compartment.doc.txt
Click here to get the file
Size
6.1 kB
-
File type
text/plain
File contents
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