WordNet

of or relating to the cochlea of the ear; "cochlear implant"

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/18 21:50:04」(JST)

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The cochlear nerve (also auditory or acoustic nerve) is one of two parts of the vestibulocochlear nerve, a cranial nerve present in higher vertebrates. The cochlear nerve carries sound waves from the cochlea of the inner ear directly to the brain. The other portion of the vestibulocochlear nerve is the vestibular nerve, which carries spatial orientation information to the brain from the semicircular canals.

Anatomy and connections

In terms of their anatomy, auditory nerve fibers are bipolar, with the most distal portion being called the peripheral process and the central projection being called the axon; these two projections are also known as the "peripheral axon" and the "central axon". The peripheral process is sometimes referred to as a dendrite, although that term is somewhat inaccurate. Unlike the typical dendrite, the peripheral process generates and conducts action potentials, which then "jump" across the cell body (or somata) and continue to propagate along the central axon. In this respect, auditory nerve fibers are somewhat unique bipolar cells in that action potentials pass through the soma. Both the peripheral process and the axon are myelinated.

In humans, the number of nerve fibers within the cochlear nerve averages around 30,000.^[1] The number of fibers varies significantly across species for example; the domestic cat has some 50,000 fibers. Auditory nerve fibers provide synaptic connections between the hair cells of the cochlea and the cochlear nucleus within the brain-stem. The cell bodies of the cochlear nerve lie within the central aspect of the cochlea and are collectively known as the spiral ganglion. This name reflects the fact that the cell bodies, considered as a unit, have a spiral (or perhaps more accurately, a helical) shape, reflecting the shape of the cochlea. The terms "cochlear nerve fiber" and "spiral ganglion cell" are used, to some degree, interchangeably, although the former may be used to more specifically refer to the central axons of the cochlear nerve. These central axons exit the cochlea at its base, where it forms a nerve trunk. In humans, this aspect of the nerve is roughly one inch in length. It projects centrally to the brain-stem, where its fibers synapse with the cell bodies of the cochlear nucleus. A good anatomical description of human auditory nerve fibers is provided by Spoendlin and Schrott (1985). Important earlier work was done by Schuknecht.

It was once believed that most of the cochlear nerve fibers were directed to the outer hair cells, but it is now understood that at least 90% of the cochlear ganglion cells terminate on inner hair cells, the rest terminating on the outer hair cells.

The transmission between the inner hair cells and the neurons is chemical, using glutamate as a neurotransmitter.

Types of neurons

The cochlear neurons can be divided into two groups: Type I and Type II.

Type I neurons make up 90-95% of the neurons and innervate the inner hair cells. They have a relatively large diameter, and are bipolar and myelinated. Each type I axon innervates only a single hair cell, but each hair cell directs its output to an average of 10 nerve fibers
Type II cells, which have a relatively small diameter, connect with the outer hair cells, are mono-polar and are not myelinated.

Cochlear nuclear complex

The axons from each cochlear nerve terminate in the cochlear nuclear complex which are ipsilaterally located in the medulla of the brain-stem. The cochlear nucleus is the first 'relay station' of the auditory nervous system and receives mainly ipsilateral afferent input.

The three major components of the cochlear nuclear complex are: (see figure below)

the dorsal cochlear nucleus (DCN)
the anteroventral cochlear nucleus (AVCN)
the posteroventral cochlear nucleus (PVCN)

Each of the three cochlear nuclei are tonotopically organized. The axons from the lower frequency area of the cochlea innervate the ventral portion of the dorsal cochlear nucleus and the ventrolateral portions of the anteroventral cochlear nucleus, while the higher frequency axons project into the dorsal portion of the anteroventral cochlear nucleus and the uppermost dorsal portions of the dorsal cochlear nucleus. The mid frequency projections end up in between the two extremes, in this way the frequency spectrum is preserved.

References

^ Spoendlin H, Schrott A (1989). "Analysis of the human auditory nerve". Hear Res 43 (1): 25–38. doi:10.1016/0378-5955(89)90056-7. PMID 2613564.

Additional images

Ear anatomy
Cochlear nucleus innervated by a branching auditory nerve fibre
Terminal nuclei of the vestibular nerve, with their upper connections.
Transverse section of the cochlear duct of a fetal cat.
Floor of ductus cochlearis.
Diagrammatic longitudinal section of the cochlea
Organ of corti

External links

Illustration at cytochemistry.net
Gray's page #1059

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English Journal

Hearing restoration in NF2 patients and patients with vestibular schwannoma in the only hearing ear: report of two cases.

