Lecture 3 - The motor unit and muscle action

Question 1

What is a motor unit?

Answer 1

• A motor neuron

- PLUS skeletal muscle fibres that it innervates

Question 2

What is the basic unit of contraction?

Answer 2

A motor unit

Question 3

What is controlled by the central nervous system?

Answer 3

The motor units

Question 4

Roughly how many muscle fibres are in each motor unit?

Answer 4

~ 10s - 1,000s

Question 5

What is a muscle unit?

Answer 5

• The muscle fibres innervated by a single motor neuron

- (Excludes motor neuron)

Question 6

What plays a huge role in athletic ability?

Answer 6

Muscle fibre types

Question 7

What are the types of muscle? [2]

Answer 7

• Red

- Pale

Question 8

What are the three types of motor unit? [3]

Answer 8

• S (slow twitch, type I)
• FR (fast fatigue-
  resistant, type IIA)
• FF (fast fatigable, type IIB)

Question 9

What kind of motor units are in the red muscles?

Answer 9

Only S

Question 10

What kind of motor units are in the pale muscles?

Answer 10

• S
• FR
• FF

Question 11

What kind of metabolism do type I fibres have?

Answer 11

• Low intensity

- Delayed muscle fatigue

Question 12

What kind of metabolism do type II fibres have?

Answer 12

• High intensity

- Rapid muscle fatigue

Question 13

How does the motor neuron affect the muscle fibre it innervates?

Answer 13

Changing the motor neuron can change the type of muscle fibre

Question 14

How do muscle fibres vary?

Answer 14

• Speed of contraction
• Size/strength
• Fatigue resistance/endurance

Question 15

What determines a Motor units contractile properties?

Answer 15

• The muscle fibres

- All muscle fibres in the same motor unit are the same type

Question 16

What are the properties of a S motor unit?

Answer 16

• Slow contraction (50-100ms)
• Small force (<20g)
• Fatigue resistance

Question 17

What are the properties of a FR motor unit?

Answer 17

• Fast contraction (25-45ms)
• Intermediate force (20-60g)
• Resistant to fatigue

Question 18

What are the properties of a FF motor unit?

Answer 18

• Very fast contraction (<10ms)
• High force (50-150g)
• Fatigue easily

Question 19

What is the order of recruitment of the motor unit types?

Answer 19

• S > FR > FF

Question 20

What determines how a muscle will use each type?

Answer 20

How much force is needed

Question 21

What is the strength of contraction controlled by? [2]

Answer 21

• Recruitment of motor units

- Firing rates of motor units

Question 22

What is the main factor of muscle force?

Answer 22

The recruitment of motor units