found in walls of hollow organs (stomach, intestines, bladder, uterus)
-fibers can stimulate each other
-can display pattern of repeated spontaneous contractions (rhythmicity)
-wavelike motion called peristalsis (alternating contraction and relaxation) that moves materials through digestive system.

64. Smooth muscle contraction
Smooth muscles lack troponin
In smooth muscles, calmodulin (protein) binds to calcium ions and activates the contraction mechanism.
Both ACh and norepinephrine are neurotransmitters for smooth muscles.
Hormones stimulate or inhibit contraction
Ex: oxytocin stimulates uterus to contract during childbirth

65. Stretching smooth muscle can stimulate contractions
Ex: food stretches wall of intetines.
Smooth muscle can maintain a contraction for a longer time than skeletal muscle.
Smooth muscles can change lengths without changing tautness
Ex: walls can stretch as the organ fills up
Smooth muscles are slower to contract and relax than skeletal muscle

66. Smooth Muscle

67. Cardiac Muscle Appears only in the heart
Composed of striated cells joined end to end
Fibers are interconnected in branching 3-D networks
Each cell has a single nucleus
Contains actin and myosin similar to skeletal muscle
Has a well developed SR and many mitochondria

68. Larger transverse tubules supply more Ca ions in response to an impulse
Ca ions come from fluid outside the muscle fiber
Contracts for a longer time than skeletal muscle because transverse tubules supply extra Ca ions.
Intercalated disks connect the ends of adjacent cardiac muscle cells and hold the cells together.

69. A network of fibers contracts as a unit and respond in an all-or­none manner.
Cardiac muscle is self-exciting, rhythmic, and remains refractory until a contraction is completed (no tetanic contractions).

70. Cardiac Muscle

71. Skeletal Muscle

72. Skeletal Muscle Actions
Origin and insertion
One end of skeletal muscle is attached to an immovable part (origin: and the other end is attached to a movable end (insertion)
A muscle is pulled toward its origin when it contracts
Some muscles have more than one origin or insertion Ex: biceps (2 heads) brachii

73. Skeletal Muscle Actions

74. Interaction of skeletal muscles
Skeletal muscles function in groups.
A prime mover is responsible for most of a movement
Synergists aid prime movers

75. Antagonists can resist movement of a prime mover and cause movement in the opposite direction.
Smooth movements depend upon antagonists giving way to the actions of prime movers.

76. Characteristics of Muscle Tissue

77. Life-Span Changes myoglobin, ATP, and creatine phosphate decline
by age 80, half of muscle mass has atrophied
adipose cells and connective tissues replace muscle tissue
exercise helps to maintain muscle mass and function