From Big Medical Encyclopedia

ACOUSTIC ANALYZER — set of the sound carrying out and receptor elements, and also structures of c. the N of page, activity to-rykh provides perception and the analysis by the person and animals of sound vibrations.

At the person S. and. consists of the peripheral link including outside ear (see), middle ear (see) and inner ear (see), and central — the acoustical centers of c. N of page and the carrying-out nerve pathways (see. Acoustical centers, ways ). S.'s activity and. investigate electro-acoustic (e.g., an impedansometriya), holographic and electrophysiologic (pulse activity of nervous cells, membrane and receptor biopotentials, the caused answers) methods. Also disturbances at experimental destruction at animal various sites of c are studied. N of page or at local (vascular, infectious, etc.) defeats at patients.

Perception of a sound begins in an outside ear. The auricle promotes definition of localization of a source of a sound in space. Outside acoustical pass acts as the rezonsgtor strengthening sound vibrations approximately on 10 dB in the field of own frequency of a resonance equal 3 pgts. Further the sound wave causes fluctuations of a tympanic membrane, to-rye are transmitted through system of acoustical stones (a hammer, an anvil and a stirrup) to an oval window. Fluctuations of acoustical stones, causing the shift of a stirrup in an oval window, are transformed to fluctuations of liquid circles of a snail, to-rye cause fluctuations of a basilar membrane (a basilar plate, T.), carrying out primary analysis of audibles signal (see. Kortiyev body ). Excitement of receptors causes excitement of an acoustical part eighth cranial nerve (see), on Krom the impulsation is transferred to the acoustical centers. Frequency sound (see) it is coded thanks to frequency selectivity of separate nervous elements and the tonotopichesky organization — to the arranged arrangement in the centers of the acoustic analyzer of the neurons having the maximum sensitivity to a certain frequency of tone. A frequency analysis in S. and. is considered as result of decomposition of a signal on a frequency axis of a basilar membrane with the subsequent excitement of a tonotopicheska of organized neurons in the centers C. and. Intensity of a sound in S. and. it is coded by quantity of the excited elements and frequency of an impulsation in separate neurons. Increase in duration of a signal causes reduction of the threshold of reaction of neuron and increase in number of impulses. Since the level of a kernel of an upper olive, S.'s neurons and. find selective sensitivity to the space provision of a source of a sound. Number of neurons of cortical departments of S. and. (so-called neurons detectors) selectively react to difficult signs of audibles signal (e.g., the direction of frequency modulation, the direction of the movement of a source of a sound). In these centers also trace reactions which are perhaps correlates of short-term acoustical memory are registered.

For assessment of activity of S. and. at the person from the surface of a skull register and process by means of the COMPUTER caused (verteksny) korotkolatentny (the eclipse periods of components 0,5 — 10 ms; reflect activity of the trunk centers C. and.) and dlinnolatentny (eclipse periods from 50 to 300 — 400 ms; reflect activity of associative acoustical structures) potentials of small amplitude (unit mkv). At experimental destruction of an inner ear at animals or its defeat at the person decrease in hearing of different degree of manifestation is observed (see. Deafness , Hearing , Relative deafness ). Destruction of trunk departments at animals leads to the expressed disturbance of distinguishing of frequency and intensity while destruction of sites of an acoustical zone of a cerebral cortex breaks distinguishing of temporary properties of an incentive (e.g., the temporary sequences), raises a hearing threshold on short (to 20 ms) sounds and sharply breaks distinguishing of space provision of a source of a sound. At defeats of bark of a temporal share of a brain (a tumor, an injury, hemorrhage, etc.) similar disturbances of acoustical perception are observed (e.g., increase in hearing thresholds at action of short sounds). Now specialization of the right cerebral hemisphere to space hearing is established — defeats of this hemisphere lead to sharp disturbances of space hearing.

See also Hearing .

Bibliography: Altman Ya. A. Space hearing, localization of motionless and moving sources of a sound, Usp. fiziol. sciences, t. 12, No. 4, page 28, 1981, bibliogr.; The analysis of signals on the periphery of acoustical system, under the editorship of Ya. A. Altman, L., 1981; To Bar A. B. Acoustical centers and identification of audibles signal, JI., 1978; Vartanyan I. A. Acoustical analysis of difficult sounds, D., 1978; Physiology of touch systems, under the editorship of G. V. Gershuni, the p. 2, page 130, JI., 1972; In yo to yo s at G. Experiments in hearing, N. Y. and. lake, 1960; Handbook of sensory physiology, ed. by H. Autrum a. o., v. 5, pt 1 — 3, V. a. o., 1974 — 1976.

Ya. A. Altman.