| Nerve: Cochlear nerve | |
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| Diagrammatic longitudinal section of the cochlea. (Cochlear nerve is in center, shown as striped. ) | |
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| Part of the cochlear division of the acoustic nerve, highly magnified. The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve Cranial nerves, and is responsible for transmitting sound | |
| Latin | nervus cochlearis |
| Gray's | subject #203 906 |
| From | Vestibulocochlear nerve |
| MeSH | Cochlear+Nerve |
The cochlear nerve (also auditory nerve or VIIIth nerve) is part of the vestibulocochlear nerve, (or 8th cranial nerve) that is found in higher vertebrates. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. This is a list of the subjects in Gray's Anatomy: IX Neurology The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve Cranial nerves, and is responsible for transmitting sound Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve Cranial nerves, and is responsible for transmitting sound Cranial nerves are Nerves that emerge directly from the Brain stem in contrast to Spinal nerves which emerge from segments of the Spinal cord. It is a sensory nerve, i. e. , one that conducts information about the environment (in this case, acoustic energy that impinges on the external ear) to the brain. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain The other portion of the 8th nerve is the vestibular nerve. The cochlear nerve arises from within the cochlea and extends to the brainstem, where its fibers make contact with the cochlear nucleus, the next stage of neural processing in the auditory system. The cochlea is the auditory portion of the Inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along The brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord. The cochlear nuclei consist of (a the Dorsal cochlear nucleus, corresponding to the Tuberculum acusticum on the dorso-lateral surface of
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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 projection are also known as the "peripheral axon" and the "central axon". An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell A bipolar cell is a type of Neuron which has two extensions Bipolar cells are specialized sensory neurons for the transmission of special senses An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell The peripheral process is sometimes referred to as a dendrite, although that term is somewhat inaccurate. Dendrites (from Greek δένδρον déndron, “tree” are the branched projections of a Neuron that act to conduct the electrochemical 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 Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal 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 the axon are myelinated. Myelin is an electrically-insulating Dielectric Phospholipid layer that surrounds only the Axons of many Neurons It is an outgrowth
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 fibres provide synaptic connections between the hair cells of the cochlea and the cochlear nucleus within the brainstem. The cochlea is the auditory portion of the Inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along The cochlear nuclei consist of (a the Dorsal cochlear nucleus, corresponding to the Tuberculum acusticum on the dorso-lateral surface of 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,has 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 brainstem, where its fibers synapse with the cell bodies of the cochlear nucleus. The cochlear nuclei consist of (a the Dorsal cochlear nucleus, corresponding to the Tuberculum acusticum on the dorso-lateral surface of 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 fibres 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. Hair cells are the Sensory receptors of both the Auditory system and the Vestibular system in all Vertebrates.
The transmission between the inner hair cells and the neurons is chemical, using glutamate as a neurotransmitter. Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its
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 fibres
- Type II cells, which have a relatively small diameter, connect with the outer hair cells, are monopolar 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 brainstem. 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 organised. 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.
See also
References
- ^ Spoendlin H, Schrott A (1989). A cochlear implant (CI is a surgically implanted electronic device that provides a sense of Sound to a person who is profoundly deaf or severely hard of hearing "Analysis of the human auditory nerve". Hear Res 43 (1): 25–38. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. 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. |
External links
Henry Gray's Anatomy of the Human Body (or Gray's Anatomy as it has commonly been shortened is an English-language Human anatomy Textbook
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