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TEXT-BOOK OF PHYSIOLOGY 



the lateral lemniscus for fillet of the opposite side, while others enter the 

 lemniscus of the same side. The lemniscus then passes upward to the in- 

 ternal geniculate body around the nerve-cells of which its fibers terminate. 

 From the geniculate body the acoustic radiation arises which then passes 

 upward and outward through the posterior limits of the internal capsule 

 to terminate finally around the cells of the super-temporal convolution. 

 From the nuclei around which the vestibular branch terminates, axons 



arise which in all probability pursue a 

 somewhat similar course and terminate in 

 the temporal lobe. 



Properties. Stimulation of the coch- 

 1 ear nerve is unattended by either motor 

 or sensor phenomena. Division of the 

 nerve is followed by a loss of the sense 

 of hearing. Irritative pathologic lesions 

 give rise to sensations of sound of vary- 

 ing character and intensity. Degenera- 

 tion of the nerve or destruction by tumors, 

 etc., will also be followed by a loss of 

 the sense of hearing. 



Experimental lesions of the semicir- 

 cular canals involving a destruction of 

 the physiologic relations of the vestibular 

 nerve are followed by a loss of the 

 coordinating and equilibratory power. 

 Disordered movements, such as rotation 

 to the right or left, somersaults back- 

 ward and forward, follow destruction of 

 these canals. Pathologic lesions in the 

 peripheral distribution of the nerve are 

 attended in man by disturbances of equi- 

 librium, e.g., vertigo, or a sense of sway- 

 ing, pitching, and staggering. 



Functions. The function of the 

 cochlear nerve is to convey nerve impulses 

 from its origin to the pons, from which 

 they are transmitted by the auditory tract 

 to the acoustic area in the cerebral cortex 

 where they evoke sensations of sound and 

 its different qualities, intensity, pitch, and timbre. The specific physiologic 

 stimulus to the development of these impulses is the impact of atmospheric 

 undulations on the tympanic membrane, received and transmitted by the 

 chain of bones to the structures of the internal ear the organ of Corti with 

 which the peripheral terminations of the nerve are connected. 



The function of the vestibular nerve is the transmission of nerve impulses 

 to the pons, whence they are transmitted to the cortex of both the cerebrum 

 and cerebellum and to other centers. The specific physiologic stimulus is 

 supposed to be a variation in pressure in the ampullae of the semicircular 

 canals caused by inertia of the endolymph during changes in the position of 

 the head and body. The impulses carried by the vestibular nerve give rise 



FIG. 



OF THE. ACOUSTIC NERVE, i. Cochlea. 

 2. Spiral ganglion (Corti). 3. Cochlear 

 nerve. 4. Ventral acoustic nucleus. 5. 

 Lateral acoustic nucleus. 6. Semi- 

 circular .canals. 7. Ganglion of Scarpa. 

 8. Vestibular nerve. 9. Dorso-external 

 nucleus (D eiters). 10. Dorso-internal 

 nucleus. (After Moral and Doyon.} 



