![]() ![]() The neural fibers from the superior olivary nuclei are then transmitted to the ipsilateral inferior colliculus via the lateral lemniscus tract. The cochlear nucleus is located at the posterolateral portion of the brainstem and is cochleo-topically divided with low-frequency fibers on its ventral region and high-frequency fibers on its dorsal region.Īfter the cochlear nucleus, the majority of neural fibers decussate across the midline into the contralateral superior olivary complex. The cochlear nucleus is the first relay point of the brainstem along the auditory pathway. Auditory nerve fibers from the low-frequency, apical portion of the cochlea and the high-frequency, basal portion travel along with the central and peripheral parts of the auditory nerve, respectively. The cochlea has a unique tonotopic organization with high frequency sounds stimulating the basal component and low frequency sounds stimulating the apical component. The cochlear hair cells transform physical sound input into bioelectrical action potentials that are then transmitted to the spiral ganglion which comprise the main component of the auditory nerve. Electrical information to the auditory cortex travels along an ascending path through a series of nuclei including the cochlear nuclei, superior olivary complex, lateral lemniscus, inferior colliculi, and medial geniculate nuclei. Mechanical sound is transformed into electrical signals in the cochlea and transmitted to the brain through the auditory nerve or vestibulocochlear nerve (cranial nerve VIII). ĪBR measures the synchronous neural fiber activity along the auditory pathway to determine hearing thresholds. It is now essential in the diagnosis of hearing loss, acoustic tumors, and cerebellopontine angle (CPA) tumors. It was first introduced into audiology in the 1970s, and its importance has increased with the contemporary guidelines of newborn hearing screening for hearing loss within 3 months of age. The readings consist of a sequence of up to 7 positive wave peaks labeled I-VII with negative troughs in-between. Įlectrical activity from the eighth cranial nerve and neurons along the brainstem auditory pathway are recorded by surface electrodes placed on the scalp, forehead, and near the ears for 10 milliseconds after an acoustic stimulus. ABR tests synchronous neural function and can estimate hearing sensitivity thresholds in individuals who are unable to tolerate traditional behavioral audiometry. Roux I, Safieddine S, Nouvian R, Grati M, Simmler MC, Bahloul A, Perfettini I, Le Gall M, Rostaing P, Hamard G, Triller A, Avan P, Moser T, Petit C (2006) Otoferlin, defective in a human deafness form, is essential for exocytosis at the auditory ribbon synapse.Auditory brainstem response (ABR), also known as brainstem auditory Evoked Potentials (BAEP), is an objective measurement of auditory pathway function from the auditory nerve to the mesencephalon. Goutman JD, Glowatzki E (2007) Time course and calcium dependence of transmitter release at a single ribbon synapse. Glowatzki E, Fuchs PA (2002) Transmitter release at the hair cell ribbon synapse. Nouvian R, Beutner D, Parsons TD, Moser T (2006) Structure and function of the hair cell ribbon synapse. Pfeiffer RR, Kim DO (1975) Cochlear nerve fiber responses: distribution along the cochlear partition. ![]() Johnson DH (1980) The relationship between spike rate and synchrony in responses of auditory-nerve fibers to single tones. ![]() New York, Berlin, Hiedelberg, Springer-Verlag, pp 34–93 In: Popper AN, Fay, RR (eds) The mammmalian auditory pathway: neuroanatomy. Ruggero MA (1992) Physiology and coding of sound in the auditory nerve. Ear Hear 27:589–607ĭelano PH, Elgueda D, Hamame CM, Robles L (2007) Selective attention to visual stimuli reduces cochlear sensitivity in chinchillas. Guinan JJ (2006) Olivocochlear efferents: anatomy, physiology, function, and the measurement of efferent effects in humans. New York, Berlin, Hiedelberg, Springer-Verlag, pp 23–65 In: Webster DB, Popper AN, Fay RR (eds) The mammmalian auditory pathway: neuroanatomy. Ryugo DK (1992) The auditory nerve: peripheral innervation, cell body morphology, and central projections. ![]()
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