Sound waves are gathered by the pinna and directed down the auditory canal to the ear drum or tympanic membrane. The mechanical energy of the sound causes the ear drum to vibrate. This in turn causes vibration of the 3 middle ear bones, first the malleus, then the incus, and finally the stapes. These tiny bones amplify the vibrations. The stapes comes in contact with the inner ear at the oval window. The fluid-filled inner ear is a coiled structure called the cochlea. Vibrations conveyed to the fluid cause bending of hair cells. If we examine this cross section of the cochlea, the tectorial membrane can be seen at the top. In it are embedded the tips of hair cells, which are shown circled in yellow. When the hair cells bend in response to vibration, the rate of firing by the neurons at their bases changes. These signals are conveyed to the brain and perceived as sound.