1. Muscle Physiology

2. Structure of Skeletal Muscle
Muscle = group of fascicles
Muscle fibers extend length of muscle from tendon to tendon
Figure 12.1
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3. Skeletal Muscle Fiber Figure 12.2
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4. Structure of a Sarcomere
Figure 12.3
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5. Thin Myofilament Figure 12.4
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6. Thick Myofilament Figure 12.5a–c
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7. Thick Myofilament Figure 12.5d–e
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8. Sliding Filaments Figure 12.6a
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9. Sliding Filaments Figure 12.6b
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10. Crossbridge Cycle Figure 12.7 ATP is hydrolyzed ATP Unbinding of
myosin and actin
Rigor (myosin in
low-energy form)
Cocking of the
myosin head
(myosin in
high-energy form)
Binding of
myosin to actin
Power stroke
Inorganic
phosphate
is released
ADP is
released
Actin gets
pulled towards
middle of
sarcomere Pi
ADP
New ATP
binds to 1 2 3 4 5
Figure 12.7
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11. Excitation Contraction Coupling
Motor end
plate
Ca2+
Acetylcholine (ACh) is released from the
axon terminal of a motor neuron and binds
to receptors in the motor end plate. This binding
elicits an end-plate potential, which triggers an
action potential in the muscle cell.
Action potential
propagates along
the sarcolemma
and down T tubules
Ca2+ is actively
transported back
into lumen of SR
following the
action
potential
Neuromuscular junction
Sarcolemma
T tubule
Sarcoplasmic
reticulum (SR)
Synaptic cleft
Axon terminal
ACh
receptors
The action potential
triggers Ca2+ release
from SR
Tropomyosin blocks
myosin-binding sites
(muscle fiber relaxes)
Ca2+ binds to troponin,
exposing myosin-binding sites
Crossbridge cycle begins
(muscle fiber contracts) 1 2 3 4 5 7 6
Figure 12.8
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12. Troponin & Tropomyosin Actions
Figure 12.9
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13. Sarcoplasmic Reticulum Gating
Figure 12.10
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14. Termination of Contraction
Calcium must leave troponin, allowing tropomyosin to cover myosin binding sites on actin
To remove calcium from cytosol
Ca2+ ATPase in sarcoplasmic reticulum
Transports calcium from cytosol into sarcoplasmic reticulum
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15. Sources of ATP Phosphorylation of ADP by creatine phosphate
Oxidative phosphorylation of ADP in mitochondria
Anaerobic glycolysis
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16. Creatine/Creatine Phosphate
Creatine phosphate + ADP  Creatine + ATP
Law of Mass Action
Use of ATP drives the reaction to the right
Creatine
kinase
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17. Creatine Phosphate Energy Stores
Creatine phosphate = first source of ATP
Can provide 4–5 times the amount of ATP present in cell at rest
One step process—very rapid
Very limited amount—used up rapidly
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18. Oxidative Phosphorylation
Primary energy source during light to moderate exercise
Oxygen supply is adequate
Example: aerobic exercises
To maintain adequate oxygen
Increase ventilation
Increase heart rate and contraction
Dilate vessels to muscle
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19. Energy Source for Oxidative Phosphorylation
Muscle stores limited amount of glucose as glycogen
Substrate of oxidative phosphorylation up to 30 minutes
Glucose and fatty acids delivered to muscle by blood
Dominant after 30 minutes
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20. Anaerobic Glycolysis
When oxygen supply to muscle is limited (during intense exercise), anaerobic glycolysis = primary source of ATP
Rapid source of ATP
Only two ATP/glucose
Limited glucose availability
Build up lactic acid (burning sensation)
Limited duration of high intensity (anaerobic) exercise
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21. After Exercise
Following exercise, respiration is still increased because oxidative phosphorylation continues
Replenish creatine-P and glycogen stores
Convert lactic acid to pyruvic acid
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22. Metabolic Pathways Figure 12.11
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23. Phases of a Muscle Twitch
Figure 12.12
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24. Isometric Contraction
Figure 12.13a
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25. Isotonic Contraction Figure 12.13b
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26. Effect of Load on Tension
Figure 12.14
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27. Normal Muscle Activity
Some purely isometric contractions occur
Purely isotonic contractions are rare
Even if load is constant, isometric precedes isotonic phase of contraction
Isometric continues (tension increases) until tension exceeds load
Then isotonic contraction begins
Tension remains constant as muscle shortens
Load generally not constant
Load is changing as limb position is changing
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28. Treppe
Figure 12.15
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29. Basis of Summation Action potential Contraction
Two msec
Contraction
10–200 msec
Contractions can overlap and sum
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30. Isometric Twitch Duration
Figure 12.16
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31. Summation and Tetanus Figure 12.17
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32. Length-Tension Graph Figure 12.18
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33. Motor Unit Size Principle
Figure 12.20
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34. Muscle Shortening and Load
Figure 12.21
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35. Load-Velocity Graph Figure 12.22
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