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Flashcards in EMG and NCV Deck (25)
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1
Q

Define Electromyography (EMG) and Nerve Conduction Velocity (NCV).

A

EMG Recording of spontaneous and voluntary motor unit activity to examine the integrity of muscle and nerve. NCV Measurement of the speed of transmission of a motor or sensory impluse along a nerve.

2
Q

In a motor unit, alpha motor neuron axons with branches are not bundled, but distributed. True or false?

A

True.

3
Q

What’s the duration of a MUAP (motor unit action potential) in normal tissue? They typically have a frequency of 5-15 seconds and an amplitude of 300 microV. Can a motor unit be poly phasic?

A

3-16 seconds. Typically, a MU is bi or tri phasic (<10% polyphasic), with each phase representing a time the potential crosses baseline. Seen with minimal effort.

4
Q

For a normal muscle, there is insertional activity lasting about 300 msec. What causes this? Is it normal for this activity to persist?

A

Disruption of muscle membrane -when placing the needle in skin -not a contraction In a normal muscle, there is silence at rest with the insertional activity dying off.

5
Q

In a normal muscle, with adequate recruitment there is an increase in amplitude. What causes this?

A

The recruitment of more muscle fibers increases firing frequency and amplitude (some summation).

6
Q

True of false: with a normal muscle with a maximal contraction, the interference pattern is full and normal.

A

True.

7
Q

With a neuropathy there is an abnormal EMG, most notably, there is prolonged insertional activity. What causes this?

A

The muscle membrane becomes unstable, so with the stimulation of a needs, there is excessive exchange of ions across the muscle membrane. These are called fibrillation potentials or end positive sharp waves (spontaneous potentials).

8
Q

Are denervated muscles slient at rest like normal muscles?

A

No, there are fibrillation potentials and positive sharp waves. FPs looks like MUAPs, but smaller - they are a depolarization of a single muscle unit. PSWs are V shaped.

9
Q

Fasiculations can be present in normal individuals at a rate of <10%. What do they represent?

A

The contraction of a small group of muscle fibers, usually in a fatigued muscle. Increase is sign of pathology (e.g. amyotrophic lateral sclerosis).

10
Q

In a denervated muscle, if some innervation is intact you’ll see a normal MUAP, but in a smaller quantity. What does the interference pattern for a moderate contraction look like?

A

Incomplete. There are gaps and the amplitude may not be normal. Complete denervation means no pattern because there’s no contraction.

11
Q

In ___, high frequency discharges are created by the muscle itself. This myopathy has characteristicly prolonged muscle contractions with needle insertion or movement.

A

Myotonia.

12
Q

Instead of having a nice ___, a newly reintervated muscle has a rough, polyphasic wave can still have positive short waves (PSW) and fibrillation potentials as reinervation progresses and at rest, fewer of these with present. What does the interference pattern look like?

A

Triphasic wave. Increased interference pattern.

13
Q

As a muscle renervates, you see nascent units. What are they?

A

As the muscle fibers begin to reinnervate you begin to see nascent units. These are very small amplitude, short duration polyphasic potentials.

14
Q

With renervation, there is no guarantee the regrowing nerve will connect with its endoneurial sheeth. What happens in this case?

A

Some muscle fibers may not ever be reinnervated in which case you will continue to see fibrillation potentials for some time. Sometimes there is collateral sprouting from adjacent axons in an effort to pick up denervated muscle fibers. These collateral innervated muscle fibers can produce polyphasic long duration MUAP at 6-8 weeks (sooner than nascent units would appear.)

15
Q

What causes giant motor units?

A

Sometimes either surviving axons or regenerated axons to pick up more than the normal number of muscle fibers and form giant motor units but the reorganization of the MU takes at least 12-18 months and may not reach their final size for years.

16
Q

What produces long duration, polyphasic units seen earlier (6-8 wks) than nascent units from regrowing axons? What is a downside to this process?

A

Distal terminal ends of preserve MU can sprout and pick up adjacent dennervated muscle fibers by srpouting collaterals. -Can develop into giant motor units in 12-18 months if they pick up a lot of uscle fibers (typical in post polio).

17
Q

NCV requires stimluation to receive input. What is its purpose?

A

To measure both motor and sensory action potential velocities along an axon. Motor can be measured with surface electrodes and sensory on the fingers and toes.

18
Q

When measured NCV, the stimluation is intense enough that all MU s contract. For ___ it is orthodromically activated, and for ___ it is antidromically activated.

A

Motor, sensory.

19
Q

For each stimulation there is an artifact that identifies when the stimulus was applied to the nerve. The contraction of the muscle is recorded by surface electrodes and the muscle contraction produces a wave form called the ___ wave.

A

M = all muscle fibers contracting. Distal latency

20
Q

The amplitude of the M wave occurs because all muscle fibers are contract. Why is there a duration to the wave?

A

Not all of the muscle fibers contract at the same time, giving duration to the contraction.

21
Q

With a neuropathy, such as a compression or partially reinnervated muscle, the M wave will be dispersed. Why does this happen?

A

Some of the motor units don’t fire because they aren’t yet innervated.

22
Q

With nerve regeneration there are ___ myelin segments, meaning NCV is ___.

A

More, slower.

23
Q

What is an H reflex?

A

Similar to a monosynaptic stretch reflex. Amplitude is measured to test integrity of dorsal and ventral roots (sensory and motor). Only used for S1 nerve root. Occurs after the M wave.

24
Q

An F response is usually submaximal and is antidromically activated. What is an F response and how is it used with the H reflex?

A

It tests the ventral root via the alpha motor neuron. Antidromic means stimulation occurs distal to proximal. It is used with the H reflex in the following way. -If H is slow, you don’t know if it’s motor or sensory -If F is okay combined with a slow H, you know it’s the sensory group -If F is always slow, you know motor is involved, but don’t know if sensory is also involved

25
Q
A