Motor pathways: Neuromuscular & Spinal cord

Question 1

What defines how readily a neuron can reach threshold potential?

Answer 1

EPSPs and IPSPs

Question 2

What is a miniature end-plate potential?

Answer 2

The potential created by individual vesicles of ACh being released at a slow and steady rate by the pre-synaptic neuron

Question 3

What are the alpha motor neurons?

Answer 3

Lower motor neurons of the brainstem and spinal cord

Question 4

What are extrafusal muscle fibres?

Answer 4

Standard skeletal muscle fibres

Question 5

In which horn of the spinal cord are motor neurons located?

Answer 5

Ventral horn

Question 6

Describe the somatotropic organisation of neurons in the ventral horn

Answer 6

Organisation in terms of proximal/ distal muscles and flexors/ extensors

Question 7

What is a “motor unit”?

Answer 7

A single motor neuron together with all the muscle fibres that it innervates

Question 8

Describe the innervation of each individual muscle fibre

Answer 8

Not innervated by more than one motor unit

Question 9

Describe the innervation ratio of of muscle fibres

Answer 9

Ratio depends on whether you want motor unit to produce lots of force or to have fine control of movement

Question 10

Recall the 3 types of muscle fibre

Answer 10

Type 1 - slow
Type 2a - Fast, fatigue resistant
Type 2b - Fast, fatiguable

Question 11

Compare the cell body diameter of the different types of muscle fibre

Answer 11

Slow = small, fast = large

Question 12

Compare the dendritic tree of the different types of muscle fibre

Answer 12

Slow = small, fast = large

Question 13

Compare the axonal diameter of the different types of muscle fibre

Answer 13

Small = thin
Fast = thick

Question 14

Explain the principal that governs muscle fibre recruitment

Answer 14

Size principle - smaller fibres are recruited first, and as more force is required more type 2a and then 2b fibres are recruited

Question 15

What 2 things control the regulation of muscle force?

Answer 15

Recruitment

Rate coding

Question 16

What is rate coding?

Answer 16

The chane of AP frequency according to muscle force requirement

Question 17

What is the highest AP frequency possible?

Answer 17

20 times per second

Question 18

Describe the frequency of AP firing in summation

Answer 18

Units fire at a frequency too fast to allow the muscle to relax between APs arriving

Question 19

What is a neurotrophic factor?

Answer 19

Type of GF that prevents neuronal death and promotes neuronal growth after injury

Question 20

What is the effect of neurotropic factors on muscle characteristics?

Answer 20

As well as each fibre having its own type, it is influenced by the neurons innervating it and the associated NFs

Question 21

Describe the plasticity of motor units

Answer 21

In many conditions fibres can change type: in general type 1/2 does not interchange but 2b–> 2a is common in sports training