Force generation, energy usage and fibre types

Question 1

What is excitation contraction coupling?

Answer 1

Linkage between excitation of the muscle fibre membrane and the onset of contraction

Question 2

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

Answer 2

The interaction of the contractile proteins actin and myosin

Question 3

In the sliding filament mechanism, which band(s) and/or zone(s) are reduced?

Answer 3

• The I band

* The H zone

Question 4

In the sliding filament mechanism, what zone(s) and/or band(s) remain unchanged

Answer 4

• The A band

Question 5

What are the structural proteins in skeletal muscle?

Answer 5

• Titin (connection)
• Z-line protein (alpha-actinin)
• M-line proteins (myomesin, M-protein)
• Nebulin

Question 6

What are the contractile proteins in muscle?

Answer 6

• Actin
• Myosin
• Tropomyosin
• Troponin complex

Question 7

What is the role of Nebulin?

Answer 7

It helps to align actin

Question 8

What is the role of Titin?

Answer 8

It provides elasticity and stabilises myosin

Question 9

Describe the cross-bridge cycle

Answer 9

1. Ca++ increases Cross-bridge binds to actin, creating tension within the muscle
2. The cross bridge moves
3. ATP binds to the myosin causing cross-bridge to detach
4. Hydrolysis of ATP energises the cross-bridge

Question 10

What enzymes are involved in the breakdown of ATP to ADP + Pi in the contraction

Answer 10

• Ca2+ ATP-ase

* Myosin ATP-ase

Question 11

How much ATP do the muscles contain?

Answer 11

4mM/kg

Question 12

What is rigor mortis?

Answer 12

Stiffening of skeletal muscles after death

Question 13

When does rigor mortis begin and when is it at its maximum?

Answer 13

• 3-4 hours after death

* Max after 12 hours

Question 14

Why does rigor mortis happen?

Answer 14

• Cells accumulate calcium

* In the absence of ATP cross bridges can bind to the actin but the cross-bridge linkage is irreversible

Question 15

What does contraction of a muscle refer to?

Answer 15

The activation of the force-generating sites within muscle fibres- the cross bridges

Question 16

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

Answer 16

• Phosphorylation of ADP by creatine phosphate
• Oxidative phosphorylation of ADP in the mitochondria
• Phosphorylation of ADP by the glyhcotic pathway in the cytosol

Question 17

What are muscle fibres classified on the basis of?

Answer 17

• Maximal velocities of shortening

* Major pathway they use to form ATP- oxidative or glycolytic

Question 18

Describe oxidative muscle fibres

Answer 18

• More mitochondria so have a higher capacity for oxidative phosphorylation
• Dependent on blood flow to deliver oxygen and fuel molecules
• Contain myoglobin
• Appear darker
• Muscles containing more of the oxidative muscle fibres are used for long term contraction e.g. muscles used for standing

Question 19

Describe glycolytic muscle fibres

Answer 19

• Few mitochondria
• High concentration of glycolytic enzymes and large store of glycogen
• Used for quick bursts of activity
• Muscles containing a lot of these fibres are known as ‘white’

Question 20

Type I

Answer 20

Slow oxidative fibres
• Red
• Combine low myosin ATP-ase activity with high oxidative capacity

Question 21

Type IIa

Answer 21

Fast oxidative fibres
• Pink
• Combines high myosin ATP-ase activity with high oxidative capacity and intermediate glycolytic capacity

Question 22

Type IIb

Answer 22

Fast glycolytic fibres
• White
• Combines high myosin ATP are activity with high glycolytic capacity

Question 23

Describe what happens in full muscle contraction in terms of the contraction of the muscle fibres

Answer 23

• Slow oxidative fibres contract first
• Fast oxidative fibres contract second
• Fast glycolytic fibres contract last

Question 24

What factors determine muscle tension?

Answer 24

1) Tension developed by each type of muscle fibre
    • Action potenital frequency
    • Fibre length
    • Fibre diameter 
    • Fatigue 

2) Number of active fibres
• Number of fibres per motor units
• Number of active motor units

Question 25

What does the control of shortening velocity depend on?

Answer 25

• Load of muscle
• Type of motor unit
• Number of motor units

Question 26

How does muscle adapt to exercise

Answer 26

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

Question 27

What are the two types of atrophy?

Answer 27

• Disuse atrophy e.g. an arm in a cast

* Denervation atrophy (nerve damage resulting in loss of function)