Lower Motor Neurones, Motor Units and Neurophysiology of Skeletal Muscle

Question 1

What do alpha motor neurones supply?

Answer 1

The bulk of the muscle fibres that generate force

Question 2

What do gamma motor neurones innervate?

Answer 2

The muscle spindle (sensory organ)

Question 3

Greater number of motor neurones in which enlargements?

Answer 3

Cervical and lumbar

Question 4

Cervical enlargement level

Answer 4

C3-T1

Question 5

Lumbar enlargement

Answer 5

L1-S3

Question 6

What is the motor neurone pool?

Answer 6

The group of alpha neurones that innervate a muscle

Question 7

What contributes to muscle strength?

Answer 7

The firing rates of the LMNs involved

The number of a LMNs that innervate a muscle (i.e. number of motor units)

The co-ordination of the movement (innervation of agonist versus antagonist, integration / control of reflex responses etc).

Question 8

Large and fast vs. slow and small

Answer 8

Small motor units tend to be innervated by small neurones
-low threshold

Fast motor units tend to be innervated by large neurone
-high threshold

Question 9

What is the Henneman Size Principle?

Answer 9

BASICALLY : small motor units are more easily activated

The susceptibility of a motorneurone to discharge action potentials is a function of its size. Smaller alpha motor neurones (part of slow motor units) have a lower threshold than larger ones (part of fatigue resistant, or fast fatiguing, motor units). Slow motor units are more easily activated and “trained” by any training that activates the muscle

Question 10

Which types of skeletal muscle fibre are fatigue resistant?

Answer 10

Type I and Type IIB

slow oxidative and fast glycolytic