[Neuroscience] Re: action potential at the beginning of hodgkin huxley simulation

[Gangadhar]

i too faced this kind on situation when i was trying to code HH model.

the probable typos are :
1)in writing functions of alpha , beta of m,n,h.
2)interpretaion of parameter's  units.


Any way i am giving my code u go thru it. Mail me if you find
difficulties.


% author  Gangadhar.G , Computational Neuroscience Laboratory
% Indian Institute of Technology - Madras.
% email : ganges.g at gmail.com or ganges_g at yahoo.co.in
% date : 20 Nov 2005

clc;clear;

Iext = 0.1; % external current



cm = 0.01;  % membrane capacitance
dt = 0.05;  % time step

ENa = 55.17;
EK = -72.14;
El =-49.42;

gNamax = 1.2;   %max conductances
gKmax = 0.36;
glmax = 0.003;

niter = 6000;  % max number of iterations

% Intial conditions
vm(1) = -60;    % intial membrane voltage
V(1) = vm;

% calculating alphas abd betas for the intial membrane voltage
alpn = 0.01*(vm+50)/(1-exp(-(vm+50)/10));
alpm = 0.1*(vm+35)/(1-exp(-(vm+35)/10));
alph = 0.07*exp(-0.05*(vm+60));

betn = 0.125*exp(-(vm+60)/80);
betm = 4*exp(-0.0556*(vm+60));
beth = 1/(1+exp(-0.1*(vm+30)));

% intial m,n & h
n = alpn/(alpn+betn);
m = alpm/(alpm+betm);
h = alph/(alph+beth);

%  the loop for calculation of membrane voltage dynamics is here.
for i = 1:niter,

    dm = dt*(alpm*(1-m)-betm*m);
    dn = dt*(alpn*(1-n)-betn*n);
    dh = dt*(alph*(1-h)-beth*h);

    m = m + dm;
    n = n + dn;
    h = h + dh;


    gNa = gNamax*m^3*h;
    gK  = gKmax*n^4;
    gl  = glmax;


    INa = gNa*(vm-ENa);
    IK = gK*(vm-EK);
    Il = gl*(vm-El);

    dvm = (dt/cm)*(Iext-( INa + IK + Il));

    vm = vm + dvm;
    V(i+1) = vm;

    alpn = 0.01*(vm+50)/(1-exp(-(vm+50)/10));
    alpm = 0.1*(vm+35)/(1-exp(-(vm+35)/10));
    alph = 0.07*exp(-0.05*(vm+60));
    betn = 0.125*exp(-(vm+60)/80);
    betm = 4*exp(-0.0556*(vm+60));
    beth = 1/(1+exp(-0.1*(vm+30)));


end
tim = dt*(1:niter+1);
plot(tim,V);
xlabel('time in ms');
ylabel('v_m mv');

---------------------------------

regards
Ganges.