Skip to main content


Showing posts from September, 2007

Station to Station: Action Potentials in Neurons

From Sandra Ackerman's book Discovering the Brain: The actual signals transmitted throughout the brain come in two forms, electrical and chemical. The two forms are interdependent and meet at the synapse, where chemical substances can alter the electrical conditions within and outside the cell membrane.
A nerve cell at rest holds a slight negative charge (about –70 millivolts, or thousandths of a volt, mV) with respect to the exterior; the cell membrane is said to be polarized. The negative charge, the resting potential of the membrane, arises from a very slight excess of negatively charged molecules inside the cell.
A membrane at rest is more or less impermeable to positively charged sodium ions (Na+), but when stimulated it is transiently open to their passage. The Na+ ions thus flow in, attracted by the negative charge inside, and the membrane temporarily reverses its polarity, with a higher positive charge inside than out. This stage lasts less than a millisecond, and th…