Superior to the handle, the lateral process projects laterally as a slight cone at the root of the handle. auditory ossicles The chain of three tiny bone in the middle ear which acts as an impedance transformer, efficiently coupling the relatively large low-impedance movement of the ear drum to the smaller, high-impedance movement of the fluid in the cochlea of the inner ear. Journal of Otology. This converts large-amplitude low-force vibrations into small-amplitude, high-force vibrations. The features that can be identified on the stapes are the head (capitulum), anterior limb, posterior limb, and base (footplate). The auditory ossicles transmit vibrations of the tympanic membrane through the middle ear to the oval window. National Institute on Deafness and Other Communication Disorders. The purpose of the auditory ossicles (also called the ossicular chain) is to transmit sound via a chain reaction of vibrations that connects the eardrum to the inner ear and cochlea. Information about Hybrid Cochlear Implants, Here Are Some Possible Causes Of That Ringing in Your Ears, Inside the History of the Cochlear Implant, Balance Problems for Children With Hearing Loss, Everything You Need to Know About Auditory Training, What You Should Know About Otoacoustic Emissions (OAE) Hearing Tests, What to Expect With Cochlear Implant Surgery, older people more vulnerable to hearing damage, Otitis media (middle ear infection) in adults, Otosclerosis: thirty-year follow-up after surgery, Dislocation of the auditory bones due to a fracture, trauma, or a chronic infection, Eardrum perforation or infection (myringitis) which reduces the vibrational impulses to the auditory bones, Middle ear infections which can cause fluid buildup that restricts auditory bone movement. The term ossicles may also refer to the smaller bones of the human body. Ear bone, also called Auditory Ossicle, any of the three tiny bones in the middle ear of all mammals. The auditory ossicles are a chain of small bones in the middle ear that transmit sound from the outer ear to the inner ear through mechanical vibration. The top or head of the malleus and the body of the incus are held together by a tightly fitting joint and are seated in the attic, or upper portion, of the eardrum cavity. When it contracts, it pulls the handle of the malleus medially which tenses the tympanic membrane. It's important to note, however, that this is not an instantaneous response. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The base of the stapes (footplate) then sits in the oval window of the labyrinthine (medial) wall of the tympanic cavity. Learn the anatomy of the ear very fast and most efficiently using Kenhub's labelling ear diagrams and quizzes! Ossicular chain discontinuity is typically treated with a hearing aid, or through ossicular chain reconstruction surgery. Register now doi:10.7860/JCDR/2017/23906.9147. Last reviewed: September 21, 2020. On its posterior side, it articulates with the body of the incus posterolaterally by a small synovial joint: the incudomalleolar joint. All rights reserved. Two ligaments suspend the incus in place: The most medial and smallest auditory ossicle is the stapes (stirrup). The handle of the malleus (also known as the manubrium) is a downward extension embedded into the medial surface of the tympanic membrane. The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. Though the term may refer to any small bone throughout the body, it typically refers to the malleus, incus, and stapes (hammer, anvil, and stirrup) of the middle ear. In addition to facilitating hearing, the auditory ossicles serve a protective function when exposed to continuous, loud noises. Injury can cause hearing loss, sometimes severe, and may include: Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. The tightening reduces the eardrum's ability to vibrate, thereby limiting the movement of auditory ossicles and the impact of the sound. This action tightens the annular ligament of the stapes, reducing oscillation and preventing excessive movement of the stapes. Jamie Berke is a deafness and hard of hearing expert. Movement of the oval window generates a wave in the fluid filled internal ear which stimulates receptor cells to transmit electrical signals to the brain via the cochlear part of the vestibulocochlear nerve (CN VIII). Updated July 17, 2018. Together they form a short chain that crosses the middle ear and transmits vibrations caused by sound waves from the eardrum membrane to the liquid of the inner ear. Once the vibrations reach the cochlea, a hollow, snail-like chamber filled with fluid, they are translated into nerve impulses which the brain interprets as sound. There are a number of causes including trauma, infection, malformation of the bones from birth, otosclerosis (abnormal growth of the ossicles), or chronic suppurative otitis media (inflammation). When we hear something, this sound must be converted from sound waves into electrical signals for the brain to process. This article will explore the function of the auditory ossicles, their bony features, articulations, associated muscles, and some clinical aspects. This process allows sound to be transformed into electrical signals which are then sent to the brain. Together they form a short chain that crosses the middle ear and transmits vibrations caused by sound waves from the eardrum membrane to the liquid of the inner ear. American Hearing Research Foundation. The names of the bones that comprise the auditory ossicles are taken from Latin. The anterior and posterior limbs arise from the head, and attaches to the oval shaped base. