The geniculate ganglion is a sensory ganglion, which is situated along the course of the facial nerve, inside the bony facial canal within the petrous temporal bone. Its locations is closely related to the site where the greater petrosal nerve branches off from the facial nerve at its genu.
The geniculate ganglion comprises of cell bodies of special visceral afferent neuronal fibers that transmit taste sensations from the anterior two-thirds of the tongue to the nucleus (of tractus solitarius; rostra part) in the brainstem. The ganglion also contains cell bodies of general somatic afferent neurons which transmit general sensations from areas including the pinna of the external ear and its canal, and palate, to the spinal trigeminal nucleus in the brainstem.
In case of reactivation of latent herpes zoster in the geniculate ganglion, the formation of vesicles in the central portion of the auricle, ear canal and the anterior two-thirds of the tongue region, can be explained based on the sensory distribution of neurons in the ganglion.
Please note that the remaining neuronal fibers of facial nerve, such as the special visceral efferent neurons to various muscles and general visceral efferent neurons to salivary glands, traverse through the geniculate ganglion enroute to their target organs, however, they do not synapse inside the ganglion.
The blood supply to the geniculate ganglion arises from branches of middle meningeal artery, explaining the rare instances where a facial nerve injury could result by an embolic infarct within the middle meningeal or the maxillary artery.