Terminal nerve

Terminal nerve
Left The terminal nerve as it is shown on the ventral side of a dog-fish brain. (Topmost label)
Details
Identifiers
Latinnervus terminalis
TA98A14.2.01.002
TA26179
FMA76749
Anatomical terminology
Cranial nerves

The terminal nerve, also known as cranial nerve zero or simply as CN 0, is a nerve that was not included in the seminal classification of the cranial nerves as CN I through CN XII, but has since been recognized and listed in TA2.[1] It was discovered by German scientist Gustav Fritsch in 1878 in the brains of sharks, and was first found in humans in 1913.[2] Studies have confirmed that the terminal nerve is a common finding in the adult human brain.[3][4]

The accepted name of terminal nerve is due to its entrance in the lamina terminalis regions.[1] The nerve has previously been called cranial nerve XIII, zero nerve, nerve N, and NT.[5][6]

Structure

The original images (1878) of Fritsch's dogfish shark brain showing the nerve marked by an asterisk

The terminal nerve appears just in front of the other cranial nerves and would, if earlier recognized, have been classified as cranial nerve one. It first appears bilaterally as a microscopic plexus of unmyelinated peripheral nerve fibers in the subarachnoid space covering the straight gyrus. The plexus appears near the cribriform plate and travels posteriorly toward the olfactory trigone and lamina terminalis.[3]

The terminal nerve is clearly seen in the human embryo but loses some of its ganglion cells before birth making it less recognizable in adults.[7] The nerve is therefore often overlooked in autopsies, and is often torn out upon exposing the brain.[5] Careful dissection is necessary to visualize the nerve.

Development

The zebrafish was used as a developmental model in research from 2004.[8]

The connections between the terminal nerve and the olfactory system have been extensively studied in human embryos. olfactory nerve fibers enter the brain at stage 17, fibers from the vomeronasal organ and fibers of the terminal nerve enter the brain at stages 17 and 18.[9] During prenatal development some of the ganglion cells are lost.[7]

Function

The functions of the terminal nerve are only speculated on together with possible pathological implications.[1] Although very close to the olfactory nerve, the terminal nerve is not connected to the olfactory bulb, where smells are analyzed. This suggests that the nerve is either vestigial or may be related to the sensing of pheromones.[10] The nerve may modulate olfactory inputs making pheromones (particularly sex pheromones) more detectable.[1] This hypothesis is further supported by the fact that the terminal nerve projects to the medial and lateral septal nuclei and the preoptic areas, all of which are involved in reproduction in mammals.[2] A 1987 study found that mating in hamsters is reduced when the terminal nerve is severed.[11]

Clinical significance

Alterations in the terminal nerve structure may be implicated in Kallmann syndrome.[7][12]

Additional images

  • Three forms of the nerve on the underside of human brains
    Three forms of the nerve on the underside of human brains
  • Brain viewed from below. Gyrus rectus seen at anterior centre.
    Brain viewed from below. Gyrus rectus seen at anterior centre.

References

  1. ^ a b c d Ruqa WA, Pennacchia F, Rusi E, Zoccali F, Bruno G, Talarico G, Barbato C, Minni A (March 2024). "Smelling TNT: Trends of the Terminal Nerve". Int J Mol Sci. 25 (7): 3920. doi:10.3390/ijms25073920. PMC 11011448. PMID 38612730.
  2. ^ a b Fields, R. Douglas (2007). "Sex and the Secret Nerve". Scientific American Mind. 18: 20–7. doi:10.1038/scientificamericanmind0207-20.
  3. ^ a b Fuller GN, Burger PC (1990). "Nervus terminalis (cranial nerve zero) in the adult human". Clin Neuropathol. 9 (6): 279–83. PMID 2286018.
  4. ^ Berman, Laura (March 25, 2008). "Scientists discover secret sex nerve". TODAY.com. Archived from the original on June 27, 2019. Retrieved June 27, 2019.
  5. ^ a b Bordoni, Bruno; Zanier, Emiliano (March 13, 2013). "Cranial nerves XIII and XIV: nerves in the shadows". Journal of Multidisciplinary Healthcare. 6. Dove Medical Press: 87–91. doi:10.2147/JMDH.S39132. eISSN 1178-2390. ISSN 1178-2390. OCLC 319595339. PMC 3601045. PMID 23516138.
  6. ^ Vilensky, JA (January 2014). "The neglected cranial nerve: nervus terminalis (cranial nerve N)". Clinical Anatomy. 27 (1): 46–53. doi:10.1002/ca.22130. PMID 22836597. S2CID 21454488.
  7. ^ a b c Peña-Melián Á, Cabello-de la Rosa JP, Gallardo-Alcañiz MJ, Vaamonde-Gamo J, Relea-Calatayud F, González-López L, Villanueva-Anguita P, Flores-Cuadrado A, Saiz-Sánchez D, Martínez-Marcos A (March 2019). "Cranial Pair 0: The Nervus Terminalis". The Anatomical Record. 302 (3): 394–404. doi:10.1002/ar.23826. PMID 29663690.
  8. ^ Whitlock KE (September 2004). "Development of the nervus terminalis: origin and migration". Microscopy Research and Technique. 65 (1–2): 2–12. doi:10.1002/jemt.20094. PMID 15570589. S2CID 8736656.
  9. ^ Müller F, O'Rahilly R (2004). "Olfactory structures in staged human embryos". Cells Tissues Organs. 178 (2): 93–116. doi:10.1159/000081720. PMID 15604533. S2CID 43056268.
  10. ^ Von Bartheld CS (September 2004). "The terminal nerve and its relation with extrabulbar "olfactory" projections: lessons from lampreys and lungfishes". Microscopy Research and Technique. 65 (1–2): 13–24. doi:10.1002/jemt.20095. PMID 15570592.
  11. ^ Wirsig, Celeste (11 August 1987). "Terminal nerve damage impairs the mating behavior of the male hamster". Brain Research. 417 (2): 293–303. doi:10.1016/0006-8993(87)90454-9. PMID 3308003. S2CID 33371658.
  12. ^ Taroc EZ, Naik AS, Lin JM, Peterson NB, Keefe DL, Genis E, Fuchs G, Balasubramanian R, Forni PE (January 2020). "Gli3 Regulates Vomeronasal Neurogenesis, Olfactory Ensheathing Cell Formation, and GnRH-1 Neuronal Migration". J Neurosci. 40 (2): 311–326. doi:10.1523/JNEUROSCI.1977-19.2019. PMC 6948949. PMID 31767679.