Size Principle

Question 0

Who suggested the size principle ?

Answer 0

Henneman

Henneman size principle

Question 1

What is the size principle ?

Answer 1

This is the process of motor unit recruitment that suggest that as we make contraction , small , slow oxidative , large mitochondrial slow fibres are recruited first and then later stages the large fast fatigable fibres are recruited

Question 2

What is the motor

Unit again ?

Answer 2

The motor unit is the smallest part of the muscle that is Innervated said sherrington et al

Question 3

So why are the type 1 recruited first ?

Answer 3

This is due to the small fibres having a smaller diameter for the AP to travel so thus mean there is a lower threshold so thus why they are activated first

Question 4

Why are larger fibres activated last ?

Answer 4

This is due to a large diameter of the neurons so therefore due to large threshold they are activated later on for larger contraction

Question 5

What are type 2 fibres

Answer 5

These are fast , glycolytic , fast fatigable fibres that produce quickest movement and largest force

Question 6

What are type 1 fibres

Answer 6

These are small oxidative fibres , fatigue resistant , high mitochondria , low force , low velocity

Question 7

What is the rate of coding in muscle recruitment ?

Answer 7

This is the progressive activation of a muscle by a successive recruitment of the contractile units to accomplish increasing gradations of contractile strength

Question 8

Aging effect of recruitment on motor units ?

Answer 8

Your get cross innervation of muscle motor units. As the motor unit dies out , the NMJ activity decreases , and motor unit recruitment decreases so results in deinnervation.
Fibre size decreases , and ageing shows that the large motor units are the ones that cause the slow movement in elderly .

Question 9

Physical activity decreases with again , erm so ?

Answer 9

Well it explains muscle atrophy and loss of motor unit diversity