The ear is more than the fleshy protrusion coming from the side of the head that is used to hold our glasses in place. In fact, the ear contains a multitude of intricate anatomic and physiologic specializations that very efficiently convert mechanical vibrations of the outside world into a digital “code” that travels along a nerve “cable” that runs to the brain. Vibrations to which the ear is sensitive include both sounds and movements of the head. The ear is thus responsible for the senses of hearing and balance.
The Three Anatomic Divisions of the Ear
Anatomically, there are three major divisions of the ear. This gets confusing, primarily because you can’t readily see all of them.
- The outer ear includes both the fleshy protrusion from the head and the canal that leads to the ear drum. The ear canal is where cerumen (i.e. ear wax) is generated and stored. The outer ear acts as a funnel for sound, directing sound towards the ear drum.
- The inner ear is composed of a series of interconnected fluid-filled canals encased in the dense bone of the skull (the temporal bone). Lining portions of these canals are the cells that have tiny hairs at their tops that vibrate with movement of the inner ear fluids. Vibration of these hairs induce these cells – appropriately called “hair cells” -- to begin the chain reaction that leads to nerve impulses carried along the hearing and balance nerves.
- The middle ear is an air-filled cavity that bridges the ear drum with the membranous window of the inner ear fluids. The middle ear contains the three smallest bones in the body – the incus, malleus, and stapes – that form this bridge. These three bones, or “ossicles,” are interconnected so as to focus the forces of ear drum motion in order to drive the inner ear fluids to vibrate during sound stimulation. The middle ear in abnormal cases can collect body fluid and bacteria, and this situation is what occurs in the typical “ear infection” commonly seen primarily in children.
The Eustachian Tube
- The middle ear tends to keep slightly negative pressure with respect to the outside. An opening into the middle ear is the eustachian tube, which runs from the back of the nose into the middle ear. Although the eustachian tube is usually closed shut, we can open it by yawning, swallowing, or blowing air through the nose while pinching it shut. This acts to equalize pressure in the middle ear – and this is how we “pop” our ears. If the eustachian tube does not work properly or gets blocked in the back of the nose, the middle ear holds too strong a vacuum. Not only is this uncomfortable, especially on an airplane or underwater where the outside pressure is even higher than normal, but it can lead to ear infections and cholesteatomas in the long term. Sometimes, a small grommet (or “ear tube”) needs to be placed in the ear drum to prevent this build up of vacuum pressure by holding open a hole in the drum. The procedure to place these ear tubes is the most commonly performed procedure done by an ear-nose-and-throat physician.