Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android. Learn more here!


For the nervous system to function properly, nervous must communicate with each other. Along with muscle cells, neurons are unique in that they are excitable; that is, they respond to stimuli by generating electrical impulses. Electrical responses of neurons (modifications of the electrical potential across their membranes) may be local (restricted to the place that received the stimulus) or propagated (may travel through the neuron and its axon). Propagated electrical impulses (nerve impulses) are termed action potentials. Neurons communicate with each other at synapses by a process called synaptic transmission.


The membranes of nerve cells are structured so that a difference in electrical potential exists between the inside (negative) and the outside (positive). This results in a resting potential across the cell membrane, which is normally about −70 mV (70 one-thousandths of a volt).

The electrical potential across the neuronal cell membrane is the result of its selective permeability to charged ions. Cell membranes are highly permeable to most inorganic ions, but they are almost impermeable to proteins and many other organic ions. The difference (gradient) in ion composition inside and outside the cell membrane is maintained by ion pumps in the membrane, which maintain a nearly constant concentration of inorganic ions within the cell (Fig 3–1 and Table 3–1). The pump that maintains Na+ and K+ gradients across the membrane is Na, K-ATPase; this specialized protein molecule extrudes Na+ from the intracellular compartment, moving it to the extracellular space, and imports K+ from the extracellular space, carrying it across the membrane into the cell. In carrying out this essential activity, the pump consumes adenosine triphosphate (ATP).


Na+ and K+ flux through the resting nerve cell membrane. Notice that the Na+/K+ pump (Na+/K+-ATPase) is fueled by ATP and tends to extrude Na+ from the interior of the cell, but it carries K+ ions inward. (Eccles, John C.. The Physiology of Nerve Cells. pp. 26 Figure 8. © 1957 Johns Hopkins University Press. Reprinted with permission of Johns Hopkins University Press.)

TABLE 3–1Concentration of Ions Inside and Outside Mammalian Spinal Motor Neurons.

Two types of passive forces maintain an equilibrium of Na+ and K+ across the membrane: A chemical force tends to ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.