Force Generation, Energy usage and Fibre Types

Question 1

What are the structural proteins?

Answer 1

Titin (connectin)
Z-line protein (alpha-actinin)
M-line proteins ( Myomesin and M-protein)
Nebulin

Question 2

What are the roles of titin and nebulin?

Answer 2

Titin provided elasticity and stabalizes myosin.

Nebulin helps align actin.

Question 3

What are the contractile proteins?

Answer 3

Actin
Myosin
Tropomyosin
Troponin complex

Question 4

Describe the activation of cross-bridge cycling by Ca2+

Answer 4

1 - Low cytosolic calcium and so the muscle is relaxed. Energised cross bridges cannot bind to actin.
2 - High cytosolic calcium and so the muscle is activated. Cross-bridge binding sites are exposed and the cross-bridge binds to actin and generates force.

Question 5

What is Rigor Mortis and how does it work?

Answer 5

It is the stiffening of skeletal muscling after death which begins 3-4 hours after death. It occurs as cells accumulate calcium however with the absence of ATP the cross bridges can bind to actin but the cross-linking is irreversible.

Question 6

Name the three ways a muscle fibre can form ATP?

Answer 6

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

Question 7

How are skeletal muscle fibres classified?

Answer 7

• Their max velocity of shortening (fast or slow)

- Their major pathway they use to form ATP (Glycolytic or oxidative)

Question 8

What are the differences in myosin in fast and slow muscle fibres?

Answer 8

The maximum rates at which myosin uses ATP, therefore determines the max rate of cross bridge cycling.

Question 9

Describe what makes a skeletal muscle fibre an oxidative fibre and what its ATP production is dependant on.

Answer 9

They have many mitochondria so have a high capacity for oxidative phosphorylation. The ATP produced is dependant on the blood flow to deliver oxygen, fuel and myoglobin to the muscle.

Question 10

What colour are oxidative and glycolytic fibres

Answer 10

Dark and white respectively.

Question 11

What makes skeletal muscle fibres a glycolytic fibre

Answer 11

The high concentration of glycolytic enzymes and the large store of glycogen. This allows for quick bursts of activity.

Question 12

With these determining features, what three skeletal muscle fibres are distinguished.

Answer 12

• Slow oxidative fibres (type 1). Low myosin-ATPase activity with high oxidative capacity.
• Fast-oxidative-glycolytic fibres (Type 2a) High myosin- ATPase activity with high oxidative and intermediate glycolytic capacity
• Fact-glycolytic fibre (Type 2b) High myosin-ATPase activity and high glycolytic capacity.

Question 13

What does the total tension of a muscle depend on?

Answer 13

1. The amount of tension developed by each fibre

2. The number of fibres contracting at any time.

Question 14

An increase in the amount of contractile activity will do what?

Answer 14

Increase size of muscle fibres and increase their capacity for ATP production

Question 15

What are the two types of muscle atrophy?

Answer 15

Disuse Atrophy - arm in cast

Denervation atrophy - nerve damage resulting in loss of function.

Question 16

What is the cross bridge cycle?

Answer 16

The time between when attachment occurs, movement taking place and the detachment taking place.

Question 17

Describe what occurs in the cross-bridge cycle

Answer 17

1) Cytosolic calcium concentation increases, allowing the cross bridge to bind to actin.
2) Release of ATP and Pi causes cross bridge to move
3) ATP binds to myosin’s ATP binding sites causing the myosin to detach
4) Hydrolysis of ATP energises the cross-bridge