Figure 1.

Neurons are fluids that generate strong contractile forces in the growth cone. (A) Phase image of a chick sensory neuron attached to a force-calibrated glass towing needle. (B) Plot of the external force over time. (C) The distribution of mitochondria labeled with MitoTracker (Life Technologies). (D) A color-inverted kymograph of mitochondrial position over 12 min. (E) The kymograph from (D) was duplicated, with docked mitochondria (blue arrows) and fast transported mitochondria (red arrows). (Black arrow, 5 min; bar, 10 μm.) (F) The velocity distribution for all of the mitochondria. This graph spans the range between 15,000 and −15,000 μm/h; each bin is 500 μm/h wide and the tall bin in the center spans the range from 250 to −250 μm/h. (G) The velocity distribution of docked mitochondria. This graph spans the range between 300 and −300 μm/h, with each bin covering a 10 μm/h velocity range and the central bin spanning 5 to −5 μm/h. (H) Docked mitochondria move forward with a velocity profile that increases along the axon. (Red arrow) Boundary between the axon and growth cone; error bars are 95% CI. (I) Cartoon of a neuron showing the boundary between the axon and growth cone; adapted with permission from Suter and Miller (8). To see this figure in color, go online.