Topic 10: Skeletal Muscle Physiology - Muscle Tension Flashcards

1
Q

What is muscle tension?

A
  • force exerted by a muscle or muscle fiber
    in lecture, more globular heads tagging on to myofilaments means more tension
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2
Q

What is muscle tension determined by?

A
  • number of cross bridges formed
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3
Q

In a muscle fiber, what is muscle tension affected by? (4)

A
  1. Frequency of Stimulation
  2. Fiber length
  3. Size of Fiber
  4. Fatigue
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4
Q

What are the factors of frequency of stimulation? (4)

A
  1. Single Stimulus
  2. Second stimulus arrives before complete relaxation from first
  3. Rapid sequence of stimuli
    4.High frequency of stimuli
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5
Q

What happens when you have a single stimulus? (5)

A
  1. Produces a twitch (a weak contraction and relaxation not normally occurring in skeletal muscles)
  2. Causes an AP (lasts 1-2 msec)
  3. Latent period (2 msec) where excitation-contraction coupling occurring
  4. Contraction period (10-100 msec) increased tension
  5. Relaxation that decreases tension
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6
Q

What happens during the contraction period of a single stimulus? (4)

A
  • increased tension
    1. Cross bridge attachment and sliding filaments
    2. a lot of calcium released from SR on stimulation, but taken back rapidly by SR Ca2+-ATPase so not all myosin heads attach
    3. Does not reach maximum possible tension
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7
Q

What happens in relaxation of a single stimulus? (2)

A
  • calcium pumped into SR
  • ATP releases myosin, etc
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8
Q

What happens if a 2nd stimulus arrives before complete relaxation from first stimulus? (5)

A
  • muscle AP always completed (refractory period) but uptake of calcium by SR is not yet complete (fiber relaxing)
  • second stimulus causes release of more calcium, adding to that already in the cytosol
  • more myosin heads then attach
  • produces second contraction with increased tension, aka wave summation
  • this contraction has no refractory period
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9
Q

What happens during rapid sequence of stimuli? (2)

A
  • tension increases further (increased calcium availability to wave summation)
  • partial relaxation between contractions produces quivering, called INCOMPLETE TETANUS
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10
Q

What happens during high frequency of stimuli? (2)

A
  • no relaxation between contraction (ie. sustained contraction) called COMPLETE TETANUS
  • all troponin saturated with calcium and fiber warm (ATP synthesis makes heat) so it works faster
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11
Q

Which of the following occurs normally in the body, rapid sequence of stimuli or high frequency of stimuli?

A

high frequency

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