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UNITS {
        (mA) = (milliamp)
        (mV) = (millivolt)
}
 
NEURON {
        POINT_PROCESS HHok
        USEION na READ ena WRITE ina
        USEION k READ ek WRITE ik
        NONSPECIFIC_CURRENT il
        RANGE gnabar,gkbar,gl,el,m_inf,h_inf,n_inf,tau_m,tau_n,tau_h,ina,ik ,g_m,g_h,g_n
GLOBAL Nna, NK
}
 
PARAMETER {
        v (mV)
        celsius = 6.3 (degC)
        dt (ms)
        gnabar =120
        ena = 50 (mV)
        gkbar = 36 
        ek = -77 (mV)
        gl = .3 (mho/cm2)
        el = -54.4 (mV)
area=100
Nna
NK

}
 
STATE {
        m h n
}
 
ASSIGNED {
        ina	(mA/cm2)
        ik	(mA/cm2)
        il	(mA/cm2)
        m_inf h_inf n_inf tau_m tau_h tau_n
	tadj
g_m g_n g_h p_m p_n p_h
}
 
BREAKPOINT {
        SOLVE states
        ina = gnabar * m*m*m*h * (v - ena)
        ik = gkbar * n*n*n*n * (v - ek)      
        il = gl * (v-el)
}
 :PROCEDURE states() { 
  :      rates(v)   
   :     m = m + (1-exp(-dt/tau_m)) * (m_inf-m)+g_m

    :    h = h + (1-exp(-dt/tau_h)) * (h_inf-h)+g_h

     :   n = n + (1-exp(-dt/tau_n)) * (n_inf-n)+g_n

:}
DERIVATIVE states { : exact Hodgkin-Huxley equations 
rates(v)
 m' = (m_inf - m) / tau_m +g_m
h' = (h_inf - h) / tau_h +g_h
n' = (n_inf - n) / tau_n +g_n
}

UNITSOFF
INITIAL {
Nna=60*area
NK=18*area
	tadj = 3.0^((celsius-23.5)/10)
	rates(v)
	m = m_inf
	h = h_inf
	n = n_inf
}


 
PROCEDURE rates(v) { LOCAL alpha, beta, q10, tinc
        TABLE m_inf, tau_m, h_inf, tau_h, n_inf, tau_n, p_m,p_h,p_n,g_m,g_h,g_n DEPEND dt, 
	      celsius FROM -100 TO 100 WITH 200
	:"m" sodium activation system
          alpha = .091 * vtrap(v+38,5)
          beta =  .062 * vtrap(-(v+38),5) 
		p_m=2/Nna*alpha*beta/(alpha+beta)
		g_m=sqrt(p_m)*normrand(-1,1)
       	  tau_m = 1 / (alpha+beta) / tadj
       	  m_inf = alpha/(alpha+beta)
	:"h" sodium inactivation system
       	  alpha = .016 * exp(-(v+55)/15)
       	  beta = 2.07 / (1+exp((17-v)/21))
		p_h=2/Nna*alpha*beta/(alpha+beta)
		g_h=sqrt(p_h)*normrand(-1,1)       	  
			tau_h = 1 / (alpha+beta) / tadj
       	 	h_inf = alpha/(alpha+beta)

	:"n" potassium activation system
       	  alpha = .01*vtrap(v+45,5) 
       	  beta = .17*exp(-(v+50)/40)
			p_n=2/NK*alpha*beta/(alpha+beta)
			g_n=sqrt(p_n)*normrand(-1,1)

       	  tau_n = 1 / (alpha+beta) / tadj
       	  n_inf = alpha/(alpha+beta)
}
 
FUNCTION vtrap( x, b) {
	: Traps for 0 in denominator of rate equations
	if (fabs(x/b) < 1e-6) {
	  vtrap = b+x/2 }
	else {
	  vtrap = x / (1-exp(-x/b)) }
}
UNITSON