Motor Control 2

Question 1

What is EMG?

Answer 1

The registration and interpretation of the electrical activity associated with the contraction of skeletal muscle

Question 2

What is the instrument used to record EMG?

Answer 2

Electromyograph

Question 3

Give a general overview of the source of EMG

Answer 3

alpha motor neurons are activated by CNS or reflexes
Action potential propagates down to motor plates and neuromuscular transmission elicits action potential in/along the muscle fibre

Question 4

What is a motor unit?

Answer 4

Motor neuron and the group of muscle fibres it innervates

Question 5

What is motor unit innervation ratio?

Answer 5

The number of muscle fibres per motor neuron

Question 6

Explain Muscle Fibre Action Potential (MAP)

Answer 6

• Axonal AP triggers acetylcholine release
• which causes sodium ion channels to open in the sarcolemma
• depolarising the membrane,
• which causes an MAP that proapagates down the T-tubules,
• which causes release of calcium ions by the sarcoplasmic reticulum
• which stimulates the interaction of contractile proteins

Question 7

How does the shape and amplitude of a recorded MAP vary?

Answer 7

• Varies with fibre type

- Varies with measurement site

Question 8

How does measurement site cause shape and amplitude of recorded MAP to vary?

Answer 8

-Amplitude decreases with distance from motoneuron fibre

Question 9

How does fibre type cause the shape and amplitude of recorded MAP to vary?

Answer 9

Amplitude is higher, and conduction is faster in fast twitch fibres

Question 10

What is MUAP?

Answer 10

Motor Unit Action Potential: The sum of the electrical signals generated by all the fibres of a motor unit

Question 11

What is MUAPT?

Answer 11

The sequence of MUAPs from repeated neural stimulation

Question 12

What are the two factors that determine muscle force generation?

Answer 12

Recruitment and Firing Rate

Question 13

what is the relationship between muscle force generation and motor unit recruitment?

Answer 13

Henneman’s Size Principle: Motor units are recruited in order of increasing size.
And the more motor units recruited the higher the amplitude of the signal

Question 14

What is the relationship between motor unit firing rate and muscle force generation?

Answer 14

The higher the frequency of activation, the larger the signal amplitude

Question 15

What is the difference between bipolar and monopolar electrodes for EMG collection?

Answer 15

Bipolar has a better signal to noise ratio because the difference between the two electrodes can attenuate common noise between the two inputs

Question 16

What are the two forms of electrodes?

Answer 16

• Surface Electrodes on Skin

- Indwelling electrodes inside muscle

Question 17

Explain optimal electrode location and orientation

Answer 17

• Aligned parallel to the muscle fibres

- Midpoint between origin and insertion

Question 18

Can you compare EMG from different collection times?

Answer 18

No

Question 19

What should be done to ensure good electrode-skin contact?

Answer 19

• Shave hair
• Abrade dead skin cells off
• Rubbing with alcohol wipe

Question 20

What can affect signal:noise ratio apart from skin preparation?

Answer 20

Subcutaneous fat

Question 21

What information does EMG NOT give?

Answer 21

Force

Question 22

What information does EMG give?

Answer 22

-Timing of activation/co-contraction

Question 23

How do you rectify EMG?

Answer 23

Turn all negatives to positives

Question 24

How do you integrate EMG?

Answer 24

Integrate/area under the curve over certain time periods, like 50 - 250 ms

Question 25

What is sampling frequency

Answer 25

1/T (T = time between samples)