January 23, 2008
How Hearing Happens
Robin L. Davis
Professor of Cell Biology and Neuroscience, Rutgers University
Minutes of the 16th Meeting of the 66th Year
President Joe Giordmaine called the meeting to order at 10:15 AM. It was the 17th meeting of the Old Guard’s 66th year.
[George Folkers led the invocation. Charlie Stenard and Barney Barnhart introduced visitors. Two guests were introduced: Sherman Gray introduced Dean Chace, retired RCA lawyer and former Old Guard member. Dick Hanson introduced Dennis Micai, who heads the Trenton Area Soup Kitchen and who will be the speaker at next week’s Old Guard meeting.
Dana Fearon gave an excellent summary of the previous meeting’s talk by Leticia Ufford on “The Struggle for Syria in 1840.”
President Giordmaine asked for a moment of silence in memory of Hugh Wynn, who had died on July 4, 2007.]
John Brinster introduced the speaker of the day, after first noting that recent advances in neuroscience have been recognized by the design- nation of the Decade of the Brain.
The speaker, Dr. Robin L. Davis, is Professor of Cell Biology at Rutgers University, and a leader in the field of audiology research. Dr. Davis began her career as a clinical audiologist, but she was soon impelled to seek a deeper understanding of the physiology of hearing. She earned a doctorate in neuroscience at Stanford University, after which she worked in the Eaton-Peabody Lab at M.I.T. Since 1991, she has been at Rutgers University, where she now heads the Davis Lab for research on the mechanism of hearing. Dr. Davis serves on numerous agencies related to hearing, including the American Association for Research in Otolaryngology and the Scientific Advisory Board of the National Institutes of Health.
The human ear consists of three divisions: the outer ear or pinna, which catches sound waves and carries them inward; the middle ear, which consists of three little bones or ossicles, which transmit the sound inward; and the inner ear, which consists of the semi-circular canals, the organ of balance, and the cochlea, which is the organ of hearing.
The cochlea is a complex coiled structure, a spiral cavity which contains the structures essential for hearing. [By the way, the name cochlea is derived from the Greek word kokhlias, which means snail.] The cochlea is imbedded within the temporal bone, the hardest bone in the body. It is lined by specialized hair cells which have cilia or micro-hairs at their tips. The hair cells are connected to neurons (or nerve cells) which are assembled into a structure called the spiral ganglion. The neurons have long exten- sions which lead via the eighth cranial nerve to the auditory cortex of the brain. The mode of transmission of the signals is by electrical energy.
Dr. Davis compared the cochlea to a coiled harp in which a membrane vibrates at various frequencies to create a range of sounds from high frequency to low frequency. [The structure and function of the cochlea was first elucidated by the Hungarian scientist George von Bekesy, in research for which he won the Nobel Prize in 1961.]
The hair cells vary in size and function depending on their location within the cochlea. At the apical or uppermost region of the cochlea are longer hair cells which transmit low frequency sounds. At the basal reg- ion of the cochlea are shorter hair cells which transmit high frequency sounds. When the basilar membranes of the hair cells vibrate, positive potassium ions enter the hair cell and generate electrical energy.
The hair cells are very delicate, and in most cases of hearing loss, they are the weakest link, the first thing to go wrong. Cochlear implants are recent inventions which bypass the hair cells so as to stimulate the neurons of the spiral ganglion directly. However, at the present time, cochlear implants are appropriate only for young children and not for older adults.
Present research in Dr. Davis’ lab is focused on seeking to understand the physiology and functioning of the spiral ganglion neurons. It is difficult to study these neurons in their natural site within the temporal bone. So Dr. Davis and her co-workers grew the neurons in tissue culture, which makes it possible to measure electrical action potentials and other phenomena from individual neurons. The individual neurons have been found to contain specific ion channel proteins.
Chemical substances have been identified in the brain which affect the functioning of the neurons or nerve cells. These substances are called neurotrophic factors. Two of them have been identified: BDNF or Brain-Derived Neurotrophic Factor, and NT3 or Neurotropin 3. Both of these substances enhance survival of neurons, but they have opposite and complementary effects. Dr. Davis noted that future cochlear implants may be able to take advantage of this knowledge, so that they will be able to benefit a larger spectrum of persons with hearing loss, possibly including older individuals.
Following Dr. Davis’ talk, she fielded a number of questions. [She indicated that audiometric testing is of value in defining the specifics of an individual’s hearing loss so that the best hearing aid for a particular individual can be prescribed. Dr. Davis noted the danger of constant and excessive noise such as may result from I-Pods and other modern devices. With regard to sudden hearing loss, Dr. Davis speculated that this might have an immunologic basis.]
At the end of her presentation, Dr. Davis gave full credit to the contribution of her assistants, and she acknowledged the support of Rutgers University and the National Institute for Deafness and Communicative Disorders.
