1. The Muscular System
Chapter 7

2. There are four characteristics associated with muscle tissue:
Excitability
Contractility
Extensibility
Elasticity
- Tissue can receive & respond to stimulation
- Tissue can shorten & thicken
- Tissue can lengthen
- After contracting or lengthening, tissue always wants to return to its resting state

3. The characteristics of muscle tissue enable it to perform some important functions, including:
Movement – both voluntary & involuntary
Maintaining posture
Supporting soft tissues within body cavities
Guarding entrances & exits of the body
Maintaining body temperature

4. Types of muscle tissue: Skeletal muscle tissue
Associated with & attached to the skeleton
Under our conscious (voluntary) control
Microscopically the tissue appears striated
Cells are long, cylindrical & multinucleate -c
Rapid onset, rapid fatigue

5. Slower onset, fatigue resistant, can’t tetanize
Cardiac muscle tissue
Makes up myocardium of heart
Unconsciously (involuntarily) controlled
Microscopically appears striated
Cells are short, branching & have a single nucleus
Cells connect to each other at intercalated discs
Slower onset, fatigue resistant, can’t tetanize

6. Slow onset, fatigue resistant
Smooth (visceral) muscle tissue
Makes up walls of organs & blood vessels
Tissue is non-striated & involuntary
Cells are short, spindle-shaped & have a single nucleus
Tissue is extremely extensible, while still retaining ability to contract
Slow onset, fatigue resistant

7. Anatomy of a Skeletal Muscle
Entire muscle is surrounded by epimysium (fibrous ct)—at the end forms a tendon
Contains blood vessels and nerves
Made up of fascicles (bundles of muscle fibers) surrounded by perimysium
Fascicles made up of muscle fibers surrounded by endomysium
Fibers are the cells-made of myofibrils

8. Sarcolemma—muscle cell membrane
Sarcoplasm—cytoplasm-many mitochondria, many nuclei

9. Myofibrils are surrounded by sarcoplasmic reticulum which stores Ca needed for contraction
Myofibrils are bundles of thick filaments (myosin) and thin filaments (actin)
Repeating units of these filaments form a sarcomere
Interactions between the myosin and actin filaments produce contraction

10. Organization of Skeletal Muscles

11. Anatomy of skeletal muscles
epimysium
tendon
perimysium
Muscle Fascicle
Surrounded by perimysium
endomysium
Skeletal muscle
Skeletal muscle fiber (cell)
Surrounded by epimysium
Surrounded by endomysium
Play IP Anatomy of Skeletal muscles (IP p. 4-6)

12. Microanatomy of a Muscle Fiber

13. transverse (T) tubules sarcoplasmic reticulum
Microanatomy of a Muscle Fiber (Cell)
transverse (T) tubules
sarcoplasmic reticulum
sarcolemma
terminal cisternae
mitochondria
myoglobin
thick myofilament
thin myofilament
myofibril
triad
nuclei

14. myofibril Muscle fiber sarcomere Z-line Thin filaments Thick filaments
Myosin molecule of
thick myofilament
Thin myofilament

15. Myofilaments of sarcomere
Z line
M line
Z line
Thin myofilaments
Thick myofilaments

16. Muscle contraction Under control of nervous system
Nerves and skeletal muscle fiber connect at neuromuscular junctions
Neuron branches out and ends in expanded knobs-synaptic knobs which contain a neurotransmitter Acetylcholine (Ach) that changes the sarcolemma and triggers contraction

17. Neuromuscular junction
telodendria
Synaptic terminal (end bulb)
Synaptic vessicles containing Ach
Synaptic cleft
Neuromuscular junction
Motor end plate
of sarcolemma

18. Muscle contraction 1. electrical impulse from brain 2. release of Ach
3. triggers Ca ions to be released from SR into sarcoplasm
4. linkages (cross bridges) form between the actin and myosin filaments –requires ATP
5. actin filaments slide inward along myosin filaments
6.muscle fiber shortens (contraction)

