The Circuit of Awareness 105
He was right. Not bad for a physicist! The nerve did divide, but the
two parts were held together by the nerve sheath until they got past the
knee. I was able to remove the sheath and isolate both portions. When
we measured these, we found that the two sections were polarized in
opposite directions. The voltage drop of the front branch was positive
toward the toes. The posterior branch was polarized in the same direc-
tion as the sciatic trunk, but it always had a higher voltage gradient.
The current in the front branch apparently flowed in the direction op-
posite to that in the rest of the nerve. The interesting thing was, when
we added up the voltage increases from 1-centimeter lengths of the two
branches—4 millivolts positive and 8 negative in a typical frog—we got
roughly the same voltage gradient that we found in the main nerve,
about 4 millivolts negative in every centimeter. At first that didn't make
On a hunch I took
pieces of each nerve and sent them to the pa-
thology department to have microscope slides made.
I found that the
fibers in the front fork were smaller than those in the other. A light bulb
went on! The sciatic nerve is what's called a mixed nerve. It has both