Chapter 10: Muscle Tissue

1
Chapter 10Muscle Tissue
2
Muscle Tissue

• A primary tissue type, divided into
• skeletal muscle
• Voluntary striated muscle, controlled by nerves
  of the central nervous system
• cardiac muscle
• Involuntary striated muscle
• smooth muscle
• Involuntary nonstriated muscle

3
Characteristics of all Muscle Tissues

• Specialized Cells
• - elongated, high density of myofilaments
  cytoplasmic microfilaments of actin and myosin
• Excitability/Irritability
• - receive and respond to stimulus
• Contractility
• - shorten and produce force upon stimulation
• Extensibility
• - can be stretched
• Elasticity
• - recoil after stretch

4
Skeletal Muscle Tissue

• Skeletal muscles make up 44 of body mass
• Skeletal muscle an organ
• composed of
• skeletal muscle cells (fibers) and CT
• nerves and blood vessels

5
Functions of Skeletal Muscles

1. Produce skeletal movement
2. Maintain posture and upright position
3. Support soft tissues
4. Guard entrances and exits
5. Maintain body temperature by generating heat
6. Stabilize joints

6
Muscle Tissue Organized at the Tissue Level
7
Formation of Skeletal Muscle Fibers

• Skeletal muscle cells are called fibers

Figure 102
8
Skeletal Muscle Anatomy

• Each muscle is innervated by one nerve
• Nerve must branch and contact each skeletal
  muscle fiber (cell)
• One artery, branches into extensive capillaries
  around each fiber
• supply oxygen
• supply nutrients
• remove wastes.

9
Organization of Connective Tissues
Figure 101
10
Organization of Connective Tissues

• Muscles have 3 layers of connective tissues that
  hold the muscle together
• Epimysium
• - covers the muscle (exterior collagen layer),
  separates muscle from other tissues, composed of
  collagen, connects to deep fascia
• Perimysium
• - composed of collagen and elastin, has
  associated blood vessels and nerves, bundles
  muscle fibers into groups called fascicles
• - perimysium covers a fascicle
• Endomysium
• - composed of reticular fibers, contains
  capillaries, nerve fibers and satellite cells (
  stem cells ? repair), surrounds individual muscle
  fibers

11
Muscle Attachments

• Endomysium, perimysium, and epimysium come
  together
• at ends of muscles
• to form connective tissue attachment to bone
  matrix
• Tendon cord-like bundles
• Aponeurosis sheet-like

12
How would severing the tendon attached to a
muscle affect the muscles ability to move a body
part?

1. Uncontrolled movement would result from a severed
   tendon.
2. Movement would be greatly exaggerated with no
   tendon.
3. No movement is possible without a muscle to bone
   connection.
4. Limited movement would result.

13
Muscle
14
Skeletal Muscle Fibers

• Huge cells
• up to 100 µm diameter, 30 cm long
• Multinucleate
• Formed by fusion of 100s of myoblasts
• Nuclei of each myoblast retained to provide
  enough mRNA for protein synthesis in large fiber
• Unfused myoblasts in adult satellite cells
• Satellite cells are capable of division and
  fusion to existing fibers for repair but cannot
  generate new fibers

15
Organization of Skeletal Muscle Fibers
Figure 103
16
Skeletal Muscle Fibers

• Cell membrane sarcolemma
• Sarcolemma maintains separation of electrical
  charges resulting in a transmembrane potential
• Na pumped out of the cell creating positive
  charge on the outside of the membrane
• Negative charge from proteins on inside give
  muscle fibers a resting potential of -85mV
• If permeability of the membrane is altered, Na
  will flow in causing a change in membrane
  potential
• Change in potential will signal the muscle to
  contract

17
Transverse Tubules

• Tubes of sarcolemma called transverse tubules (T
  tubules) reach deep inside the cell to transmit
  changes in transmembrane potential to structures
  inside the cell
• Transmit action potential through cell
• Allow entire muscle fiber to contract
  simulataneously

18
Skeletal Muscle Fibers

• Cytoplasm sarcoplasm
• rich in glycosomes (glycogen granules) and
  myoglobin (binds oxygen)
• Fiber is filled with myofibrils extending the
  whole length of the cell
• Myofibrils consist of bundles of myofilaments
• Myofilaments are responsible for muscle
  contraction
• made of actin and myosin proteins
• 80 of cell volume

19
Organization of Skeletal Muscle Fibers
Figure 103
20
Skeletal Muscle Fibers

• Actin
• makes up the thin filament
• Myosin
• makes up the thick filament
• When thick and thin filaments interact,
  contraction occurs

