Inhomogeneous channel distribution

Physical System

Conceptual Model

The conceptual model is a much simplified stylized representation of a pyramidal cell with active soma and axon, passive basilar dendrites, and weakly excitable apical dendrites.

Computational Model

Here is the complete specification of the computational model:

Geometry
Section L
(um)
diam
(um)
Biophysics
soma 20 20 hh
ap[0] 400 2 hh*
ap[1] 300 1 hh*
ap[2] 500 1 hh*
bas 200 3 pas
axon 800 1 hh

*--gnabar_hh, gkbar_hh, and gl_hh in the apical dendrites decrease linearly with path distance from the soma. Density is 100% at the origin of the tree, and falls to 0% at the most distant termination.
To ensure that resting potential is -65 mV throughout the cell, e_pas in the basilar dendrite is -65 mV.
Other parameters: cm = 1 uf/cm2, Ra = 160 ohm cm, nseg governed by d_lambda = 0.1.

The exercise

1. Use the GUI to implement and test a model cell with the anatomical and biophysical properties described above.

2. Pick any anatomically detailed morphology you like, import it into NEURON, and implement a model with biophysical channel densities similar to those described above.

Hints

1. Before doing anything, think about the problem. In particular, determine the formulas that will govern channel densities in the apical tree.

In each apical section, gnabar_hh at any point x in that section will be
    gnabar_hh = gnabar_max * (1 - distance/max_distance)
where
distance = distance from origin of the apical tree to x
and
max_distance = distance from {origin of the apical tree} to {the most remote dendritic termination in the apical tree}.

The formulas for gk_hh and gl_hh are similar.

distance/max_distance is "normalized distance into the apical tree from its origin." So the distance metric p should be 0 at the origin of the apical tree, and 1 at the end of the most remote dendritic termination in the apical tree.

2. Hints for using the CellBuilder to specify an inhomogeneous channel distribution.


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