19. Sliding Filament Theory
Myosin heads attach to actin molecules (at binding (active) site)
Myosin “pulls” on actin, causing thin myofilaments to slide across thick myofilaments, towards the center of the sarcomere
Sarcomere shortens, I bands get smaller, H zone gets smaller, & zone of overlap increases

23. relaxation 1. cholinesterase is secreted and causes ACh to decompose
2. Ca are pumped back into SR
3. linkages between actin and myosin broken
4. actin and myosin slide apart
5. muscle relaxes

24. Muscle mechanics All or none response
A muscle fiber contracts or doesn’t
The amount of tension produced by a whole muscle is determined by the frequency of stimulation and the # of fibers stimulated

25. Twitch—single stimulus contraction relaxation sequence
Latent period-getting ready
Contraction-tension rises to a peak
Relaxation-tension falls to resting lines
contraction
latent
relaxation

26. Summation-(sustained contraction)-stimuli arrive before relaxation complete
Complete tetanus-(sustained powerful contraction)-frequency of stimulation so high-relaxation eliminated
Motor unit- all muscle fibers controlled by a single neuron (finer control, fewer muscle fibers)

27. small motor units  precise control (e.g. eye muscles
The size of the motor unit determines how fine the control of movement can be –
small motor units  precise control (e.g. eye muscles
large motor units gross control (e.g. leg muscles)
Recruitment is the ability to activate more motor units as more force (tension) needs to be generated
There are always some motor units active, even when at rest. This creates a resting tension known as muscle tone, which helps stabilize bones & joints, & prevents atrophy
PLAY
Play IP Contraction of motor units p. 3-7

28. Recruitment- increased tension produced by increase in the number of motor units
muscle tone-resting tension
Isotonic contraction-increased tension to move resistance (lifting, walking, running)
Isometric contraction-resistance doesn’t move (pushing against wall, maintaining posture)

30. Muscle fatigue-muscles cannot contract due to:
Exhaustion of ATP
Damage to SR
Decrease in oxygen
Decreased blood flow

31. Recovery period-return to preexertion levels
Oxygen debt-breathing rate increases until homeostasis is reached (preexertion level)
Hypertrophy
Increased muscle size due to increased numbers of mitochondria, myofibrils, and glycogen reserves
Due to repeated exhaustive stimulation

32. Atrophy Muscle not stimulated on a regular basis
Loss of muscle tone and mass

33. Muscle performance Types of Fibers
1. fast- contract .01 seconds or less, large, powerful contractions, fatigue rapidly, “white color”
2. Slow- ½ size of fast, takes 3 times longer to contract, increased endurance, increased blood flow, red pigment (myoglobin) carries oxygen darker in color
3. intermediate- pale, more capillaries than fast fibers, resistant to fatigue
Humans are a mixture of types.
Fast & intermediate in eyes & hand
Slow in legs

34. Physical Conditioning
Increased blood flow improves oxygen and nutrient availability
Anaerobic endurance-fast fibers, brief intensive workouts that stimulate hypertrophy
Aerobic endurance-sustained low level workouts, jogging, distance swimming, warm up to increase blood flow & treppe

35. Hormones for muscles 1. growth hormone & testosterone
Increase synthesis of proteins and enlargement of muscles
2. thyroid hormone
Increases the rate of energy consumption
3. Adrenaline
Stimulates muscle metabolism and increases the duration of stimulation and force of contraction

36. Aging
Muscle fibers decrease in diameter due to a decrease in myofibrils
Decrease in ATP, strength and endurance
Increased fibrous connective tissue-less flexible
Rapid fatigue, may overheat
Decreased healing, increased scar tissue

37. Thin Myofilament
(myosin binding site)

38. Thick myofilament
(has ATP & actin binding site)
*Play IP sliding filament theory p.5-14 for overview of thin & thick filaments

39. Sarcomere A band Z line Z line I band Zone of overlap M line
H zone
I band
Zone of overlap
Zone of overlap
M line
Thin myofilaments
Thick myofilaments

40. As sarcomeres shorten, myofibril shortens
As sarcomeres shorten, myofibril shortens. As myofibrils shorten, so does muscle fiber
Once a muscle fiber begins to contract, it will contract maximally
This is known as the “all or none” principle

