The auditory system transforms mechanical energy—sound waves—into nerve impulses.
Sounds enter the system via the inch-long ear canal, which terminates at the tympanic membrane (eardrum) whose vibrations represent an exquisitely complex response to pressure variations. A series of tiny bones (ossicles) in the middle ear amplify and transmit these vibrations to the cochlea of the inner ear, a fluid-filled tube rolled up like a snail shell.
Hair cells within the cochlea are the receptors of the auditory system. Movement of the membrane lining the cochlea stretches the tips of hair cells to allow an influx of K+ and Ca+2 ions—charged particles that build up to generate electrical signals in acoustic nerve fibers. The frequencies to which each hair cell responds depends on its position in the cochlea.
Auditory signals pass through intermediate brain regions to the primary auditory cortex in the temporal lobe.
Direct connections facilitate quick reaction to loud sounds. Another pathway permits processing en route—coordinating signals from both ears, for example.
Past the primary auditory cortex, signals divide into streams that locate and analyze what we hear. The latter include Wernicke’s area in the dominant hemisphere, essential for language comprehension, and a right-hemisphere area that processes emotional aspects of speech.
Hearing is the first sense for which a device was developed to replace non-working receptors. By 2010, some 219,000 people had received cochlear implants, which restore functional hearing by directly stimulating the auditory nerve.
Stein, J.F. Neuroscience: an introduction. Wiley. 2006
Shepherd, G M. The Major Senses: Sight, Hearing, Smell, Taste, and Touch—The Dana Guide. Dana Foundation website. November 2007 http://www.dana.org/news/brainhealth/detail.aspx?id=10064
The Brain from Top to Bottom: The Senses: Vision. Canadian Institute of Health Research; Institute of Neurosciences, Mental Health and Addiction. http://thebrain.mcgill.ca/flash/a/a_02/a_02_cr/a_02_cr_vis/a_02_cr_vis.html
Baldassano C, Beck DM, Fei-Fei L Differential connectivity within the Parahippocampal Place Area. Neuroimage. 2013 Jul 15;75:228-37. Epub 2013 Mar 16. http://www.ncbi.nlm.nih.gov/pubmed/23507385
Dehaene, S. Inside the Letterbox: How Literacy Transforms the Human Brain. Cerebrum. June 03, 2013. http://dana.org/news/cerebrum/detail.aspx?id=43644
Henshaw, J. M. A Tour of the Senses: how your brain interprets the world. Johns Hopkins University Press. 2012
Neuroscience Online: an electronic textbook for the neurosciences. Sensory Systems—auditory systems: structure and function. University of Texas Medical School. http://neuroscience.uth.tmc.edu/s2/chapter12.html
Bossomaier, T. R. J. Introduction to the Senses: from biology to computer science. Cambridge University Press. 2012
Wildgruber D, Riecker A, et al. Identification of emotional intonation evaluated by fMRI. Neuroimage. 2005 Feb 15;24(4):1233-41. Epub 2004 Dec 15. http://www.ncbi.nlm.nih.gov/pubmed/15670701
National Institute on Deafness and other Communication Disorders: Cochlear Implants. http://www.nidcd.nih.gov/health/hearing/pages/coch.aspx
Monell Chemical Senses Center: advancing discovery in taste and smell. http://www.monell.org/news/category/fact_sheets
Neuroscience Online: an electronic textbook for the neurosciences: Sensory systems—Chemical Senses: Olfaction and Gustation. University of Texas Medical School. http://neuroscience.uth.tmc.edu/s2/chapter09.html
Brynie, F.H. Brain Sense: the science of the senses and how we process the world around us. Amacom. 2009
Beauchamp GK. Sensory and receptor responses to umami: an overview of pioneering work. Am J Clin Nutr. 2009 Sep;90(3):723S-727S. doi: 10.3945/ajcn.2009.27462E. Epub 2009 Jul 1.
Wyart C, Webster WW, Chen JH, et al. Smelling a single component of male sweat alters levels of cortisol in women. J Neurosci. 2007 Feb 7;27(6):1261-5. http://www.jneurosci.org/content/27/6/1261.long
Savic I, Berglund H, et al. Smelling of odorous sex hormone-like compounds causes sex-differentiated hypothalamic activations in humans. Neuron. 2001 Aug 30;31(4):661-8.
Neuroscience Online: an electronic textbook for the neurosciences: Sensory systems—Somatosensory systems. University of Texas Medical School. http://neuroscience.uth.tmc.edu/s2/chapter02.html
Rosenblum, L. D, A confederacy of senses. Sci Am. 2013 Jan;308(1):72-5.
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