TITLE nax
: Na current for axon. No slow inact.
: M.Migliore Jul. 1997
: added sh to account for higher threshold M.Migliore, Apr.2002
NEURON {
SUFFIX nax
USEION na READ ena WRITE ina
RANGE gbar, sh, ina
GLOBAL minf, hinf, mtau, htau,thinf, qinf
}
PARAMETER {
sh = 5 (mV)
gbar = 0.010 (mho/cm2)
tha = 30 (mV) : v 1/2 for act
qa = 7.2 (mV) : act slope (4.5)
Ra = 0.4 (/ms) : open (v)
Rb = 0.124 (/ms) : close (v)
thi1 = 45 (mV) : v 1/2 for inact
thi2 = 45 (mV) : v 1/2 for inact
qd = 1.5 (mV) : inact tau slope
qg = 1.5 (mV)
mmin=0.02
hmin=0.5
q10=2
Rg = 0.01 (/ms) : inact recov (v)
Rd = .03 (/ms) : inact (v)
thinf = 50 (mV) : inact inf slope
qinf = 4 (mV) : inact inf slope
ena (mV) : must be explicitly def. in hoc
celsius
v (mV)
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(pS) = (picosiemens)
(um) = (micron)
}
ASSIGNED {
ina (mA/cm2)
thegna (mho/cm2)
minf hinf
mtau (ms) htau (ms)
}
STATE { m h}
BREAKPOINT {
SOLVE states METHOD cnexp
thegna = gbar*m*m*m*h
ina = thegna * (v  ena)
}
INITIAL {
trates(v,sh)
m=minf
h=hinf
}
DERIVATIVE states {
trates(v,sh)
m' = (minfm)/mtau
h' = (hinfh)/htau
}
PROCEDURE trates(vm,sh2) {
LOCAL a, b, qt
qt=q10^((celsius24)/10)
a = trap0(vm,tha+sh2,Ra,qa)
b = trap0(vm,thash2,Rb,qa)
mtau = 1/(a+b)/qt
if (mtau<mmin) {mtau=mmin}
minf = a/(a+b)
a = trap0(vm,thi1+sh2,Rd,qd)
b = trap0(vm,thi2sh2,Rg,qg)
htau = 1/(a+b)/qt
if (htau<hmin) {htau=hmin}
hinf = 1/(1+exp((vmthinfsh2)/qinf))
}
FUNCTION trap0(v,th,a,q) {
if (fabs(vth) > 1e6) {
trap0 = a * (v  th) / (1  exp((v  th)/q))
} else {
trap0 = a * q
}
}