Ozdek A1, Bayır O2, Dönmez T3, Ozışık P3, Sahin M4, Tulgar M4, Tatar EÇ4, Korkmaz MH5.
American journal of otolaryngology.Am J Otolaryngol.2014 Jul-Aug;35(4):538-41. doi: 10.1016/j.amjoto.2014.03.014. Epub 2014 Mar 26.
OBJECTIVE: To explore audiologic outcome of auditory brain stem implantation (ABI) and cochlear implantation (CI) in NF2 patients and patients with vestibular schwannoma (VS) in the only hearing ear.PATIENTS AND METHODS: Study includes retrospective analysis of 2 cases. One is totally deaf patient d
PMID 24746329

Early complications following cochlear implantation in children and their management.

Li S1, Qin Z2, Zhang F1, Li L1, Qi S1, Liu L1.
International journal of pediatric otorhinolaryngology.Int J Pediatr Otorhinolaryngol.2014 Jul;78(7):1040-4. doi: 10.1016/j.ijporl.2014.03.036. Epub 2014 Apr 12.
OBJECTIVES: To report the early postoperative complications of cochlear implantation (CI) in the pediatric population and discuss the intervention measures.METHODS: We retrospectively analyzed 260 consecutive pediatric cochlear implantations performed at the First Affiliated Hospital of Zhengzhou Un
PMID 24809767

Hearing preservation surgery for vestibular schwannomas via the retrosigmoid transmeatal approach: surgical tips.

Wanibuchi M1, Fukushima T, Friedman AH, Watanabe K, Akiyama Y, Mikami T, Iihoshi S, Murakami T, Sugino T, Mikuni N.
Neurosurgical review.Neurosurg Rev.2014 Jul;37(3):431-44. doi: 10.1007/s10143-014-0543-9. Epub 2014 Apr 22.
Maximum tumor extirpation with preservation of the facial and cochlear nerve function is the goal of surgery for vestibular schwannoma. To preserve cochlear nerve function, the surgeon must employ a detailed knowledge of microanatomy, precise microsurgical techniques, and persistence. This paper des
PMID 24752423

Japanese Journal

定型的症候を示さない聴神経腫瘍例

高石司,高田知宜,堀洋二,大津信也,山下利幸,平本博之
耳鼻咽喉科臨床　補冊 1993(Supplement61), 45-53, 1993
… symptoms or findings have been reported.<BR>This paper reports the following six cases of acoustic neurinoma with atypical symptomology experienced in Tokushima Municipal Hospital: 1) two patients first developed sudden hearing loss,2) one patient had an abnormal tongue sense as the chief complaint,3)two patients had normal hearing, and 4) one patient showed a normal ABR.<BR>The nerves of the internal acoustic meatus are the pars superior vesti bularis, pars inferior vestibularis, pars cochlearis, and nervus …
NAID 130004683562

Parvalbumin-like immunoreactivity in the human central auditory system.

SETO-OHSHIMA AKIKO,AOKI EIKO,OMORI AKIRA,TADA TOYOHIRO,MIZUTANI AKIRA
ACTA HISTOCHEMICA ET CYTOCHEMICA 25(1/2), 153-159, 1992
… In the auditory pathway, the nervus vestibulocochlearis, striae acusticae, nuclei cochlearis ventralis et dorsalis, nucleus medialis olivaris superioris, lemniscus lateralis, nuclei lemniscus lateralis ventralis et dorsalis and colliculus inferior were found to contain immunopositive neurons and/or fibers. …
NAID 130000933126

外聽道内氣壓ノ變化殊ニ空氣皷膜按摩ニ因ル聽器ノ變化ニ就テノ實驗的研究

吉田政次郎
京都府立医科大学雑誌 6B(4/5/6), 2287-"2305-2", 1932
… 5) Der Nervus cochlearis und das Ganglion spirale in den Schneckenwindnngen werden bedeutend zerstort und in extremen Fallen zum Schwund gebracht. …
NAID 110007106753

「蝸牛神経」

Nerve: Cochlear nerve
	Diagrammatic longitudinal section of the cochlea. (Cochlear nerve is in center, shown as striped.)
	Part of the cochlear division of the acoustic nerve, highly magnified.
Latin	nervus cochlearis
Gray's	p.906
From	Vestibulocochlear nerve
MeSH	Cochlear+Nerve