neuro

Question 1

What is a motor unit?

Answer 1

muscle fibers and the anterior horn cells that supply those muscle fibers

Question 2

What are the two mechanisms that control force production at the level of motor units?

Answer 2

recruitment of additional motor neurons and increased rate of firing of motor neurons

Question 3

Why are smaller motor units recruited before larger motor units during active contraction?

Answer 3

Smaller MUs have higher input resistance, so they reach threshold much faster.

Question 4

What is muscle weakness that originates from central origin?

Answer 4

volitional activation failure (VA)

Question 5

In VA failure, are spinal motor neurons and peripheral nerves intact? Why is VA occurring?

Answer 5

Yes, but factors influencing the spinal motor neuron firing are deficient.

Question 6

What do 1-A sensory neurons detect from muscle spindle?

Answer 6

stretch

Question 7

If you cut 1-A, why do you lose force?

Answer 7

You lose excitation on agonist so you lose force due to decreased firing rate.

Question 8

What is the effect of activation of 1-A afferents on motor neurons of the agonists?

Answer 8

Excitation

Question 9

What part of the brain does fear originate from in volitional movement?

Answer 9

Supraspinal pathways

Question 10

What is CAR?

Answer 10

Central Activation Ratio: theoretical max force generating ability of the muscle (i.e., volitional force plus any force increment from the superimposed stimulus)