The Physics
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Voltage of a Nerve Cell

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Bibliographic Entry Result
(w/surrounding text)
Modern Human Physiology. Holt Rinehart Winston, 1982. "The Resting Membrane Potential measures about −70 mV, and the membrane is said to be polarized … This accounts for the drop in the potential difference on the surface from −70 mV to zero." −70 mV
McGraw-Hill Encyclopidia of Science and Technology. "Most nerve cells have steady Resting Membrane Potential (RMP) of from 50 to 90 mV, with the inside of the cell negatively charged with respect to the outside." 5–90 mV
Gerard J. Tortora and Sandra Reynolds Grabowski. Principles of Anatomy and
Physiology: 7th ed
. New York: HarperCollins, 1993.
"The voltage across the plasma memebrane of cells throughout your body is usually between −20 and −200 mV … In neurons the RMP ranges from −40 to −90 mV. A typical value is −70 mV." −20 to −200 mV
(all cells)
−40 to −90 mV
(nerve cell, range)
(nerve cell, typical)
Cell depolarization and action potential diagram. VRML Biology Page. Tomaz Amon. "In the resting state the cell interior is negative relative to the cell exterior for about −70 mV." −70 mV

Communication by neurons depends on two things. One of them is an electrical voltage known as the resting membrane potential (RMP) across the membrane. Since the inside of a cell is negative relative to the outside, a voltage across the membrane results.

The voltage across the plasma membrane of cells in the body is usually between −20 to −200 millivolts (mV). The negative sign means that the inside is negative relative to the outside. The greater the difference in charge across the membrane, the larger the voltage. The resting membrane potential (RMP) for nerve cells is from −40 mV to −90 mV. The most common value is −70 mV, and the membrane is said to be polarized.

Ions carrying most of the current, flow across the membrane through ion channels. Two factors contribute to the resting membrane potential: the distribution of ions across the plasma membrane and the relative permeability of the membrane to Na (Sodium) and K (Potassium). This voltage is established when the Na that diffuses in, is pumped out and the K that diffuses out is pumped back in.

When an action potential occurs two voltage-gated ion channels open and close, one for Na and one for K. When the voltage-gated channel of Na opens depolarization occurs. And the opening of the K voltage-gated channels and closing of the Na voltage-gated channels causes repolarization. Both of these phases occur in only a few milliseconds. During an action potential the internal voltage of the cell goes from its resting potential (−70 mV) to a positive value. However, it goes back to its resting potential right away.

Yana Nisanov -- 2001