| acoustic pressure | In ultrasound, the instantaneous value of the total pressure minus the ambient pressure; unit is pascal (Pa). (05 Mar 2000) |
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| acoustic radiation | The fibres that pass from the medial geniculate body to the transverse temporal gyri of the cerebral cortex by way of the sublentiform part of the internal capsule. Synonym: radiatio acustica. (05 Mar 2000) |
| acoustic reference level | The biological reference level for sound measurements. When the term decibel is used to indicate the noise level, a reference quantity is implied; this reference value is usually expressed as a sound pressure of 20 micronewtons per square meter. The reference level is referred to as 0 decibels, the baseline of the scale of noise level's; this baseline is considered the weakest sound that can be heard by a person with very good hearing in an extremely quiet location. Other equivalent reference level's still being used include 0.0002 microbar and 0.0002 dyne per square centimeter. (05 Mar 2000) |
| acoustic schwannoma | <tumour> A benign neoplasm of the intracranial segment of the eighth cranial nerve, producing cerebellar, lower cranial nerve, and brainstem signs and symptoms. Synonym: acoustic neuroma, cerebellopontine angle tumour, eighth nerve tumour. (05 Mar 2000) |
| acoustic shadow | Sonographic appearance of reduced echo amplitude from regions lying beyond an attenuating object. Compare: acoustic enhancement. (05 Mar 2000) |
| acoustic spots | See: macula of utricle, macula of saccule. Bitot's spots, small, circumscribed, lusterless, grayish white, foamy, greasy, triangular deposits on the bulbar conjunctiva adjacent to the cornea in the area of the palpebral fissure of both eyes; occurs in vitamin A deficiency. (05 Mar 2000) |
| acoustic striae | Slender fascicles of fibres extending transversally below the ependymal floor of the ventricle from the median sulcus to enter the inferior cerebellar peduncle. They arise from the arcuate nuclei on the ventral surface of the medullary pyramid. Synonym: striae medullares ventriculi quarti, acoustic striae, auditory striae, Bergmann's cords, medullary teniae, teniae acusticae. (05 Mar 2000) |
| acoustic tetanus | Experimental tetanus induced by a faradic current, the speed of which is estimated by the pitch of the vibrations. (05 Mar 2000) |
| acoustic tolerance | The maximum sound pressure level that can be experienced without producing pain or permanent defect of hearing in a normal individual. (05 Mar 2000) |
| acoustic trauma deafness | Sensorineural hearing loss due to overexposure to high intensity noise levels. Synonym: boilermaker's deafness, industrial deafness, occupational deafness. (05 Mar 2000) |
| acoustic tubercle | The slight prominence of the floor of the lateral recess of the fourth ventricle, corresponding to the underlying cochlear and vestibular nuclei. Synonym: acoustic tubercle, trigonum acustici. (05 Mar 2000) |
| acoustic vesicle | One of the paired sacs of invaginated ectoderm that develop into the membranous labyrinth of the internal ear. Synonym: acoustic vesicle, otic vesicle. (05 Mar 2000) |
| bony part of external acoustic meatus | The medial two-thirds of the external acoustic meatus which is formed as the tympanic plate of the temporal bone develops; it extends approximately 16 mm. From its junction with the cartilaginous part to the tympanic membrane. (05 Mar 2000) |
| cartilage of acoustic meatus | The cartilage that forms the wall of the lateral part of the external acoustic meatus. It is incomplete above and is firmly attached to the margins of the bony part of the external meatus. Synonym: cartilago meatus acustici, meatal cartilage. (05 Mar 2000) |
| cartilaginous part of external acoustic meatus | The lateral third of the external acoustic meatus which is continuous with the auricular cartilage and attached to the circumference of the bony part. (05 Mar 2000) |