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Interactive Modeling

Physical System

Giant axon from the squid: Loligo pealei

Conceptual Model

Hodgkin-Huxley cable equations

img/hh.gif

Simulation

Computational implementation of the conceptual model

We could implement this model in Python:

from neuron import h, gui

axon = h.Section(name='axon')
axon.L = 2e4
axon.diam = 100
axon.nseg = 43
axon.insert(h.hh)

But for this exercise, let's instead use the CellBuilder tool to create the model:

img/cbgeom.gif

img/cbbio.gif

Save the model in hhaxon.ses using :menuselection:`NEURONMainMenu --> File --> savesession`

Using the computational model

If starting from a fresh launch of python, you can load the saved ses file by loading NEURON and its GUI: from neuron import h. gui and then selecting :menuselection:`NEURONMainMenu --> File --> loadsession`

Alternatively you can use NEURON to execute hhaxon.ses

  1. Change to the appropriate directory in your terminal
  2. Start python, and at the >>> prompt enter the commands
from neuron import h, gui
h.load_file('hhaxon.ses')

Exercises

  1. Stimulate with current pulse and see a propagated action potential.

    The basic tools you'll need from the :ref:`NEURON Main Menu <NEURONMainMenu>`

    :menuselection:`Tools --> Point Processes --> Manager -->` :ref:`Point Manager <pointman>` to specify stimulation

    :menuselection:`Graph -->` :ref:`Voltage axis <voltage_axis>` and :menuselection:`Graph -->` :ref:`Shape plot <shape_plot>` to create graphs of v vs t and v vs x.

    :menuselection:`Tools -->` :ref:`RunControl <runctrl>` to run the simulation

    :menuselection:`Tools --> Movie Run` to see a smooth evolution of the space plot in time

  2. Change excitability by adjusting sodium channel density.

    Tool needed: :menuselection:`Tools --> Distributed Mechanisms --> Viewers -->` :ref:`Shape Name <shapename>`

  3. Use two current electrodes to stimulate both ends at the same time

  4. Up to this point, the model has used a very fine spatial grid calculated from the Cell Builder's d_lambda rule

    img/geometry.gif

    Change nseg to 15 and see what happens