Insertional and Spontaneous activity

1. What causes insertional activity and what causes it to be increased or decreased?
2. What are MEPPs and what do they look like?
3. What are EPPs and what do they look like?
4. What causes abnormal spontaneous activity?
5. What are fibrillation potentials and how do they look?
6. What are positive sharp waves and how do they look?

Answers:
1. Insertional activity is caused my disruption of cell membranes with the needle. It is increased by denervation or irritable cell membranes. It is decreased by fat, fibrosis, edema, or electrolyte abnormalities.
2. MEPPs, aka endplate noise, is due to spontaneous quanta release, which occurs every 5 seconds. MEPPs are 10-50uV negative potentials seen as an irregular baseline and sound like a seashell murmur. They are seen at the neuromuscular junction, indicating the muscle has maintained its innervation.
3. An EPP is a spike due to increased ACh release, provoked by needle irritation of the muscle fiber or synchronization of MEPPs. It is irregular, has a biphasic waveform with initial negative deflection, ampliude <1mV, rate of 50-100Hz, and sounds like sputtering fat in a frying pan.
4. This is caused by a RMP that is less negative and therefore unstable, causing it to fire independently or induced by needle movement.
5. Fibs are spontaneously firing APs from denervated single muscle fibers due to uncontrolled ACh release. They are regular at a rate of 1-10Hz, with an initial positive deflection, and sound like rain on a tin roof.
6. PSWs are spontaneous APs stimulated by needle movement of an injured muscle fiber. They are regular at a rate of 1-20Hz, with an initial positive deflection, amp <1mV, and sound like a dull thud or chug.