The portion of a nerve cell thatconducts signals is called an axon. Many of the electrical properties ofaxons are governed by ion channels, which are protein molecules thatspan the axon’s cell membrane. When open, each ion channel has apore that is filled with fluid of low resistivity and connects the interiorof the cell electrically to the medium outside the cell. In contrast, thelipid-rich cell membrane in which ion channels reside has very highresistivity. In a simple model of an axon conducting a nerve signal, ionsmove across the cell membrane through open ion channels, which actas purely resistive elements. If a typical current density (current perunit cross-sectional area) in the cell membrane is 5 mA/cm2 when thevoltage across the membrane (the action potential) is 50 mV, what isthe number density of open ion channels in the membrane? (a) 1/cm2;(b) 10/cm2; (c) 10/mm2; (d) 100/mm2.
The portion of a nerve cell that
conducts signals is called an axon. Many of the electrical properties of
axons are governed by ion channels, which are protein molecules that
span the axon’s cell membrane. When open, each ion channel has a
pore that is filled with fluid of low resistivity and connects the interior
of the cell electrically to the medium outside the cell. In contrast, the
lipid-rich cell membrane in which ion channels reside has very high
resistivity. In a simple model of an axon conducting a nerve signal, ions
move across the cell membrane through open ion channels, which act
as purely resistive elements. If a typical current density (current per
unit cross-sectional area) in the cell membrane is 5 mA/cm2 when the
voltage across the membrane (the action potential) is 50 mV, what is
the number density of open ion channels in the membrane? (a) 1/cm2;
(b) 10/cm2; (c) 10/mm2; (d) 100/mm2.
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