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The spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30 mm long and makes 2 3 ⁄ 4 turns about the modiolus. The cochlear structures include: Three scalae or chambers: the vestibular duct or scala vestibuli (containing perilymph), which lies superior to the cochlear duct and abuts the oval ...
Each type I axon innervates only a single inner hair cell, but each inner hair cell is innervated by up to 30 such nerve fibers, depending on species and location within the cochlea. Type II neurons make up the remaining 5-10% of the neurons and innervate the outer hair cells.
The spiral (cochlear) ganglion is a group of neuron cell bodies in the modiolus, the conical central axis of the cochlea. These bipolar neurons innervate the hair cells of the organ of Corti . They project their axons to the ventral and dorsal cochlear nuclei as the cochlear nerve , a branch of the vestibulocochlear nerve (CN VIII).
[5] [6] The human cochlea contains on the order of 3,500 inner hair cells and 12,000 outer hair cells at birth. [7] The outer hair cells mechanically amplify low-level sound that enters the cochlea. [8] [9] The amplification may be powered by the movement of their hair bundles, or by an electrically driven motility of their cell bodies.
The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucleus is layered. Auditory nerve fibers, fibers that travel through the auditory nerve (also known as the cochlear nerve or eighth cranial nerve) carry information from the inner ear, the cochlea, on the same side of the head, to the nerve root in the ventral cochlear ...
The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. Three distinct, primarily inhibitory, cellular groups are located interspersed within these fibers, and are thus named the ...
Cross-section through the spiral organ of Corti at greater magnification, showing position of the hair cells on the basement membrane. The organ of Corti is located in the scala media of the cochlea of the inner ear between the vestibular duct and the tympanic duct and is composed of mechanosensory cells, known as hair cells. [2]
All of these structures together constitute the cochlea. [12] In therian mammals, the lagena is extended still further, becoming a coiled structure (cochlea) in order to accommodate its length within the head. The organ of Corti also has a more complex structure in mammals than it does in other amniotes. [12]