21
Skeletal Muscle Fibers

• Sarcoplasm contains networks of SER called
  sarcoplasmic reticulum (SR)
• Sarcoplasmic Reticulum
• A membranous structure surrounding each myofibril
  
• Function
• store calcium and help transmit action potential
  to myofibril
• SR forms chambers (terminal cisternae) attached
  to
• T-tubules
• Cisternae
• Concentrate Ca2 (via ion pumps)
• Release Ca2 into sarcomeres to begin muscle
  contraction
• All calcium is actively pumped from sarcoplasm to
  SR (SR has 1000X more Ca2 than sarcoplasm)

22
Skeletal Muscle Fibers

• Triads are located repeated along the length of
  myofilaments
• Triads T-tubule wrapped around a myofibril
  sandwiched between two terminal cisternae of SR
• Formed by 1 T tubule and 2 terminal cisternae of
  SR
• Triads are located on both ends of a sarcomere
• Sarcomere smallest functional unit of a
  myofibril

23
Sarcomere
24

• Each muscle 100 fascicles
• Each fascicle 100 muscle
• fibers
• Each fiber (cell) 1 thousand
• myofibrils
• Each myofibril 10 thousand
• sarcomeres

25
The structural components of a sarcomere.
26
Sarcomeres

• The contractile units of muscle
• Structural units of myofibrils
• Form visible patterns within myofibrils

27
Sarcomeres

• Composed of
• 1. Thick filaments myosin
• 2. Thin filaments actin
• 3. Stabilizing proteins
• -hold thick and thin
• filaments in place
• 4. Regulatory proteins
• - control interactions of
• thick and thin filaments
• Organization of the proteins in sarcomere causes
  striated appearance of the muscle fiber

Figure 104
28
Muscle Striations

• A striped or striated pattern within myofibrils
• alternating dark, thick filaments (A bands) and
  light, thin filaments (I bands)

29
Regions of the Sarcomere

• A-band
• - whole width of thick filaments, looks dark
• microscopically
• M line at midline of sarcomere
• - Center of each thick filament, middle of
  A-band
• - Attaches neighboring thick filaments
• H-zone
• - Light region on either side of the M line
• - Contains thick filaments only
• Zone of overlap
• - ends of A-bands
• - place where thin filaments intercalate between
  thick
• filaments (triads encircle zones of
  overlap)

30
Regions of the Sarcomere

• I-band
• - Contains thin filaments outside zone of
  overlap
• - Not whole width of thin filaments
• Z lines/disc
• - the centers of the I bands
• - constructed of Actinins
• - Anchor thin filaments and bind neighboring
  sarcomeres
• - Constructed of Titin Proteins
• - Bind thick filaments to Z-line, stabilize
  the
• filament

31
(No Transcript)
32
Why does skeletal muscle appear striated when
viewed through a microscope?

1. Z lines and myosin filaments align within the
   tissue.
2. Glycogen reserves are linearly arranged.
3. Capillaries regularly intersect the myofibers.
4. Actin filaments repel stain, appearing banded.

33

• Sarcomere Function
• Transverse tubules encircle the sarcomere near
  zones of overlap
• Ca2 released by SR causes thin and thick
  filaments to interact
• Muscle Contraction
• Is caused by interactions of thick and thin
  filaments
• Structures of protein molecules determine
  interactions

34
Thin Filament
Figure 107a
35
Thin Filaments (5-6 nm diameter)

• Made of 4 proteins
• Actin
• Nebulin
• Holds F actin strands together
• F-actin (filamentous) consists of rows of G-actin
  (globular)
• Each G-actin has an active site that can bind to
  myosin
• Tropomyosin
• - Covers the active sites on G actin to prevent
  actinmyosin binding
• Troponin holds tropomyosin on the G-actin
• Also has receptor for Ca2
• when Ca2 binds to the troponin-tropomyosin
  complex it causes the release of actin allowing
  it to bind to myosin

36
Troponin and Tropomyosin
Figure 107b
37
Initiating Contraction

• Ca2 binds to receptor on troponin molecule
• Troponintropomyosin complex changes
• Exposes active site of F actin

38
Thick Filament
Figure 107c
39
Thick Filaments (10-12 nm diameter)

• Composed of
• bundled myosin molecules
• titin strands that recoil after stretching
• Each Myosin has three parts
• 1. Tail
• - tails bundled together to make length of
• thick filament
• - all point toward M-line
• 2. Hinge
• - flexible region, allows movement for
• contraction

