The ansa cervicalis and superior cervical ganglion contribute to the fiber composition of the human hypoglossal nerve and its branches

The hypoglossal nerve is considered a pure motor nerve. Yet, there are indications that it contains sensory and sympathetic fibers in the periphery. We analyzed changes in the fiber composition along the human hypoglossal nerve, delineating the pathways through which non-motor fibers enter this nerve and describing the direction in which these fibers extend. Five key positions along the nerve were selected for fiber analyses. Position 1 was intracranial. Positions 2-5 were extracranial and in relation to the C1 component of the ansa cervicalis, which is attached to the hypoglossal nerve. Nerve samples were subjected to multicolor immunofluorescence and quantitative analyses. Intracranially, all axons of the hypoglossal nerve were motor. The extracranial portion of the hypoglossal nerve has a mixed fibers composition of motor, sensory, and sympathetic fibers. The number of all types of fibers increased, reaching a maximum after the C1 component of the ansa branched off from the hypoglossal nerve. At this position, the proportion of motor fibers, sensory fibers, and sympathetic fibers was 63: 11: 26. Our findings suggest that sensory and sympathetic fibers enter the hypoglossal nerve via the ansa cervicalis. Most fibers extend in a distal direction, reaching the tongue, while a smaller number extend in a proximal direction, most likely to become integrated in the meningeal branch of the hypoglossal nerve.