Page 159 - The Miracle in the Cell Membrane

Signal

Movement potential
region progressing
along the neuron

Repolarization
region

Movement potential forms through the action of the closed voltage sodium
and potassium channels in the axon membrane. At rest, these channels are
generally closed, and open when the cell membrane potential attains a neg-
ative value. Potassium channels open in a millisecond, and sodium chan-
nels in even less time. It has become possible to identify and follow all
these processes through 20th-century technology.

The Neuron at Rest

When a nerve cell is not trans mit ting a sig nal, it is at
rest, but is not entire ly immo bile. It must be ready to for -
ward mes sa ges that may arrive at any moment from
neigh bor ing cells. A neu ron at rest must always be polar -
ized, so that the fluid with in it is more neg a tive ly
charged than the fluid out side. Along its mem brane, a

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