The enlarged motile tip of an elongating axon (nerve fibre) that determines the direction of axon growth. It has numerous finger-like projections, called filopodia (see filopodium), which bear surface receptors. These sense specific signal molecules and other chemical cues in the immediate environment that guide elongation of the axon along its proper pathway so that the neuron connects to its target cell, thereby ensuring correct wiring of the nervous system. Directional growth is achieved by the forward migration of actin filaments inside the filopodia and the elongation of microtubules at the leading edge of the axon.