Spinal Cord and Movement Control

Question 1

What are the 4 main components that contribute to the control of movement?

Answer 1

1- Spinal cord and brainstem ( LMN)

2- Descending systems (UMN)

3- Cerebellum

4- Basal Ganglia

Question 2

Where are the 2 spinal cord enlargements?

Answer 2

cervical (for the arms) and lumbar (for the legs)

Question 3

What is the cauda equina?

Answer 3

It contains all nerves to/ from the legs and pelvic floor

Question 4

Where does the cauda equina begin?

Answer 4

At L1 (because that’s where the cord ends)

Question 5

What type of neuron does this describe:

Large cell body, extensive dendritic tree, large axons and myelinated with schwann cells, rapid conduction velocity

Answer 5

Lower motor neurons

Question 6

Where are lower motor neurons distributed?

Answer 6

They are distributed along the length of the spinal cord

Question 7

What is found in the medial ventral horn?

Answer 7

Lower motor neurons to proximal muslces

Question 8

What is found in the lateral ventral horn?

Answer 8

Lower motor neurons to distal muslces

Question 9

What is the lower motor neuron pool?

Answer 9

Total of all lower motor neurons innervating a given muscle (it is usually distributed over 2-3 neurologic segments)

Question 10

How is the spinal cord organized?

Answer 10

It is arranged from dorsal to ventral into various laminae (the organization is based on histological composition)

Question 11

What composes a motor unit?

Answer 11

Cell body, axon, all the muscle fibers that the axon innervates

Question 12

How many muscles does each axon innervate?

Answer 12

Axons only innervate 1 muscle

Question 13

Where do Lower Motor Neurons synapse?

Answer 13

They synapse on muslce fibers (neuromuscular junctions)

Question 14

What is the neurotransmitter at the site of lower motor neuron synapse?

Answer 14

Acetylcholine

Question 15

Why are the neuromuscular junction connections described as “extremely reliable connections”?

Answer 15

Because every time the axon fires the muscle fiber will contract

Question 16

What is the functional unit that generates force?

Answer 16

Sarcomere

Question 17

What are the necessary components of force generation?

Answer 17

Ca2+ binding, rotation of myosin cross- bridge, consumption of energy (ATP)

Question 18

What type of motor unit does this describe:

Slow rate of force increase during twitch and little or no force loss with repeated twitches

Answer 18

“S” or Slow motor units

Question 19

What is the firing rate of S motor units?

Answer 19

60-120 ms

Question 20

What type of motor unit does this describe:

Relatively fast rate of force increase during twitch and moderate force loss with repeated twitches

Answer 20

“FR” or Fast, fatigue resistant

Question 21

What is the firing rate of FR motor units?

Answer 21

30-80 ms

Question 22

What type of motor unit does this describe:

Fastest rate of force increase during twitch and rapid force loss with repeated twitches

Answer 22

“FF” or Fast, fatiguable

Question 23

What is the firing rate of FF motor units?

Answer 23

20-40 ms

Question 24

What is a “twitch”?

Answer 24

One single stimulus to the motor units axon

Question 25

What is tetanus?

Answer 25

Repeated stimuli to the axon before the mechanical increase in force recovers to zero

Question 26

Describe the force during a partially- fused contraction:

Answer 26

Total force varies a lot

Question 27

What is the fatigue test?

Answer 27

A standardized pattern of electrical stimulation of 2 seconds of stimulation then 2 seconds of rest

Question 28

During a fatigue test what happens to S, FR and FF motor units?

Answer 28

S- little to no force drop
FR- Eventual force drop
FF- Very rapid force drop

Question 29

What are two ways to moderate force generation?

Answer 29

Recruitment and rate coding

Question 30

What is recruitment

Answer 30

Recruitment is based on size principle. Smaller motor units are recruited first, then larger (previously silent) motor units are recruited.

Stronger inputs lead to recruitment of more powerful motor units

Question 31

What is rate-coding?

Answer 31

This is an increase in the firing rate/ discharge of an already recruited motor unit. Can lead to a partially-fused output and even a fully fused force at highest firing rates

Question 32

Which motor units have the higher excitability….smaller or larger?

Answer 32

Smaller because they are more easily recruited

Question 33

Why is it important that recruitment is not random?

Answer 33

Because it would lead to a loss of movement precision and loss of function

Question 34

What motor units are recruited for standing?

Answer 34

S

Question 35

What are FR motor units recruited for?

Answer 35

Walking and running

Question 36

What are FF motor units recruited for?

Answer 36

galloping and jumping

Question 37

How are motor unit types determined?

Answer 37

1- muscle fibers are poly-innervated at birth

2- pruning of innervation

3- Coincident with motorneuron loss within spinal cord

4- availability of tropic factors

Question 38

What is EMG?

Answer 38

Electromyogram

Question 39

What is EMG typically used for?

Answer 39

Commonly used for diagnosis or neuromusclar disorders

Question 40

Why are EMG signals easy to record?

Answer 40

Because the muscle unit of a single motor unit serves as a natural biogenic amplifier of a nerve action potential

Question 41

What does electrode design influence?

Answer 41

1- volume of muscle recorded from

2- signal characteristics

3- frequency response

4- sensitivity to noise

Question 42

What are the different types of electrodes that can be used for EMG?

Answer 42

Surface, needle, non-selective, highly-selective