+-90 seems like allot of range of motion. A spine in a vertebrate would not rotate that much for each bone. In a neuron I don't know but it would probably be more pleasing to the eye not to allow the tendril to bend at a right angle at any one location and allow a smoother silhoutte but whateve the director wants.
On thing you can do is to bias which way the direction of bend is occuring by setting one direction to say +45 and the other to -90. It would then favor movement in the larger range of motion axis.
So you can scrub the timeline and it looks one way when you render just a frame and the batch render renders something else? Now that's just plain odd, no really good answer for that one.
I'll wip up a similar neuron thing and post it.