Ossicles

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

Khera et al. (1970) also reported reproductive studies with Dlquat. Pregnant rats were injected with 7 or 14 mg/kg on one of several days during organogenesis. (Higher doses frequently resulted in maternal death). Skeletal sternum defects and non-ossification or absence of one of the auditory ossicles were noted in some fetuses (ref. 118, abstr. 395) ... 

When a sound pressure wave impinges on the ear, it is amplified by the external auditory meatus and causes the tympanic membrane to vibrate in a characteristic manner. This vibration is transformed by the auditory ossicles of the middle ear into movements of the stapedial footplate. These movements create pressure waves in the fluids of the inner ear which displace the basilar membrane of the cochlear duct and cause the hair cells located on the top of the basilar membrane to generate electrical potentials. This potential elicits impulses in the auditory nerve. After the auditory nerve, the nerve impulses are transmitted through the cochlear nuclei, the trapezoid body, the... 

Grossly the tumors are white, gray, red, brown, or yellow and may be localized or fill the entire middle ear, often encasing the ossicles. Microscopically, MEAs are characterized by architectural diversity and cytologic uniformity. Some are composed of well-formed glands, sheets of cells, small cells/or clusters, short trabeculae, or a combination of these patterns (Eig. 9.31). Individual cells vary from round or cuboidal to columnar... 

The TGF-/J isoforms are powerful inducers of endochondral bone when implanted in the rectus abdominis muscle of the primate Papio ursinus at doses of 1, 5, and 25 gg per 100 mg of collagenous matrix as carrier, yielding large corticalized ossicles by day 90 (Figs. 4 and 5). Endochondral bone initiated by TGF-y3 isoforms expresses mRNA of bone induction markers including BMP-3 and OP-1 [55-57]. 

The ear consists of three parts the external, middle, and inner ear. The external ear consists of the pinna and the external auditory canal that transmits sound to the middle ear. The middle ear has an air-filled cavity that contains auditory ossicles, which are the malleus, incus, and stapes. The auditory ossicles forward the sound to the inner ear where the eardrum is located. Pressure on both sides of the eardrum is equalized by the eustachian tube that connects to the nasopharynx. The eardrum could rupture if pressure becomes unequal. The inner ear also contains a series of canals called the labyrinths that are made up of the vestibule, cochlea, and semicircular canals. The vestibule maintains equilibrium and balance and the cochlea is the principal hearing organ. 

Polymeric materials have been used to replace the external part of the ear (usually silicones) and also to replace the ossicles (PTFE, polyethylene, silicones) as well as serving as drainage tubes for the ear (ll). In addition some research has been done in which electrodes are implanted into the cochlea and are connected to an external microphone. Such devices have been able to restore a significant amount of hearing to deaf people. Plastics are used in these primarily as coatings for the wires and electronic parts (lU, 53, 5 ). 

Human hearing arises from airborne waves alternating 50 to 20,000 times a second about the mean atmospheric pressure. These pressure variations induce vibrations of the tympanic membrane, movement of the middle-ear ossicles connected to it, and subsequent displacements of the fluids and tissues of the cochlea in the inner ear. Biomechanical processes in the cochlea analyze sounds to frequency-mapped vibrations along the basilar membrane, and approximately 3,500 inner hair cells modulate transmitter release and spike generation in 30,000 spiral ganghon cells whose proximal processes make up the auditory nerve. This neural activity enters the central auditory system and reflects sound patterns as temporal and spatial spike patterns. The nerve branches and synapses extensively in the cochlear nuclei, the first of the central auditory nuclei. Subsequent brainstem nuclei pass auditory information to the medial geniculate and auditory cortex (AC) of the thalamocortical system. 

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. 

Recent research has focused on the use of PPF to fill irregular-shaped bone defects such as ear ossicle or mandibular defects. In both circumstances, PPF-based scaffolds allow the design of structures that may not be attainable from non-cross-linkable degradable polymers. -" ... 

S. Danti, D. D Alessandro, A. Pietrabissa, M. Petrini, S. Berrettini, Development of tissue-engineered substitutes of the ear ossicles PORP-shaped poly(propylene fumarate)-based scaffolds cultured with human mesenchymal stromal cells. J. Biomed. Mater. Res. A 92 (4) (2010) 1343-1356, doi 10.1002/jbm.a.32447. 

As a result of this combination of properties bioactive glasses are not found in load-bearing applications, rather they are used as coatings on metals, in low-loaded or compressively loaded devices, in the form of powders, and in composites. The first successful use of Bioglass 45S5 was as a replacement for the ossicles (tiny bones) in the middle ear. The position of these bones (the malleus, incus and stapes) is illustrated in Figure 35.6. 

FIGURE 35.6 (a) The middle ear cavity and the auditory ossicles, (b) Ear implants. 

Incus (anvil) The middle of the three ear ossicles of the mammalian middle ear. 

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