Auditory ossicles

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The ossicles are three tiny bones in the ear called the hammer, anvil, and stapes. They are located in the middle ear in the tympanic cavity and are connected to one another in an articulated manner. They form the so-called ossicular chain through which the sound is conducted from the eardrum via the middle ear to the inner ear. Read everything you need to know about the ossicles: hammer, anvil & stirrup (ear)!

What are the ossicles?

The ossicles (hammer, anvil, stirrup) are located in the upper part of the tympanic cavity and represent the connection between the eardrum and the labyrinth wall of the tympanic cavity (the border to the inner ear).

hammer

The hammer is the largest of the three ossicles. It is roughly shaped like a club. With its handle it is firmly connected to the eardrum. A small protrusion of bone bulges the eardrum outward. The head is rounded and communicates with the anvil.

anvil

The anvil is the middle of the three ossicles and is roughly the shape of a tooth with two roots. It has a joint surface for the hammer and at the other end a small oval head that connects to the head of the stapes.

stirrup

The stirrup is the only bone in the ear whose name actually matches its appearance: it consists of a head, two legs and a footplate. The head of this ossicle forms the joint surface for the anvil with a concave cartilage plate. The kidney-shaped footplate is movably fixed in the oval window.

The function of the ossicles

The function of the small bones in the ear is to transmit the vibrations that act on the eardrum due to the sound pressure - via the chain of the ossicles (hammer, anvil, stirrup) to the oval window of the labyrinth (of the inner ear).

The hammer and anvil swing around an axis. They pass the vibrations of the eardrum on to the stapes without much loss of energy, which presses the liquid in the labyrinth (perilymph) like a stamp with its footplate over the oval window and thus transmits the sound pressure to it - the perilymph is set in motion. With this sound transmission, there is a 22-fold amplification.

Protection from noise

There are two muscles that ensure that sound transmission is optimal. One, the tensioner of the eardrum, pulls the handle of the hammer and thus the eardrum inward. He can change the tension of the eardrum, adjust it to the volume and thus protect the inner ear from damage.

The other muscle, called the stapes muscle, attaches next to the head of the stapes and pulls the head backwards. As a result, the front part of the stirrup plate is levered out of the oval window and the rear part is pushed in. This slows down excessive movements of the stapes and protects the inner ear.

What problems can the ossicles cause?

There are isolated malformations of the ossicles that lead to congenital middle ear hearing loss, inner ear hearing loss, or deafness.

If the footplate of the stapes is fixed in the oval window and therefore unable to move (otosclerosis), middle ear deafness results.

The paralysis of a facial nerve, the facial nerve, can also affect the ossicles: The nerve supplies the stapes muscle, among other things. If the nerve is paralyzed, the person affected is over-sensitive to sounds (hyperacusis).

Middle ear suppurations can destroy the ossicles and thus impair hearing.

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