Skeletal muscle physiology

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Skeletal muscle physiology

• Muscle contraction in the body
• Summation of muscle twitches
• Motor units
• Muscle contraction and loads
• Friday ch. 14 Cardiavascular Physiology (After
  ch. 14, well cover smooth muscle located at the
  end of ch. 12)

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A twitch is a single contraction/relaxation cycle
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The muscle does not relax completely before the
second stimulus occurs, resulting In a more
powerful contraction summation
Stimulus
Stimulus
Stimulus
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Motor unit

• One somatic motor unit and the muscle fibers that
  it innervates

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A muscle may have many motor units of many
fiber types.
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Recruitment of motor unit activity during muscle
activity

• Each motor neuron has its own threshold potential
  for firing action potentials
• Each motor unit has its own threshold
• A muscles activity varies with the number of
  motor units that are recruited
• Recruitment is controlled by the nervous system

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Recruitment

• Weak stimulus activates low threshold neurons.
  These regulate slow fatigue resistant fibers.
• Stronger stimuli ? fatigue resistant oxidative
  fast twitch fibers
• Very strong stimuli ? glycolytic fast twitch
  fibers

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Isotonic contraction any contraction that
creates a force and moves a load
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Isometric contraction - Create force without
movement
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How can a muscle generate force without changing
its length?

• Each muscle elastic elements
• Tendons
• Intracellular cytoskeletal proteins with elastic
  properties
• Contractile proteins themselves can stretch
• These are included in the term series elastic
  elements.

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