Neurofilaments (NFs) – the major cytoskeletal constituent of myelinated axons in vertebrates – consist of three molecular-weight subunit proteins NF-L (low), NF-M (medium), and NF-H (high), assembled to form mature filaments with protruding unstructured C-terminus sidearms. Liquid crystal gel networks of sidearm-mediated NF assemblies play a key role in the mechanical stability of neuronal processes. Disruptions of the NF-network, due to NF over-accumulation or incorrect sidearm interactions, is a hallmark of motor neuron diseases including amyotrophic lateral sclerosis. In this talk I will present our recent tapping mode atomic force microscopy study on single NFs. We traced, in sub-pixel resolution, photo-immobilized NFs and measured their persistence length at various monovalent salt conditions and at various subunit protein ratios thereby modifying sidearm length and chain density charge distribution. I will show that specific polyampholyte sequences of the sidearms can form salt switchable intra-filament attractions that compete with the net electrostatic and steric repulsion, and can reduce the total persistence length by half. The results are in agreement with present x-ray and microscopy data, yet present a theoretical challenge for polyampholyte inter-chain interactions.