EMG

Question 1

What does the EMG look like with spontaneous activity?

Answer 1

fibrillation potentials

positive sharp waves

Question 2

On the EMG reading, above the baseline is considered ______ (pos/neg).

Answer 2

negative

Question 3

What accounts for spontaneous activity?

Answer 3

acutely denervated muscle fibers have Ach receptors over the whole muscle fiber membrane rather than just at the neuromuscular jxn. This means the fiber is supersensitive and discharges spontaneously.

Question 4

The wave in spontaneous potentials represents depolarization of ______.

Answer 4

single muscle fibers

NOT whole MUs

Question 5

At rest, normal muscle is SILENT. What is it called when the EMG picks up sound at rest?

Answer 5

spontaneous potential

AKA fibrillation AKA pwave

Question 6

Why would insertional activity be prolonged with diseased muscle or enervated muscle?

Answer 6

excessive exchange of ions across muscle membrane with needle stimulation

Question 7

How can you distinguish fibrillations from fasciculations/?

Answer 7

fasculations are larger and more complex than fibrillation potentials

Question 8

How can fasciculations can be distinguished from MUs discharging due to poor relaxation?

Answer 8

fasciculations are NOT under voluntary control

Question 9

What is a fasciculation?

Answer 9

waveform that represents contraction of a group of muscle fibers; arises from discharge of part or all of a single MU

Question 10

How does a fasciculation appear?

Answer 10

isolated discharges that recur at irregular intervals

Question 11

How do you distinguish MUAP and fibrillation potentials?

Answer 11

look similar but MUAP are much bigger

Question 12

What may be absent in complete denervation or reduced in partial denervation?

Answer 12

Interference pattern and MUAP

Question 13

Positive sharp waves at rest are indicative of

Answer 13

spontaneous conductance

Question 14

“Dive Bomber” is characteristic of

Answer 14

myotonic discharge

Question 15

High frequency discharges are characteristic of

Answer 15

myopathies

myotonic dystrophy

Question 16

At rest, what do you see as nerve recovers and muscle begins to be reinnervated?

Answer 16

increased insertional activity until all muscle fibers are reinnervated

Question 17

Until all muscle fivers are re-innervated, what will you see?

Answer 17

some fibrillation potentials and positive sharp waves

Question 18

With minimal contraction, what do you see as muscle fibers begin to reinnervate?

Answer 18

nascent units

Question 19

What are nascent units?

Answer 19

very small amplitude
short duration
polyphasic potentials

Question 20

Why are nascent units small and polyphasic?

Answer 20

few muscle fibers in reinnervated MU
asynchronous
terminals conduct at different velocities

Question 21

What adaptation occurs to assist fibers that where not reinnervated successfully?

Answer 21

collateral sprouting

Question 22

Describe collateral innervation.

Answer 22

distal terminal ends of preserved MUs sprout and pick up adjacent dennervated muscle fibers

Question 23

What does collateral innervation produce?

Answer 23

polyphaisc
long duration MUAP
at 6-8 weeks (sooner than nascent units)

Question 24

What two elements constitute giant motor units?

Answer 24

nascent units

collateral sprouting

Question 25

Giant motor units may form over a period of ___-___ months.

Answer 25

12-18 months

Question 26

With reinnervation, what happens to insertional activity?

Answer 26

reduces to normal over time

Question 27

What happens to MUAP after reinnervation begins?

Answer 27

MUAP gains amplitude and duration with time

Question 28

As more MUs become reinnervated, what happens to interference pattern?

Answer 28

pattern fills in and gains amplitude

Question 29

What accounts for interference pattern? (3)

Answer 29

1. more units are recruited (larger ones) 2. firing frequency increases 3. some summation occurs (some units fire simultaneously)

Question 30

With maximum contraction (normal EMG), what pattern is observed?

Answer 30

full interference pattern

Question 31

Normal EMG summary: (4)

Answer 31

1. minimal insertional activity 2. electrical silence at rest 3. MUAP bi- or triphasic 4. full interference pattern with maximal contraction

Question 32

MUAP represents?

Answer 32

activity of muscle fibers of a single MU (unit is milliVolts) can be bi- or triphasic

Question 33

MUAP amplitude is?

Answer 33

sum of muscle fibers contracting at the same time

Question 34

The first upward deflection is the activity of what muscle fibers? Later deflections represent what muscle fibers?

Answer 34

fibers closest to electrode first | more distal fiber activity later

Question 35

What factors influence size, shape, and duration of MUAP? (5)

Answer 35

1. distance b/w electrodes 2. location of electrodes 3. size of electrodes 4. size of MU and fiber dispersion 5. depth of MU and distance from electrodes

Question 36

Why is there asynchrony of muscle fiber contractions in MU?

Answer 36

variation of collateral axon length

Question 37

What occurs with normal EMG insertion?

Answer 37

disruption of muscle membrane duration up to 30 msec (some insertional activity is normal)

Question 38

After insertional activity, there is _______ at rest in normal MUs.

Answer 38

electrical silence

Question 39

Single MU with minimal effort appears?

Answer 39

3-16msec duration @ 5-15/sec frequency sound-thumping bi- or triphasic

Question 40

EMG evaluates _____ qualities of nerve and muscle.

Answer 40

passive

Question 41

EMG examines _____ contraction on _____ MU level.

Answer 41

voluntary contraction on single MU level

Question 42

EMG only examines ____ system.

Answer 42

motor