Force generation, energy usage and fibre types Flashcards

1
Q

Describe the sliding filament mechanism?

A

Force generation produces shortening of skeletal muscle fibre, the overlapping of thick and thin filaments in each sarcomere move past each other, propelled by movements of the cross bridges

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2
Q

What does the ability of a muscle fibre to generate a force and movement dependent of?

A

It is dependent on the interaction of the contractile proteins actin and myosin

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3
Q

What happens in the sliding filament mechanism from relaxation to contraction?

A

Z-lines move closer to one another and towards the M line in the middle of the Sarcomere

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4
Q

Where does the sliding filament mechanism occur?

A

In A band where there is overlap of Mysoin and actin filaments

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5
Q

What are the events involved in the cross-bridge cycle?

A

1) . Calcium levels rise and Troponin pulls Tropomyosin to allow Myosin binding sites to be free
2) . Cross-bridge binds to Actin, ADP + Pi is stored in cross bridges
3) . Cross bridge moves and ADP and Pi are released as a bi-product, filaments are moved
4) . ATP binds to Myosin, causing cross-bridge to detach
5) . ATP is stored in head of cross bridge
6) . ATP is hydrolysed to energise the cross-bridge giving ADP + Pi in the cross-bridge
7) . The muscle is now at rest

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6
Q

What converts ATP into ADP + Pi

A

Calcium ATPase and Myosin ATPase

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7
Q

What event occurs in Rigor Mortis?

A

In Rigor mortis after there is no ATP to bind to the cross-bridge after contraction to detach the cross-bridge from the Myosin filament

Hence all muscles are still contracted and stiff after death

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8
Q

What is Rigor Mortis?

A

Stiffening of skeletal muscles after death

  • Begins 3-4 hours after death and is at maximum after 12 hours
  • Cells accumulate in Calcium
  • In the absence of ATP, cross bridges can bind to actin but cross-linkage is irreversible
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9
Q

What does hydrolysis of ATP in the plasma membrane maintain?

A

Hydrolysis of ATP by the Sodium Potassium pump in the plasma membrane maintains the sodium and potassium gradients which allows the membrane to produce and propagate action potentials

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10
Q

What does hydrolysis of ATP by the Calcium ATPase pump in the Sarcoplasmic reticulum provide?

A

Hydrolysis of ATP by the Calcium ATPase pump in the Sarcoplasmic reticulum provides the energy for the active transport of Calcium ions into the reticulum, lowering cytosolic Calcium ion concentration to pre-release concentrations, ending the contraction and allowing the muscle fibre to relax

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11
Q

What does hydrolysis of ATP by Myosin-ATPase do?

A

Hydrolysis of ATP by Myosin-ATPase energises the cross-bridges providing the energy for force generation

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12
Q

What does the binding of ATP by Myosin do?

A

The binding of ATP by Myosin dissociates cross-bridges bound to Actin, allowing the bridges to repeat their cycle of activity

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13
Q

What does contraction mean?

A

It refers to the activation of the force-generating sites within muscle fibres - the cross bridges

(Not necessarily ‘shortening’ of muscle)

e.g - holding a dumbbell at a constant position requires muscle contraction but not muscle shortening

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14
Q

What are the 3 ways that a muscle fibre can form ATP?

A

1) . Phosphorylation of ADP by creatine phosphate (rapid response)
2) . Oxidative phosphorylation of ADP in the mitochondria (most ATP made this way)
3) . Phosphorylation of ADP by the glycolytic pathway in the cytosol

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15
Q

What resources do the 3 different ways to form ATP in a muscle fibre require ?

A

1) . Phosphorylation of ADP by creatine phosphate - requires: Creatine Phosphate
2) . Oxidative phosphorylation of ADP in the mitochondria - requires; Proteins to be broken into amino acids or fatty acids from blood

3). Phosphorylation of ADP by the glycolytic pathway in the cytosol - requires; Glycogen to be converted to Glucose or Glucose from the blood to undergo Glycolysis
(this makes Lactic acid as a bi-product)

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16
Q

How do Skeletal muscles vary?

A

They all have different mechanical and metabolic characteristics

17
Q

How are Skeletal muscle fibre types classified?

A

Their maximal velocities of shortening (fast or slow)

The major pathway they use to form ATP; either oxidative or glycolytic

18
Q

What are the 2 types of Skeletal muscle fibres in terms of velocities?

A

Fast and slow fibres

19
Q

How do fast and slow Skeletal muscle fibres vary?

A

They contain forms of Myosin that vary in maximal rates when they use ATP, which determines the maximal rate of cross-bridge cycling and thus the maximal shortening velocity.

20
Q

What is the difference between Dark and White fibres?

A

Dark Oxidative fibres - have many mitochondria and therefore have a high capacity for oxidative phosphorylation. Dependent upon blood flow to deliver oxygen, fuel molecules to the muscle and contain myoglobin. A muscle with many of these fibres is used in long term contractions like standing

White fibres - Have few mitochondria but a high concentration of glycolytic enzymes and a large store of glycogen. Allows for quick bursts of activity

21
Q

What are the 3 types of Skeletal muscle fibres and their differences?

A

Slow-oxidative fibres (Type 1) combine low myosin-ATPase activity with high oxidative capacity

Fast-oxidative-glycolytic fibres (Type 2a) combine high myosin-ATPase activity with high oxidative capacity and intermediate glycolytic capacity

Fast-glycolytic fibres (Type 2b) combine high myosin ATPase activity with high glycolytic capacity

22
Q

How much tension and for how long can each fibre produce?

A

Slow-oxidative fibres (Type 1) - Can produce some tension/force for a long time

Fast-oxidative-glycolytic fibres (Type 2a) - Can produce a fair amount of tension quickly but slowly fatigues

Fast-glycolytic fibres (Type 2b) - Can produce a high amount of tension but very quickly fatigues

23
Q

What is the control of Muscle tension dependent upon?

A

The amount of tension being developed by each fibre

The number of fibres contracting at any time

24
Q

What else controls whole-muscle tension as well as shortening velocity ?

A

The nervous system

25
Q

What are the 2 main factors and sub factors which determine muscle tension?

A

Tension developed by Each fibre

  • Action potential frequency (frequency - tension relation)
  • Fibre length (length - tension relation)
  • Fibre diameter
  • Fatigue

Number of active fibres

  • Number of fibres per motor unit
  • Number of active motor units
26
Q

What is the shortening velocity controlled by?

A

The shortening velocity of a whole muscle depends upon: - the load on the muscle

  • types of motor units in the muscle
  • number of motor units recruited to work against the load
27
Q

How do muscles adapt to exercise?

A

An increase in the amount of contractile activity increases the size of muscle fibres and increases their capacity for ATP production

28
Q

What happens to muscles not being used?

A

Muscle atrophy occurs (muscle wastes away)

29
Q

What are the 2 types of muscle atrophy ?

A

Disuse atrophy - arm in a cast

Denervation atrophy - nerve damage = loss of function