Organ of Corti

• supporting cells (Deiter's, Hensen's, Claudius' cells) provide nutrients and support

Figure 6—2. Cross-sectional anatomy of the cochlea. Reprinted with permission from Bailey BJ. Head and Neck Surgery—Otolaryngology [ill by Tony Pazos]. Copyright 1993, Lippincott, Williams & Wilkins.

• Tectorial Membrane: fibrogelatinous structure arises from the bony spiral lamina, the tips of the stereocilia of the outer hair cells are partially embedded into the tectorial membrane which causes shearing forces with vibration of the basilar membrane resulting in stimulation of the hair cells

Inner Hair Cells

• may act as the principal transducer of motion from the basilar membrane to a nerve impulse

• single row, fewer than outer hair cells

• rounded, flask-like shape with nucleus in the center, low intracellular glycogen

• few cilia in a curved shape

• loose connection to tectorial membrane

• completely surrounded by supporting cells

• Afferent Innervation: Type I (radial, bipolar, myelinated), form 95% of fibers of the cochlear nerve, each inner hair cell is innervated by 10—20 neurons (low hair to ganglion ratio) ^ cochlear nucleus

Outer Hair Cells

• may act as a motor to amplify motion from the basilar membrane (cochlear amplifier)

• source of otoacoustic emissions

• 3 rows, more numerous than inner hair cells

• cylindrical-shaped with nucleus at base and organelles aligning the cell membrane, high intracellular glycogen

• many stereocilia in a "w" or "v" shape

• tight connection to tectorial membrane

• supported only at base

• Afferent Innervation: Type II (spiral, pseudomonopolar, unmyelinated), form 5% of fibers of the cochlear nerve, 10 outer hair cells are innervated by one neuron (high hair to ganglion ratio) ^ cochlear nucleus

• Efferent Innervation: begins from the auditory cortex down to the level of the cochlear nuclei, additional contributions from the superior olive join and terminate predominantly on the outer hair cells

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