Currents and Voltages in the Body
Lecture 6
1/25/2016
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Assignment
 1 Read Chapter s 2 and 3
 2. Read two papers and write a 1 page summary or
each.
 3. In some cases I have suggested papers to read as
follow up to the first paper you read.
 4. Monday next week we will look at some issues in
setting standards
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Electrical Voltages and Currents In the Body
1. The Body is an Electro Chemical System
A. Basic Sources of Energy are the Metabolic Processes
in the mitochondria which supply about 95% of the
energy for the cell by combining O2 with glucose to
form ATP. This in turn supplies the energy for the
pumps that maintain the ion gradients across
membranes and generate the electric potentials of
-50 to -100mV between the outside and the inside
of a cell. This leads to trans membrane fields on the
order of 107V/m
B. There are also endogenous electric fields in the
extracellular fluids in the range of 10 to 100V/m
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Cell Models
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1
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Source of Electric Fields
1. Plasma membrane that defines the cell boundary
and the voltage is negative on the inside.
2. The Epithelium that surrounds every organ and
the skin. This leads to the Transepithelial
Potential, TEP, which is positive on the inside.
3. The TEP fields move ions and molecules around and
are the driving force for the growth of embryos
and wound healing etc.
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A Cell Membrane Cartoon
 Voltage inside - 50 to -100mV about 1 charge per 106
atoms
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1
1
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Transepithelial Potential
 1. Note separation of the Na and K channels 15-60mV
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Current Densities
1.
2.
3.
Currents across cell membranes 1 μA/cm2 to 10
μA/cm2 the interior of the cell is negative.
The Transepithelial Potential (TEP) is positive at
the inside of the skin. Current densities from 10
μA /cm2 to 100 μA /cm2
Shocks at approximately 10 mA
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Chick Embryos
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Effects are Time Dependent
 Applied external currents can cause abnormalities in
the neural-stage embryo stage and not Gastrula-stage
 At 25-75 mV/mm leads to abnormalities
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Measurements Around an
Chick Embryo
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Currents As Function of
Position
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Voltage Gradients
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Growth of Planarian Flatworm
In an Electric Field.
Wendy Beane
 In vivo studies show that electric fields have a lot to do
in controlling the size and shape of the growth.
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• Amputated Limbs 10 to 100μA/cm2 out of the cut.
60 mV/mm to start and down to 25mV/mm within 6hr
(Note in other units these are Volts/meter)
• Growth occurs toward negative electrode. Used to
guide direction of nerve growth.
• The currents during growth in a root or other cell can
flow in one end and back into the side of the cell.
• We have seen effects as low as 0.2 mV across a
membrane in changing the oscillation of pacemaker
cells or fields of 0.01V/m
• Electroporation 1 .5 to 3V/cell
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Currents Near Wounds
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Current Flow at a Cut
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Electric Fields Near a Cut
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Equivalent Circuit Model
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