Object Type: compartment Description: Axially asymmetric compartment. Ra is located on one side of the compartment. This is slightly more computationally efficient than the symmetric counterpart. Author: M. Wilson, Caltech (6/88) ------------------------------------------------------------------------------ ELEMENT PARAMETERS DataStructure: compartment_type [in src/segment/seg_struct.h] Size: 124 bytes Fields: Rm total membrane resistance Cm total membrane capacitance Em membrane resting potential Ra axial resistance inject injected current in membrane dia compartment diameter len compartment length Vm voltage across the membrane previous_state Vm at previous time step Im approximation to the total membrane current initVm initial value to set Vm on reset ------------------------------------------------------------------------------ SIMULATION PARAMETERS Function: Compartment [in src/segment/compartment.c] Classes: segment membrane Actions: INIT assign previous_state = Vm PROCESS update Vm, calculate Im RESET assign Vm = Em CHECK make sure Rm>0, Cm>0, Ra'>0 (if RAXIAL message is present), Ra>0 (if AXIAL message is present) SAVE2 RESTORE2 Messages: CHANNEL Gk Ek delivers the conductance and equilibrium potential of channel within the compartment RAXIAL Ra Vm delivers the Ra and Vm of a compartment AXIAL Vm delivers the Vm of a compartment INJECT inject sets the inject field to the message value EREST Em sets the Em field to the message value ------------------------------------------------------------------------------ Notes: Simulates a section of passive membrane or cable. The potential across the membrane is given by Vm. There is a leakage path for current through the resistance Rm. This resistance is in series with a leakage battery Em. This compartment can be coupled to other compartments with an axial resistance Ra. The compartment is not symmetrical, with Ra lumped to one side of the compartment. Any number of ionic channels can be introduced into the membrane (Gk, Ek in the circuit diagram). The membrane also allows current injection. The compartment Im is the sum of axial currents and injected current only. The (transmembrane) channel currents or the leakage current are not included. For a multicompartment cell, under a quasistatic approximation (C*dV/dt is small), Im is approximately equal to the sum of the channel and leakage currents, due to charge conservation. This approximation is used in the efield object (see efield.doc) to allow Im to be used to calculate external field potentials. The exception to this is when Im is calculated with hsolve in chanmode 4. In that case, Im is directly calculated as the sum of the channel currents and leakage current though Rm. When a compartment performs its RESET action (usually invoked by the reset command), Vm is set to the value of the initVm field. Normally, initVm follows any changes to Em, so Vm will be initialized to Em upon reset. If, as in the Hodgkin-Huxley model, Em is a leakage potential that is different from the rest potential, initVm may be set to the rest potential. It will then no longer follow Em, and Vm will be set to the rest potential upon reset. Calculates Vm using: dVm/dt = {(Em - Vm)/Rm + SUM[(Ek - Vm)*Gk] + (Vm' - Vm)/Ra' + (Vm'' - Vm)/Ra + inject}/Cm In the diagram, the compartment shown in the middle receives the Vm' and Ra' of the upper compartment with an RAXIAL message, and the Vm'' of the lower compartment with an AXIAL message. Channels deliver their Gk and Ek with a CHANNEL message. Vm' o_________________________________________________ | | | | | \ / Ra' \ | | | Vm o_________________________________________________ | | | | | \ | | | | / Ra \ \ | | \ --/--> / | ___|___ | Gk \ Rm \ / \ _______ Cm | | | / A \ | | | | \ | / | | Ek --- Em --- \ / | | ------- ------- | Iinject| | | | | | | |_____________|________|________| | | Vm'' o_________________________________________________ | | | | | Example: See also: symcompartment