Sound waves are transmitted to the cochlea in the inner ear by the ossicles vibrating the oval window, which pushes fluid through the cochlea, causing the basilar membrane to vibrate. The basilar membrane is narrower and stiffer at the basal end, the side nearest to the oval window; and wider and more flexible at the apical end. As a result, the basal end vibrates maximally in response to high frequencies; and the apical end vibrates maximally in response to low frequencies, creating tonotopy, a topographic map of pitch. Vibration of the basilar membrane creates a shearing force on the hair cells that are sandwiched between it and the stiffer tectorial membrane, generating a neural signal onto the auditory nerve cells in that location. Therefore, high frequencies activate auditory nerve cells at the basal end of the cochlea, while low frequencies activate those at the apical end. This tonotopy is maintained through the auditory pathway to the brain where it aids in pitch discrimination.