You insert a microelectrode into the axon of a neuron and inject positive current while also measuring the membrane potential at a distance of TWO length constants from the site of current injection.If the neuron does not reach its threshold,this voltage measurement will be about
A)1/3 of the value at the injection site.
B)2/3 of the value at the injection site.
C)1/9 of the value at the injection site.
D)the same as the value at the injection site.

Question

Quizplus · Accepted Answer

The voltage measurement at a distance of two length constants from the site of current injection will be approximately 1/9 of the value at the injection site. This is because the voltage decays exponentially with distance along the axon, with a decay constant equal to the length constant. After two length constants, the voltage will have decayed to 1/9 of its original value. If the neuron does not reach its threshold, the voltage at this location will not be sufficient to trigger an action potential.

You Insert a Microelectrode into the Axon of a Neuron