How to generate spike for infinite time

I am trying to generate spikes using below code. On running this code, the spikes are generated for the range: tspan = 0:tau:100; Could you suggest me the updates needed so that the spikes get generated (graph continue plotting) for infinite time.

Parameters = [0.02 0.2 -65 6]; V=-70; u=Parameters(2)*V; Vrest = -65; VV=[]; uu=[]; tau = 0.25; tspan = 0:tau:100; T1=tspan(end)/10; % param = [alpha beta ephsilon tauH nH] % Detail param = [75000 950 16 0.021 0.2]; %Tonic Spike

for t=tspan if (t>T1) I=14; else I=0; end; V = V + tau*(param(1)*(cosh( ( V-Vrest)/param(2))-1)-param(3)-u+I); u = u + tau*param(4)*(param(5)*V-u); if V > 30 VV(end+1)=30; V = Parameters(3); u = u + Parameters(4); else VV(end+1)=V; end; uu(end+1)=u; end; plot(tspan,VV,[0 T1 T1 max(tspan)],-90+[0 0 10 10]); axis([0 max(tspan) -90 40]) xlabel('Time');ylabel('Membrane Potential'); title('SPIKES');