The Organ Of Corti

Auditory hair cells are arranged within a structure called the organ of Corti that rests on the basilar as frequency of vibration in hertz (cycles per second.) Doubling the frequency raises the pitch one octave. (C) Pressure oscillations are plotted for these notes over a 7.8-ms interval. Because sound travels 340 m/s in air, one can calculate the wavelength as: wavelength (meters/cycle) = 340 m/s/frequency (Hz). Very low C is produced by a 64-Hz vibration, and only half a cycle occurs in 7.8 ms. Human hearing extends between 20 and 20,000 Hz, and it is the high pitches that are necessary to understand the consonants in speech. (D) Increasing the amplitude of the pressure changes will increase the loudness of the sound.

A. Structure of the right ear external ear vestibular apparatus cochlea

A. Structure of the right ear external ear vestibular apparatus cochlea

temporal bone pinna auditory canal tympanic membrane eustachian tube vestibular & auditory nerves temporal bone pinna auditory canal tympanic membrane eustachian tube

B. Structures of the middle ear membrane within the scala media (Fig. 5). Multiple rows of outer hair cells are separated from a single row of inner hair cells by a supporting structure called the columns of Corti. Rows of cells are arranged linearly along the curved length of the cochlear structure. Both inner and outer hair cells respond to movement of the fluid in the cochlear duct systems, with movement in one direction causing depolarization and movement in the other direction causing hyperpolarization. As described in Chapter 52, extracellular filaments connect the tips of stereocilia protruding from the surface of hair cells. The stereocilia are of different lengths and are arranged in descending order on each cell. Increased tension on these connecting filaments is generated by movement of endolymph fluid, pushing the stereocilia toward the direction of the longest stereocilium. The increased tension opens potassium channels in the cell membrane. As in the vestibular system, the potassium concentration of endolymph surrounding the stereocilia is high compared to intracellular levels, so that increasing potassium conductance leads to an influx of potassium ions and depolarization. Movement of the stereocilia in the opposite direction releases normal resting tension on the connecting filaments, closes potassium channels, and causes hyperpolarization.

ossicles in middle ear malleus (hammer)

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B. Structures of the middle ear ossicles in middle ear malleus (hammer)

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tympanic membrane (ear drum)

C. Movement of the middle ear structures

C. Movement of the middle ear structures

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