Chapter 16 - Section 16.4 - Hearing and Equilibrium - Before You Go On - Page 605: 19

The process by which the vibration of the tympanic membrane (eardrum) ultimately leads to fluctuations in membrane voltage in a cochlear hair cell involves several intricate steps in the auditory system. This process can be summarized as follows: 1. Sound Wave Transmission: - When sound waves enter the ear canal and strike the eardrum, they cause the eardrum to vibrate. These vibrations carry the acoustic energy from the sound wave to the middle ear. 2. Transfer of Vibrations to the Ossicles: - The vibrations of the eardrum are transferred to the three tiny bones of the middle ear known as the auditory ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup). These bones amplify the vibrations and transmit them further into the inner ear. 3. Movement of Oval Window: - The stapes bone is attached to a membrane-covered opening in the cochlea called the oval window. As the stapes vibrates due to the movements of the ossicles, it pushes and pulls on the oval window. This action sets up waves of pressure within the fluid-filled cochlea. 4. Fluid Waves in the Cochlea: - The cochlea is a spiral-shaped, fluid-filled structure that is lined with specialized sensory cells known as hair cells. The pressure waves created by the movements of the oval window travel through the cochlear fluid, causing it to move in a wave-like fashion. 5. Deflection of Hair Cells: - Inside the cochlea, there are hair cells with hair-like projections called stereocilia. As the fluid waves move through the cochlea, they cause the basilar membrane (a flexible membrane within the cochlea) to vibrate. This vibration causes the stereocilia on the hair cells to be deflected. 6. Mechanoelectrical Transduction: - The deflection of stereocilia on the hair cells triggers mechanoelectrical transduction. When stereocilia are deflected toward the tallest stereocilium, ion channels on the stereocilia are opened. This allows positively charged ions, such as potassium and calcium, to enter the hair cell. 7. Changes in Membrane Voltage: - The influx of ions into the hair cell leads to changes in its membrane potential or voltage. Specifically, the influx of positive ions depolarizes the hair cell's membrane, creating an electrical signal. 8. Release of Neurotransmitters: - The change in membrane voltage in the hair cell ultimately leads to the release of neurotransmitters (e.g., glutamate) from the hair cell into the synapse between the hair cell and auditory nerve fibers. 9. Auditory Nerve Signal: - The neurotransmitters released by the hair cell activate receptors on the auditory nerve fibers. This activation generates action potentials (electrical impulses) in the auditory nerve fibers, which then travel to the brain via the auditory pathway to be processed as sound perception. In summary, the vibration of the tympanic membrane sets in motion a complex chain of events that ultimately results in the deflection of stereocilia on cochlear hair cells, leading to changes in membrane voltage and the generation of electrical signals. These electrical signals are the basis for the transmission of auditory information to the brain, where sound is perceived and interpreted.

The process by which the vibration of the tympanic membrane (eardrum) ultimately leads to fluctuations in membrane voltage in a cochlear hair cell involves several intricate steps in the auditory system. This process can be summarized as follows: 1. Sound Wave Transmission: - When sound waves enter the ear canal and strike the eardrum, they cause the eardrum to vibrate. These vibrations carry the acoustic energy from the sound wave to the middle ear. 2. Transfer of Vibrations to the Ossicles: - The vibrations of the eardrum are transferred to the three tiny bones of the middle ear known as the auditory ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup). These bones amplify the vibrations and transmit them further into the inner ear. 3. Movement of Oval Window: - The stapes bone is attached to a membrane-covered opening in the cochlea called the oval window. As the stapes vibrates due to the movements of the ossicles, it pushes and pulls on the oval window. This action sets up waves of pressure within the fluid-filled cochlea. 4. Fluid Waves in the Cochlea: - The cochlea is a spiral-shaped, fluid-filled structure that is lined with specialized sensory cells known as hair cells. The pressure waves created by the movements of the oval window travel through the cochlear fluid, causing it to move in a wave-like fashion. 5. Deflection of Hair Cells: - Inside the cochlea, there are hair cells with hair-like projections called stereocilia. As the fluid waves move through the cochlea, they cause the basilar membrane (a flexible membrane within the cochlea) to vibrate. This vibration causes the stereocilia on the hair cells to be deflected. 6. Mechanoelectrical Transduction: - The deflection of stereocilia on the hair cells triggers mechanoelectrical transduction. When stereocilia are deflected toward the tallest stereocilium, ion channels on the stereocilia are opened. This allows positively charged ions, such as potassium and calcium, to enter the hair cell. 7. Changes in Membrane Voltage: - The influx of ions into the hair cell leads to changes in its membrane potential or voltage. Specifically, the influx of positive ions depolarizes the hair cell's membrane, creating an electrical signal. 8. Release of Neurotransmitters: - The change in membrane voltage in the hair cell ultimately leads to the release of neurotransmitters (e.g., glutamate) from the hair cell into the synapse between the hair cell and auditory nerve fibers. 9. Auditory Nerve Signal: - The neurotransmitters released by the hair cell activate receptors on the auditory nerve fibers. This activation generates action potentials (electrical impulses) in the auditory nerve fibers, which then travel to the brain via the auditory pathway to be processed as sound perception. In summary, the vibration of the tympanic membrane sets in motion a complex chain of events that ultimately results in the deflection of stereocilia on cochlear hair cells, leading to changes in membrane voltage and the generation of electrical signals. These electrical signals are the basis for the transmission of auditory information to the brain, where sound is perceived and interpreted.