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Sonne J, Reddy V, Lopez-Ojeda W (2023) Neuroanatomy, Cranial Nerve 0 (Terminal Nerve). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 29083731.
https://pubmed.ncbi.nlm.nih.gov/29083731/ Accessed 12 Jun 2024.
Excerpt
Despite the plethora of literature describing the traditional 12 pairs of cranial nerves, very little has been published on the seemingly innocuous nerve known as nervus terminalis, commonly referred to as the terminal nerve, nerve nulla (n), cranial nerve zero “0,” and cranial nerve XIII. However, this nerve has been identified in numerous invertebrate and vertebrate species, including humans, for more than a century. Interestingly, this structure remains largely unrecognized in the medical literature, especially because most anatomy and medical books have overlooked its existence, even though it has been identified in the human brain since 1914. Ever since, a wide repertoire of studies has described its embryology, histology, neurophysiology, and its clinical significance.
Studies in adult brains and fetuses have shown its fibers and those of the vomeronasal organ independent from the olfactory nerve embryologically, as early as stages 17 and 18. In the late 1980s, it was named “cranial nerve 0” (CN0) for its position rostral to the official 12 cranial nerves. The CN0 neurons are associated with gonadotropin-releasing hormone (GnRH), suggesting a potential role in controlling human reproductive functions and behaviors. It has been speculated to play a role in the unconscious perception of special odorants influencing autonomic and reproductive hormonal systems via the ubiquitous hypothalamic-pituitary-gonadal axis (HPG). Furthermore, the literature points to a potential role in detecting pheromones for mate selection and neuromodulation of reproductive functions.
Researchers hypothesize that CN0 may trigger hormonal responses independently or with other neuroanatomical circuits, such as the kisspeptin neural network. In females, these cells are mainly localized in the preoptic area and the infundibular regions of the hypothalamus, posing a riveting sexually dimorphic trait that may have significant clinical considerations. Thus, the presence of CN0 is relevant to medicine from a myriad of different clinical perspectives.
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