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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
Small vs Large motor units: Action Potential conduction
Small = slower conduction Large = faster conduction
26
Small vs Large motor units: how many fibres do they excite?
Small - fewer fibres that tend to be Type I Large = many fibres that tend to be Type II
27
How are motor units recruited?
Smallest (weakest) to largest (strongest)
28
What are muscle fibres classified on the basis of?
Maximal velocities of shortening - fast or slow Pathway they use to form ATP - oxidative or glycolytic
29
Why does form of myosin change maximal rate of using ATP?
Determines maximal rate of cross-bridge cycling and maximum shortening velocity
30
Fibres with many mitochondria:
High oxidative capacity - oxidative fibres
31
Fibres with few mitochondria:
High glycolytic capacity as high conc. of glycolytic enzymes Large store of glycogen Glycolytic fibres
32
Different types of skeletal muscle fibres:
Slow-oxidative fibres (Type 1) Fast-oxidative-glycolytic fibres (Type IIa) Fast-glycolytic fibres (Type IIb or IIx in human)
33
Slow-oxidative fibres:
Low myosin-ATPase activity High oxidative capacity
34
Fast-oxidative-glycolytic fibres:
High myosin-ATPase activity High oxidative capacity Intermediate glycolytic capacity
35
Fast-glycolytic fibres:
High myosin-ATPase activity High glycolytic capacity
36
2 ways Type I and II fibres can be identified:
Nature of myosin-ATPase Amount of specific mitochondrial enzyme succinctly dehydrogenase
37
Nature of myosin-ATPase micrograph:
Type I = dark Type II = light
38
Enzyme succinctly dehydrogenase micrograph:
Type I = dark Type IIa = middle Type IIx = light
39
What does one action potential result in?
Single skeletal muscle twitch
40
What does multiple action potentials result in?
Temporal summation - multiple muscle twitches before fully relaxing
41
What happens when multiple AP occur close together?
Frequency summation - infused tetanus Plateau of contraction and relaxation
42
What happens when frequency of AP is super high?
Fuses Tetanus Can’t identify individual contractions and relaxations
43
Type I - muscle twitches
Long twitch Low tension Not fatiguable
44
Type IIa - muscle twitch
Long twitch More tension than type I Has some fatigue resistance but will eventually fatigue
45
Type IIx - muscle twitch
Fast twitch Lots of tension Very fatiguable
46
WHat does contraction refer to?
Activation of force-generating sites within cross-bridges
47
Isometric contraction:
Muscle length fixed Increase in tension but no shortening
48
Isotonic contraction:
Muscle length not fixed Muscle shortening if tension greater than opposing load
49
What is length-tension relationship a result of?
Thick and thin filaments within sarcomeres
50
Total tension:
Tension measured at various muscle lengths during contraction
51
Passive tension:
Tension measured at any fixed length before contraction
52
Active tension:
Tension measured at any fixed length during contraction
53
What happens when applied load increases?
Decrease in shortening velocity
54
Why does velocity of shortening increase with limiting lighter load?
Same muscle length but fewer cross-bridges needed to oppose load
55
What does velocity of shortening limited by?
Time for ATP-consuming cross-bridge cycle to occur

Semester 2 Year 1 (12 decks)

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