The pinna receives sound waves and directs them to the ear drum. The ear drum vibrates, and the vibrations are sent to the ear ossicles in the middle ear. The ear ossicles further transmit the vibrations to the oval window. The oval window passes the vibrations to the fluid of cochlea and causes vibrations in it. The vibrations induce a ripple in the basilar membrane which bends the hair cells, which are pressed against the tectorial membrane. This causes the generation of the nerve impulse which is transmitted to the brain via the auditory nerve. The impulses are analysed, and the sound is recognised or heard.