Lecture 3 - The motor unit and muscle action Flashcards
What is a motor unit?
- A motor neuron
- PLUS skeletal muscle fibres that it innervates
What is the basic unit of contraction?
A motor unit
What is controlled by the central nervous system?
The motor units
Roughly how many muscle fibres are in each motor unit?
~ 10s - 1,000s
What is a muscle unit?
- The muscle fibres innervated by a single motor neuron
- (Excludes motor neuron)
What plays a huge role in athletic ability?
Muscle fibre types
What are the types of muscle? [2]
- Red
- Pale
What are the three types of motor unit? [3]
- S (slow twitch, type I)
- FR (fast fatigue-
resistant, type IIA) - FF (fast fatigable, type IIB)
What kind of motor units are in the red muscles?
Only S
What kind of motor units are in the pale muscles?
- S
- FR
- FF
What kind of metabolism do type I fibres have?
- Low intensity
- Delayed muscle fatigue
What kind of metabolism do type II fibres have?
- High intensity
- Rapid muscle fatigue
How does the motor neuron affect the muscle fibre it innervates?
Changing the motor neuron can change the type of muscle fibre
How do muscle fibres vary?
- Speed of contraction
- Size/strength
- Fatigue resistance/endurance
What determines a Motor units contractile properties?
- The muscle fibres
- All muscle fibres in the same motor unit are the same type
What are the properties of a S motor unit?
- Slow contraction (50-100ms)
- Small force (<20g)
- Fatigue resistance
What are the properties of a FR motor unit?
- Fast contraction (25-45ms)
- Intermediate force (20-60g)
- Resistant to fatigue
What are the properties of a FF motor unit?
- Very fast contraction (<10ms)
- High force (50-150g)
- Fatigue easily
What is the order of recruitment of the motor unit types?
- S > FR > FF
What determines how a muscle will use each type?
How much force is needed
What is the strength of contraction controlled by? [2]
- Recruitment of motor units
- Firing rates of motor units
What is the main factor of muscle force?
The recruitment of motor units
