Auditory ossicle

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... 

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. 

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

Li, D. J., Ohsa, K., Li, K., Ye, Q., Nobuto, Y, Tenshin, S., and Yamamoto, T. T. 1997. Long-term observation of subcutaneous tissue reaction to synthetic auditory ossicle (Apaceram") in rats. The Journal of Laryngology and Otology ill 702-06. 

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. 

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. 

Fig. 11.2a,b. Inflammation. Coronal MPR. Secondary cholesteatoma of the middle ear (a) with completely opacified tympanic cavity, destructed ossicles, small erosions along the walls of the tympanic cavity, and at the canal tympanic facial nerve segment (arrow), protrusion of the drum, soft tissue masses in the external auditory canal, reduced mastoid pnemiiatisation. 

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