40
Thick Filaments (10-12 nm diameter)

• 3. Head
• - hangs off tail by hinge, will bind actin at
  active
• site.
• - No heads in H-zone
• - also contains core of titin
• - elastic protein that attaches thick
• filaments to Z-line
• - Titin holds thick filament in place and aid
• elastic recoil of muscle after stretching
• - Each thick filament is surrounded by a
• hexagonal arrangement of thin filaments with
• which it will interact

41
The Myosin Molecule
Figure 107d
42
Myosin Action

• During contraction, myosin heads
• interact with actin filaments, forming
  cross-bridges
• pivot, producing motion

43
Sliding Filaments
Figure 108
44
Sliding Filament Theory

• Contraction of skeletal muscle is due to thick
  filaments and thin
• filament sliding past each other
• not compression of the filaments
• H-zones and I-bands decrease width during
  contraction
• Zones of overlap increase width
• Z-lines move closer together
• A-band remains constant
• Sliding causes shortening of every sarcomere in
  every myofibril in every fiber
• Overall result shortening of whole skeletal
  muscle

45
The components of the neuromuscular junction,
and the events involved in the neural control of
skeletal muscles.
46
Skeletal Muscle Contraction

1. Excitation
2. Excitation-Contraction Coupling
3. Contraction
4. Relaxation

Figure 109 (Navigator)
47
Excitation and the Neuromuscular Junction

• Excitation of muscle fiber is controlled by the
  nervous system at the neuromuscular junction
  using neurotransmitter

48
The Neuromuscular Junction

• Is the location of neural stimulation
• Action potential (electrical signal)
• travels along nerve axon
• ends at synaptic terminal

49
Components of Neuromuscular Junction

• Neuromuscular Junction
• - where a nerve terminal interfaces with a
  muscle fiber at
• the motor end plate
• - one junction per fiber control of fiber
  from one neuron
• Synaptic Terminal
• - expanded end of the axon, contains vesicles
  of
• neurotransmitters ? Acetylcholine (Ach)
• Motor End Plate
• - specialized sarcolemma that contains Ach
  receptors
• and the enzyme acetylcholinesterase
  (AchE)
• Synaptic Cleft
• - space between the synaptic terminal and
  motor end
• plate where neurotransmitters are released

50
Skeletal Muscle Neuromuscular Junction
Figure 1010a, b (Navigator)
51
(No Transcript)
52
2. Skeletal Muscle Excitation
Figure 1010c
53
The Neurotransmitter

• Acetylcholine or ACh
• travels across the synaptic cleft
• binds to membrane receptors on sarcolemma (motor
  end plate)
• causes sodiumion rush into sarcoplasm
• is quickly broken down by enzyme
  (acetylcholinesterase or AChE)

54
Action Potential

• Generated by increase in sodium ions in
  sarcolemma
• Travels along the T tubules
• Leads to excitationcontraction coupling

55
The Process of Contraction

• Neural stimulation of sarcolemma
• causes excitationcontraction coupling
• Cisternae of SR release Ca2
• which triggers interaction of thick and thin
  filaments
• consuming ATP and producing tension

56
3. ExcitationContraction Coupling

• Action potential reaches a triad
• releasing Ca2
• triggering contraction
• Requires myosin heads to be in cocked position
• loaded by ATP energy

57
The key steps involved in the contraction of a
skeletal muscle fiber.
58
Exposing the Active Site

1. The action potential of the transverse tubules
   reaches a triad and causes the release of calcium
   ions from the cisternae of the SR into the
   sarcoplasm around the zones of overlap of the
   sarcomeres
2. Calcium binds to troponin on the thin filaments
3. Troponin pulls tropomyosin off the active sites
   of the actin so that cross bridges can form.

Figure 1011
59
The Contraction Cycle
Figure 1012 (1 of 4)
60
5 Steps of the Contraction Cycle

1. Exposure of active sites
2. Formation of cross-bridges
3. Pivoting of myosin heads
4. Detachment of cross-bridges
5. Reactivation of myosin

61
The Contraction Cycle
2. Cross bridges are formed Actin active
sites are bound to myosin heads
1. Actin, free of tropomyosin, binds to myosin
via its active site
Figure 1012 (2 of 4)
62
The Contraction Cycle

• Myosin heads have been pre-primed for movement
  via ATP energy prior to cross bridge formation
  and are pointed away from the M line.
• Upon actin binding, the myosin heads pivot
  toward the M line in an event called the power
  stroke, which pulls the thick filament along the
  thin filament

