Oval window:

oval window.

membrane-covered opening from the middle ear to the cochlea of the inner ear. Sound waves cause vibration of the tympanic membrane and the ossicles transmit those vibrations to the oval window, which leads to movement of fluid within the cochlea and activation of receptors for hearing.

Read more: Know your brain - Cochlea

Watch this 2-Minute Neuroscience video to learn more about the cochlea.