Quick Facts
The cochlear ganglion is the sensory ganglion located within the spiral canal of the modiolus. It consists of bipolar cells that send fibers peripherally through the foramina nervosa to the spiral organ and centrally through the internal acoustic meatus to the cochlear nuclei of the brainstem (Dorland, 2011).
Structure and/or Key Feature(s)
The cochlear ganglion is a collection of neural cell bodies located within the bony labyrinth of the cochlea. Cochlear ganglia are situated throughout the body of the modiolus, within bony canals called Rosenthal’s canal. These canals share the same spiraling course as the osseous spiral lamina.
There are two distinguishable types of cells in the cochlear ganglion, type 1 and type 2 cells, making up roughly 95% and 5% of the population, respectively. Each cell body emits a central process that protrudes toward the organ of Corti and a central axon that projects back toward the cochlear nerve. Type 1 cells are larger, with a round nucleus and plentiful cytoplasmic organelles, and their central and peripheral branches are myelinated. Type 2 cells are smaller, with an irregularly shaped nucleus and a large number of neurofilaments in their cytoplasm. Their central and peripheral nerve branches are unmyelinated with a smaller diameter (Nayagam, Muniak and Ryugo, 2011). While the neurofilament proteins are in a greater abundance in the type 2 cell cytoplasm, they are also expressed in type1 cells albeit to a much lesser extent. These neurofilament proteins are involved in the development and maintenance of structural integrity of these neurons from childhood to adulthood.
The processes of these cell bodies form afferent synapses at the bases of the hair cells. They are grouped into three different groups depending on the route to the hair cells. These groups are the inner radial group, the basilar group, and the outer spiral bundle.
Anatomical Relations
The cochlear ganglion occupies the open space of Rosenthal’s canal and so is in contact with the inner surface of this canal. Its path in this canal spirals up from the base to midway of the modiolus. On this course it provides slips of nerve fibers which travel interjacent to the two bony plates of the osseous spiral lamina.
Function
The cochlear ganglion relays efferent and afferent signals to and from the outer and inner hair cells of the cochlea. The spiral ganglion neurons allow for the feedback of auditory information via their central axons, which carry the signal to the auditory nerve, and from there to the auditory processing centers in the central nervous system. The primary neurotransmitter involved in cochlear neurotransmission is glutamate.
List of Clinical Correlates
—Degeneration of cochlear ganglion
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Nayagam, B. A., Muniak, M. A. & Ryugo, D. K. (2011) The spiral ganglion: connecting the peripheral and central auditory systems. Hear Res, 278(1-2), 2-20.