41. Physiology of skeletal muscle contraction
Skeletal muscles require stimulation from the nervous system in order to contract
Motor neurons are the cells that cause muscle fibers to contract
cell body
dendrites
Synaptic terminals (synaptic end bulbs)
axon
telodendria
(motor neuron)

42. Overview of Events at the neuromuscular junction
An action potential (AP), an electrical impulse, travels down the axon of the motor neuron to the end bulbs (synaptic terminals)
Release of Acetylcholine (Ach) into the synaptic cleft
Ach diffuses across the synaptic cleft & binds to Ach receptors on the motor end plate
The binding of Ach to its receptors causes a new AP to be generated along the muscle cell membrane
Immediately after it binds to its receptors, Ach will be broken down by Acetylcholinesterase (AchE) – an enzyme present in the synaptic cleft

43. Action potential
Arrival of an action potential at the synaptic terminal
Axon
Arriving action potential
Synaptic terminal
Sarcolemma
Vesicles
ACh
Synaptic
cleft
AChE molecules
ACh
receptor
site
Muscle
fiber
Sarcolemma of
motor end plate
An action potential (AP), an electrical impulse, travels down the axon of the motor neuron to the end bulbs (synaptic terminals)
Figure 7-4(b-c)
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44. Release of Acetylcholine (Ach) into the synaptic cleft
Action potential
Arrival of an action potential at the synaptic terminal
Axon
Arriving action potential
Synaptic terminal
Sarcolemma
Vesicles
ACh
Synaptic
cleft
AChE molecules
ACh
receptor
site
Muscle
fiber
Sarcolemma of
motor end plate
Release of acetylcholine
Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft.
Release of Acetylcholine (Ach) into the synaptic cleft
Figure 7-4(b-c)
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Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

45. Action potential
Arrival of an action potential at the synaptic terminal
Axon
Arriving action potential
Synaptic terminal
Sarcolemma
Vesicles
ACh
Synaptic
cleft
AChE molecules
ACh
receptor
site
Muscle
fiber
Sarcolemma of
motor end plate
ACh binding at the motor and plate
Ach diffuses across the synaptic cleft & binds to Ach receptors on the motor end plate
Release of acetylcholine
Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft.
The binding of ACh to the receptors increases the membrane permeability to sodium ions. Sodium ions then rush into the cell.
Na+
Na+
Na+
Figure 7-4(b-c)
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46. The binding of Ach to its receptors causes a new AP to be generated along the muscle cell membrane
Immediately after it binds to its receptors, Ach will be broken down by Acetylcholinesterase (AchE) – an enzyme present in the synaptic cleft

47. Play IP neuromuscular junction p. 14
Action potential
Arrival of an action potential at the synaptic terminal
Axon
Arriving action potential
Synaptic terminal
Sarcolemma
Vesicles
ACh
Synaptic
cleft
AChE molecules
ACh
receptor
site
Muscle
fiber
Sarcolemma of
motor end plate
ACh binding at the motor and plate
Appearance of an action potential in the sarcolemma
Release of acetylcholine
Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft.
The binding of ACh to the receptors increases the membrane permeability to sodium ions. Sodium ions then rush into the cell.
An action potential spreads across the surface of the sarcolemma. While this occurs, AChE removes the ACh.
Action
potential
Na+
Na+
Na+
Play IP neuromuscular junction p. 14

48. Physiology of Skeletal Muscle Contraction
Once an action potential (AP) is generated at the motor end plate it will spread like an electrical current along the sarcolemma of the muscle fiber
The AP will also spread into the T-tubules, exciting the terminal cisternae of the sarcoplasmic reticula
This will cause Calcium (Ca+2 ) gates in the SR to open, allowing Ca+2 to diffuse into the sarcoplasm
Calcium will bind to troponin (on the thin myofilament), causing it to change its shape. This then pulls tropomyosin away from the active sites of actin molecules.
The exposure of the active sites allow the sliding of the filaments
Table 7-1

