Emg Preston And Shapiro Chapter 6

Front 1

What three pathologies is repetitive nerve stim most useful for?

Back 1

Myasthenia gravis, Lamber-Eaton Myasthenic Syndrome, and botulinism.

Front 2

How many molecules of acetylcholine are in each quanta?

Back 2

approximately 10k

Front 3

What are the three stores of quanta? How many are in each store and where are they?

Back 3

Primary or immediately available have 1k quanta and are just beneath the presynaptic nerve terminal membrane. Secondary or mobilization store has 10k quanta and resupply the primary after a few seconds. Tertiare store of 100k are in the axon and soma.

Front 4

How is the amount of Ach released related to the amount of Na channels opened on the postsynaptic membrane?

Back 4

The more quanta bound to the Ach receptors, the more sodium is allowed in. Thus, the more Ach released, the larger the endplate potential.

Front 5

In relation to the EPP and action potential, what is the safety factor?

Back 5

the amount of extra depolaration elicited by the EPP above and beyond necessity for an all or none action potential to occur.

Front 6

Describe slow RNS in relation to EPP in a normal situation

Back 6

2-3 Hz stim causes progressive depletion of quanta released with decline in EPP each time. However, due to safety factor there is always enough quanta. After a few seconds, the secondary store further replenishes the lost quanta.

Front 7

Describe rapid RNS in relation to EPP in a normal situation

Back 7

it takes 100ms to evacuate influxed calcium out of the terminal bouton. Stim faster than this causes accumulation of Ca2+, causing increased EPP with each successive stim.

Front 8

Describe what happens with slow and rapid RNS in pathologic NMJ conditions.

Back 8

slow RNS causes progressive depletion of quanta wherein threshold may not be reached. Rapid RNS can cause a subsequent increase in EPP back above baseline.

Front 9

What are the three physiological assumptions underlying RNS modeling in NMJ disorders?

Back 9

1) m=pn where m is the quanta released with each stim, p is the probability of release based on the concentration of calcium, n is the number of quanta immediately available. 2) the mobilization store takes effect after 1-2 seconds. 3) 100 ms are required to pump Ca out of the presynaptic terminal.

Front 10

At 3 Hz RNS, what is the largest absolute drop in EPP? When is the EPP the lowest?

Back 10

Between the first and second stim. The EPP is lowest in the stim just before mobilization of secondary stores. This takes around 1-2 seconds, so between the third and sixth stim.

Front 11

In regards to the formula m = pn, describe what's abnormal with MG and LEMS.

Back 11

All is normal with MG. There are fewer ACHRs, thus less EPP and less safety factor. With LEMS, p is decreased because of less calcium influx because of the antibodies to the calcium channels. This results in a lower m.

Front 12

Describe the appearance of EPPs and action potentials with presynaptic slow RNS.

Back 12

They typically start below threshold and subsequently decline further until mobilization stores kick in, causing an increase in EPPs, potentially back above baseline.

Front 13

What is the typical frequency of maximally contracting musscle during exercise?

Back 13

30-50 Hz.

Front 14

Describe posttetanic facilitation.

Back 14

After about 10 s of exercise/tetanic activity, there is an increase in the EPP, typically above baseline.

Front 15

Describe posttetanic exhaustion.

Back 15

After about a minute of exercise/tetanic activity, there is a prolonged decline in the EPP for several minutes.

Front 16

Describe pseudofacilitation.

Back 16

Increase in CMAP amplitude following 10 seconds of maximal contraction. No increase in number of MUAPs recruited, but increase in amplitude due to increased synchronicity.

Front 17

Describe the effect of temperature with function in myasthenia gravis.

Back 17

Increased temperature usually makes symptoms worse (and colder temps better). Reason not certain but likely because of relatively increased (and decreased) activity of acetylcholinestherase.

Front 18

What distribution of muscles does MG clinically affect most?

Back 18

ocular, bulbar, and proximal extremity.

Front 19

What proximal nerve does Preston and Shapiro recommend stimulating (and recording) for MG?

Back 19

The spinal accessory with recording over the trapezius.

Front 20

How do you calculate amplitude decrement and what value is considered abnormal?

Back 20

(baseline CMAP - lowest CMAP) / baseline CMAP. 10% or greater decrement is considered abnormal.

Front 21

When calculating posttetanic facilitation, what does an increase of 40% tell you? 100%?

Back 21

40% doesn't tell you much as this can happen in normal individuals because of increased synchronicity. 100% indicates a presynaptic NMJ disorder.

Front 22

What are three types of disorders that can show a decrement with slow RNS?

Back 22

Nerve damage with newly sprouted, unstable nerves. Some alpha motor neuron diseases. Certain myopathies, especially metabolic (e.g. McArdle's).