- What are the ossicles?
- The function of the ossicles
- What problems can the ossicles cause?
The ossicles There are three tiny bones in the ear called a hammer, anvil and stirrup. They are located in the tympanic cavity in the middle ear and are hinged together. So they form the so-called ossicular chain through which the sound from the eardrum is passed over the middle ear to the inner ear. Read all 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 from the eardrum to the labyrinth wall of the tympanic cavity (the border to the inner ear).
The hammer is the largest of the three ossicles. He's about the shape of a club. With his handle, he is firmly connected to the eardrum. A small bone protrusion bulges the eardrum outward. The head is rounded and communicates with the anvil.
The anvil is the middle of the three ossicles and has approximately the shape of a tooth with two roots. He has a joint surface for the hammer and at the other end a small oval head, which connects to the head of the stirrup.
The stirrup is the only bone in the ear whose name actually matches its appearance: it consists of a head, two thighs and a foot plate. The head of this ossicle, with a concave cartilage plate, forms the articular surface for the anvil. The kidney-shaped base plate 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 through the sound pressure - via the chain of ossicles (hammer, anvil, stirrup) to the oval window of the labyrinth (the inner ear).
Hammer and anvil swing around an axis. Without much loss of energy, they pass on the vibrations of the eardrum to the stirrup, which presses like a stamp with his foot plate over the oval window on the liquid in the labyrinth (perilymph) and so passes the sound pressure to them - the perilymph is set in motion. In this sound transmission, a reinforcement takes place 22 times.
Protection from noise
There are two muscles that make sure the sound transmission is optimal. The one, the tensioner of the eardrum, pulls the handle of the hammer and thus the eardrum inwards. He can thus change the tension of the eardrum, adjust it to the volume and thus protect the inner ear from damage.
The other muscle, called stapes muscle, attaches to the head of the stirrup and pulls the head backwards. As a result, the front part of the stirrup plate is levered out of the oval window, the rear part pushed in. This slows down excessive movements of the stirrup and thus protects the inner ear.
What problems can the ossicles cause?
There are isolated malformations of the ossicles that lead to congenital middle ear deafness, inner ear deafness or deafness.
If the foot plate of the stirrup is fixed in the oval window and thus unable to move (otosclerosis), results in a Mittelohrtaubheit.
The paralysis of a facial nerve, the facial nerve, may also affect the ossicles: the nerve supplies, among other things, the stapes muscle. If the nerve is paralyzed, the affected person is hypersensitive to noises (hyperacusis).
Middle ear suppurations can be ossicles destroy and thus reduce the hearing.