Structure & Function 

(Note: Move your mouse over the above images to highlight the various anatomical parts of the human ear.)

The auricle is the visible part of the outer ear. It consists of floppy, oval irregular shaped cartilage tightly covered with skin. It acts like a cupped hand to focus the sound waves into the ear hole (external auditory canal).

The skin of the outer part of the external auditory canal has hairs and glands which produce wax and oils. The canal is about 1 inch/2.5 cm long and ends at the ear drum (tympanic membrane). It collects and directs the sound wave energy to move the ear drum, which is a thin, flexible transparent membrane resembling cling-film stretched over a small hoop.

The middle ear is an air-filled cavity about 0.1 in3 /1-2 cm3 in volume. It contains 3 hearing bones (ossicles), namely the hammer bone (malleus), anvil bone (incus) and stirrup bone (stapes), which amplify the sound energy nearly 20x by a lever mechanism. The stapes connects to a window (oval window) in the inner ear.

In front the middle ear cavity connects with the Eustachian tube, which joins the back of the junction of the nose and throat. Swallowing opens the tube by pulling the muscles in its walls, which allows air to pass into the middle ear. For optimum sound transmission it is essential for the air pressure in the middle ear to be the same as the outside air pressure in the external canal. Behind the cavity connects with the air cells inside the mastoid bone, which provides a reserve air supply should the Eustachian tube become blocked.

The inner ear is a system of soft walled tubes embedded about 2 inches/5 cm inside the head within the hardest bone in the human body. Internally the hearing hair cells in the cochlea and balance hair cells in the labyrinth are bathed in fluids (endolymph and perilymph), which nourish and clear waste products. Sound energy arriving at the outer ear, amplified by the middle ear, sends a shock wave through the inner ear fluids. This excites delicate hairs in the cochlea creating a nerve impulse which in turn is transferred along the hearing (auditory) nerve, through pathways in the lower part of the brain to the auditory cortex, the site where sound is actually heard.