subdivided into parallel ascending pathways, which can simultaneously extract different types of information. The cells of the ventral cochlear nucleus extract information that is carried by the auditory nerve in the timing of firing and in the pattern of activation of the population of auditory nerve fibers. The cells of the dorsal cochlear nucleus perform a non-linear spectral analysis and place that spectral analysis into the context of the location of the head, ears and shoulders and that separate expected, self-generated spectral cues from more interesting, unexpected spectral cues using input from the auditory cortex, pontine nuclei, trigeminal ganglion and nucleus, dorsal column nuclei and the second dorsal root ganglion. It is likely that these neurons help mammals to use spectral cues for orienting toward those sounds. The information is used by higher brainstem regions to achieve further computational objectives (such as sound source location or improvement in signal-to-noise ratio). The inputs from these other areas of the brain probably play a role in sound localization. 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. Each fiber is an axon of a spiral ganglion cell that represents a particular frequency of sound, and a particular range of loudness. Information in each nerve fibre is represented by the rate of action potentials as well as the particular timing of individual action potentials. The particular physiology and morphology of each cochlear nucleus cell type enhances different aspects of sound information. See also Auditory system Cochlear nerve Unipolar brush cell Additional images References External links Medical research council Shore lab Cranial nerve nuclei Auditory system Medulla oblongata Pons Otology Audiology