Nerve fibre: an elongated projection of a nerve cell or NEURON(E) that carries an electrical impulse to the tissue at the end of the axon. Large axons are covered by a sheath of insulating myelin which is interrupted at intervals by nodes of Lanvier, where other axons branch out. An axon may be more than a metre long. It ends by branching into several filaments called telodendria, and these are in contact with muscle or gland membranes and other nerves (see NERVE).