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The calcium dynamics are usually modeled in the following simple
fashion.
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(6) |

or with just a linear term. Here *F* is the Faraday constant, *d* is
the depth of the shell between the membrane (usually, e.g., ),
*k*=0.1 for *I* in , [*Ca*] in millimolar, *K*_{T}=10^{-4}
*mM*/*ms* and *K*_{d}=10^{-4} *mM*. Note that as the calcium current
increases in an inward direction, -*I*_{Ca} becomes positive and thus
intracellular calcium increases. The uptake of calcium is modeled
here as a Michaelis-Menten type reaction. An even simpler uptake would
be simply linear. These constants are for thalamic neurons
but are in the right ballpark for most models. Finally, in general,
extracellular calcium is about 2 mM and intracellular tends to be
around 2.4 10^{-4} mM.

*G. Bard Ermentrout*

*1/29/1998*