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..
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
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?
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