# Example: spike_initiation

> Note

> You can launch an interactive, editable version of this example without installing any local files using the Binder service (although note that at some times this may be slow or fail to open):

Ball and stick with Na and K channels

    from brian2 import *

    defaultclock.dt = 0.025*ms

    # Morphology
    morpho = Soma(30*um)
    morpho.axon = Cylinder(diameter=1*um, length=300*um, n=100)

    # Channels
    gL = 1e-4*siemens/cm**2
    EL = -70*mV
    ENa = 50*mV
    ka = 6*mV
    ki = 6*mV
    va = -30*mV
    vi = -50*mV
    EK = -90*mV
    vk = -20*mV
    kk = 8*mV
    eqs = '''
    Im = gL*(EL-v)+gNa*m*h*(ENa-v)+gK*n*(EK-v) : amp/meter**2
    dm/dt = (minf-m)/(0.3*ms) : 1 # simplified Na channel
    dh/dt = (hinf-h)/(3*ms) : 1 # inactivation
    dn/dt = (ninf-n)/(5*ms) : 1 # K+
    minf = 1/(1+exp((va-v)/ka)) : 1
    hinf = 1/(1+exp((v-vi)/ki)) : 1
    ninf = 1/(1+exp((vk-v)/kk)) : 1
    I : amp (point current)
    gNa : siemens/meter**2
    gK : siemens/meter**2
    '''

    neuron = SpatialNeuron(morphology=morpho, model=eqs,
                           Cm=1*uF/cm**2, Ri=100*ohm*cm, method='exponential_euler')
    neuron.v = -65*mV
    neuron.I = 0*amp
    neuron.axon[30*um:60*um].gNa = 700*gL
    neuron.axon[30*um:60*um].gK = 700*gL

    # Monitors
    mon=StateMonitor(neuron, 'v', record=True)

    run(1*ms)
    neuron.main.I = 0.15*nA
    run(50*ms)
    neuron.I = 0*amp
    run(95*ms, report='text')

    plot(mon.t/ms, mon.v[0]/mV, 'r')
    plot(mon.t/ms, mon.v[20]/mV, 'g')
    plot(mon.t/ms, mon.v[40]/mV, 'b')
    plot(mon.t/ms, mon.v[60]/mV, 'k')
    plot(mon.t/ms, mon.v[80]/mV, 'y')
    xlabel('Time (ms)')
    ylabel('v (mV)')
    show()