Module 1.3 Muscle fibre types

Question 1

What are the different classes of muscle fibres?

Answer 1

• slow, type I muscle fibres

- fast, type II muscle fibres, which can be further divided into; type IIa fibres, type IIx fibres

Question 2

Explain fast twitch (type II) muscle fibres

Answer 2

They are used in high anaerobic metabolism, fatigue quickly, and have high force production.

Question 3

Explain slow twitch (type I) muscle fibres

Answer 3

Used for high aerobic metabolism, resistant to fatigue, low force production

Question 4

What determines the colour of a muscle?

Answer 4

The dominance of the fibre type and the concentration of myoglobin and by its blood supply; so a predominantly fast twitch muscle appears white, whereas a predominantly slow twitch muscle fibre appears red.

Question 5

Explain the difference in muscle size between type I and type II

Answer 5

Type I muscle fibres are smaller which aids O2 diffusion to the mitochondria = higher aerobic capacity
Type II muscle fibres are larger meaning more actin and myosin and a greater number of cross bridges = more force!

Question 6

Explain capillary density in type I muscle fibres

Answer 6

Type I muscle fibres have a higher capillary density = greater O2 diffusion into the muscle, and a greater oxidative capacity. Some type I fibres are surrounded by 8-10 capillaries.

Question 7

How do type I muscle fibres differ to type II in terms of mitochondrial content?

Answer 7

Type I muscle fibres have a higher mitochondrial density = greater O2 utilization, and a greater oxidative capacity

Question 8

How do type I muscle fibres differ to type II in terms of myoglobin?

Answer 8

Type I muscle fibres have a higher myoglobin content. Mitochondria has a higher affinity for O2 than haemoglobin and therefore aids in the diffusion of O2 from the blood into the muscle

Question 9

How do type II muscle fibres differ to type I in terms of sarcoplasmic reticulum and the t-tubule system?

Answer 9

Type II muscle fibres have a more extensive SR and t-tubule system. These fibres are therefore activated rapidly due to rapid spread of action potential (t-tubule) and Ca2+ release. Type II fibres are also able to relax more rapidly due to efficient Ca2+ re-uptake.