Auditory ossicles12/4/2023 ![]() The main function of the middle ear is to transmit the sound waves from the external environment to the inner ear. The stapes articulates with the oval window of the inner ear. It is known as the smallest bone within the human body. The stapes is the third ossicle and consists of the head, legs, and footplate. The incus connects with the stapes and forms the incudo-stapedial joint. The incus is the second ossicle and is divided into the body, short process, and long process. The head of the malleus attaches to the incus and forms the incudo-malleolar joint. The handle of the malleus attaches loosely to the tympanic membrane. It is divided into four parts: the head, neck, short process, and handle. The malleus is the first ossicle and attaches to and moves with the tympanic membrane. These three ossicles connect the tympanic membrane to the inner ear allowing for the transmission of sound waves. The middle ear consists of the tympanic membrane and the bony ossicles called the malleus, incus, and stapes. The ear structures are classically divided into three parts: the external ear, middle ear, and inner ear. The ossicles play a role in multiple clinical scenarios, including otosclerosis, choleastoma, and facial nerve palsy. Middle ear anatomy consists of intricate relationships between nerves, blood supply, and muscles. The stapes connects to the oval window allowing for mechanical energy to be transferred to the fluid-filled inner ear. The malleus connects to the tympanic membrane transferring auditory oscillations to the incus and then the stapes. The auditory ossicles (malleus, incus, and stapes) play a key role in this function. Verifies Bekesy's recent optical analysis.The middle ear functions to connect the sound waves from the external environment and transfer them to the inner ear for auditory transduction. Resulting foot plate motion is rotation around an axis at the posterior margin, with increased displacement the rotation around the inferior margin becomes more dominant. Resulting thrust gives a maximum displacement to a point on the margin of the foot plate located 33° superior to the anterior margin. Arch of Stapes found to tilt 23° down from perpendicular to foot plate and 7° forward. Head of Stapes when attached to Incus, contact at inferior side, thrust up and anterior or down and posterior. A second displacement component exists at right angles to the axis of the long crus of Incus. Corrugations of articulating surfaces exist but no locking of “Sperrzähne” determinable. Resulting undistorted motion makes 57° angle with axis of long crus of Incus in an anterior direction. ![]() The articulating surfaces turn this motion 39°. Motion communicated to lenticular process of Incus recorded with a 1/100 mm displacement gauge. Manubrium of Malleus given deflections to 10° in horizontal plane. Lever arms with locked Malleus‐Incus joint, 1.27 to 1.00. ![]() Axis of rotation, vertically down, without passing through Incus, passing through center of gravity of Malleus and terminating in its anterior process. Incus' short crus pointed upward about 80° with rotating plane, supported at this end by a small depression simulating the fossa incudis. Model mounted on a turntable with anterior process of Malleus in axis of rotation, and articulating surface up, that of Incus down. Ossicles model, 24 magnification, was constructed with accurate scale reproduction of articulating surfaces. ![]()
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