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Musculoskeletal System > Muscle Physiology 2 > Flashcards

Muscle Physiology 2 Flashcards

1
Q

What is a muscle twitch?

A

Contraction produced in a muscle fiber in response to a single action potential

Twitch is an all or nothing event for given muscle fiber at rest

-twitch can be defined for a muscle fiber, motor unit, or whole muscle level

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2
Q

What is preload?

A

The load on a muscle in a relaxed state, I.e, before it contracts

Applying preload to the muscle results in:
-stretching of the muscles

-generation of passive tension in the muscle

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3
Q

What is afterload?

A

The load of the muscle works against during contraction

Contractile elements= sarcomere

Series elastic elements= connective tissue, tendons

Force exerted by contracting muscle= tension

Force opposing contraction (such as weight to be moved)= load

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4
Q

What is isotonic contraction?

A
  • constant tension
  • when tension > load
  • load is lifted as muscle shortens
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5
Q

What is isometric contraction?

A
  • length constant
  • contractile elements contract, generating tension
  • when load > tension
  • stretches series elastic elements
  • muscle does NOT shorten, load not lifted
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6
Q

What is the function of the isometric contraction?

A

These create force without moving a load

  • series elastic elements
  • sarcomere shorten while elastic elements stretch, resulting in little change in overall length
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7
Q

What is the function of the isotonic contraction?

A
  • Create force and move a load
  • Concentric action is a shortening action
  • Eccentric action is a lengthening action
  • There are 4 phases of the isotonic contraction
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8
Q

What are the 4 phases of isotonic contraction?

A

Phase 1 isometric contraction

Phase 2 isotonic contraction

Phase 3 isotonic relaxation

Phase 4 isometric relaxation

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9
Q

What is the function of series elastic elements in muscles?

A

Elastic elements allow isometric contractions:
-In an isometric contraction, sarcomeres shorten, generating force, but elastic elements stretch, allowing muscle length to remain the same.

-In isotonic contractions, sarcomeres shorten more but, because elastic elements are already stretched, the muscles shorten

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10
Q

Summarize the mechanics of normal muscle activity

A

Some purely isometric contractions occur

  • Purely isotonic contractions are rare
    • Even if load is constant, isometric precedes isotonic phase of contraction (remember the phases of isotonic contraction)

Load generally not constant
-load changes with the change of limb position

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11
Q

What is passive tension force ?

A

The elastic component of skeletal muscle creates a resistance to stretch. The force of this resistance is measured as passive tension.

Preload inversely proportional to length inversely proportional to passive tension

Note: passive tension is force

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12
Q

How does active tension affect sarcomere length?

A

Sarcomere length and the amount of myosin-actin filament overlap on the active tension developed by a contracting muscle fiber

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13
Q

What is caused by an increase in preload?

A

Increase Fmax:

  • shifts curve to the right
  • increase Crossbridge overlap
  • increases maximum weight that can be moved, max force generated
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14
Q

What is caused by increased velocity?

A

Same weight/after load can be moved faster

No change Vmax:
-ATPase. Activity not allowed

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15
Q

What is the function of Myosin-ATPase?

A

Hydrolysis of ATP- step to energize myosin head group

  • Activity determine the rate of myosin head resetting in Crossbridge cycling (how fast it spins)
  • Vmax is determined by myosin ATPase activity—> how fast Crossbridge cycle spins
  • Increased myosin ATPase activity also increases ATP utilization during contraction
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16
Q

Explain the functioning of the type 1 muscle fibers

A

Slow, oxidative fibers

Generally, this is smaller (less powerful) muscle, utilized long term (endurance muscle), e.g. postural muscle. Major characteristics:

  • lower myosin ATPase activity (slower muscle)
  • Contains a large amount of myoglobin pigment
  • High capacity for aerobic Metabolism
  • Slow twitch, fatigue resistant motor units
17
Q

Describe type 2 muscle fibers

A

Fast, glycolytic

Generally, this is the large (powerful) muscle that is utilized short-term, e.g. ocular muscles, leg muscles of a sprinter.

Major characteristics:
-High Myosin ATPase activity(fast muscle)

  • low myoglobin
  • high capacity for anaerobic glycolysis.
  • Vast twitch fibers, which have rapid conduction rate, and which are adapted to fast, short lived forces
18
Q

How do skeletal muscles regulate their force?

A

Graded muscle contractions

  1. Temporal summation: tension produced by each fiber (due to high frequency stimulation)
  2. Spatial summation (recruitment): number of fibers contracting
19
Q

What determines the tension produced by individual muscle fibers?

A

Number of active crossbridges that bind to actin
-More crossbridges that bind —> more force

Factors affecting force of individual muscle fiber

  • frequency of stimulation
  • fiber diameter
  • changes in fiber length (already covered before)
20
Q

What does the basis of summation represent?

A

Increases in frequency of action potential in muscle fibers increases tension

21
Q

What are the events at each phase of tension-timr(msec) graph?

A
  • action potential (two msec) -action potential causes Ca2+ release
  • contraction (20-100msec)- release of Ca2+ evokes muscle contraction. Muscle membrane has completely depolarized before relaxation of the muscle
  • contractions can overlap and sum
22
Q

What causes tetanus?

A

Amount of tension developed depends on amount of calcium bound to troponin

  • At high frequencies, release exceeds re-uptake
    • Calcium increases in cytosol
  • Eventually saturates system
    • All troponin has calcium bound to it
    • Crossbridge cycling maxed out
    • Maximum tetanic contraction
23
Q

What causes tetanus?

A

A neurological disorder caused by the toxin produced in the bacterium clostridium tetani.

The toxin that is released blocks the release of inhibitory transmitters, y-aminobutyric Acid (GABA)

Diminished inhibition leads to increase in the resting firing rate of motor rate

-Increased repetitive stimulation of the motor neuron, the calcium released from the SR remains bound to troponin and extends the time for cross-bridge cycling, resulting in muscles that do not relax

24
Q

What are the symptoms of tetanus?

A

“Lockjaw” and the neck, shoulder, back, upper and lower extremities spasms. Generalized spasms may jeopardize. Breathing

25
Q

How can tetanus be managed?

A

Not a comprehensive management

Antitoxin- neutralize circulating and unbound toxin

Diazepam (GABA agonist)- to control spasm

26
Q

What are the factors affecting whole muscle contraction

A

Spatial summation /motor unit recruitment

Force developed by the whole muscle depends on:

  • number of muscle fibers contracting
  • more muscle fibers contracting, greater force

More fibers contracting —> greater tension

  • recruit motor units
    • Activate motor neuron activates all muscle fibers in the motor unit
    • Increases in tension occur in steps proportional to size of motor unit
27
Q

What is the motor unit size principle?

A

Order of motor unit recruitment related to size of motor units

Musculoskeletal System (41 decks)

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