Oval window

Tower of the Art itself. From this prospect, the circular shaft of the tower is featureless, save for the westward-facing, oval window of the Chamber of Indwelling. And, above the tower s battlements shines the White Sun of Kether—never-setting, constant, and abiding. No matter what time of day or night, or what seasonal appearance may impose itself upon your inner kingdom, the White Sun ever crowns the tower. It is the true beacon by which we ever navigate on the Path of Return. 

Rise and retrace your steps across the little bridge, up the Mound of Power, and over the moat via the draw bridge. Enter the courtyard. As you walk toward the tower—the castle s keep—look up at the oval window. Something about it beckons you. 

Auditory ossicles Oval window of cochlea Inner ear (cochlea] ... 

The 514-inch floppy disks are made from a polyester disk coated with iron oxide and a flexible outer covering. The disk has a large hole in the center, called the drive hole, that is used by the motor in the disk drive to spin the disk. In addition, there is also a 114-inch oval window cut into the case to allow the read/write heads access to the disk media. A small round hole cut into the disk shell next to the drive hole lines up with an even smaller hole cut into the disk media. When this smaller hole spins past the slightly larger hole in the shell, it allows a light to shine all the way through the disk system. In this way, the floppy drive can tell how fast the disk is rotating by how many times in a second that hole appears. 

The bounding interface between the external and middle ear is the tympanic membrane. Pressure variations across the membrane move three ossicles, the malleus (hammer) connected to the membrane, the incus (anvil), and the stapes (stirrup) whose footplate is a piston-Hke structure fitting into the oval window, an opening to the fluid-filled cavities of the inner ear. Ligaments and muscles suspend the middle-ear ossicles so that they move freely. If sound reaches fluids of the inner ear directly, 99.9% of the energy is reflected [Wever and Lawrence, 1954], a 30-dB loss due to the mismatch in acoustic impedance between air and inner-ear fluids. Properties of the external meatus, middle-ear cavity, tympanic membrane, and middle-ear ossicles shape the responsiveness of a species to different frequencies. 

Sound-induced vibrations of the oval window are transmitted through the perilymph and endolymph and stimulate the hair cells that line the cochlea. These in turn stimulate nerve cells that transmit information, via the auditory nerve, to the brain for interpretation of the sounds. 

These vibrations are transferred through the middle ear by a set of three small bones, known as the ossicles, to the oval window of the inner ear. 

The oval window transmits the vibrations to the fluid in the inner ear. 

The middle ear begins on the inner side of the ear drum. The middle ear is an air-filled chamber that vents to the throat through the Eustachian tube. It contains three small bones (ossicles) and two suspensory muscles for them. The three bones are the maleus (hammer), the incus (anvil), and the stapes (stirrup). Sound energy travels across the three bones from the tympanic membrane of the outer ear to the oval window of the inner ear. The action of these three bones produces an amplification of about 2.5 dB. The suspensory muscles are the tensor tympani and the stapedius. When there is a loud sound, these muscles contract and provide some attenuation of energy transmitted across the three bones. 

The main element for hearing is the cochlea or inner ear. It is a fluid-filled coil that has two chambers over its length divided by thin tissue. Sound energy travels from the oval window or base of the cochlea to the distant end or apex of the coil. The waves travel through one chamber and reflect back through the second chamber to the round window, which deflects to adjust for the pressure from the waves. The round window and oval window both separate the inner ear from the middle ear. 

Fig. 7.6. CT virtual endoscopy of the middle ear generated from a point of view located in the external auditory canal, shows the incus (/), malleus (M), promontory (P) and oval window (OVy)...

In the last decade some authors (Mafee et al. 1992) advocated the use of sagittal imaging because it approximates the surgical plane of exposure now it is possible with MPR, and with slightly different degrees of axial and coronal obliquity, para-sagit-tal reconstructions are useful for evaluating most of the relevant structures of the middle and inner ear, except the oval window. 

At VE the posterior sinus tympani can be seen under the eminence of the facial nerve canal and posterior to the oval window. The sinus tympani appears as a parietal depression whose landmarks are given by the ponticulus (superior), the subiculum (inferior-anterior), the pyramidal crest and eminence (posterior-lateral), and the promontory (anterior). Thomassin (1994) describes three types of sinus tympani on the basis of the feasibility of trans-tympanic endoscopy, but their morphology can be easily recognized also at VE sinus tympani of easy exploration, characterized by a simple depression of the tympanic wall sinus tympani of difficult exploration, represented by a depression of the wall that continues into a deep canal through the tympanic wall and opens into the retrotympanum with a little orifice intermediate sinus tympani, with deep canal and large orifice. 

These vibrations are transmitted through the middle ear by three tiny bones known as the ossicles, being the hammer (malleus), anvil (incus) and stirrup (stapes). The hammer bone is fixed to the ear-drum and the stirrup to another membrane (the oval window) which separates the middle and inner parts of the ear. The section of the inner ear which receives sound waves is shaped like a snail s shell (the cochlea) and contains strands of tissue under varying tensions. These strands vibrate in response to sound waves of particular frequency which have entered the inner ear from the bones of the middle ear and produce nerve impulses in the auditory nerve which are then transmitted to the cortex of the brain. It is at this point that the signals are received as sound of a certain pitch, intensity and quality. 

The footplate of the stapes is joined to the round window. Since the eardrum and the membrane of the oval window can be stretched taut by means of muscles, a strong damping effect is achieved for frequencies exceeding 1000 Hz. Young people perceive frequencies of between 18,000 and 20,000 Hz. With advancing age, the audibility of the higher frequencies—namely above 12,000 Hz in people over 50—will decrease. This is called presbyakusia. 

Otosclerosis is an osteodystrophy of unknown aetiology in the enchondral labyrinthine capsule. Described demineralised areas (otospongiotic foci) occur that ossify later (otosclerotic foci). Most of them are very well detectable on CT. Commonly, they are localised near the oval window (Fig. 11.6), less commonly near the round window and around the cochlea and/or vestibular structures. According to the site of foci, fenestral, retrofenestral, and mixed forms are differentiated. 

Fig. 11.6. Otosclerosis, fenestral type. Axial MSCT scan. Otospongiotic plaque at the fissula ante fenestram (arrow)-ventral of the oval window...

---