Download connor2 - Chris Elliott

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# $Contents: Simple Connor 2-cell Model
Settings
Synaptic potentials
Stimulus current
Synaptic strength
Menus
Text or picture?
Commands
Neurobiology
Explanation
Reference
Copyright
This program and its help files are copyright by Chris Elliott, University of York, January 1999.
Bugs should be sent to [email protected]
The latest copy is available at http://www.york.ac.uk/~cje2/connor2
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IDH_CONTENTS
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Contents; Copyright; Reporting Bugs; Updates - obtaining; Current version
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Simple Connor 2-cell Model
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#$KSynaptic Potentials
In this model, three common kinds of synapses are provided. A cell will usually increase its permeability
to either Na+ or K+ or Cl- ions, irrespective of the transmitter used. The kind of synaptic interaction
desired can be selected by clicking the appropriate radio button.
Na+ (sodium) synapses will have a reversal potential of about 0mV as they also usually allow K+ ions to
enter. K+ (potassium) synapses will reverse at -72mV and Cl- (chloride) synapses about -50mV.
The time constant of the synapse is fixed and does not depend on the synaptic type selected.
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IDH_SYNAPSE
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Synaptic Potentials
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Synapses; Cell interactions; Reversal potentials
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#$KStimulus current
The stimulus current can be adjusted from -20 to +50 µA/cm²
controls.
for each cell
independently by using the slider
In the Connor model, a stimulus current of about 8.2 µA/cm² is needed to elicit any action potentials. In
the Hodgkin-Huxley (HH) model, it requires about –10 µA/cm² to prevent any action potentials.
The difference is due to the large steady-IA current.
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IDH_STIM
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Stimulus current
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Stimulus; Current; Threshold current
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#$KSynaptic strength
This can be varied for each cell independently by adjusting the slider. Stronger synapses arise from
moving the slider to the right.
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IDH_STRENGTH
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Synaptic strength
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Synapses; Stronger connections; Weaker connections
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#$KText or Picture
The results of the simulation can be displayed either as a picture (the default) or as text. The text values
can be copied to other windows applications (e.g. Excel) or saved in a plain text file (e.g. data.txt).
The mode can be changed from Picture to Text using the Edit | Show Hide values as text menu
command.
In Picture mode the picture may be printed using File | Print
In Text mode the data may be saved or copied to the windows clipboard. Note that, in this simulation,
running the simulation automatically replaces the picture and data in the text window without asking
for confirmation even if the data is unsaved.
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IDH_PICTURE
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Picture or Text
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Text, Picture; Edit | Copy: File | Save Text
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#$KCommands
Menus
In the File menu, you can run a new simulation, (shortcut key F9), or Print the picture. If the text window
is showing, you can save the data into a text file.
In the Edit menu, you can show the data in text format and copy it to the windows clipboard.
The Settings menu item allows you to invoke a dialog box to change the stimulus current and synaptic
output of each cell type independently.
The Help menu allows access to this file and to the copyright notice in the About Box.
Speed Buttons
This button starts a new simulation run
This button opens the settings dialog
Short Cut Keys
F9 starts a new simulation run
F3 opens the settings dialog
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IDH_MENU
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Picture or Text
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Text, Picture; Edit | Copy: File | Save Text
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#$KExplanation of the model
The model is derived from Connor’s
simulation of the crab axon. Three kinds of ionic currents flow
across the neuronal membrane: INa IK and IA. The first two are the same currents as in the
Hodgkin-Huxley equations, but IA is the transient potassium current. This is activated quickly when a cell
is depolarized (made less negative). The presence of IA allows a greater range of firing frequencies and
ensures that all action potentials look very similar. You can explore the model by turning on and off the
IA current in the tabbed dialog by clicking between HH and Connor radio buttons.
The A-current dominates over a voltage range from –70 to –45 mV, so that any input (either synaptic or
stimulus current has to overcome this “hump” in order to activate the neuron. the graph below shows
the steady state levels of the A-current as well as I Na, I K and the leak current.
The synaptic interactions are modeled quite unphysiologically: the release of the transmitter is
determined by the voltage of the presynaptic cell, as no calcium component is present in the model. The
relation between the voltage and the transmitter release used is sigmoid, as shown in the picture below.
The removal of the transmitter from the synaptic cleft is modelled by simple exponential decay.
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IDH_EXPLAIN
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Model & Ionic currents
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Ionic currents; Transmitter release; Model
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#$KReference
Connor, JA; Walter, D; McKown, R: (1977) Neural repetitive firing: modifications of the Hodgkin-Huxley
axon suggested by experimental results from crustacean axons. Biophys-J. 18(1): 81-102
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IDH_REF
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Connor, Reference
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Connor; Reference; Biophys J