RNS

Question 1

A quantum contains how many molecules of ACh?

Answer 1

About 10k

Question 2

How much quanta is in the primary store (immediately available)? Secondary (mobilization)? Tertiary (reserve)?

Answer 2

1k; 10k, 100k

Question 3

The size of the end plate potential is proportional to

Answer 3

the amount of ACh binding the ACh receptors

Question 4

What is the safety factor?

Answer 4

Amplitude of the EPP above the threshold value needed to generate a muscle fiber action potential

Question 5

How much times does it take to pump out Ca? Why does this matter?

Answer 5

100 ms;
If there is rapid RNS (10-50 Hz), quanta is depleted faster but [Ca] increases and probability of release of ACh quanta increases, and more quanta released

Question 6

What type of decrement can be seen with both pre-synaptic and post-synaptic disorders?

Answer 6

U-shaped decrement (repair of CMAP decrement after fifth or sixth stimulus due to secondary stores mobilized)

Question 7

What is characteristic of the baseline CMAP amplitude with pre-synaptic disorders?

Answer 7

EPP is usually below threshold at baseline, and muscle fiber action potential never generated

Question 8

Explain post-exercise facilitation?

Answer 8

Exercise or rapid RNS can facilitate EPP’s that remain above threshold due to mobilization of quanta from secondary to primary store, and Ca accumulation in presynaptic terminal which increases probability of release

Question 9

How to test for post-exercise exhaustion?

Answer 9

1. Max exercise muscle for 1 minute
2. Slow RNS performed immediately after and 1, 2, 3, and 4 mins later
3. With impaired NMJ transmission, decrement in CMAP amplitude and area in response to slow RNS becomes more marked 2-4 mins after prolonged exercise
4. Can then repair decrement toward normal with 10 secs of maximal voluntary exercise

Question 10

Technical factors in RNS

Answer 10

1. Immobilization (minimize limb movement, stimulator movement, or recording electrode movement)
2. Supramaximal stimuli
3. Temp (ideally 33 degrees C) to avoid reduction of the decrement
4. Hold AChase Inhibitors (could diminish decrement)
5. Nerve selection (SAN may be ideal…)
6. Stimulation freq (2-3 Hz)
7. Number of stims (5-10 pulses for low-rate rep stim); if rapid RNS to be done, stimulus train of 5-10 secs i.e. 200-500 stims