Motor System and Electromyography

Question 1

Equivalent name for neuromuscular junctions

Answer 1

motor end plates

Question 2

Why does Acetylcholine depolarize the muscle?

Answer 2

Both K+ and Na+ can flow through ACh receptor however, more Na+ enters than K+ leaves

Question 3

Thin muscle filament

Answer 3

actin

Question 4

Thick muscle filament

Answer 4

myosin

Question 5

sliding filament theory

Answer 5

shortening (overlap) causing contraction

Question 6

Inward Ca2+ flow causes…

Answer 6

the release of ACh at the neuromuscular junction

Question 7

ACh diffuses to the motor end plates, binds to the receptors and…

Answer 7

opens the Na+ channels leading to an action potential

Question 8

The action potential in the sarcolemma (exterior) travels inward via…

Answer 8

the T-tubules to the triads

Question 9

Once the action potential has reached the interior (triads) where is Ca2+ released from?

Answer 9

terminal cisternae (of sarcoplasmic reticulum)

Question 10

Once Ca2+ is released for a second time what happens?

Answer 10

Ca2+ binds with troponin, and moves tropomyosin, exposing actin/myosin binding site, and triggering power strokes (muscle shortening)

Question 11

What must be moved aside to expose the actin/myosin binding site?

Answer 11

Tropomyosin

Question 12

What is the first step in excitation contraction coupling?

Answer 12

Ca2+ binds with troponin

Question 13

Describe the power stroke?

Answer 13

Hinging of myosin head causing actin to slide across myosin (uses ATP)

Question 14

What are some attributes of Type 1: slow, oxidative fibres

Answer 14

1) less force
2) less energy
3) slow fatigue
4) fast recovery
ie. walking

Question 15

What are some attributes of Type 2: fast, glycolytic fibres

Answer 15

1) more force
2) more energy
3) fast fatigue
4) slow recovery
ie. sprinting

Question 16

In a myoglobin stain are the slower, more oxidative/aerobic fibres darker or lighter?

Answer 16

Darker

Question 17

Def: motor unit

Answer 17

single motorneuron and all of the muscle fibres it innervates

Question 18

Def: motor pool

Answer 18

all the motor units innervating a given muscle

Question 19

Why might the distribution of lower motor neurons (spanning multiple spinal segments) be beneficial?

Answer 19

In case of a minor injury, if one level is injured you will still have use of the muscle

Question 20

The summation of successive isometric twitches will result in…

Answer 20

a build up of force

Question 21

Unfused tetanus (contraction/relaxation) will result in…

Answer 21

sub-maximal force output (not perfect summation)

Question 22

Fused tetanus will result in…

Answer 22

maximum force output (smooth curve)

Question 23

Which muscle fibres produce more force output?

Answer 23

Fast twitch (more glycolytic)

Question 24

Sarcomere

Answer 24

contractile unit btwn two
“z” discs

Question 25

Muscle fibres consist of many…

Answer 25

myofibrils

Question 26

Myofibrils contain…

Answer 26

thin filament (actin), and thick filament (myosin)

Question 27

Given the same synaptic input, which motor units are more excitable- smaller/larger?

Answer 27

Smaller, b/c larger are leakier

Question 28

Where are alpha motor neurons located?

Answer 28

Ventral horn of spinal cord

Question 29

What does is mean for larger motor units to be less excitable/leakier?

Answer 29

Na+ leaks out making depolarization (positive inside) more difficult

Question 30

Do motor units begin firing action potentials (“get recruited”) at the same time?

Answer 30

No, they get recruited at different levels of force output (and de-recruit in the opposite order)

Question 31

Smaller (slow twitch) motor units get recruited…

Answer 31

first (and de-recruit last)

Question 32

Larger (fast twitch) motor units get recruited…

Answer 32

later because they require more force to fire

Question 33

Surface electromyography uses…

Answer 33

standard EMG placements across the body that measure muscle fibre action potentials as they pass below the electrode

Question 34

How do you correctly place electrodes in surface electromyography?

Answer 34

-placed over the thickest part of muscle (belly)
-aligned with the direction of muscle fibres (pennation angle)

Question 35

What are some characteristics of larger motor units (MU)?

Answer 35

-fast conduction velocity
-more force
-fatigable

Question 36

What are some characteristics of smaller motor units?

Answer 36

-least amount of muscle fibres
-slower

Question 37

Rectification

Answer 37

make all negative values (EMG) positive… like taking the absolute value

Question 38

Smoothing

Answer 38

filtering/averaging the rectified EMG data

Question 39

Muscle force output

Answer 39

Rectified and smooth EMG trace that corresponds to the approximate amount of force produced by the muscle

Question 40

EMG signal is approximately ________ in relation to muscle force output

Answer 40

linear

Question 41

Maximal Voluntary Contraction

Answer 41

Highest amplitude measured on EMG

Question 42

Indwelling electromyography (“fine-wire” EMG)

Answer 42

Needle inserted into target muscle and wire remains in muscle, hooked to muscle fibres

Question 43

What are some benefits of indwelling EMG

Answer 43

-can measure smaller amounts of motor units
-can measure deeper fibres clearer
-“less noise”
-eliminates “cross talk” (signal contamination)

Question 44

Can we increase the amplitude of EMG during maximum voluntary contraction

Answer 44

Yes, with strength training

Question 45

In what ways can training make you faster, stronger, better?

Answer 45

-increase # of fast muscle fibres
-neurons can also grow in size (increasing conduction velocty)

Question 46

Immobilization of motor neurons

Answer 46

-decrease in EMG amplitude
-bedrest, casting, exposure to long periods of microgravity