(A–C) illustrate a BFP experiment (the full recording is in the video Figure 8–source data 1) . (A) The bead is slightly pushed against the axon (with deflection angle ), negative deformation (compression) of the RBC is recorded. (B,C) Different stages of the probe exerting a pulling force on the axon; the RBC undergoes positive deformation (extension), the axon deflection angle . Index of corresponds to the numbering of plateaux in panel D and data points in panel E. The tracked point on pipette and the tracked bead are marked by blue and red circles. (D) Time dependence of the force measured on the probe (evaluated for each frame at 65 fps), and the angle (evaluated each second). The deflection angle corresponds to deflection by pushing, means deflection by pulling. The deflection angle determines the lateral projection of axial tension acting at the apex, that is lateral tensile force . (E) Blue data points represent time-averaged qualities of individual plateaux (labelled by appropriate numbers), abscissa corresponds to average deformation and ordinate to average perpendicular probe force . The error bars represent a standard deviation of the quantities during each plateau. The red line is a linear fit of BFP data points, i.e. vs. , the slope corresponds to axon tension . Goodness of the fit is =0.97. (F) Distribution of axon tensions, calculated as a normalized sum of linear fit results from all BFP experiments—each fit was represented by a Normal distribution, with mean at given by the fit slope, and standard deviation , given by the standard deviation of the fit. The tension mode value is 678 pN, mean 679 pN (designated by the dashed red line), interquartile range (529–833) pN (delimited by the red box). The distribution of tension in based on =7 measurements, containing at least three force plateaux each, originating from four distinct cultures (each obtained from a different mother animal). The time course of force and angle (D), plateaux points and the fit (E), mean values of tension of all experiments and the distribution values (F) are available in the Figure 8—source data 2.