874 



THE NERVOUS SYSTEM 



VI. THE AUDITORY CONDUCTION PATHS 



Vestibular division (vestibular nerve). 



1. Vestibular ganglion gives origin to the peripheral utricular and three ampullar 



branches and to the combined and centrally directed vestibular nerve. 



2. Lateral vestibular nucleus (I)eiters'), medial nucleus, superior nucleus, and nucleus 



of descending vestibular root (nuclei of termination) give origin to fibres as 



follows: 



(a) From lateral and superior nuclei to nucleus fastigii of opposite side and to 



cortex of vermis and to dentate nucleus (eerebellar connection). 

 (by From medial and superior nuclei to nuclei of origin of eye-muscle nerves of 



same and opposite sides, by way of medial longitudinal fasciculi. 



(c) From lateral nucleus and nucleus of descending root through reticular 



formation into lateral fuiiieulus of spinal cord. 



(d) It is probable that all the nuclei of termination give off fibres bearing ascending 



impulses which ultimately reach the somaesthetic area, but the course 

 pursued and neurones involved in such a chain are uncertain. 



FIG. 649. DIAGRAM SHOWING SOME OF THE CONNECTIONS or THE ACOVSTIC NERVE. 



Xl'f'I.KCS KMBOLIFORMIS 



I'.oll Y 

 . NUCLEUS HI-' rniil'HLEAR 



NUCLEUS OF LATERAL LEMNISCUS 

 MEDIAL LONGITUDINAL FASCICULUS - - 



LA TERAL LEMNISCUS- - 



PEDUNCLE OF SUPERIOR 

 OLIVE 



/-.I TKRAL Xl'CLKUS OF 

 -- YKSTIBULAR XERVE 



. . - l:KXTIFORM BODY 



, IICIRSAI. XUCLEUS OF 



' XKRVE 



- YKXTSAL Xl-CLKUS OF 

 I'li'-IILEAR XER-FE 



, 'COCBLEAR XERTE 



VESTIBULAR XERVE 

 i 



SUPERIOR OLIVARY NUCLEUS 

 \ 



TRAPEZOID BODY 



B. Cochlear division (cochlear nerve). 



1. Spiral ganglion of the cochlea gives origin to short peripheral fibres to organ of 



Corti, and to the centrally directed cochlear nerve. 



2. Dorsal and ventral nuclei of the cochlear nerve (nuclei of termination). 



(a) Stria) medullares arise from dorsal nucleus and pass around outer side of resti- 

 form body (acoustic tubercle), then medianwards under ependyma of floor 

 of fourth ventricle to mid-line, then ventralwards into tegmentum, where 

 it decussates and joins trapezoid body to lateral lemniscus of opposite side. 



(6) Fibres arising in ventral nucleus pass ventrally medianwards and some 

 terminate in the superior olivary nucleus of same side; others pass by way of 

 trapezoid body and lateral lemniscus to terminate in superior olivary 

 nucleus, nucleus of lateral lemniscus, medial geniculate body and nucleus of 

 inferior quadrigeminate bodv of the opposite side. 



3. Nuclei of superior olives of both sides and nucleus of lateral lemniscus send fibre? 



by way of lateral lemniscus to inferior quadrigeminate body and through inferior 

 brachium to medial geniculate body, and some may pass uninterrupted, even to 

 the cortex of the temporal lobe. 



