Your Audiology Tutorial: Ossicular Chain

You may be familiar with the terms hammer, anvil, and stirrup to describe the three bones that connect the eardrum to the inner ear.   A more academic/medical restatement of that sentence:  You may be familiar with the terms malleus, incus, and stapes to describe the ossicular chain that connects the tympanic membrane in the middle ear space with the oval window in the inner ear.  Stated either way, these tiny bones (the tiniest in the human body, by the way) transmit sounds via vibrations from the drum and exert force on that oval window (a membrane covered opening).

You could think of the bones' vibration as sort of a piston-like action.  Moving medially from the tympanic membrane, the malleus' handle or "head" attaches to it, and articulates with the incus, which in turn articulates with the stapes, which rests against the oval window.   The stapedius muscle stabilizes the stapes by preventing excessive movement of it by pulling it back from the oval window.  If the stapedius muscle isn't contracting properly, normal sounds may be perceived as excessively loud.  The tensor tympani muscle in turn stiffens the ossicular chain by pulling the malleus into the middle ear space.  This physiology is known as the acoustic reflex, which will be explored in more detail in a later entry.

If the stapes' "footplate" is fused/fixed into the oval window, hearing loss may result.  The surgical procedure known as the stapedectomy involves replacement of the entire stapes or within the fused footplate with a prosthesis. Most procedures are successful but I have encountered a few patients who've reported otherwise.