DOCUMENTATION FOR AXOCALC UTILITY

September 15, 1995

AXOCALC is a utility written in Microsoft BASIC (GWBASIC, MBASIC, QuickBASIC, etc) for calculating cable parameters for uniform cylindrical pieces of neuronal processes. I find it very handy because I can never keep the units and the equations accurately in mind, so this saves a lot of book look-ups. When first called, it asks if you want to print (hard-copy) the results (this requires a printer arrangement compatible with the LPRINT statement in BASIC). It then asks for three numbers:

1. Internal resistivity (Rhoi in ohm-cm) (default is 50: squid axoplasm)
2. Membrane resistivity (Rhom in ohm-cm^2)(default is 1000: squid membrane)
3. Diameter of the process (in microns)

It will calculate and display:

• specific membrane resistance (rm for a 1-cm length, megohm-cm)
• specific longitudinal resistance (ri of a 1-cm length, megohms/cm)
• length constant (cm)
• specific capacitance (nF/cm)
• membrane time constant (msec)
• input resistance [conductance] of an infinite cylinder (megohms [micromho])
• input resistance of a sphere of the same diameter (megohms)
• capacitance of a sphere of the same diameter (nF)

After this, a menu will appear allowing various options:

1. Input new Ri
2. Input new Rm
3. Input new diameter
4. Input infolding ratio (initially=1) = capacitance(uF)/ surface (cm^2)
5. Calculate input impedance of a specified segment of cylinder. A termination impedance will be asked for (=0 for shunt to bath; = infinity for a sealed end, coded with a "-1" response).
6. Calculate the attenuation at any specified point along a segment. I.e. starting with a voltage of 1 at the input end, this gives the voltage at any other point in the segment.
7. Calculate the equivalent compartment parameters for a segment of specified length. Included are compartment capacitance, membrane resistance, longitudinal coupling resistance (for the whole segment, not a half-segment) and inter-compartmental time-constant (again whole-segment).
8. Change the units used in specifying length. Choices: lambdas, cm, mm, microns (mu), nF

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