Summary — Part I
Sound is modified by the external ear before causing tympanic membrane to move.
Ossicles transfer this acoustic energy efficiently into the cochlea, resulting in alternating pressure differences between oval and round window (that is, across the cochlear partition — basilar membrane & organ of Corti).
Variations in the mechanical properties of the BM cause a a sinusoidal sound to initiate a travelling wave with maximum displacement at one point on the partition.