Practice question

Neuronal cytoskeleton requires robust ten nanometer filaments to stabilize long processes subjected to bending and tension during growth and circuitry formation. Neurofilament proteins comprise heteropolymers of NF-L light sixty one kDa, NF-M medium one hundred two kDa and NF-H heavy one hundred twelve kDa subunits, each with conserved central rod domain forming coiled-coil dimers and variable C-terminal tails enriched in Lys-Ser-Pro repeats heavily phosphorylated to extend as sidearms regulating interfilament spacing and axonal diameter, which directly influences conduction velocity. Alpha-internexin and peripherin coassemble in developing and peripheral neurons. Lamin A is nuclear lamina present in differentiated somatic cells, not neuronal process specific; vimentin expressed in progenitors then replaced; actin forms seven nanometer microfilaments mediating growth cone motility. Immunostaining for neurofilaments distinguishes neuronal tumors and marks axonal injury where accumulation forms spheroids. Mutations in NF genes or associated kinases perturb axonal transport and are linked to amyotrophic lateral sclerosis, Charcot-Marie-Tooth and Parkinson pathologies emphasizing functional specialization.