Expert: John Locke - 10/28/2006

Question
Hello.
Where does sciatic nerve runs under?
Is the ansver (gluteus medius) correct?
Does it runs under semimembranous muscle?
2) If the resting voltage become more positive by +5 mv and treshold became more negative by -10 mv, the membrane is....?
a) depolarizing
b) hyperpolarizing
Please help.
This were the question on my quiz and i dont think that they were asked correctly
Thanks
Ulia  

Answer
Thanks for using AllExperts, Ulia. I've pulled this question out of the Question Pool in order to clarify for you, while recognizing that you asked this some time ago.

1) The sciatic nerve does not run underneath the gluteus medius, but rather the gluteus maximus. The sciatic nerve runs closer to the bottom of the pelvis than the medius muscle, which lies toward the top. A branch of the sciatic nerve lies on top of the semimembranosus muscle and innervates it, but does not pass underneath. The nerve does pass underneath the biceps femoris, however.

2) Two things are going on here simultaneously. The threshold becomes more negative, while the membrane becomes more positive; given that the resting voltage is negative, this means that the threshold and resting voltage are approaching each other. Remember that hyperpolarization and depolarization are measured relative to resting voltage: the new resting voltage is depolarized relative to the old, and the new gap between resting and threshold is smaller relative to the old one. Together, we may take these to mean that the membrane itself is depolarizing.