Physiology of the Auditory System

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Physiology of the Auditory System

Otology/Audiology
Author Credentials 

Dr. Prashant M. Naik, MS (ENT), DLO
21, Central Excise Colony 
Ring Road 
Nagpur (MS) 440015
India

Phone: 0919823298575
Email: prasima@hotmail.com
           prasima25@gmail.com

Module Summary

Sound energy is in the form of longitudinal pressure waves and for hearing, the sound needs to travel from the air medium to the fluids of inner ear. 

The auditory system is a unique sensory system having intricate anatomy, mechanics, and physiology. This is because the auditory system must do six different hearing functions - sensitivity, discrimination, frequency resolution, intensity resolution, temporal resolution, and adaptation. And hence, the typical layout of the tympanic membrane, the impedance matching mechanism, the intricate cochlear lanes, the lateral placements of two ears, and the spiral arrangement of the ganglionic cells.  

The module starts with the basic appraisal of the anatomic aspects pertaining to the topic and then goes on to discuss the relevant physical properties of sound energy and the conduction of sound from the air to the auditory cortex. The transformer mechanism of the cochlea is elaborated and the coding of the sound in the auditory cortex is discussed.

Module Learning Objectives 
  1. Define the various terminologies needed to understand the physics of sound.
  2. Relate the basic anatomy of the auditory system.
  3. Explain comprehensively the conduction of sound from air to the auditory cortex.
  4. Describe and compare the various theories of hearing.
  5. Discuss and/or debate the active role of cochlea in hearing.
  6. Appraise the role of auditory cortex in perceiving the finer qualities of sound.

 

Anatomy

Learning Objectives 
  1. Explain the anatomy of the external, middle, and inner ear.
  2. Describe the anatomy of the Eustachian tube, central auditory pathways, and auditory cortex.

 

References 
  1. Adunka OF, Buchman CA. Otology, Neurotology, and Lateral Skull Base Surgery - An Illustrated Handbook. New York: Thieme Medical and Scientific Publishers; 2011. Vol1, p. 9-24. 
  2. Rebillard G, Pujol R, Irving S.(2016, Dec 27). Primary auditory pathways; Journey into the world of hearing. Retrieved May 19, 2019, from http://www.cochlea.eu/en/cochlea
  3. Pujol R, Nouvian R, Lenoir M, Irving S. (2016, Sep 19) Hair cells: structure; Journey into the world of hearing. Retrieved May 19, 2019, from http://www.cochlea.eu/en/hair-cells
  4. Pujol R. (2018, Jun 6). Spiral (cochlear) ganglion; Journey into the world of hearing. Retrieved May 19, 2019, from http://www.cochlea.eu/en/spiral-ganglion
  5. Pujol R, Irving S. (2016, Dec 27). Primary auditory pathways; Journey into the world of hearing. Retrieved May 19, 2019, from http://www.cochlea.eu/en/auditory-brain

Basic Science

Learning Objectives 
  1. Define the various terminologies needed to understand the physics of sound.
  • Sound as a pressure wave
  • Pitch and frequency of sound
  • Intensity and decibel scale
  • The sound velocity
  1. Comprehend the conduction of sound from air to the auditory cortex.
  • External and middle ear physiology
  • Cochlear physiology
  • Hair cells: Transduction, tuning, and transmission in the inner ear
  1. Discuss an overview of the role of auditory cortex in understanding.
  • Pitch
  • Timbre
  • Sound location
References 
  1. Dobie RA, Van Hemel S, editors. Basics of sound, the ear, and hearing. National Research Council (US) Committee on Disability Determination for Individuals with Hearing Impairments; Washington (DC). National Academies Press (US); 2004. 
  2. Lorenzi A, Chaix B, Irving S. (2016, Dec 27). What is sound?; Journey into the world of hearing. Retrieved May 19, 2019, from: http://www.cochlea.eu/en/sound
  3. Henderson T. (1996-2019): The Physics classroom; Sound is a pressure wave. Retrieved May 19, 2019 from: https://www.physicsclassroom.com/class/sound/Lesson-1/Sound-is-a-Pressure-Wave
  4. Henderson T. (1996-2019): The Physics classroom; Pitch and frequency. Retrieved May 19, 2019 from: https://www.physicsclassroom.com/class/sound/Lesson-2/Pitch-and-Frequency
  5. Henderson T. (1996-2019): The Physics classroom; Intensity and decibel scale. Retrieved May 19, 2019 from: https://www.physicsclassroom.com/class/sound/Lesson-2/Intensity-and-the-Decibel-Scale
  6. Henderson T. (1996-2019): The Physics classroom; The speed of sound. Retrieved May 19, 2019 from: https://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound
  7. Kollmeier B. Anatomy, Physiology and Function of the Auditory System. In: Havelock D, Kuwano S, Vorlander M, editors. Handbook of Signal Processing in Acoustics, vol 1. Ney Yorl: Springer Science+Business Media, LLC; 2008. p.147-158.
  8. Adunka OF, Buchman CA. Otology, Neurotology, and Lateral Skull Base Surgery - An Illustrated Handbook. , New York: Thieme Medical and Scientific Publishers; 2011. Vol1, p. 25-35. 
  9. Suarez A, Goycoolea M. Physiology of hearing. In: Kirtane MV, Brackmann DB, Borkar DM, de Souza C, editors. Comprehensive textbook of otology - Diagnosis, management, and operative techniques. Reprint 2011. Mumbai: Bhalani Publishing House; p.36-43. 
  10. Guinan Jr. JJ, Salt A, Cheatham MA: Progress in cochlear physiology after Bekesy. Hearing Research 293 (2012) 12-20. 
  11. Hudspeth A J: The cellular basis of hearing: The biophysics of hair cells. Science 15 Nov 1985, vol 230, number 4727, p 745-52.
  12. Roberts WM, Howard J, Hudspeth AJ.: Hair cells: Transduction, Tuning, and Transmission in the Inner Ear. Ann. Rev. Cell Bioi. 1988. 4: 63-92.
  13. Bizley JK, Walker KMM: Sensitivity and Selectivity of Neurons in Auditory Cortex to the Pitch, Timbre, and Location of Sounds. The Neuroscientist 2010 Aug;16(4):453-69.
  14. Lonsbury-Martin BL, Martin GK, Hannley MT. Physiology of the auditory and vestibular systems. In: Snow Jr JB, Wackym PA, editors. Ballenger’s Otorhinolaryngology Head and neck Surgery. Centennial edition. Connecticut: People’s Medical Publishing House; 2009. Vol1, p. 45-62. 
  15. Alper CM, Luntz M, Takahashi H, Ghadiali SN, Swarts D, Teixeira MS, Kanyi ZC, Yehudai N, Kania R, Poe DS: State of the Art Review Panel 2: Anatomy (Eustachian Tube, Middle Ear, and Mastoid—Anatomy, Physiology, Pathophysiology, and Pathogenesis); Otolaryngology– Head and Neck Surgery 2017, Vol. 156(4S) S22–S40. 

Review

Review Questions 
  1. What are the basic components of the auditory system?
  2. How does sound energy differ from other forms of energy?
  3. What is the necessity of such a complex auditory system?
  4. What is the active role of cochlea in hearing?
  5. What are the currently accepted theories of hearing?
  6. Where and how is the sound differentiated in its pitch, and timbre? 
  7. What is sound location? How is it achieved?

 

Resources 

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