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Chapter 52: The Sense of Hearing Guyton and Hall, Textbook of Medical Physiology, 12 th edition.

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Presentation on theme: "Chapter 52: The Sense of Hearing Guyton and Hall, Textbook of Medical Physiology, 12 th edition."— Presentation transcript:

1 Chapter 52: The Sense of Hearing Guyton and Hall, Textbook of Medical Physiology, 12 th edition

2 Tympanic Membrane and Ossicles Conduction of Sound from the Tympanic Membrane to the Cochlea Fig Tympanic membrane, ossicular system of the middle and inner ear

3 Tympanic Membrane and Ossicles “Impedance Matching” by the Ossicular System a.Reduces the distance between the ossicles but increases the force of movement b.Because of size difference, the force exerted is a total of 22x on the fluid of the cochlea c.Without the tympanic membrane and ossicles the sound waves would still pass through to the cochlea, but at a greatly reduced sensitivity

4 Tympanic Membrane and Ossicles Attenuation of Sound by Contraction of the Tensor Tympani and Stapedius Muscles a.When a loud sound is transmitted the stapedius muscle contracts and to a lesser extent, the tensor contracts b.Can reduce decibels by c.Function of the attenuation reflex 1.To protect the cochlea from damaging vibrations 2.Mask low frequency sounds in loud environments

5 Tympanic Membrane and Ossicles Transmission of Sound Through Bone a.Because the inner ear is embedded in bone, vibrations of the entire skull can cause fluid vibrations in the cochlea b.Energy available in loud sound is generally not enough to cause hearing via bone conduction

6 Cochlea Functional Anatomy Fig Cochlea

7 Cochlea Functional Anatomy Fig Section through one of the turns of the cochlea

8 Cochlea Functional Anatomy- consists of three tubes a.Scala vestubli, scala media, scala tympani b.Scala vestubli and scala media are separated by the vestibular membrane c.Scala tympani and scala media are separated by the basilar membrane d.On the surface of the basilar membrane lies the organ of Corti (contains hair cells; the receptors)

9 Cochlea Functional Anatomy Fig Movement of fluid in the cochlea after forward thrust of the stapes

10 Cochlea Basilar Membrane and Resonance- high frequency and low frequency resonance Transmission of Sound Waves in the Cochlea— “Traveling Wave” Pattern of Vibration of the Basilar Membrane for Different Sound Frequencies

11 Cochlea Fig “Traveling waves” along the basilar membrane for high, medium, and low frequency sounds

12 Cochlea Fig Amplitude pattern of vibration of the basilar membrane for medium frequency sound Amplitude Pattern of Vibration of the Basilar Membrane

13 Cochlea Function of the Organ of Corti a.Receptor organ that generates nerve impulses in response to vibration of the basilar membrane b.Actual receptors are called “hair” cells c.Nerve fibers that are stimulated lead to the spiral ganglion of Corti which sends axons to the cochlear nerve

14 Cochlea Fig Organ of Corti showing hair cells and the tectorial membrane

15 Cochlea Fig Stimulation of the hair cells by movement of hairs projecting into the gel casing of the tectorial membrane

16 Cochlea Auditory Signals are Transmitted Mainly by the Inner Hair Cells Hair Cell Receptor Potentials and Excitation of Auditory Nerve Fibers- polarization or hyperpolarization depending on the direction the hair cells are bent

17 Cochlea Determination of Loudness a.As sound becomes louder, the amplitude of vibration of the basilar membrane and hair cells also increases so that the hair cells excite the nerve endings at more rapid rates b.Causes more and more hair cells on the fringes to become stimulated, thus causing spatial summation of impulses

18 Cochlea Determination of Loudness c.Outer hair cells do not become stimulated until the vibration of the basilar membrane reaches high intensity Detection of Changes in Loudness a.The Power Law- a person interprets changes in intensity approximately in proportion to an inverse power of the function of the actual intensity (can interpret an increase of 1 trillion times

19 Central Auditory Mechanisms Auditory Nervous Pathways Fig

20 Central Auditory Mechanisms Function of the Cerebral Cortex in Hearing Fig Auditory cortex

21 Central Auditory Mechanisms Function of the Cerebral Cortex in Hearing a.Sound frequency perception b.Discrimination of sound patterns c.Determination of direction from which sound comes

22 Cochlea Determination of Sound Frequency a.The “Place” Principle- major method to detect different sound frequencies is to determine the position along the basilar membrane that is most stimulated


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