The Motor Unit

Question 1

What is a motor unit?

Answer 1

Is the motor neuron and all the muscle fibres that it innervates.

Question 2

How can you increase force production?

Answer 2

Recruit more motor units.

Question 3

What are the types of motor units?

Answer 3

• Type S (slow)
• Type FR (fast fatigue resistant)
• Type FF (fast, fatigable)

Question 4

What are Type S motor units?

Answer 4

• Small motor neurons.
• Innervate slow + highly oxidative muscle fibres.

Question 5

How else are type slow motor units known as?

Answer 5

Type I muscle fibres.

Question 6

What are Type FR motor units?

Answer 6

• Larger motor neurons.
• Innervate ‘intermediate’ muscle fibres.

Question 7

How else are Type FR motor units known as?

Answer 7

Type IIa muscle fibres.

Question 8

What are type FF motor units?

Answer 8

• Largest motor neurons.
• Innervate ‘fast’ muscle fibres.

Question 9

How else are type FF motor units known as?

Answer 9

Type IIx muscle fibres.

Question 10

What neurological adaptations can occur to optimised force generating capacity?

Answer 10

• Motor unit recruitment.
• Motor unit synchronization.
• Motor unit rate coding.
• Motor unit activation of agonist.
• Co-activation: antagonist.
• Co:activation: synergists.
• Central + neural drive.

Question 11

Where does the early rate of force development occur?

Answer 11

Happens at a neurological aspect.

Question 12

Where does the late rate of force development occur?

Answer 12

Happens largely due to structural elements.

Question 13

What are muscle spindles?

Answer 13

• Sensory receptors within skeletal muscles.
• They inform CNS about changes in muscle length + contraction speed.

Question 14

What are extrafusal muscle fibres?

Answer 14

Are large skeletal muscle fibres.

Question 15

What are intrafusal muscle fibres?

Answer 15

Are small specialised muscle fibres embedded within the extrafusul muscle.

Question 16

What do muscle spindles contribute to?

Answer 16

Proprioception.

Question 17

Outline the process on how Golgi tendon organs operate.

Answer 17

1. Golgi tendon organs detect tension applied to a tendon.
2. Sensory neurons conduct action potentials to the spinal cord.
3. Sensory neurons synapse with inhibitory interneurons that synapse with alpha motor neurons.
4. Inhibition of the alpha motor neurons causes muscle relaxation, relieving tension applied to the tendon.

Question 18

What is proprioception?

Answer 18

• ABility to tell where and how joints + extremities are moving in space.
• The body’s ability to sense movement, action + location.

Question 19

Why is proprioception important?

Answer 19

• Critical for meaningful interactions with the environment.
• Important for motor control and movement.

Question 20

What are the different mechanoreceptors?

Answer 20

• Muscle spindles.
• Golgi tendon organs.
• Pacinian corpuscles.
• Meissners corpsucles.
• Ruffini endings
• Free nerve endings.