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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.
In order to understand in more detail the specific functions of the cochlear nuclei it is first necessary to understand the way sound information is represented by the fibers of the auditory nerve. Briefly, there are around 30,000 auditory nerve fibres in each of the two auditory nerves.
Type I neurons make up 90-95% of the neurons and innervate the inner hair cells. They have relatively large diameters, are bipolar, and are myelinated. 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.
The cochlea, dedicated to hearing; converting sound pressure patterns from the outer ear into electrochemical impulses which are passed on to the brain via the auditory nerve. The vestibular system, dedicated to balance. The inner ear is found in all vertebrates, with substantial variations in form and function.
[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 fundamental function of this part of the ear is to gather sound energy and deliver it to the eardrum. Resonances of the external ear selectively boost sound pressure with frequency in the range 2–5 kHz. [2] The pinna as a result of its asymmetrical structure is able to provide further cues about the elevation from which the sound originated.
The purpose of this frequency map (known as a tonotopic map) likely reflects the fact that the cochlea is arranged according to sound frequency. The auditory cortex is involved in tasks such as identifying and segregating "auditory objects" and identifying the location of a sound in space. For example, it has been shown that A1 encodes complex ...
Axon guidance (also called axon pathfinding) is a subfield of neural development concerning the process by which neurons send out axons to reach their correct targets. Axons often follow very precise paths in the nervous system, and how they manage to find their way so accurately is an area of ongoing research.