Motor Control of Musculoskeletal System

Question 1

How does the twitch tension force of slow fibres compare to fast fibres?

Answer 1

Lower in slow fibres

Question 2

How does the size of motor units in slow fibres compare to fast fibres?

Answer 2

Smaller in slow fibres

Question 3

What does the Henneman size principle tell us?

Answer 3

It establishes that at lower levels of force production, smaller motor units are recruited and at higher demands for force production, larger and faster motors are recruited

Question 4

What is motor unit recruitment?

Answer 4

A measure of how many motor neurones are activated in a particular muscle and, therefore, a measure of how many muscle fibres of that muscle are activated

Question 5

What is rate coding?

Answer 5

Refers to the firing rate of neural impulses travelling down the motor neurone

Question 6

In small muscles how is the demand to increase force production met?

Answer 6

At about 50% of maximum force, all motor units have been recruited, meaning that any further increase in force must come from rate coding

Question 7

In large muscles how is the demand to increase force production met?

Answer 7

Primarily by an increase in motor unit recruitment. Rate coding only makes a contribution over the last 10-15% of max force production

Question 8

What is the efferent (effector) nervous system responsible for?

Answer 8

For sending out nerve impulses from the brain to the peripheral nervous system

Question 9

What is the afferent (sensory) nervous system responsible for?

Answer 9

For delivering nerve impulses from the peripheral nervous system to the brain

Question 10

What detects the degree of tension (or stretch)?

Answer 10

Muscle spindles (intrafusal fibres)

Question 11

How are muscle spindles/intrafusal fibres characterised?

Answer 11

As either nuclear chain or nuclear bag fibres. Both have an efferent (γ motorneurones) and afferent (1a primary) nerve supply

Question 12

What do nuclear bag fibres indicate and how does it do this?

Answer 12

Stretch

Their firing rate rapidly increases at the onset of a change in muscle length

Question 13

What do nuclear chain fibres indicate and how does it do this?

Answer 13

Changes in muscle length

Their firing rate rapidly increases at the onset of a change in muscle lenth

Question 14

What effect does increasing γ efferent output have on muscle spindle and Af output?

Answer 14

Stretching central portion of the muscle spindle and therefore increasing Af output