| acoustic lens | In ultrasonography, a lens used to focus or diverge a sound beam; may be simulated by electronic manipulation of signals. (05 Mar 2000) |
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| acoustic maculae | Thickened areas of the saccule and utricle where the termination of the vestibular nerve occurs. (12 Dec 1998) |
| acoustic meatus | The passage leading inward through the tympanic portion of the temporal bone, from the auricle to the tympanic membrane; it consists of a bony (inner) portion and a fibrocartilaginous (outer) portion, the cartilaginous external acoustic meatus. Synonym: meatus acusticus externus, acoustic meatus, antrum auris, auditory canal, external auditory meatus. (05 Mar 2000) |
| acoustic nerve | <anatomy, nerve> The 8th cranial nerve. The acoustic (or vestibulocochlear) nerve has a cochlear part which is concerned with hearing and a vestibular part which mediates the sense of balance and head position. The fibres of the cochlear nerve originate from neurons of the spiral ganglion and project to the cochlear nuclei. The fibres of the vestibular nerve arise from neurons of scarpa's ganglion and project to the vestibular nuclei. (12 Dec 1998) |
| acoustic nerve diseases | Diseases of the eighth cranial nerve. These include vestibular neuronitis, cochlear neuritis and acoustic neuroma. (12 Dec 1998) |
| acoustic neurilemoma | <tumour> Schwannoma arising from cranial nerve eight. (05 Mar 2000) |
| acoustic neuroma | <oncology, tumour> This is a benign tumour of the 8th cranial nerve. This tumour arises from the myelin forming Schwann cells that coat the 8th cranial nerve (acoustic nerve). Clinical presentation usually includes hearing deficit. Diagnosis can be made with auditory evoked potentials and/or MRI scanning of the brain. Vertigo and tinnitus may be associated symptoms. Surgical removal of this tumour involves dissection, cautery and obliteration with laser. Incidence: 1 in 100,000. (13 Nov 1997) |
| acoustic pressure | In ultrasound, the instantaneous value of the total pressure minus the ambient pressure; unit is pascal (Pa). (05 Mar 2000) |
| 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) |