electromyography (EMG)

[Myelinated-Man]

I have a few questions on EMGs- we did two tests in class, one one biceps flexion, and the other on tricep extension.

 

1) I still don't understand what an EMG is measuring - is it Action potential frequency?, size of action potential (action potentials aren't the same size, so it probably isn't this).

 

2) Why does an EMG have both a positive and negative y-axis if it supposed to be measuring depolarization?

 

3) What do the spikes on an EMG represent

http://www.unmc.edu/physiology/Mann/pix_14/emg.gif

 

4) What does a cluster of spikes represent?

 

Thanks, help is greatly appreciated

[Ardyen]

1.It is used to measure both.

2.Yes it measures both (De and re-polarization). Thats essential because for you to know how fast the muscle is going to respond the next time to the same action potential, you need to know the potential(at the highest point) of depolarization.

3.Spikes represent the highest action potential of that muscle, and consequently higher muscle function.

4.That the muscle is depolarizing and repolarizing quckly. i.e its twitching, or physiologically in clonus.

 

I'd just wanted to ask, Where did you perform this on? A cadaver? Or some lower organisms like a frog?

[Speldosa]

Then I have a question. What's the difference between EEG and EMG? Both just measures electrical activity, right?