ABSTRACT
The auditory pathway can be divided into the peripheral auditory system, comprising the ear and the auditory nerve, and the central auditory system, comprising the nuclei and pathways from the cochlear nucleus to the auditory cortex. The external ear is comprised of the pinna and the external auditory canal (EAC). The EAC acts as an open-ended tube and has resonant peaks that coincide with the frequencies important to speech. The functions of the middle ear include impedance matching between air and cochlear fluids, protection from loud sounds, including own vocalisations and anti-masking of high frequency sounds by low frequency sounds, particularly at high sound levels. The outer hair cells appear to actively assist the mechanics of the cochlea and are responsible for, low hearing thresholds, sharp frequency tuning, otoacoustic emissions and the dynamic range of auditory nerve fibres. The ear can emit sounds, which are termed otoacoustic emissions. Otoacoustic emissions may be evoked by sound or occur spontaneously.
