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MSK-Derm by Minnie > SM 224a - Muscle Physiology and Mechanics > Flashcards

SM 224a - Muscle Physiology and Mechanics Flashcards

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1
Q

What are the 4 things that determine the force of muscle contraction?

A
  • Ca2+ available
  • Rate of action potential firing (force-stimulus frequency relationship)
  • Length of the muscle (length-tension relationship)
  • How fast the muscle moves (force-velocity relationship)
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2
Q

What determines whether a given motor unit is fast or slow?

A

The type of myosin ATPase it has

Fast motor units will fatige, either quickly or slowly depending on the type

Slow motor units do not fatigue

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3
Q

Describe the force-velocity relationship of muscle mechanics

A

Faster muscle shortening = less force generated

  • Fast-twitch muscle fibers can contract 20-30x per second
  • Slow-twitch muscle fibers are still contracting in fast movements, but not contributing significantly
    • They will help more with slower movements
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4
Q

Which section is labeled by #3?

A

H band

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5
Q

Which cellular energy source dominates in an effort that lasts 5-10 seconds?

A

Creatine phosphate (CP)

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6
Q

Does your biceps brachi contain fast or slow motor units?

A

Both!

Every muscle is heterogeneous - contains both fast and slow motor units

  • Different muscles have different percentages of each fiber
  • Your muscles are a bit trainable - you can work to increase endurance (by increasing slow motor units) or contraction velocity (by increasing fast motor units)
  • Different people natrually have more of one type or another
    • Think about Usain Bolt vs. Shalane Flanagan (accomplished marathoner)
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7
Q

Describe the length-tension relationship in muscle mechanics

A

More cross-bridges = stronger contractrion force

More overlap between actin and myosin = more cross-bridges

  • When the sarcomere length is very short, actin fibers overlap each other and one blocks the other from forming cross briges
  • As the sarcomere lengthens, more actin is available to form cross bridges and contractile force increases
  • When the sarcomere gets too long, overlap between actin and myosin decreases, which reduces the number of corss briges that can be formed. Contractile force decreases
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8
Q

Which structure is labeled by #7?

Which molecules make up this structure?

A

Thin filament

Actin + Tropomyosin + Troponin T, C, and I

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9
Q

Describe the following for stored fat:

  • Mobilization time:
  • Amount stored:
A
  • Mobilization time: 20-60 minutes
  • Amount stored: SOOO much

Note: this pathway is oxygen dependent

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10
Q

What are the mechanical characteristics of muscle?

A
  • Spring-like characteristics
    • Cushion the landing of the jump
  • Viscous-like characteristics
    • Prevent too much oscillation at the landing of a jump
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11
Q

Which cellular energy source dominates within the first second of effort?

A

ATP

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12
Q

Which molecule is labeled by #6?

What is its function?

A

Titin

A length-sensing giant molecule that acts as a stiff spring

It prevents over-stretching of the sarcomere, and recoils after stretch to pull the sarcomere back to its normal length

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13
Q

Which structure is labeled by #9?

Which molecules make up this structure?

A

Thick filament

Made from myosin light and heavy chains

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14
Q

Describe the troponin complex

A

The troponin complex is attached to tropomyosin

It is made up of…

  • Troponin T (TnT), which binds to tropomyosin
  • Troponin C (TnC), which binds to Ca2+
  • Troponin I (TnI), which inhibits contraction when it is bound to actin
    • It covers up the myosin binding site on actin
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15
Q

Which structure is labeled by #8?

A

M Line

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16
Q

During a 10 s maximum speed running race, which energy substrate is the main source of ATP to support the force generated in the muscles being used?

  1. glycogen via aerobic pathways
  2. glycogen via anaerobic glycolysis
  3. creatine phosphate (CP)
  4. fat via anaerobic pathways
  5. fat via aerobic pathways
A

C. creatine phosphate (CP)

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17
Q

What elements contrubute to the overall stiffness of a muscle?

A
  • Contractile element (sarcomere)
    • Stiffness comes from the force-length relationship
  • Connective tissue surrounding muscle fibers
    • Passive elasticity
  • Tendons
    • Series elasticity
    • Tendons are in series with the contractile element and connective tissue that surrounds the contractile element
18
Q

Describe the configuration of actin and myosin in the released state of cross-bridge cycling

A

ATP binding causes the myosin head to be released from actin

19
Q

List and describe the steps of cross-bridge cycling

A
  1. Attached state - The myosin head is attached to the thin filament after power stroke completion
  2. Released state - ATP binding causes the myosin head to be released from actin
  3. Cocked state - ATP is hydrolyzed to ADP + Pi. The products remain, and the myosin head unhinges 11 nm. It lines up with the acin monomer 2 positions over from the previous binding site
  4. Cross-bridge state - The cocked myosin head binds actin
  5. Power stroke state - Pi dissociates from myosin, leaving the muscle fiber in a rigid state
20
Q

What molecule makes up #5?