49. Physiology of skeletal muscle contraction – events at the myofilaments
Resting sarcomere
Active-site exposure
Cross-bridge formation
ADP
Myosin head
ADP + P +
Sarcoplasm P
Troponin
ADP + P
Ca2+
Ca2+
Ca2+
ADP
Active site
Ca2+
Tropomyosin
Actin +
ADP
ADP P P + P +
Myosin reactivation
Cross bridge detachment
Pivoting of myosin head
ADP
ATP
ADP + P + P
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
ADP P +
ATP
ADP + P
Figure 7-5
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50. Resting sarcomere
Active-site exposure
ADP
Myosin head
ADP + P +
Sarcoplasm P
Troponin
Ca2+
Ca2+
Tropomyosin
Actin
Active site
ADP
ADP P + P +
Calcium (Ca+2 ) gates in the SR open, allowing Ca+2 to diffuse into the sarcoplasm
Calcium will bind to troponin (on the thin myofilament), causing it to change its shape.
This then pulls tropomyosin away from the active sites of actin molecules.
Figure 7-5
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Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

51. Resting sarcomere
Active-site exposure
Cross-bridge formation
ADP
Myosin head
ADP + P +
Sarcoplasm P
Troponin
ADP + P
Ca2+
Ca2+
Ca2+
ADP
Tropomyosin
Actin
Active site
Ca2+ +
ADP
ADP P P + P +
Myosin heads are “energized” by the presence of ADP + PO43- at the ATP binding site (energy is released as phosphate bond of ATP breaks)
Once the active sites are exposed, the energized myosin heads hook into actin molecules forming cross-bridges
Figure 7-5
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52. The ADP & phosphate group are released from the myosin head
Resting sarcomere
Active-site exposure
Cross-bridge formation
ADP
Myosin head
ADP + P +
Sarcoplasm P
Troponin
ADP + P
Ca2+
Ca2+
Ca2+
ADP
Ca2+
Tropomyosin
Actin
Active site +
ADP
ADP P P + P +
Pivoting of myosin head
Using the stored energy, the attached myosin heads pivot toward the center of the sarcomere
The ADP & phosphate group are released from the myosin head
ADP + P
Ca2+
Ca2+
ADP + P
Figure 7-5
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53. Resting sarcomere
Active-site exposure
Cross-bridge formation
ADP
Myosin head
ADP + +
Sarcoplasm P P
Troponin
ADP + P
Ca2+
Ca2+
Ca2+
ADP
Active site
Ca2+
Tropomyosin
Actin +
ADP
ADP P P + P +
A new molecule of ATP binds to the myosin head, causing the cross bridge to detach from the actin strand
The myosin head will get re-energized as the ATP  ADP+P
Cross bridge detachment
Pivoting of myosin head
ATP
ADP + P
Ca2+
Ca2+
Ca2+
Ca2+
ATP
ADP + P
As long as the active sites are still exposed, the myosin head can bind again to the next active site

54. Resting sarcomere
Active-site exposure
Cross-bridge formation
ADP
Myosin head
ADP +
Sarcoplasm P + P
Troponin
ADP + P
Ca2+
Ca2+
Ca2+
ADP
Tropomyosin
Actin
Active site
Ca2+ +
ADP
ADP P P + P +
Myosin reactivation
Cross bridge detachment
Pivoting of myosin head
ADP
ATP
ADP + P + P
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
ADP P +
ATP
ADP + P
IP Sliding filament theory – p single cross bridge; p. 27 multiple cross bridges
PLAY
Figure 7-5
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55. Physiology of Skeletal Muscle Contraction
If there are no longer APs generated on the motor neuron, no more Ach will be released
AchE will remove Ach from the motor end plate, and AP transmission on the muscle fiber will end
Ca+2 gates in the SR will close & Ca+2 will be actively transported back into the SR
With Ca+2 removed from the sarcoplasm (& from troponin), tropomyosin will re-cover the active sites of actin
No more cross-bridge interactions can form
Thin myofilaments slide back to their resting state
Table 7-1

56. Key Note
Skeletal muscle fibers shorten as thin filaments interact with thick filaments and sliding occurs. The trigger for contraction is the calcium ions released by the SR when the muscle fiber is stimulated by its motor neuron. Contraction is an active process; relaxation and the return to resting length is entirely passive.

