>>11688398they remain separate nerves but form one bundle that takes a similar path up to the spine. The cortex (outer layer of the brain where all the good stuff happens) is organized in a way that corresponds to the spatial location on your body, it's called somatotopy. It's similar to how the retina and visual cortex are organized, where specific parts of the retina project to specific parts in the visual cortex, such that a spatial map of the visual field is represented in the brain (retinotopy).
