Object Type:
hh_channel
Description:
Implements the channel model described in A.L.Hodgkin
and
A.F.Huxley, J.Physiol(Lond) 117, pp 500-544 (1952)
In the Hodgkin-Huxley model, the general form for the
channel conductance is represented as being proportional to
an activation state variable raised to an integer power
times an inactivation state variable raised to another
integer power. The hh_channel object calculates the channel
conductance from the equation
Gk = Gbar*X^Xpower * Y^Ypower
In the usual Hodgkin-Huxley notation for the Na channel, X
corresponds to the activation variable, m, with Xpower = 3,
and Y corresponds to the inactivation variable, h, with
Ypower = 1.
Channel elements which are created from the hh_channel
object calculate both X and Y by solving differential
equations of the form
dX/dt = alpha*(1-X) - beta*X
The voltage-dependent rate variables, alpha and beta, can
each assume one of the three functional forms:
1 (EXPONENTIAL): alpha(v) = A exp((v-V0)/B)
2 (SIGMOID):
alpha(v) = A / (exp((v-V0)/B) + 1)
3 (LINOID):
alpha(v) = A (v-V0) / (exp((v-V0)/B) - 1)
The form to be used and the constants A, B and V0 are
specified for each rate variable by setting fields in the
hh_channel element.
Author:
M. Nelson, Caltech (8/88)
----------------------------------------------------------------------------ELEMENT PARAMETERS
DataStructure:
Size:
Fields:
hh_channel_type
[in src/hh/hh_struct.h]
184 bytes
activation
Gk
Ik
Ek
Gbar
X
Y
Xpower
Ypower
X_alpha_FORM
channel activation
channel conductance
channel current
channel reversal potential
channel maximum conductance
value of X gate (m)
value of Y gate (h)
power to raise X gate to
power to raise Y gate to
Equation form for X gate alpha rate
constant
1 = EXPONENTIAL, 2 = SIGMOID, 3 = LINOID
X_alpha_A
A constant for X gate alpha rate constant
X_alpha_B
X_alpha_V0
B constant for X gate alpha rate constant
V0 constant for X gate alpha rate
X_beta_FORM
Equation form for X gate beta rate
constant
constant
1 = EXPONENTIAL, 2 = SIGMOID, 3 = LINOID
X_beta_A
A constant for X gate beta rate constant
X_beta_B
B constant for X gate beta rate constant
X_beta_V0
V0 constant for X gate beta rate constant
Y_alpha_FORM
Equation form for Y gate alpha rate
constant
1 = EXPONENTIAL, 2 = SIGMOID, 3 = LINOID
Y_alpha_A
A constant for Y gate alpha rate constant
Y_alpha_B
B constant for Y gate alpha rate constant
Y_alpha_V0
V0 constant for Y gate alpha rate
constant
Y_beta_FORM
Equation form for Y gate beta rate
constant
1 = EXPONENTIAL, 2 = SIGMOID, 3 = LINOID
Y_beta_A
A constant for Y gate beta rate constant
Y_beta_B
B constant for Y gate beta rate constant
Y_beta_V0
V0 constant for Y gate beta rate constant
----------------------------------------------------------------------------SIMULATION PARAMETERS
Function:
hh_channel
[in src/hh/channel.c]
Classes:
segment channel
Actions:
INIT
PROCESS
RESET
CHECK
CALC_ALPHA
CALC_BETA
CALC_MINF
Messages:
VOLTAGE Vm
----------------------------------------------------------------------------Notes:
way
The tabchannel object provides a faster and more general
to implement this type of channel.
The CALC_ALPHA, CALC_BETA, and CALC_MINF actions are used
with
calls of the form
y = {call <element> CALC_ALPHA <gate> <x-value>}
in order to access values of alpha, beta or m_inf (the
steady
state activation, alpha/(alpha + beta)) for the specified gate
(X or Y) and a particular value of the independent variable.
This feature is most often used for making plots of these
quantities. Note that the activation time constant can be
calculated from tau = 1/(alpha + beta).
Example:
Scripts/neurokit/prototypes/hhchan.g
See also:
tabchannel, vdep_channel