Stapes

The stirrup ( stapes Latin ) is the third of the ossicles in the middle ear of mammals. The stirrup is the smallest bones of the human body. He is on average 3.3 mm high, the foot plate 3 mm long and 1.4 mm wide. He has a mass 3-4 mg.Der stapes bears its name because of its shape and makes a connection between the anvil and with it articulated the cochlea in the inner ear.

Phylogenesis

In the amphibians, reptiles and birds, the bone is better termed the columella, it is derived from the hyomandibular of fishes. In bony fish ( Osteichthyes ) quadratum Os and Os form the primary articular TMJ. The os on the other hand combines the hyomandibular Os quadratum with the bones of the skull roof. Also form in reptiles quadratum Os and Os articulare a primary jaw joint, but here is the Os quadratum directly connected to the skull roof. From the Os hyomandibular was among the reptiles have the columella and thus ossicles.

Anatomy

The foot plate of the stapes ( stapedis base surface about 3.2 mm ²) touches the oval window of the cochlea, and transmits the vibrations to the fluid in the interior of the screw. From the footplate go from two legs ( crura stapedis ), who meet in the throat. The latter passes into the head, which is pivotally connected to the anvil. Embryonic gives the stirrup from the upper part of the second branchial arch, called the hyomandibular ( Reicher Chernobyl cartilage). The unique in the animal kingdom form of the stapes in mammals with two legs comes about because of the stapes develops in the embryo around which later forming stirrups artery ( stapedial ).

A stirrup leading to muscle ( stapedius muscle ) may be influenced by the mobility of the ossicular chain tension. Exposure to high sound pressure on the ear, the muscle tightens reflexively and stiffens the ossicular chain. This process is attributed to the function of protecting the inner ear. The stapedius is the smallest muscle of the human striated muscle.

The acoustic reflex can be measured by means of tympanometry and says, among other things, something about the tightness of the tympanic membrane, the mobility of the ossicular chain and on the state of nerve connections in the brain stem and the auditory and facial nerves.