Muscle Control & Energetics

Question 1

What is a motor unit?

Answer 1

A motor unit is a group of muscle fibers in a muscle innervated by a single motor neuron

Question 2

What do small motor units do? + an example

Answer 2

They are responsible for very fine motor control; Ex: Extraocular eye muscles and movements in the fingers

Question 3

What are large motor units and what are they responsible for? + an example

Answer 3

Large motor units are an arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle; they are responsible for “gross” movements like extending the knee joint

Question 4

What is recruitment and when can it be used?

Answer 4

Recruitment is the increasing activation of motor units producing an increase in muscle contraction when more strength is needed.

Question 5

How do you prevent complete muscle fatigue?

Answer 5

motor units are generally not all simultaneously active, but instead some motor units rest while others are active, which allows for longer muscle contractions

Question 6

True or False: Recruitment of additional motor units will increase the strength of a muscle’s contraction

Answer 6

True

Question 7

A muscle that is primarily used for powerful but imprecise movements is likely to have motor units that are ____________.

Answer 7

Large in size

Question 8

What is the Length-Tension relationship of sarcomeres?

Answer 8

Muscles generate the greatest force when at their resting length, and the least amount of force when shortened or stretched relative to the resting length.

Question 9

At what percentage of normal resting length is maximum tension produced in a sarcomere?

Answer 9

80-120%; This length maximizes the overlap of actin-binding sites and myosin heads.

Question 10

What happens if a sarcomere is stretched past ideal length (beyond 120%)?

Answer 10

Thick and thin filaments do not overlap sufficiently, which results in less tension produced

Question 11

What happens if a sarcomere is shortened 80%?

Answer 11

The zone of overlap is reduced with the thin filaments jutting beyond the last of the myosin heads and shrinks the H zone. Eventually, there is nowhere else for the thin filaments to go and the amount of tension is diminished

Question 12

What will happen if the muscle is stretched to the point where thick and thin filaments do not overlap at all?

Answer 12

No cross-bridges can be formed, and no tension is produced in that sarcomere

Question 13

A sarcomere that is at a resting length of 1.7um will generate __________________ force compared to a sarcomere at 2.15um.

Answer 13

Less

Question 14

Which of the following describes a sarcomere within the optimal resting length range for generating maximal contraction?

Answer 14

At rest, the H-band is about half the length of the A-band