Calcium diffusion in a nerve cell body. Pseudocolor is used to represent calcium ion concentra- 
tion at various points along a diameter of a spherical nerve cell. The top edge of the image 
corresponds to the top edge of the cell ( Oiim ), and the bottom edge of the image to the bottom edge 
of the cell (40 nm ). Time is represented from left to right. Thus at 0 time, all points along the cell's 
diameter had a low calcium level (blue ). Calcium remained low until the cell was given a voltage 
pulse (diagrammed at top of figure), which caused calcium channels in the cell membrane to 
open. Calcium immediately entered the edge of the cell (yellow and then red) and rapidly spread 
toward the center. The color bar shown is only approximate. Image obtained by combined whole- 
cell recording and FLUO confocal fluorescence microscopy. 
Modified from Hernandez- Cruz, A., Sala, P., and Adams, P.R. 1990. Science 247:858-862. 
Copyright 1990 by the AAAS. 
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