ossikler

Ossikler, or ossicles, are the three small bones in the middle ear that transmit sound from the eardrum to the inner ear. The set comprises the malleus (hammer), incus (anvil), and stapes (stirrup). They form the core of the ossicular chain that connects the tympanic membrane to the oval window of the cochlea.

Their primary function is to convey and amplify sound vibrations. When the eardrum vibrates, the malleus moves the incus, which in turn moves the stapes. This lever action increases the pressure of the vibrations at the oval window, aiding the efficient transfer of air-based sound into fluid in the inner ear. The stapedius and tensor tympani muscles can stiffen the ossicular chain to protect the inner ear from loud sounds.

Anatomically, the malleus is anchored to the tympanic membrane, the incus links the malleus to the stapes, and the joints between the bones allow precise movement. The entire apparatus is housed in the air-filled tympanic cavity and is connected by ligaments and tiny muscles.

development and evolution notes: in mammals, the ossicles originate from pharyngeal arches during embryonic development—malleus and incus derive from the first arch, while the stapes comes from the second arch. This trio is a key feature distinguishing mammals from many other vertebrates, which may utilize a single or fewer middle-ear bones.

Clinical relevance: disorders of the ossicles, such as otosclerosis, can immobilize the stapes and cause conductive hearing loss. Disruption of the ossicular chain from trauma or disease may be treated with ossiculoplasty or prosthetic reconstruction to restore hearing.