Size Principle

Question 1

What is the size principle?

Answer 1

The process of Motor Unit recruitment
Suggests as contraction is made slow fibres are recruited first
large, fast, fatiguable fibres recruited later

Question 2

Who suggested the size principle?

Answer 2

Henneman

Question 3

What is the Motor Unit?

Answer 3

‘the smallest part of the muscle that is innervated’ sherrignton et al

Question 4

Why are type I fibres recruited first?

Answer 4

Smaller fibres
Smaller diameter for AP to travel
this means that there is a lower threshold so thus activated first

Question 5

why are the larger fibres activated last?

Answer 5

Due to the large diameter of the neurons they have a higher threshold
therefore activated later on for larger contraction

Question 6

What are type I fibres

Answer 6

small
oxidative
fatigue resistant
high mitochondria
low force
low velocity

Question 7

What are type II fibres

Answer 7

fast
glycocytic
fast fatiguable
produce quickest movement and largest force

Question 8

What is the rate of coding in muscle recruitment?

Answer 8

progressive activation of a muscle by a succesive recruitment of the contractile units to accomplish increasing graduations of contractile strength

Question 9

What are the effects of ageing on motor unit recruitment?

Answer 9

Cross innervation of muscle motor units
As the motor unit dies, NMJ activity and motor unit recruitment decreases
results in deinnervation
fibre size decreases
large motor units are the ones that cause slow movement in the elderly

Question 10

What is explained by the decreased activity with ageing?

Answer 10

Muscle atrophy

Motor Unit diversity