Electric currents in dendrites
From the Ohm’s law we could calculate the axial current ia if we know the
applied voltage V0 upon the dendritic projection:
(71)
ia
∂V i_ = і
. ---- .
∂lriri
where l is the direction along the axis of the dendrite. The same equation is valid
for the axial current outside the dendrite; the only difference is that we should use
the re value. The currents flowing along the dendrite under applied depolarizing
or hyperpolarizing impulses are known as local currents. If we have depolarizing
impulse there is positive current i+ flowing from the excited area towards the
non-excited regions inside the cytoplasm, while outside of the dendrite the
positive currents flow towards the place of excitation.
4R
Taking into account that ri - 2 we obtain:
πd2
(72)
= ∂V πd2 = πd2
I, - .------- E.-----
a ∂l 4 RA 4 RA
Calculation of the current through the dendrite after applied EPSP with
magnitude of 0.2mV gives us:
(73)
ia
0.57V.m~1 × 3.14 × 10-12m2
4 × 1Ω m
≈ 0.45pA
This result is less than the registered evoked inhibitory postsynaptic currents
(eIPSCs) which amplitude varies from 20pA to 100pA (Kirischuk et al., 1999;
Akaike et al., 2002; Akaike & Moorhouse, 2003).
43
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