Anatomy of the Ear

The human ear is divided into three compartments: the external ear, middle ear, and inner ear. The external ear is the auricle, or pinna, a cartilage-supported fleshy flap that helps to funnel sound waves into the external auditory canal. Sound waves travel down this canal to the tympanic membrane, a thin sheet of connective tissue also known as the eardrum. When sound waves strike the tympanic membrane, it vibrates. The mechanical energy of the sound waves is converted into the mechanical energy of eardrum vibration. On the other side of the tympanic membrane lies the middle ear, or tympanic cavity. This is an air-filled, mucosa-lined cavity, which lies within the petrous portion of the temporal bone. The middle ear is flanked laterally by the eardrum and medially by a bony wall with two membrane-covered openings, the oval window and the round window. Running from the middle ear to the nasopharynx is the Eustachian, or phayngotympanic tube. The tube allows air pressure in the middle ear to equalize with air pressure in the atmosphere. Medial to the middle ear is the inner ear, which contains the spiral-shaped cochlea, where sound waves are transduced into neural signals, and the vestibular complex, which contains the receptors for our sense of equilibrium. These sensory organs of the inner ear lie within the so-called “membranous labyrinth”, which is visible here as the blue tube within the cochlea. Surrounding and protecting the membranous labyrinth is the bony labyrinth. Note that within the cochlea, the membranous labyrinth is known as the cochlear duct and the bony labyrinth is known as the bony cochlea. Between the bony and membranous labyrinths flows the perilymph. Within the membranous labyrinth is a fluid called endolymph.