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. At its inferior end, it bends on a 90° angle to form the lenticular process which articulates with the head of the stapes by the incudostapedial joint. This process lessens movements of the auditory ossicles and thus dampens vibrations caused by loud sounds to protect structures of the internal ear. 2017;11(1):AC01-04. At the end of the handle is the spatulate process of the malleus which attaches to the pars tensa of the tympanic membrane with ligaments. There are three tiny articulating bones in the middle ear known as ossicles (from lateral to medial): malleus. Read more. The ossicles transmit mechanical vibrations of the tympanic membrane across this chain to the oval window where fluids of the inner ear will move and excite receptors. There are two tiny muscles in the middle ear, which serve to alter the tension on the ear bones and thus the intensity (degree of loudness) of sounds. These are the malleus, or hammer, the incus, or anvil, and the stapes, or stirrup. The malleus translates to the "hammer," the incus is the "anvil," and the stapes is the "stirrup.". Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. These are the malleus, or hammer, the incus, or anvil, and the stapes, or stirrup. The body of the incus articulates with the head of the malleus anterolaterally. The bones of the ear, also known as the auditory ossicles, are the three smallest bones in the human body. Morphological variations of middle ear ossicles and its clinical implications. Superior to the lateral process, and inferior to the neck, it projects anteriorly like a spindle and attaches to the anterior wall of the middle ear. Our editors will review what you’ve submitted and determine whether to revise the article. Their role is to mechanically amplify the vibrations of the tympanic membrane and transmit them to the cochlea where they can be interpreted as sound. Ann Otol Rhinol Laryngol. The evolution of mammalian auditory ossicles was an evolutionary event that resulted in the formation of the bones of the mammalian middle ear. First, movements of the medial portion of the tympanic membrane will move the handle of the malleus medially as well. Thank you, {{form.email}}, for signing up. The most lateral and largest of the auditory ossicles is the malleus (hammer). Three small ligaments hold the head of the malleus, and a fourth attaches a projection (called the short process) from the incus to a slight depression in the back wall of the cavity. Kenhub. 2011;120(9):608-614. doi:10.1177/000348941112000909. As such, the eardrum and hearing may not be protected from a sudden, loud burst of noise.. The stapedius muscle runs from its attachment on the inside of the pyramidal eminence of the mastoid (posterior) wall of middle ear, through a foramen at the apex of the pyramidal eminence, passes anteriorly, and inserts onto the posterior aspect of the neck of the stapes. Like the head of the malleus, it sits in the epitympanic recess. The base of the stapes is attached to the oval window, and so the medial movement of the stapes means that the oval window is also moved medially. It consists of the: body, short limb, long limb/process, and lenticular process. The long process of the incus is bent near the lower end and carries a small knoblike bone that is jointed loosely to the head of the stapes—the third and smallest of the ossicles. Auditory ossicles: want to learn more about it? On the opposite side of the tympanic membrane, the medial side, the malleus is attached with its handle. Medline Plus. Dahlin Redfors Y, Möller C. Otosclerosis: thirty-year follow-up after surgery. When it contracts, the stapes is pulled posteriorly and its base is tilted inside the oval window. They articulate with each other through synovial joints to form a chain across the length of the middle ear from the tympanic membrane (laterally) to the oval window (medially). This type of injury can be due to trauma like a head injury or infection. The auditory ossicles are a chain of small bones in the middle ear that transmit sound from the outer ear to the inner ear through mechanical vibration. Otitis media (middle ear infection) in adults. Age-related hearing loss. The word ossicle is derived from the Latin word Ossiculum that literally means tiny bone. This leads to a hypersensitivity to loud noises known as hyperacusis. Alexandra Osika In turn, this moves the head of the malleus laterally, which moves the head of the incus laterally as well because the head of the malleus and head of the incus articulate with each other. Stanford Children's Health. The event is well-documented and important as a demonstration of transitional forms and exaptation, the re-purposing of existing structures during evolution. The ossicles are situated in the middle ear and suspended by ligaments. The short limb projects posteriorly from the body and is the site of attachment for the posterior ligament of the incus. Read more. • The second, called stapedius, tends to pull the footplate of the stapes out of the oval window. The handle of the malleus adheres to the upper half of the drum membrane. As the head of the incus moves laterally, its long process is moved medially. First, sound waves enter the external acoustic meatus, or ear canal, and vibrate the tympanic membrane that is located at the end of this canal. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. The anterior process is also called the Folian or Rau’s process. One, the tensor tympani, is attached to the handle of the malleus (itself attached to the eardrum membrane) and by its contraction tends to draw the malleus inward, thus increasing drum membrane tension. Since the base of the stapes (attached to the oval window) is much smaller than the tympanic membrane, the vibratory forces at the base is 10 times greater than that at the tympanic membrane. 2020 This is accomplished by tipping the stirrup, or stapes, backward.