Figure 1012 (3 of 4)
63
The Contraction Cycle

• Myosin ATPase uses ATP to break the cross bridges
  releasing the myosin head from the actin active
  site, and resets the myosin head pointed away
  from the M-line

64
The Contraction Cycle

• The myosin head is now primed to interact with a
  new active site on actin
• Myosin can carry out 5 power strokes per second
  while calcium and ATP are available.
• Each power stroke shortens the sarcomere by 1

Figure 1012 (Navigator) (4 of 4)
65
Fiber Shortening

• As sarcomeres shorten, muscle pulls together,
  producing tension

Figure 1013
66
Contraction Duration

• Depends on
• duration of neural stimulus
• number of free calcium ions in sarcoplasm
• availability of ATP

67
4. Relaxation

• Ca2 reabsorbed by sarcoplasmic reticulum
• Ca2 ions detach from troponin
• Troponin, without Ca2, pivots tropomyosin back
  onto active sites on actin, no cross bridges can
  form
• Sarcomeres stretch back out
• Gravity
• Opposing muscle contractions
• Elastic recoil of titin protein
• Result Muscle returns to Resting Length

68
A Review of Muscle Contraction
Table 101 (1 of 2)
69
A Review of Muscle Contraction
Table 101 (2 of 2)
70
Rigor Mortis

• A fixed muscular contraction after death
• Caused when
• SR can not absorb Ca2
• ion pumps cease to function
• calcium builds up in the sarcoplasm
• Ca2 bind troponin
• Tropomyosin frees actin
• Cross bridges from
• No ATP to detach myosin head because ATP is
  already all used up
• fixed cross bridge
• Contractions occur until necrosis releases
  lysosomal enzymes which digest cross bridges

71
Disease of Muscle Contraction

• Botulism/Botox
• Bacteria Clostridium botulinum (grows in
  improperly canned foods) produces botulinum toxin
• Toxin prevents the release of Ach at the
  neuromuscular junction
• Results in flaccid paralysis
• Tetanus
• Bacteria Clostridium tetani (grows in soil)
  produces tenanus toxin
• Toxin causes over stimulation of motor neurons
• Results in spastic paralysis
• Myasthenia gravis
• Autoimmune disease
• Causes loss of Ach receptors ? muscles become
• non-responsive

72
KEY CONCEPT

• Skeletal muscle fibers shorten as thin filaments
  slide between thick filaments
• Free Ca2 in the sarcoplasm triggers contraction
• SR releases Ca2 when a motor neuron stimulates
  the muscle fiber
• Contraction is an active process
• Relaxation and return to resting length is
  passive

73
Where would you expect the greatest concentration
of Ca2 in resting skeletal muscle to be?

1. T tubules
2. surrounding the mitochondria
3. within sarcomeres
4. cisternae of the sarcoplasmic reticulum

74
How would a drug that interferes with
cross-bridge formation affect muscle contraction?

1. interferes with contraction
2. slows contraction
3. speeds contraction
4. increases strength of contraction

75
Predict what would happen to a muscle if the
motor end plate failed to produce
acetylcholinesterase.

1. Muscle would lose strength.
2. Muscle would be unable to contract.
3. Muscle would lock in a state of contraction.
4. Muscle would contract repeatedly.

76
What would you expect to happen to a resting
skeletal muscle if the sarcolemma suddenly became
very permeable to Ca2?

1. increased strength of contraction
2. decreased cross bridge formation
3. decreased ability to relax
4. both A and C

77
The mechanism responsible for tension production
in a muscle fiber, and the factors that determine
the peak tension developed during a contraction.
78
Tension Production

• Muscle tension
• Force exerted by contracting muscle
• Force is applied to a load
• Load weight of the object being acted upon
• For a single muscle fiber contraction is
  allornone
• as a whole, a muscle fiber is either contracted
  or relaxed

79
Tension of a Single Muscle Fiber

• Once contracting tension depends on
• 1. The number of pivoting cross-bridges
• The fibers resting length at the time of
• stimulation
• 3. The frequency of stimulation

80
Resting Length

• Greatest tension produced at optimal resting
  length
• Optimal resting length Optimum overlap
• Overlap determines the number of pivoting
  cross-bridges
• Enough overlap, so that myosin can bind actin,
  not so much that thick filaments crash into
  Z-lines

Figure 1014
81
Why is it difficult to contract a muscle that has
been overstretched?

