Branching Dendritic Trees and Motoneuron Membrane Resistivity values. On the basis of the evidence considered here, this range extends approximately from 1000 to 8000 11cm2. The low end of this range corresponds to the possibility that the lowest RN values, around 0.5 megohm, actually represent the true resistance values of large cells with D312 values around 300 t3I2. The high end of this range corresponds to the possibility that the largest RN values, around 2.5 megohms, actually represent

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... true resistance values of small cells with D3!-° values around 180 1.1312; see Fig. 6 . However, if the mid-range of the physiological samples corresponds with the mid-range of the anatomical sample, a value around 4000 to 5000 11cm2 would be indicated for R",. Then the RN value of 1.2 megohms (7) would correspond to a D312 value of about 250 t312 The 1.65megohm value of Frank and Fuortes ( 14 ) was obtained with finer microelectrodes and may have been less weighted for the largest motoneurons; thus, while a 250-li3!2 value for D32 would imply R" 7000 11cm2 for this RN value, a reduction of D32 to 200 li3'2 would imply Rm = 4700 11cm2.