Kuuloluut

Kuuloluut are the three small bones in the middle ear that transmit sound from the eardrum to the inner ear. They are the malleus (hammer), incus (anvil), and stapes (stirrup). The malleus is connected to the eardrum, the incus bridges the malleus and the stapes, and the stapes footplate fits into the oval window of the cochlea.

These bones form a chain of synovial joints that converts airborne vibrations into mechanical energy suitable for the fluid-filled inner ear. Together, they provide impedance matching, enhancing the pressure and movement of sound as it passes into the cochlea. The arrangement functions as a lever system and an area transformer, increasing the efficiency of sound transmission across the middle ear.

Embryologically, the kuuloluut arise from pharyngeal arches: the malleus and incus derive mainly from the first arch (Meckel’s cartilage), while the stapes originates from the second arch (Reichert’s cartilage). In mammals, these three bones form a distinctive middle ear apparatus that contrasts with the structures found in many non-mammalian vertebrates.

Clinically, dysfunction or fixation of the kuuloluut can cause conductive hearing loss. Otosclerosis, for example, stiffens the stapes and reduces mobility. Surgical interventions such as stapedotomy or stapedectomy aim to restore ossicular mobility and improve hearing. Inflammation or infection of the middle ear (otitis media) can also affect the bones’ function and the transmission of sound.