1. Myosin filaments break.
2. Crossbridges can not be formed.
3. Z lines are unable to sustain contractile forces.
4. Tendons lose elasticity.

82
Frequency of Stimulation

• Twitch single contraction due to a single
  neural stimulation, 3 phases
• Latent period post stimulation but no tension
• Action potential moves across the sarcolemma
• Ca2 is released
• Contraction phase peak tension production
• - Ca2 bind
• - Active cross bridge formation
• Relaxation phase decline in tension
• Ca2 is reabsorbed
• Cross bridges decline

83
Myogram

• A graph of twitch tension development

84
Twitch

• Single twitch will not produce normal movement
• requires many cumulative twitches
• Repeat stimulation will result in higher tension
  due to Ca2 not being fully absorbed
• - Ca2 ? more cross bridges
• Types of Frequency Stimulation
• Treppe
• Wave summation
• Incomplete Tetanus
• Complete Tetanus

85
Treppe

• Stepping up of tension production to max level
  with repeat stimulation of the same fiber
  following relaxation phase
• Repeated stimulations immediately after
  relaxation phase
• stimulus frequency lt 50/second
• Causes a series of contractions with increasing
  tension

86
Treppe

• A stair-step increase in twitch tension

Figure 1016a
87
Wave Summation

• Repeat stimulation before relaxation phase ends
  resulting in more tension production than max
  treppe
• stimulus frequency gt 50/second
• Typical muscle contraction
• Increasing tension or summation of twitches

Figure 1016b
88
Incomplete Tetanus

• Rapid cycles of contraction and relaxation
  produces max tension
• Twitches reach maximum tension

Cardiac muscle ? incomplete tetanus Only
to prevent seizure of heart
Figure 1016c
89
Complete Tetanus

• Relaxation eliminated, continuous contraction
• Fiber is in prolonged state of contraction
• Produces 4x more tension than maximum treppe
• Quick to fatigue

Most Skeletal muscle ? complete tetanus
when contracting
Figure 1016d
90
During treppe, why does tension in a muscle
gradually increase even though the strength and
frequency of the stimulus are constant?

1. Increased blood flow improves contraction.
2. Sarcomeres shorten with each contraction.
3. Calcium ion concentration increases with
   successive stimuli.
4. Generated heat improves contraction.

91
The factors that affect peak tension production
during the contraction of an entire skeletal
muscle, and the significance of the motor unit in
this process.
92
Tension Produced by Whole Skeletal Muscles

• Depends on
• Internal tension produced by sarcomeres
• - Not all the tension is transferred to the load,
  some of it is lost due to the elasticity of
  muscle tissues
• External tension exerted by muscle fibers on
  elastic extracellular fibers
• - Tension applied to the load
• 3. Total number of muscle fibers stimulated

93
Total Number of Muscle Fibers Stimulated

• Each skeletal muscle has thousands of fibers
  organized into motor units
• Motor units all fibers controlled by a single
  motor neuron
• Axon branches to contact each fiber
• Number of fibers in a motor unit depends on the
  function
• Fine control 4/unit (e.g. eye muscles)
• Gross control 2000/unit (e.g. leg muscles)
• Fibers from different units are intermingled in
  the muscle so that the activation of one unit
  will produce equal tension across the whole muscle

94
Motor Units in a Skeletal Muscle
Figure 1017
95
Recruitment (Multiple Motor Unit Summation)

• In a whole muscle or group of muscles, smooth
  motion and increasing tension is produced by
  slowly increasing size or number of motor units
  stimulated
• Recruitment order of activation of a motor unit
• Slower weaker units are activated first
• Strong units are added to produce steady
  increases in tension

96
Contraction Skeletal Muscle

• During sustained contraction of a muscle
• Some units rest while others contract to avoid
  fatigue
• For maximum tension, all units in complete
  tetanus
• Leads to rapid fatigue
• Muscle tone maintaining shape/definition of the
  muscle
• Some units are always contracting
• Exercise Increase of units contraction ?
• Increase in metabolic rate ?
• Increase in speed of recruitment (better tone)

97
KEY CONCEPT

• Voluntary muscle contractions involve sustained,
  tetanic contractions of skeletal muscle fibers
• Force is increased by increasing the number of
  stimulated motor units (recruitment)

98
The types of muscle contractions.
99
Contraction Skeletal Muscle

• All contractions produce tension but not always
  movement
• Isotonic Contractions
• - Muscle length changes resulting in movement
• Isometric Contractions
• - Tension is produced with no movement