The meeting was adjourned at 11:30 AM.
Respectfully submitted,
Harvey Rothberg, M.D.
[George Folkers led the invocation. Charlie Stenard and Barney Barnhart introduced visitors. Two guests were introduced: Sherman Gray introduced Dean Chace, retired RCA lawyer and former Old Guard member. Dick Hanson introduced Dennis Micai, who heads the Trenton Area Soup Kitchen and who will be the speaker at next week’s Old Guard meeting.
Dana Fearon gave an excellent summary of the previous meeting’s talk by Leticia Ufford on “The Struggle for Syria in 1840.”
President Giordmaine asked for a moment of silence in memory of Hugh Wynn, who had died on July 4, 2007.]
John Brinster introduced the speaker of the day, after first noting that recent advances in neuroscience have been recognized by the design- nation of the Decade of the Brain.
The speaker, Dr. Robin L. Davis, is Professor of Cell Biology at Rutgers University, and a leader in the field of audiology research. Dr. Davis began her career as a clinical audiologist, but she was soon impelled to seek a deeper understanding of the physiology of hearing. She earned a doctorate in neuroscience at Stanford University, after which she worked in the Eaton-Peabody Lab at M.I.T. Since 1991, she has been at Rutgers University, where she now heads the Davis Lab for research on the mechanism of hearing. Dr. Davis serves on numerous agencies related to hearing, including the American Association for Research in Otolaryngology and the Scientific Advisory Board of the National Institutes of Health.
The human ear consists of three divisions: the outer ear or pinna, which catches sound waves and carries them inward; the middle ear, which consists of three little bones or ossicles, which transmit the sound inward; and the inner ear, which consists of the semi-circular canals, the organ of balance, and the cochlea, which is the organ of hearing.
The cochlea is a complex coiled structure, a spiral cavity which contains the structures essential for hearing. [By the way, the name cochlea is derived from the Greek word kokhlias, which means snail.] The cochlea is imbedded within the temporal bone, the hardest bone in the body. It is lined by specialized hair cells which have cilia or micro-hairs at their tips. The hair cells are connected to neurons (or nerve cells) which are assembled into a structure called the spiral ganglion. The neurons have long exten- sions which lead via the eighth cranial nerve to the auditory cortex of the brain. The mode of transmission of the signals is by electrical energy.
Dr. Davis compared the cochlea to a coiled harp in which a membrane vibrates at various frequencies to create a range of sounds from high frequency to low frequency. [The structure and function of the cochlea was first elucidated by the Hungarian scientist George von Bekesy, in research for which he won the Nobel Prize in 1961.]
The hair cells vary in size and function depending on their location within the cochlea. At the apical or uppermost region of the cochlea are longer hair cells which transmit low frequency sounds. At the basal reg- ion of the cochlea are shorter hair cells which transmit high frequency sounds. When the basilar membranes of the hair cells vibrate, positive potassium ions enter the hair cell and generate electrical energy.
The hair cells are very delicate, and in most cases of hearing loss, they are the weakest link, the first thing to go wrong. Cochlear implants are recent inventions which bypass the hair cells so as to stimulate the neurons of the spiral ganglion directly. However, at the present time, cochlear implants are appropriate only for young children and not for older adults.
Present research in Dr. Davis’ lab is focused on seeking to understand the physiology and functioning of the spiral ganglion neurons. It is difficult to study these neurons in their natural site within the temporal bone. So Dr. Davis and her co-workers grew the neurons in tissue culture, which makes it possible to measure electrical action potentials and other phenomena from individual neurons. The individual neurons have been found to contain specific ion channel proteins.
Chemical substances have been identified in the brain which affect the functioning of the neurons or nerve cells. These substances are called neurotrophic factors. Two of them have been identified: BDNF or Brain-Derived Neurotrophic Factor, and NT3 or Neurotropin 3. Both of these substances enhance survival of neurons, but they have opposite and complementary effects. Dr. Davis noted that future cochlear implants may be able to take advantage of this knowledge, so that they will be able to benefit a larger spectrum of persons with hearing loss, possibly including older individuals.
Following Dr. Davis’ talk, she fielded a number of questions. [She indicated that audiometric testing is of value in defining the specifics of an individual’s hearing loss so that the best hearing aid for a particular individual can be prescribed. Dr. Davis noted the danger of constant and excessive noise such as may result from I-Pods and other modern devices. With regard to sudden hearing loss, Dr. Davis speculated that this might have an immunologic basis.]
At the end of her presentation, Dr. Davis gave full credit to the contribution of her assistants, and she acknowledged the support of Rutgers University and the National Institute for Deafness and Communicative Disorders.
The meeting was adjourned at 11:30 AM.
Respectfully submitted,
Harvey Rothberg, M.D.