Motor Units and Excitation-Contraction Coupling

Question 1

Explain the difference between unfused tetanus and fused tetanus.

Answer 1

Unfused tetanus is the force summation in response to repeated AP where there are oscillations.
Fused tetanus is the force summation without oscillations

Question 2

The smallest motor units are activated first/last and produce the largest/smallest amount of force.

Answer 2

First

Smallest

Question 3

What are the two ways in which force generation is controlled in motor units?

Answer 3

Rate coding and size principle.

Question 4

How are muscle fibres organised?

Answer 4

Individual muscle fibres are surrounded by endomysium. Several together make up a fascicle, which is surrounded by perimysium. Several Fascicles are organised into a bundle, which is surrounded by epimysium.

Question 5

What would happen if ATP is not available in muscle fibres?

Answer 5

As ATP is required for myosin to return into its primary form, lack of ATP would cause myosin heads to remain bound to the actin filaments, making muscle rigid (e.g. death).

Question 6

What be the result of Ach blockage?

Answer 6

Muscle contraction would not occur.

Question 7

What would occur as a result of blockade of ryanodine receptors?

Answer 7

Muscle contraction would not occur.

Question 8

Does acetylcholine affect the length of muscle contraction?

Answer 8

No, as acetylcholine is degrated relatively quickly by acetylchonesterase.

Question 9

What determines duration of muscle contraction?

Answer 9

Length of calcium level elevation in the cell (before calcium ATPase restores resting calcium levels).

Question 10

What limits the maximum force generation?

Answer 10

Time taken for cross-binding to occur
Passive muscle tension
Amount of overlap between actin and myosin.