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Chapter 6 The Muscle Physiology
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Nerve Stimulus Nerve Stimulus to Musclesto Muscles
Synaptic cleft – gap between nerve and muscle
- no contact
- filled with interstitial fluid
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Transmission of Nerve Impulse to MuscleTransmission of Nerve Impulse to Muscle1. Neurotransmitter (acetylcholine) released by
nerve upon arrival of nerve impulse
2. Acetylcholine attaches to receptors on the sarcolemma
3. Sarcolemma becomes permeable to sodium (Na+)
4. Sodium rushing into the cell causes an action potential
5. Once started, muscle contraction cannot be stopped
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Sliding Filament TheorySliding Filament Theory Activation by nerve
causes myosin crossbridges to attach to actin
then bind to the next site on actin
Myosin “slides” along actin
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Contraction of a Skeletal MuscleContraction of a Skeletal Muscle
Contraction is “all or none” w/in one fiber
not all fibers may be stimulated during the same interval
Different combinations of muscle fiber contractions give different responses
Graded responses – different degrees of skeletal muscle shortening
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Types of Graded ResponsesTypes of Graded Responses
1. Twitch Single, brief contraction
Not a normal muscle function
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2. Tetanus (summing of contractions) One contraction is immediately followed by
another
The muscle does not completely return to a resting state
The effects are added
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2a. Unfused (incomplete)
tetanus Some relaxation
occurs between contractions
The results are summed
Figure 6.9a, b
2b. Fused (complete)
tetanus No evidence of
relaxation before the following contractions
The result is a sustained muscle contraction
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Tetanus can be caused by bacteriaTetanus can be caused by bacteria
• Clostridium tetani is a bacteria that causes tetanus in humans, also called lockjaw.
• Produce toxin that affects the nerves and controls the activity of muscles.
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Response to Strong StimuliResponse to Strong Stimuli Muscle force
depends upon # of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract until they run out of energy
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Energy for Muscle ContractionEnergy for Muscle Contraction Initially, muscles used stored ATP for energy
- ATP broken to release energy
- 4-6 sec worth of ATP stored
After this time, other pathways used to make ATP
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Direct phosphorylation
- Muscle cells contain creatine phosphate (CP)
- CP is a high-energy molecule
- After ATP is depleted, ADP is left
- CP transfers energy to ADP, to regenerate ATP
- Used up in 15- 20 sec
Creatine monohydrate is a precursor to creatine phosphate. By supplementing with creatine monohydrate, your muscle creatine phosphate is maximised, and more muscular work can occur due to greater energy reserves.
NOT endorsed by School!
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Aerobic Respiration occur in the mitochondria
Glucose is broken down to carbon dioxide and water, releasing energy
slower reaction that requires oxygen
Makes the most ATP
Lasts for hours
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Anaerobic glycolysis
Reaction that breaks down glucose without oxygen
Glucose is broken down to pyruvic acid to produce 2 ATP
Lasts up to 1 min.
Muscle fatigue – no more O2 – burning due to lactic acid
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Muscle Fatigue and Oxygen DebtMuscle Fatigue and Oxygen Debt When muscle is fatigued, it can’t contract
Common reason is oxygen debt
- Oxygen needed to get rid of lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less
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Types of Muscle ContractionsTypes of Muscle Contractions
1. Isotonic contractions Myofilaments slide past each other during
contractions
The muscle shortens
2. Isometric contractions Tension in the muscles increases
The muscle does NOT shorten
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Muscle ToneMuscle Tone
Some fibers are contracted even in a relaxed muscle
Different fibers contract at different times
Involuntary
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Effects of Exercise on MuscleEffects of Exercise on Muscle
Results of increased muscle use
- Increase size
- Increase strength
- Increase efficiency
- more fatigue resistant