100
Isotonic Contraction

• If muscle tension gt resistance
• muscle shortens (concentric contraction)
• If muscle tension lt resistance
• muscle lengthens (eccentric contraction)

Figure 1018a, b
101
Isometric Contraction

• Skeletal muscle develops tension, but is
  prevented from changing length
• Note Iso same, metric measure

Figure 1018c, d
102
Return to Resting Length

• Expansion via
• Elastic recoil after contraction
• The pull of elastic elements (tendons and
  ligaments)
• Expands the sarcomeres to resting length
• Opposing muscle contractions
• - Reverse the direction of the original motion
• Gravity
• - Opposes muscle contraction to return a muscle
  to its resting state

103
Can a skeletal muscle contract without
shortening? Explain.

1. Yes isotonic contractions produce no movement.
2. No resistance is always less than force
   generated.
3. Yes concentric contractions are common.
4. No contraction implies movement.

104
The mechanisms by which muscle fibers obtain
energy to power contractions.
105
Muscle Metabolism

• 1 fiber 15 million thick filaments
• 1 thick filament 2500 ATP/sec
• 1 glucose (aerobic respiration) 36 ATP
• Each fiber needs 1x1012 glucose/sec to contract
• ATP unstable, muscles store respiration energy on
  creatine as Creatine Phosphate (CP)
• Creatine phosphokinase transfers P from CP at ADP
  when ATP is needed to reset myosin for next
  contraction
• Each cell as only 20 sec of energy reserved

106
ATP and CP

• Adenosine triphosphate (ATP)
• the active energy molecule
• Creatine phosphate (CP)
• the storage molecule for excess ATP energy in
  resting muscle
• Energy recharges ADP to ATP
• using the enzyme creatine phosphokinase (CPK)
• When CP is used up, other mechanisms generate ATP

107
Muscle Metabolism

• At Rest
• Use glucose and fatty acids with O2 (from blood)
  ? aerobic respiration
• Resulting ATP is used to CP reserves
• Excess glucose is stored as glycogen
• Moderate Activity
• CP used up
• Glucose and fatty acids with O2 (from blood) are
  used to generate ATP (aerobic respiration)

108
Muscle Metabolism

• High Activity
• O2 not delivered adequately
• Glucose from glycogen reserves are used for ATP
  via fermentation (glycolysis only)
• Pyruvic acid is converted to lactic acid
• Excess lactic acid production leads to muscle
  cramps

109
ATP Generation

• Cells produce ATP in 2 ways
• aerobic metabolism of fatty acids in the
  mitochondria (At rest and Moderate activity)
• Is the primary energy source of resting muscles
• Breaks down fatty acids
• Produces 34 ATP molecules per glucose molecule
• anaerobic glycolysis (fermentation) in the
  cytoplasm (High activity)
• Is the primary energy source for peak muscular
  activity
• Produces 2 ATP molecules per molecule of glucose
• Breaks down glucose from glycogen stored in
  skeletal muscles

110
Muscle Metabolism
Figure 1020a
111
Muscle Metabolism
Figure 1020b
112
Muscle Metabolism
Figure 1020c
113
Muscle Metabolism
Figure 1020 (Navigator)
114
Factors that contribute to muscle fatigue, and
the stages and mechanisms involved in muscle
recovery.
115
Muscle Fatigue

• When muscles can no longer perform a required
  activity (contraction), they are fatigued
• Depletion of reserves
• - glycogen, ATP, CP
• Decreased pH due to
• lactic acid production
• Damage to sarcolemma and sarcoplasmic reticulum
• Muscle exhaustion and pain

116
To restore function, cell need

• Intracellular energy reserves
• - Glycogen and CP
• Good Circulation
• - Nutrients in, wastes out
• Normal O2 levels
• Normal pH
• Lactic Acid Disposal

117
Normal pHLactic Acid Disposal

• Lactic acid diffuses into the blood
• Filtered out by the liver
• Converted back to glucose through the Cori Cycle
• Returned to blood for use by cells
• When O2 returns
• Remaining lactic acid in the muscle is converted
  to glucose and used in aerobic cellular
  respiration

118
KEY CONCEPT

• Skeletal muscles at rest metabolize fatty acids
  and store glycogen
• During light activity, muscles generate ATP
  through aerobic breakdown of carbohydrates,
  lipids or amino acids
• At peak activity, energy is provided by anaerobic
  reactions that generate lactic acid as a byproduct

