Chapter 6 The Muscle Physiology

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Chapter 6 The Muscle
Physiology
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• Nerve Stimulus to Muscles

• Synaptic cleft gap between nerve and muscle
• - no contact
• - filled with interstitial fluid

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• Transmission of Nerve Impulse to Muscle

1. 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
All or None!
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• Sliding 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 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 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

• 2b. Fused (complete) tetanus
• No evidence of relaxation before the following
  contractions
• The result is a sustained muscle contraction

Figure 6.9a, b
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Tetanus 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 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 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 Debt

• When muscle is fatigued, it cant 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 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 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 Muscle

• Results of increased muscle use
• - Increase size
• - Increase strength
• - Increase efficiency
• - more fatigue resistant