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The cochlea is a portion of the inner ear that looks like a snail shell (cochlea is Greek for snail). [5] The cochlea receives sound in the form of vibrations, which cause the stereocilia to move. The stereocilia then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted.
Tonotopic organization in the cochlea forms throughout pre- and post-natal development through a series of changes that occur in response to auditory stimuli. [7] Research suggests that the pre-natal establishment of tonotopic organization is partially guided by synaptic reorganization; however, more recent studies have shown that the early changes and refinements occur at both the circuit and ...
The mid frequency projections end up in between the two extremes; in this way the tonotopic organization that is established in the cochlea is preserved in the cochlear nuclei. This tonotopic organization is preserved because only a few inner hair cells synapse on the dendrites of a nerve cell in the spiral ganglion, and the axon from that ...
There are far fewer inner hair cells in the cochlea than afferent nerve fibers – many auditory nerve fibers innervate each hair cell. The neural dendrites belong to neurons of the auditory nerve, which in turn joins the vestibular nerve to form the vestibulocochlear nerve, or cranial nerve number VIII. [29]
The basal end of the cochlea, where sounds enter from the middle ear, encodes the higher end of the audible frequency range while the apical end of the cochlea encodes the lower end of the frequency range. This tonotopy plays a crucial role in hearing, as it allows for spectral separation of sounds.
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]
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).
In mammalian outer hair cells, the varying receptor potential is converted to active vibrations of the cell body. This mechanical response to electrical signals is termed somatic electromotility; [13] it drives variations in the cell's length, synchronized to the incoming sound signal, and provides mechanical amplification by feedback to the traveling wave.