Motor Unit

Question 1

In the ventral horn, motor neurons to proximal muscles are located where? motor neurons to distal muscles?

Answer 1

proximal muscles - medial ventral horn

distal - lateral ventral horn

Question 2

What is a motor neuron pool?

Answer 2

All the motor neurons that innervate a given muscle

-typically distributed over 2-3 spinal segments

Question 3

What is a motor unit comprised of?

Answer 3

cell body, axon, muscle fibers the axon innervates

Question 4

What is a muscle unit?

Answer 4

collection of muscle fibers innervated by one axon

identical properties and contract simultaneously

Question 5

T or F: a muscle fiber can be innervated by more than one axon

Answer 5

FALSE

Question 6

Which type of motor unit has the fasted rate of force loss with repeated twitches?

Answer 6

fast fatigable

Question 7

Name the four steps of force that occur with higher rates of stimulation on a motor unit?

Answer 7

1. single muscle twitch
2. temporal summation
3. unfused tetanus
4. fused tetanus

Question 8

What are two ways to modulate force generation?

Answer 8

1. recruitment of a previously silent motor unit

2. rate coding of an already firing motor unit

Question 9

As the size of a motor unit increases, what increases within ?

Answer 9

1. cell body size
2. dendritic complexity
3. short term EPSP potentiation with repeated activation
4. axonal diameter
5. number of axonal branches

Question 10

As motor unit size increases, what decreases within?

Answer 10

1. input resistance
2. EXCITABILITY
3. Ia EPSP amplitude
4. PSP decay constant
5. duration of after hyperpolarization

Question 11

What is the order of recruitment of motor units?

Answer 11

slow then fast fatigue resistance then fast fatigable

Question 12

When using an EMG, a muscle unit of a single motor unit serves as a natural amplifier of what?

Answer 12

a nerve action potential