The middle ear contains three small ossicles: the hammer (or malleus), the anvil (or incus), and the stirrup (or stapes). Named after their resemblance to three building/craft tools, these bones are the smallest in the human body, and their function is to receive sound waves, amplify them, and transmit the sounds from the ear drum into the fluid-filler the inner ear.
The three auditory ossicles function as a bridge between the eardrum and the oval window. The malleus is the most lateral middle ear ossicle, it is located in the epithympanic recess directly in contact with the eardrum. The stapes, located in a medial ear position, is connected to the cochlea and communicates with the malleus thanks to the incus, the intermediate ossicle located between the malleus and the stapes.
The malleus is the largest ossicle in the ear and its main function is to relay the vibrations of the incoming soundwaves produced by the eardrum to the incus. The malleus is made up of 5 parts: the head, the neck, the handle, the anterior process and the lateral process.
The stapes bone is the smallest of the ossicles. It has the fundamental function of enabling communication between the middle ear and the inner ear, transmitting the vibrations carried by the chain of ossicles to the inner ear. It is located in the center of the ear, connecting with the incus on one side and the oval window on the other. It was discovered by Professor Gianfilippo Ingrassia of the University of Naples in 1546.
The stapes consists of a head, two arches and a base. The head is linked to the incus lenticular process, the two arches (anterior and posterior) join the head with the base, which is a thin elliptical bone that occupies the oval window.
As far as the phylogenetically formation of the ear bones is concerned, the incus and the malleus in mammals were formed respectively from the quadrate and the articular, the two bones of the oral arch that allow maxilla-mandibula articulation in fish. The formation of the stapes, on the other hand, derives from the mandibular bone, i.e., the dorsal portion of the hyoid arch that in fish serves as the suspension of the oral arch.
Mastoiditis is the inflammation of the mastoid process, the posterior lateral portion of the temporal bone, otherwise known as the area with a palpable bony protuberance behind the ear lobe. Often middle ear infections can extend to the mastoid through the mastoid antrum. The mastoid antrum is the microorganism responsible for this inflammation as well as as for otitis. The symptoms of mastoiditis usually appear days or weeks after the onset of acute otitis.
Although the most symptoms are intense, throbbing ear pain with decreased hearing, fever and headache, the infection can worsen to the point of perforating the tympanic membrane. Generally, intensive therapy with intravenous antibiotics is the most resorted to treatment for mastoiditis.
Otosclerosis is an ear disease that leads to progressive hearing loss. The disorder originates in the otic capsule, the structure that protects the ear labyrinth, where bone tissue begins to degenerate. Over time, a buildup of newly formed bone is created, eventually affecting the oval window, the opening between the middle ear and the vestibule of the inner ear.
Otosclerosis is most often an inherited condition that reduces the mobility of the stapes, causing hearing loss. It usually occurs in adults, more frequently in women. The progression of otosclerosis can be slowed by certain medical therapies, including the administration of sodium fluoride. A hearing aid or surgery can help in restoring hearing ability and rehabilitating movement between the bracket and the oval window.