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nervus_intermedius

Nervus intermedius

The intermediate nerve, nervus intermedius or nerve of Wrisberg, is the part of the facial nerve (cranial nerve VII) located between the motor component of the facial nerve and the vestibulocochlear nerve (cranial nerve VIII). It contains the sensory and parasympathetic fibers of the facial nerve. Upon reaching the facial canal, it joins with the motor root of the facial nerve at the geniculate ganglion.

The superior salivatory nucleus contains the cell bodies of parasympathetic axons within the intermediate nerve. These fibers reach the geniculate ganglion but do not synapse. Some of these preganglionic parasympathetic fibers persist within the greater petrosal nerve as they exit the geniculate ganglion and subsequently synapse with neurons in the pterygopalatine ganglion. These postganglionic neurons send axons that provide parasympathetic innervation to the lacrimal gland.

The remaining preganglionic fibers continue as the mixed facial nerve proper as it extends through the facial canal. Before the nerve exits the skull via the stylomastoid foramen and after the nerve to the stapedius muscle has branched off, the facial nerve gives off the chorda tympani nerve. This nerve exits the skull through the Petrotympanic fissure and merges with the lingual nerve, after which it synapses with neurons in the submandibular ganglion. These postganglionic neurons provide parasympathetic innervation to the submandibular and sublingual glands.

The sensory component of the intermediate nerve carries input about sensation from the skin of the external auditory meatus, from the mucous membranes of the nasopharynx and nose, and taste from the anterior two-thirds of the tongue, floor of the mouth, and the palate. The sensory information from the mucous membranes of the nasopharynx and palate is carried along the greater petrosal nerve, while the chorda tympani nerve (and lingual nerve) carries taste input from the anterior two-thirds of the tongue, floor of mouth, and palate.

The geniculate ganglion contains the cell bodies of the sensory component of the nervus intermedius.

Pathology

Variants

The following variants were seen: 1.) the intermediary nerve lies between the facial and vestibulocochlear nerves as stated in the textbooks, in 32.9% of the cases; 2.) in 18.5% of the cases it is entirely apposited to the vestibulocochlear nerve from the beginning and branches off from that nerve only later; 3.) part of the nerve root fasciculi are apposited to the vestibulocochlear nerve and the others originate between the facial and vestibulocochlear nerves. This was seen in 49.6% of the cases 1).

Reviews

Since 1968, only approximately 50 peer-reviewed reports have been published regarding the nervus intermedius. Most of these are single-case reports and in reference to geniculate neuralgia. No report was a review of the literature 2).

1)
Tschabitscher M, Höcker K. [The intermediary nerve at its entry and exist site in the brain stem]. Neurochirurgia (Stuttg). 1991 May;34(3):73-5. German. PubMed PMID: 1886647.
2)
Tubbs RS, Steck DT, Mortazavi MM, Cohen-Gadol AA. The nervus intermedius: a review of its anatomy, function, pathology, and role in neurosurgery. World Neurosurg. 2013 May-Jun;79(5-6):763-7. doi: 10.1016/j.wneu.2012.03.023. Epub 2012 Apr 3. Review. PubMed PMID: 22484073.
nervus_intermedius.txt · Last modified: 2018/01/12 13:07 by administrador