The Motor End Plate

The Motor End Plate is a fast direct chemical synapse. This means a neurotransmitter (in this case ACh) opens cation-selective channels, allowing ions to flow down their electrochemical gradients.

The applet shows the current of sodium and potassium ions after ACh is emitted.
The current depends on the Reversalpotential V_r.
Vr can be calculated as follows:

V_r = dg_Na * E_Na + dg_K E_K / (dg_Na + dg_K)

The ratio of the sodium to potassium chances, dgNa / dgK is about 1.3.
The default value for V_r is set to -15mV but can be changed.

We assumed the current to be dependend on the concentration of ACh.
As two ACh molecules are neccesary to open one ACh channel the formula used to represent the number of open channels is:

Percentage of open Gates = c[ACh]² / (c[ACh]² + 500²)

(this means a concentration of 500 nMol opens 50% of the ACh channels.)

The percentage is also shown in the applet.

The third parameter is the Membranepotential in mV.

The function used to fit the current is:

(Membranepotential - Reversalpotential) * (Percentage of open Gates) * t^c[ACh] / ((1+ t^c[ACh])* e^(x*t1) )

where t is the time on the x-Axis, one tick equals about 1ms
t1 is the characterisitc time for the inhibition (the closing of the channels after the ACh emission)

the current on the y-Axis is about 200 nA per tick

To the Applet