119
Muscle fibers and physical conditioning that
relate to muscle performance.
120
Muscle Performance

• Power
• the maximum amount of tension produced
• Endurance
• the amount of time an activity can be sustained
• Power and endurance depend on
• Types of muscle fibers
• Fast Glycolytic Fibers (fast twitch)
• Slow Oxidative Fibers (slow twitch)
• Intermediate/Fast Oxidative Fibers
• Physical conditioning
• Aerobic Exercise
• Resistance Exercise

121
Fiber Types

• Types of fibers in a muscle are genetically
  determined and mixed
• Fast glycolytic Fibers (fast twitch)
• Myosin ATPase work quickly
• Anaerobic ATP production glycolysis only
• Large diameter fibers
• More myofilaments and glycogen
• Few mitochondria
• Fast to act, powerful, but quick to fatigue
• Catabolize glucose only

122
Fiber Types

• Slow Oxidative Fibers (slow twitch)
• Myosin ATPases work slowly
• Specialized for aerobic respiration
• Many mitochondria
• Extensive blood supply
• Myoglobin (red pigment, binds oxygen)
• Smaller fibers for better diffusion
• Slow to contract, weaker tension, but resist
  fatigue
• Catabolize glucose, lipids, and amino acids

123
Fiber Types

• 3. Intermediate/Fast Oxidative Fibers
• Qualities of both fast glycolytic and slow
  oxidative fibers
• Fast acting but perform aerobic respiration so to
  resist fatigue
• Physical conditioning can convert some fast
  fibers into intermediate fibers for stamina

124
Fast versus Slow Fibers
Figure 1021
125
Comparing Skeletal Muscle Fibers
Table 103
126
Muscles and Fiber Types

• White muscle
• mostly fast fibers
• pale (e.g., chicken breast)
• Red muscle
• mostly slow fibers
• dark (e.g., chicken legs)
• Most human muscles
• mixed fibers
• pink

127
Physical Conditioning

• Aerobic Exercise
• - Increase Capillary Density
• Increase Mitochondria and myoglobin
• Both then
• Increase efficiency of muscle metabolism
• Increase strength and stamina
• Decrease fatigue
• Resistance Exercise
• Results in Hypertrophy
• fibers increase in diameter but not number
• Increase glycogen, myofibrils, and myofilaments
  results in increase tension production

128
Physical Conditioning

• Growth Hormone (pituitary) and Testosterone (male
  sex hormone)
• Stimulate synthesis of contractile proteins
• Results in Muscle Enlargement
• Epinephrine
• Stimulates increase muscle metabolism
• Results in increase force of contraction
• Without stimulation muscles will atrophy
• Fibers shrink due to loss of myofilament proteins
• Loss up to 5/day

129
KEY CONCEPT

• What you dont use, you loose
• Muscle tone indicates base activity in motor
  units of skeletal muscles
• Muscles become flaccid when inactive for days or
  weeks
• Muscle fibers break down proteins, become smaller
  and weaker
• With prolonged inactivity, fibrous tissue may
  replace muscle fibers

130
Why would a sprinter experience muscle fatigue
before a marathon runner would?

1. Sprinters cannot utilize ATP for long periods of
   time.
2. Sprinters muscles are most efficient
   aerobically.
3. Sprinters muscles are most efficient
   anaerobically.
4. Sprinters muscles are weaker.

131
Which activity would be more likely to create an
oxygen debt swimming laps or lifting weights?

1. swimming laps
2. lifting weights
3. both A and B
4. neither A nor B

132
Which type of muscle fibers would you expect to
predominate in the large leg muscles of someone
who excels at endurance activities, such as
cycling or long-distance running?

1. slow fibers
2. fast fibers
3. nonvascular fibers
4. thick, glycogen-laden fibers

133
Cardiac Muscle Tissue
134
Cardiac Muscle Tissue

• Cardiac muscle is striated, found only in the
  heart

Figure 1022
135
Cardiac Muscle Tissue

• Forms the majority of heart tissue
• Cells cardiocytes
• One or two nuclei
• No cell division
• Long branched cells
• Myofibrils organized into sarcomeres (striated)
• No triads (no terminal cisternae)
• Transverse tubules encircle Z-lines
• Aerobic Respiration Only
• Mitochondria and myoglobin rich
• Glycogen and lipid energy reserves
• Intercalated discs at cell junctions (gap
  junctions and desmosomes)
• allow transmission of action potentials
• link myofibrils from on cardiocyte (cell) to the
  next

136
Coordination of Cardiocytes

• Because intercalated discs link heart cells
  mechanically, chemically, and electrically, the
  heart functions like a single, fused mass of cells

