Voltage and Current Clamp in the Equivalent Cylinder 

In these simulations an equivalent cylinder is attached to a soma and either a voltage clamp or a current clamp is applied at the soma. Alpha synapses are present at both the soma and at the end of the equivalent cylinder. The simulations runs for 8000 ms. The onset of the soma synapse is at 500 ms. and the onset of the “dendritic” synapse is at 4000 ms..

Voltage Clamp

Begin by editing the file “vclamp.hoc” and give the equivalent cylinder a length of 0.25, 0.5,

1.0 or 1.5 lambda. You will need to calculate lambda using the formula-

where Rm = membrane resistance, Ri = axial resistance, d=diameter of cylinder in microns

Start the voltage clamp simulation by typing spike vclamp.hoc -

Three graph windows will appear


This graph shows the voltage in the


This one shows the voltage at the end of

the dendrite


This is the current necessary to maintain

the voltage clamp

Using the right mouse button in each of the graphs choose “Keep Lines”


and run the simulation from the Family function panel


This operation clamps the cell at 7 voltage steps ranging

from -100 to +40 mV.

Compare the results from the four different dendritic lengths.You will need to exit the program, edit vclamp.hoc and then re-run.

What happens when the dendrite gets longer?

Current Clamp

Bring up the current clamp simulation by typing spike iclamp.hoc -

It is run with a Family function panel similar to the voltage clamp except there are 8 current steps ranging from -.08 to 0.2 nA. The graph windows are shown here--


Voltage in the soma

Voltage at the end of the dendrite

The holding current