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Semester 2 Year 1 > Skeletal Muscle Force > Flashcards

Skeletal Muscle Force Flashcards

1
Q

Where is ATP used in contraction?

A

Ca2+ ATP-ase

Myosin ATP-ase

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2
Q

What pump allows production and propagation of action potential?

A

Sodium/potassium-ATPase in sarcolemma

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3
Q

Why is hydrolysis of ATP required by sodium/potassium-ATPase pump?

A

MAintains sodium and potassium gradients

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4
Q

What pump is responsible for for lowering calcium ions in cytoplasm?

A

Ca2+-ATPase in sarcoplasmic reticulum

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5
Q

Why Why does ATP need to be hydrolysed by calcium-ATPase?

A

Provide energy for active transport of calcium ions back into reticulum - to lower calcium concentration + allow relaxation

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6
Q

What enzyme provides energy of force generation?

A

Myosin-ATPase on myosin filament

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7
Q

Why does ATP need to be hydrolysed for myosin-ATPase?

A

To provide energy needed for cross-bridge formation

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8
Q

Significance of binding ATP to Myosin:

A

Dissociates cross-bridges

Allows bridges to repeat cycle activity

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9
Q

Cross-bridge cycle: stage 1 - ATP binding

A

Myosin in cocked state

Binding of ATP causes dissociation of actin-myosin complex

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10
Q

Cross-bridge cycle: stage 2 - ATP hydrolysis

A

ATP hydrolysed into ADP and phosphate ion

Myosin head in relaxed state

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11
Q

Cross-bridge cycle: stage 3 - Cross-bridge formation

A

Myosin head binds to new binding site on actin

Weak cross-bridge formed

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12
Q

Cross-bridge cycle: stage 4 - phosphate ion released

A

Phosphate ion is released from myosin head

Increase in strength of cross-bridge

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13
Q

Cross-bridge cycle: stage 5 - Power stroke

A

Conformational change in myosin head causes power stroke

ADP released

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14
Q

What regulates cross-bridge cycle?

A

Increase in calcium ions not ATP

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15
Q

3 ways of ATP formation in sketch muscle:

A
  1. Creatine phosphate
  2. Glycolysis
  3. Oxidative phosphorylation
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16
Q

What is creatine phosphate?

A

Stores phosphate ions that replace phosphate used in contraction

Rapid ATP formation

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17
Q

How much ATP does oxidative phosphorylation supply?

A

Most ATP in moderate activity levels

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18
Q

Location of oxidative phosphorylation:

A

Mitochondria

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19
Q

How much ATP does glycolysis supply?

A

Small quantities

Produces at higher rate - in higher intensity exercise

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20
Q

Location of glycolysis:

A

Cytosol

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21
Q

What can muscle force be determined by?

A

Number of individual muscle fibres stimulated

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22
Q

What does one motor neuron do?

A

Sends signal down to multiple muscle fibres

Spatial summation

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23
Q

What does amount of force generated from a muscle depend on?

A

Number of active fibres

Cross-sectional area

Initial resting length of muscle

Rate of shortening

Frequency of stimulation

24
Q

Small vs large motor units: excitability

A

Small = more excitable

Large = less excitable

25
Q

Small vs Large motor units: Action Potential conduction

A

Small = slower conduction

Large = faster conduction

26
Q

Small vs Large motor units: how many fibres do they excite?

A

Small - fewer fibres that tend to be Type I

Large = many fibres that tend to be Type II

27
Q

How are motor units recruited?

A

Smallest (weakest) to largest (strongest)

28
Q

What are muscle fibres classified on the basis of?

A

Maximal velocities of shortening - fast or slow

Pathway they use to form ATP - oxidative or glycolytic

29
Q

Why does form of myosin change maximal rate of using ATP?

A

Determines maximal rate of cross-bridge cycling and maximum shortening velocity

30
Q

Fibres with many mitochondria:

A

High oxidative capacity - oxidative fibres

31
Q

Fibres with few mitochondria:

A

High glycolytic capacity as high conc. of glycolytic enzymes

Large store of glycogen

Glycolytic fibres

32
Q

Different types of skeletal muscle fibres:

A

Slow-oxidative fibres (Type 1)

Fast-oxidative-glycolytic fibres (Type IIa)

Fast-glycolytic fibres (Type IIb or IIx in human)

33
Q

Slow-oxidative fibres:

A

Low myosin-ATPase activity

High oxidative capacity

34
Q

Fast-oxidative-glycolytic fibres:

A

High myosin-ATPase activity

High oxidative capacity

Intermediate glycolytic capacity

35
Q

Fast-glycolytic fibres:

A

High myosin-ATPase activity

High glycolytic capacity

36
Q

2 ways Type I and II fibres can be identified:

A

Nature of myosin-ATPase

Amount of specific mitochondrial enzyme succinctly dehydrogenase

37
Q

Nature of myosin-ATPase micrograph:

A

Type I = dark

Type II = light

38
Q

Enzyme succinctly dehydrogenase micrograph:

A

Type I = dark

Type IIa = middle

Type IIx = light

39
Q

What does one action potential result in?

A

Single skeletal muscle twitch

40
Q

What does multiple action potentials result in?

A

Temporal summation - multiple muscle twitches before fully relaxing

41
Q

What happens when multiple AP occur close together?

A

Frequency summation - infused tetanus

Plateau of contraction and relaxation

42
Q

What happens when frequency of AP is super high?

A

Fuses Tetanus

Can’t identify individual contractions and relaxations

43
Q

Type I - muscle twitches

A

Long twitch

Low tension

Not fatiguable

44
Q

Type IIa - muscle twitch

A

Long twitch

More tension than type I

Has some fatigue resistance but will eventually fatigue

45
Q

Type IIx - muscle twitch

A

Fast twitch

Lots of tension

Very fatiguable

46
Q

WHat does contraction refer to?

A

Activation of force-generating sites within cross-bridges

47
Q

Isometric contraction:

A

Muscle length fixed

Increase in tension but no shortening

48
Q

Isotonic contraction:

A

Muscle length not fixed

Muscle shortening if tension greater than opposing load

49
Q

What is length-tension relationship a result of?

A

Thick and thin filaments within sarcomeres

50
Q

Total tension:

A

Tension measured at various muscle lengths during contraction

51
Q

Passive tension:

A

Tension measured at any fixed length before contraction

52
Q

Active tension:

A

Tension measured at any fixed length during contraction

53
Q

What happens when applied load increases?

A

Decrease in shortening velocity

54
Q

Why does velocity of shortening increase with limiting lighter load?

A

Same muscle length but fewer cross-bridges needed to oppose load

55
Q

What does velocity of shortening limited by?

A

Time for ATP-consuming cross-bridge cycle to occur

Semester 2 Year 1 (12 decks)

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