Cranial nerve zero
Encyclopedia
The terminal nerve, or cranial nerve zero, was discovered by German scientist Gustav Fritsch
in 1878 in the brain
s of shark
s. It was first found in human
s in 1913, although its presence in humans remains controversial. However, a study has indicated that the terminal nerve is a common finding in the adult human brain.
, enters the brain just a little bit ahead of the other cranial nerves
as a microscopic plexus
of unmyelinated peripheral nerve fascicle
s.
The nerve is often overlooked in autopsies because it is unusually thin for a cranial nerve, and is often torn out upon exposing the brain. Careful dissection
is necessary to visualize the nerve. Its purpose and mechanism of function is still open to debate; consequently, nerve zero is often not mentioned in anatomy
textbooks.
, nerve zero is not connected to the olfactory bulb
, where smells are analyzed. This fact suggests that the nerve is either vestigial or may be related to the sensing of pheromones. This hypothesis is further supported by the fact that nerve zero projects to the medial and lateral septal nuclei, and the preoptic area
s, all of which are involved in regulating sexual behavior in mammal
s.
The connections between cranial nerve zero and the olfactory system has been extensively studied in human embryos. It was found to enter the brain at stages 17 and 18 from olfactory origins.
Gustav Fritsch
Gustav Theodor Fritsch was a German anatomist, anthropologist, traveller and physiologist from Cottbus, best known for his work with neuropsychiatrist Eduard Hitzig on the electric localization of the motor areas of the brain...
in 1878 in the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
s of shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s. It was first found in human
Human
Humans are the only living species in the Homo genus...
s in 1913, although its presence in humans remains controversial. However, a study has indicated that the terminal nerve is a common finding in the adult human brain.
Anatomy
It projects from the nasal cavityNasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
, enters the brain just a little bit ahead of the other cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
as a microscopic plexus
Plexus
A plexus is a part of nervous system. Plexus has a slightly different definition in vertebrates and in invertebrates.- In vertebrates :In vertebrates, a plexus is an area where nerves branch and rejoin. The electrical signals do not mix; rather, the fibres travel together with their electrical...
of unmyelinated peripheral nerve fascicle
Nerve fascicle
A small bundle of nerve fibers, enclosed by the perineurium, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or nerve fascicles, which are bound together in a common membranous...
s.
The nerve is often overlooked in autopsies because it is unusually thin for a cranial nerve, and is often torn out upon exposing the brain. Careful dissection
Dissection
Dissection is usually the process of disassembling and observing something to determine its internal structure and as an aid to discerning the functions and relationships of its components....
is necessary to visualize the nerve. Its purpose and mechanism of function is still open to debate; consequently, nerve zero is often not mentioned in anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
textbooks.
Function
Although very close to (and often confused for a branch of) the olfactory nerveOlfactory nerve
The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves. It is instrumental in the sense of smell. Derived from the embryonic nasal placode, the olfactory nerve is capable of regeneration.-Anatomy:...
, nerve zero is not connected to the olfactory bulb
Olfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
, where smells are analyzed. This fact suggests that the nerve is either vestigial or may be related to the sensing of pheromones. This hypothesis is further supported by the fact that nerve zero projects to the medial and lateral septal nuclei, and the preoptic area
Preoptic area
The preoptic area is a region of the hypothalamus. According to the MeSH classification, it is considered part of the anterior hypothalamus. There are four nuclei in this region, according to Terminologia Anatomica .-Functions:The preoptic area is responsible for thermoregulation and receives...
s, all of which are involved in regulating sexual behavior in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s.
Development
The zebrafish has been used as a developmental model in recent research.The connections between cranial nerve zero and the olfactory system has been extensively studied in human embryos. It was found to enter the brain at stages 17 and 18 from olfactory origins.
External links
- Diagram at kent.edu ("nervus terminalis", #4)