57. These physiological processes describe what happen at the cellular level – how skeletal muscle fibers contract
But what about at the organ level? How do skeletal muscles (like your biceps brachii) contract to create useful movement?

58. Skeletal muscles are made up of thousands of muscle fibers
A single motor neuron may directly control a few fibers within a muscle, or hundreds to thousands of muscle fibers
All of the muscle fibers controlled by a single motor neuron constitute a motor unit

59. When skeletal muscles contract, they may produce two types of contractions:
Isotonic contraction
Isometric contraction

60. Isotonic contraction – as tension increases (more motor units recruited), length of muscle changes usually resulting in movement of a joint. The tension (load) on a muscle stays constant (iso = same, tonic = tension) during a movement. (Example: lifting a baby, picking up object, walking, etc. )

61. Isometric contraction – no change in length of muscle even as tension increases. The length of a muscle stays constant (iso = same, metric = length) during a “contraction” (Example: holding a baby at arms length, pushing against a closed door.)
Necessary in everyday life to counteract effects of gravity (e.g. postural muscles keeping head up)

62. Anatomy of the Muscular System
Origin
Muscle attachment that remains fixed
Insertion
Muscle attachment that moves
Action
What joint movement a muscle produces
i.e. flexion, extension, abduction, etc.

63. For muscles to create a movement, they can only pull, not push
Muscles in the body rarely work alone, & are usually arranged in groups surrounding a joint
A muscle that contracts to create the desired action is known as an agonist or prime mover
A muscle that helps the agonist is a synergist
A muscle that opposes the action of the agonist, therefore undoing the desired action is an antagonist

64. Skeletal muscle movements
Flexion/extension
Abduction/adduction
Rotation – left/right; internal(medial)/external(lateral)
pronation/supination
Elevation/depression
Protraction/retraction
Dorsiflexion/plantarflexion
Inversion/eversion

66. An Overview of the Major Skeletal Muscles
Figure 7-11(a)

67. An Overview of the Major Skeletal Muscles
Figure 7-11(b)

72. Anatomy of the Muscular System
Muscles of the Head and Neck
Figure 7-12(a)

73. Anatomy of the Muscular System
Muscles of the Head and Neck
Figure 7-12(b)

74. Anatomy of the Muscular System
Muscles of the Head and Neck
Figure 7-12(c)

75. Anatomy of the Muscular System
Muscles of the Anterior Neck
Figure 7-13

76. Anatomy of the Muscular System
Muscles of the Spine
Figure 7-14

77. Anatomy of the Muscular System
Oblique and Rectus Muscles and the Diaphragm
Figure 7-15(a)

78. Anatomy of the Muscular System
Oblique and Rectus Muscles and the Diaphragm
Figure 7-15(b)

79. Anatomy of the Muscular System
Oblique and Rectus Muscles and the Diaphragm
Figure 7-15(c)

80. Anatomy of the Muscular System
Muscles of the Shoulder
Figure 7-17(a)

81. Anatomy of the Muscular System
Muscles of the Shoulder
Figure 7-17(b)

82. Anatomy of the Muscular System
Muscles that Move the Arm
Figure 7-18(a)

83. Anatomy of the Muscular System
Muscles that Move the Arm
Figure 7-18(b)

84. Anatomy of the Muscular System
Muscles That Move the Forearm and Wrist
Figure 7-19

85. Anatomy of the Muscular System
Muscles That Move the Thigh
Figure 7-20(a)

86. Anatomy of the Muscular System
Muscles That Move the Thigh
Figure 7-20(b)

87. Anatomy of the Muscular System
Muscles That Move the Leg
Figure 7-21

88. Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Figure 7-22(a)

89. Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Figure 7-22(b)

90. Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Figure 7-22(c)

91. Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Figure 7-22(d)