Some of the specific parameters were experimentally estimated for real neurons.
The specific axial resistance RA is 0.6-1 Ω.m (Miller, 1980; Miller et al., 1985;
Fleshman et al., 1988). The value of the specific membrane resistance RM is
0.5-10 Ω.m2 (Miller et al., 1985; Cauller, 2003) and for the specific membrane
capacitance CM it is 0.01 F/m2 (Miller et al., 1985).
If we introduce a rectangular electric impulse with voltage V, then the voltage
across the membrane changes according to the cable equation:
(59)
-λ2
∂2V
∂x2
∂V
+ τ + V = 0
∂t
where
(60)
τ=rmcm=RmCm=RMCM
is the time constant (τ) and
(61)
λ2 = rm
is the square of the space constant (λ).
In neurons ri » re (Sajda, 2002) so we can write:
λ=
dRM
4 RA
(62)
35