0• Electric field of axons. A nerve signal is transmitted O through a neuron when an excess of Na ions suddenly enters the axon, a long cylindrical part of the neuron. Axons are approximately 10.0 µm in diameter, and meas- urements show that about 5.6 X 10" Na ions per meter (each of charge +e) enter during this process. Although the axon is a long cylinder, the charge does not all enter every- where at the same time. A plausible model would be a series of nearly point charges moving along the axon. Let us look at a 0.10 mm length of the axon and model it as a point charge. (a) If the charge that enters each meter of the axon gets distributed uniformly along it, how many coulombs of charge enter a 0.10 mm length of the axon? (b) What electric field (magnitude and direction) does the sudden influx of charge produce at the surface of the body if the axon is 5.00 cm below the skin? (c) Certain sharks can respond to electric fields as weak as 1.0 µN/C. How far from this segment of axon could a shark be and still detect its electric field?

0• Electric field of axons. A nerve signal is transmitted O through a neuron when an excess of Na ions suddenly enters the axon, a long cylindrical part of the neuron. Axons are approximately 10.0 µm in diameter, and meas- urements show that about 5.6 X 10" Na ions per meter (each of charge +e) enter during this process. Although the axon is a long cylinder, the charge does not all enter every- where at the same time. A plausible model would be a series of nearly point charges moving along the axon. Let us look at a 0.10 mm length of the axon and model it as a point charge. (a) If the charge that enters each meter of the axon gets distributed uniformly along it, how many coulombs of charge enter a 0.10 mm length of the axon? (b) What electric field (magnitude and direction) does the sudden influx of charge produce at the surface of the body if the axon is 5.00 cm below the skin? (c) Certain sharks can respond to electric fields as weak as 1.0 µN/C. How far from this segment of axon could a shark be and still detect its electric field?