(The pink cord encircling the green)

What is its function?

A

Nebulin

Regulates thin filament length

21
Q

Describe the steps requred to generate a muscle twitch, starting with a motor command from the CNS

A
  1. A motor command from the causes action potential in a motor neuron
  2. The action potential travels down motor neuron’s axon
  3. The action potential reaches the neuromuscular junction (Each neuron terminates in several muscle fibers)
  4. The muscle fiber depolarizes, causing an action potential in the membrane of the muscle fiber
  5. Depolarization travels down T-tubule system, causing Ca2+ release from sarcoplasmic reticulum
  6. Calcium release allows actin and myosin to bind, which causes a muscle twitch
    • Force is not sustained because as soon as Ca2+ is released, SERCA works to remove Ca2+ from the cytoplasm
22
Q

Describe the following for stored glycogen (aerobic):

  • Mobilization time:
  • Amount stored:
A
  • Mobilization time: 30 - 120 seconds
  • Amount stored: 30-120 minutes
23
Q

How long after starting a physical activity does it take for fat to cont10-ribute significantly as a power source?

A

20-60 minutes

24
Q

Describe the interaction of actin and myosin in the power stroke state of cross-bridge cycling

A

Power stroke state - Pi dissociates from myosin, leaving the muscle fiber in a rigid state

25
Q

The connection between motor neuron and muscle fibers is secure.

What does this mean?

A

Every time an action potential reaches the neuromuscular junction, an action potential is generated in the muscle fiber

26
Q

Which segment is labeled by #4?

A

M band

27
Q

Describe the composition of muscle thin filaments

A

Actin

Troponin

Tropomyosin

28
Q

What is the primary molecular mechanism of spring-like behavior in muscle?

A

Overlap of actin and myosin filaments

29
Q

Describe the composition of muscle thick filaments

A

Myosin

30
Q

Why do we have slow motor units if they are slow or weak?

A

They don’t get tired!

Slow motor units are responsible for things like holding up our head and sitting up

31
Q

What is the single most important control of the number of attached cross-bridges (and therefore, force generated) in a muscle?

A

Cytoplasmic calcium levels

32
Q

Describe the interaction of actin and myosin in the cocked state of cross-bridge cycling

A

ATP is hydrolyzed to ADP + Pi. The products remain, and the myosin head unhinges 11 nm. It lines up with the acin monomer 2 positions over from the previous binding site

33
Q

Which cellular energy source dominates in an effort that lasts
longer than 5 minutes?

A

Aerobic glycolysis

34
Q

Which section is labeled by #2?

A

A band

35
Q

The motor units within a single muscle:

  1. all have the same mechanical properties
  2. differ in all properties, including contraction speed, fatigue resistance, and force output
  3. differ only force output, but are the same for fatigue resistance and contraction speed
  4. differ only in fatigue resistance.
A

B. differ in all properties, including contraction speed, fatigue resistance, and force output

All muscles are heterogeneous in their motor-unit make-up

36
Q

Describe the following for stored glycogen (anaerobic):

  • Mobilization time:
  • Amount stored:
A
  • Mobilization time: 5-30 seconds
  • Amount stored: ~2 minutes
37
Q

Describe the force-stimulus frequency relationship in muscle mechanics

A

More force is generated when the frequency of muscle contractions is high.

The limit to this relationship is when contractions reach a tetanic freqency - the maximum possible frequency of muscle contractin.

This generates tetanic force

38
Q

Describe the configuration of actin and myosin in the attached state of cross-bridge cycling

A

The myosin head is attached to the thin filament after the previous power stroke completion

39
Q

If a muscle only had spring-like behavior and no viscous-like properties, what would tend to happen when you jump down from the last step to the landing in a stair well.

  1. you would bounce back up higher than where you were
  2. your landing would be smooth and free of oscillations
  3. you would be unable to stop yourself
  4. your leg joints would be so stiff that the landing would be jarring
  5. your leg joints would tend to exhibit large oscillations
A

E. your leg joints would tend to exhibit large oscillations

Spring like = we can cushion our landings

Viscous = we are not slinkies

40
Q

Describe the following for stored ATP:

  • Mobilization time:
  • Amount stored:
A
  • Mobilization time: Instantaneous
  • Amount stored: Very little; 1-5 seconds of contraction
41
Q

Describe the following for stored creatine phosphate:

  • Mobilization time:
  • Amount stored:
A
  • Mobilization time: Very fast; <1 second
  • Amount stored: Very little, but more than ATP; 10-15 seconds
42
Q

Which cellular energy source dominates in an effort that lasts
15-120 seconds?

A

Anaerobic glycolysis

MSK-Derm by Minnie (48 decks)

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