Sound level 70 dB SPL Time scale 1/1250 speed MET open probability (illustrative) 15 %
Type I afferent action potentials and release at inner hair-cell terminals (schematic)Hair cells: one row of flask-shaped inner hair cells and three rows of cylindrical outer hair cellsTectorial membrane: a colorless matrix, shown translucent for visibilitySupporting structures: basilar membrane, reticular lamina, pillar cells and Deiters cellsDimensions: 1 unit = 1 µm. Basilar-membrane width 216.1 µm and reticular-lamina slope 20° come from measurements in the estimated 500–1000 Hz region of one adult human cochlea (Giese 2024). Cell lengths, bundle heights and counts without human measurements are illustrative. Deiters-cell projections spanning 4, 3 and 2 rows use mouse data (Wang 2021). The modiolar side is shortened. Sound deflects the basilar membrane. Shear between the reticular and tectorial membranes bends bundles toward their tallest stereocilia, opening MET channels and depolarizing the cells. Outer hair cells shorten with depolarization and lengthen with hyperpolarization through prestin. Inner hair cells do not change length; receptor potentials drive transmitter release at basal ribbon synapses and firing in type I afferents. One 1 kHz cycle (1 ms) is stretched to 1.25 seconds; displacement and bundle tilt are enlarged (illustrative). Readouts show the physical mean spikes per 1 kHz cycle. Membranes run at 1/1250 speed; neural frequency and propagation time use separate schematic scales for visibility (frequency ×50, travel 0.6 display seconds, trail 0.35 seconds). Softer sound makes particles sparser; particle speed stays constant. Basilar-membrane shape and phase, with upward deflection tilting bundles outward, illustrate the classical shear model; they are not measured phases for all frequencies and locations. Inner hair-cell bundles are free of the tectorial membrane; the tallest outer hair-cell stereocilia contact it schematically. This proximity does not reproduce exact attachment. Enlarged motion can produce schematic overlap.

1 kHz cycle shown over 1.25 seconds. Time is slowed; displacement and bundle tilt are enlarged for illustration. The displacement scale is not a quantitative multiple of measured motion. Membranes run at 1/1250 speed; neural frequency and propagation time use separate schematic scales for visibility (frequency ×50, travel 0.6 display seconds, trail 0.35 seconds). Softer sound makes particles sparser; particle speed stays constant. Readouts retain physical mean firing values. Glow and fading trails represent signals, not actual light.