In this paper, we present a novel method for 3D segmentation of the nerve channels in the human mandible that contain the nervus alveolaris inferior. The technique utilizes geodesic active surfaces that are implemented with level sets. The method consists of two steps: (i) After defining two points, which denote the entry and exit of the nerve channel, a connecting path of minimal action inside the channel is calculated. This calculation is driven by the gray values in proximity to the two defined points inside the channel, (ii) Using this path as an initial configuration, an active surface evolves until the inner borders of the channel are reached. Since this initial configuration is located very close to the borders of the channel, a propagation term is not necessary in this model.