Corpus: Geniculate ganglion
from ancient Greek: γάγγλιον ("gágglion") - lump, tumour and Latin: genus - knee
Synonym: ganglion geniculi, external facial nerve ganglion, geniculum nervi facialis
1. Definition
The geniculate ganglion is a small, sickle-shaped collection of nerve fibres and cells in the facial canal of the skull.
2. Topography
The geniculate ganglion is situated in the petrous part of the temporal bone, where the facial nerve makes a distinct curve.
3. Fibres
The geniculate ganglion contains motor, sensory, and parasympathetic fibers. The nerve cells in the ganglion are pseudounipolar neurons.
3.1. Motor fibers
The motor fibers enter the ganglion with the facial nerve and pass it without synapsing. They simply continue along their path.
3.2. Sensory fibers
The sensory fibers to the tongue originate from pseudounipolar neurons within the ganglion. The central processes of these fibers terminate in the solitary tract of the medulla oblongata, while the peripheral processes travel with the chorda tympani to the tongue, providing sensory information to its anterior two-thirds.
The sensory fibers to the skin also originate from pseudounipolar neurons within the ganglion. These fibers initially continue with the facial nerve and then branch off with the posterior auricular nerve after the stylomastoid foramen. They provide sensation to a small area of the skin on the auricle.
3.3. Parasympathetic fibres
The parasympathetic fibers in the geniculate ganglion are preganglionic fibers that originate from the superior salivatory nucleus. They are carried to the ganglion via the intermediate nerve and pass through without synapsing.
The first group of these fibers exits the front side of the geniculate ganglion as the greater petrosal nerve. This nerve travels to the pterygopalatine ganglion, where it synapses and then innervates the lacrimal gland as well as the palatal and nasal mucosa.
The second group of parasympathetic fibers continues with the facial nerve and then branches off with the chorda tympani. These fibers travel to the submandibular ganglion, where they synapse and then innervate the submandibular and sublingual glands.