Myelin and the Schwann cell

Nerve fibres run fast because Schwann cells wrap them in myelin, and that wrap is built from methylated proteins and fats. Japanese work showed methylcobalamin pushing Schwann cells to mature and to lay myelin back down after a nerve was stripped, and restoring movement and sensation in the process. Nerve-sheath repair is slow work measured in weeks and months, which is why nerve symptoms are the last to improve and the ones that need the longest run.