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Exercise Physiology > 1 - Structure and Function of Exercising Muscle > Flashcards

1 - Structure and Function of Exercising Muscle Flashcards

1
Q

Three muscle tissue types

A
  1. Skeletal
  2. Smooth
  3. Cardiac
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2
Q

What are myofibrils?

A

Collective proteins grouped together within a muscle fiber that are made up of basic contractile elements of skeletal muscles
- Hundreds to thousands per muscle fibers

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3
Q

What are sarcomeres?

A

Basic contractile element of skeletal muscle that are end to end of full myofibril length
- DIstinctive striped appearance (striations)
- Contains A-bands, I-bands, H-zone and M-line

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4
Q

Actin (thin protein filaments)

A
  • show up lighter on microscope (I-band contains them)
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5
Q

What 3 proteins are thin filaments composed of?

A

Actin - myosin binding sites
Tropomyosin - covers active site at rest
Troponin - (anchored to actin) moves tropomyosin

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6
Q

Myosin (thick protein filament)

A
  • show up darker on microscope (A-bands and H-zone contains thick filaments)
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7
Q

What band contains both actin and myosin filaments?

A

A-band contains both

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8
Q

What do Myosin filaments look like?

A
  • two intertwined filaments
  • globular heads > protrude 360 degrees from thick filament axis and interact with actin filaments for contraction
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9
Q

What does Titan (third myofilament) do

A

Acts like a spring (stiffness increases with muscle activation and force development)
- Ca binds to titan, increasing muscle force when stretched
- stabilizes sarcomeres and centers myosin to prevent overstretching

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10
Q

What is a motor unit?

A
  • consists of a single a-motor + all fibers it innervates
  • more operating motor units = more contractile force
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11
Q

What is a neuromuscular junction?

A
  • consists of synapse/gap between a - motor neuron and muscle fiber
  • serve as site of communication between a neuron and the muscle
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12
Q

Actions which occur during excitation-contraction coupling

A
  • Action potential starts in the brain
  • AP arrives at the axon terminal, releases acetylcholine (ACh)
  • ACh crosses synapse, binds to ACh receptors on plasmalemma
  • Triggers Ca release from sarcoplasmic recticulum
  • Ca enables actin-myosin contraction
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13
Q

What is the role of Ca in a muscle fiber?

A
  • When AP arrives at sarcoplasmic reticulum it becomes sensitive to electrical charge causing a mass release of Ca into sarcoplasm
  • Ca binds to troponin on thin filament. At rest, tropomyosin covers myosin-binding site to block actin-myosin. The troponin-Ca complex moves tropomyosin and myosin binds to actin contraction can occur.
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14
Q

Sliding filament theory in a relaxed state

A
  • No actin-myosin interaction occurs at binding site
  • Myofilaments overlap a little
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15
Q

Sliding filament theory in a contracted state

A
  • Myosin head pulls actin toward sarcomere center (power stroke)
  • Filaments slide past each other
  • Sarcomeres, myofibrils, muscle fiber all shorten
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16
Q

Sliding filament theory after the power stroke ends

A
  • myosin detaches from active site
  • myosin head rotates back to original position
  • myosin attaches to another active site farther down
17
Q

When does the sliding filament theory process end?

A
  1. Z-disk reaches myosin filaments
    or
  2. AP stops and Ca gets pumped back into the sarcoplasmic reticulum
18
Q

What energy is necessary for muscle contraction?

A

Adenosine triphosphate (ATP) - binds to myosin head (ATPase on myosin head)

19
Q

What happens during muscle relaxation?

A
  • AP ends and electrical stimulation of SR stop
  • Ca is pumped back into SR and is stored until AP arrives (Ca release requires ATP)
  • Without Ca, troponin and tropomyosin return to resting conformation (covering myosin binding sites preventing actin-myosin cross bridging)
20
Q

Type 1 muscle fibers

A
  • 50% of fibers in an average muscle
  • Peak tension in 100ms (slow twitch)
21
Q

Type 2 muscle fibers

A
  • Peak tension in 50 ms (fast twitch)
    Type 2a and Type 2x (25% of fibers in an average muscle)
22
Q

Type 1 vs Type 2

A

Variable speed of myosin ATPase
- Fast myosin ATPase = fast contraction cycling (type 2)
- Slow myosin ATPase = slow contraction cycling (type 1)

23
Q

Example of type 1 fibers

A

A marathon runner, slower contraction

24
Q

Example of type 2 fibers

A

Weightlifter, more powerful contraction but quick to fatigue

25
Q

Tests to see what muscles contain which fiber type

A
  1. Muscle biopsy - 10-100g of muscle is removed, frozen, sliced and examined under a microscope
  2. Gel electrophoresis - process separates types of myosin by size
26
Q

What fiber types are found in the sarcoplasmic reticulum?

A

TYpe 2 fibers have more highly developed in the SR (Ca is released faster)

27
Q

Difference in motor units form type 1 vs type 2

A

Type 1 motor unit = smaller neuron < 300 fibers
Type 2 motor unit = larger neuron > 300 fibers
more motor fiber connections=more contraction

28
Q

Type 1 vs Type 2 peak power

A

Type 2x > Type 2a > Type 1
All fibers reach peak power at 20% of peak force

29
Q

How are muscle fiber types distributed?

A
  • Each person has a unique ratio of types
  • Arm and leg ratios are similar in one person
  • Type 1 predominates in endurance athletes whereas Type 2 predominates in power athletes
  • Soleus is type 1 in everyone!
30
Q

Type 1 fibers during exercise

A

Possess high aerobic endurance - maintain exercise prolonged periods
- require oxygen for ATP production
- Recruited for low-intensity aerobic exercise/daily activities
- efficiently produce ATP from fat and carbs

31
Q

Type 2 fibers during exercise

A

Type 2 in general - fatigue quickly (poor aerobic endurance) and produce ATP anaerobically
2a - produce more force faster to fatigue (used for short intense endurance)
2x - Seldom used for everyday activities (used for short explosive sprints)

32
Q

Fiber determinants

A

Genetic factors - determine which a-motor neurons innervate fibers (fibers differ based on a-motor neuron)
Training factors - differ endurance training, strength training and detraining (enduring a small 10% change)
Aging - loss of type 2 motor units

33
Q

Motor unit recruitment

A

Method altering force production
less force production = fewer/smaller motor units
More force production = more/larger motor units
T

Exercise Physiology (9 decks)

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