137
4 Functions of Cardiac Tissue

• Automaticity
• contraction without neural stimulation
• Automatically due to control by pacemaker cells
• These cells generate action potentials
  spontaneously
• Pace and amount of contraction tension
• Can be adjusted and controlled by the nervous
  system
• Extended contraction time
• - Contraction is 10x longer than skeletal muscle
• Only twitches, no complete tetanus
• - Prevention of wave summation and tetanic
  contractions by cell membranes

138
Smooth Muscle Tissue
139
Structure of Smooth Muscle

• Nonstriated tissue

Figure 1023
140
Smooth Muscle Tissue

• Lines hollow organs
• Regulates blood flow and movement of materials in
  organs
• Forms errector pili muscles
• Usually organized into two layer
• Circular
• Longitudinal
• Spindle shaped cells
• Single central nucleus
• Cells capable of division
• No myofibrils, sarcomeres, or T tubules
• SER/ER throughout cytoplasm
• No tendons

141
Smooth Muscle Tissue

• Thick filaments (myosin fibers) scattered
• Myosin fibers have more heads per thick filament
• Thin filaments are attached to dense bodies on
  desmin cytoskeleton (web)
• Adjacent cells attach at dense bodies with gap
  junctions (firm linkage and communication)
• Dense bodies transmit contractions from cell to
  cell
• Contraction compresses the whole cell

142
Smooth Muscle in Body Systems

• Forms around other tissues
• In blood vessels
• regulates blood pressure and flow
• In reproductive and glandular systems
• produces movements
• In digestive and urinary systems
• forms sphincters
• produces contractions
• In integumentary system
• arrector pili muscles cause goose bumps

143
Smooth Excitation-Contraction

• Different than striated muscle
• no troponin so active sites on actin are always
  exposed
• Events
• Stimulation causes Ca2 release from SR
• Ca2 binds calmondulin in the sarcoplasm
• - Calmondulin CALcium MODULated proteIN
• Calmondulin activates myosin light chain kinase,
  this complex phosphorylates myosin
• MLC Kinase converts ATP? ADP to cock myosin head
• Cross bridge form ? contraction, cells pull
  toward center

144
Smooth Excitation-Contraction

• Stimulation is by involuntary control from
• - Autonomic Nervous System
• - Hormones
• - Other Chemical Factors
• Skeletal Muscle Motor Neurons
• Cardiac Muscle Automatically

145
Characteristics of Skeletal, Cardiac, and Smooth
Muscle
Table 104
146
Why are cardiac and smooth muscle contractions
more affected by changes in extracellular Ca2
than are skeletal muscle contractions?

1. Extracellular Ca2 inhibits actin.
2. Crossbridges are formed extracellularly.
3. Most calcium for contractions comes from SR
   stores.
4. Most calcium for contractions comes from
   extracellular fluid.

147
Smooth muscle can contract over a wider range of
resting lengths than skeletal muscle can. Why?

1. Smooth muscle sarcomeres are longer.
2. Myofilament arrangement is less organized in
   smooth muscle.
3. Smooth muscle cells are shorter.
4. Smooth muscle actin is longer.

148
Effects of Aging

• Skeletal Muscle fibers become thinner
• Decrease myofibrils, Decrease reserves
• Decrease in strength and
  endurance and
• Increase in
  fatigue
• Decrease cardiac and smooth muscle function
• Decrease cardiovascular performance
• Increase fibrosis (CT)
• Skeletal muscle less elastic
• Decrease ability to repair
• Decrease satellite cells
• Increase scar formation

149
SUMMARY

• 3 types of muscle tissue
• skeletal
• cardiac
• smooth
• Functions of skeletal muscles
• Structure of skeletal muscle cells
• endomysium
• perimysium
• epimysium
• Functional anatomy of skeletal muscle fiber
• actin and myosin

150
SUMMARY

• Nervous control of skeletal muscle fibers
• neuromuscular junctions
• action potentials
• Tension production in skeletal muscle fibers
• twitch, treppe, tetanus
• Tension production by skeletal muscles
• motor units and contractions
• Skeletal muscle activity and energy
• ATP and CP
• aerobic and anaerobic energy

151
SUMMARY

• Skeletal muscle fatigue and recovery
• 3 types of skeletal muscle fibers
• fast, slow, and intermediate
• Skeletal muscle performance
• white and red muscles
• physical conditioning
• Structures and functions of
• cardiac muscle tissue
• smooth muscle tissue