muscles and motor units

Question 1

T/F: Reaction equals reflex

Answer 1

F: reaction does not equal reflex

Question 2

with aging, the number of motor neurons stays _______, until around age _____, then you experience a _______ in the amount of motor neurons

Answer 2

the same, 60, decline

Question 3

Re-innervation of abandoned muscle fibres

Answer 3

once their motor neuron dies off - another motor neuron will pick them up

Question 4

loss of motor neurons comes with a loss of ____ _______

Answer 4

muscle fibres

Question 5

___ of motor neurons –> ______ in number of functioning motor units –> re-innervation of _______ muscle fibres –> ______ innervation ratio –> _____ of fine motor control

Answer 5

loss, decrease, some, higher, loss

Question 6

EMG

Answer 6

electromyography

• recording of action potentials as they travel along muscle fibre
• electrical sum of all active motor units

Question 7

2 common types of EMG electrodes

Answer 7

1. intramuscular

2. surface

Question 8

intramuscular EMG

Answer 8

• needle or wire inserted in the muscle

- record action potentials from specific area

Question 9

surface

Answer 9

• records the overall activity of many motor units in a muscle using electrodes placed on the skin

Question 10

common ways to quantify EMG recordings

Answer 10

• amplitude
• average
• onset and offset
• firing frequency

Question 11

amplitude

Answer 11

• the size

- peak to peak (subtracting biggest from smallest)

Question 12

average

Answer 12

• add up all the values and divide by the total amount

- have to rectify the signals first

Question 13

rectifying EMG signal

Answer 13

• take the negative values and make them positive

essentially take the bottom half and duplicate it on the the top (all positive values now)

Question 14

onsets and offsets

Answer 14

• duration of when the muscle is active

Question 15

surface electromyography considerations

Answer 15

• muscle geometry and electrode position
• amount of subcutaneous tissue
• skin preparation

Question 16

T/F: EMG is a measure of force or strength

Answer 16

F: EMG is not a measure of force or strength

Question 17

2 ways to vary contraction force

Answer 17

• recruitment

- rate coding

Question 18

recruitment

Answer 18

change the number of motor units that are active

Question 19

rate coding

Answer 19

change the firing rate of different motor units

Question 20

Henneman’s size principle

Answer 20

• motor units are recruited from smallest to largest, and de-recruited from largest to smallest in an orderly manner

Question 21

recruitment and de-recruitment threshold

Answer 21

level of force when this motor unit starts to activate

Question 22

voltage

Answer 22

represents the membrane potential

Question 23

resting membrane potential

Answer 23

around -70mV

Question 24

if change in voltage is _____ than 15 units - action potential change occurs

Answer 24

greater or equal to

Question 25

if change in voltage is _____ than 15 units - action potential change does not occur

Answer 25

less

Question 26

current

Answer 26

the amount of signal

Question 27

resistance

Answer 27

is a property of the motor neuron itself

Question 28

_____ neurons have a _____ resistance (R value)

Answer 28

smaller, higher

Question 29

____ neurons have a _____ resistance (R value)

Answer 29

larger, smaller

Question 30

motor unit recruitment advantages

Answer 30

1. automatic
2. fatigue resistance
3. increasing force gradiation

Question 31

motor unit recruitment disadvantages

Answer 31

1. better to get larger one first, cause smaller ones do not contribute as much