L7 Muacle Fibre Type, Composition and Performance

Question 1

What are the different types of muscle fibres? structure of them?

Answer 1

Cross sectional

• Muscle cells have peripherally placed nuclei
• each cell is surrounded by endomysium
• fibres are arranged in a mosaic pattern

Longitudinal

• fibres arranged longitudinally
• they are long fibres arranged in top of one another.

Question 2

the speed of muscle contraction depends on….

Answer 2

ATPase activity if the myosin molecule

Question 3

Muscle fibre type are distinguished by…..

Answer 3

• contraction speed
• Fast + slow
• Myosin heavy chain ATPase activity
• Metabolic activity

Question 4

What are myosin heavy chain isoforms? and how many are in a myosin molecule?

Answer 4

myosin molecule = 2 heavy chains and 2 light chains

the heavy chains determine ATPase activity and exist as different isoforms

Question 5

Myosin ATPase activity is pH sensitive and can be detected histochemically. How do fast and slow myosin’s differ in this?

Answer 5

Fast - stable at an alkaline pH and are inactivated at acid

Slow - stable at an acid pH and inactivated at alkaline

Question 6

what are the 2 oxidative enzymes in the muscle fibres?

Answer 6

SDH

citrate synthase

Question 7

What are the glycolytic enzymes in the muscle fibres?

Answer 7

Phosphorylase

Pyruvate Kinase

Question 8

What is the main visual distinguish between fast and slow fibres?

Answer 8

red muscle - slow

white muscle -fast

due to myoglobin and more capillaries

Question 9

All muscle fibres that belong to the same single motor neuron are of the same fibre type

Answer 9

cool stuff

Question 10

what are the main differences between slow and fast motor units

Answer 10

slow - have small easily excited motor neurons

fast - have a higher threshold motor neurons, less easy to excite

Question 11

How can you identify muscle fibres through a muscle biopsy?

Answer 11

Stain section of muscle
Measure fibre size
count # of fibre types as a % of the total

Question 12

Explain the relationships between muscle fibre type composition and muscle performance

Answer 12

More speed at a mid to low force generation. More fast fibres mean more higher torques at a higher speed.
More type 1 fibres mean more endurance. They create lower forces at lower speeds and cant contract as quickly