Scheme of neurones of auditory pathway. 4 neuronal afferent centripetal tract terminating in the primary acoustic cortex of temporal lobe. Receptor: hairs cells of Corti organ inside the membranous cochlear duct of inner ear. Receptors are surrounded by dendrites of bipolar neurons of the cochlear ganglion (1. N). Axons of bipolar neurons form the cochlear nerve. Cochlear nerve terminates in the cochlear nuclei (2. N) in the brainstem. From cochlear nuclei information go by the lateral lemniscus into the inferior collicle (3. N) in the mesencephalon. Signals interpolate in the inferior collicle and continue to the medial geniculate body (4. N). The last part of the auditory tract – acustic radiation (geniculo-cortical tract) continue into the upper part of the temporal lobe – transverse temporal gyruses (primary acustic cortex). Between the basic neurons of the auditory pathway there are inserted interstitial (relay neurons) which are grouped into independent nuclei : nucleus olivaris superior, nucleus corporis trapezoidei, nucleus lemnisci lateralis.

Microscopic section through cochlea - section through modiolus, hematoxylin-eosin staining

Microscopic section through the organ of Corti

Cochler ganglion is placed in lamina spiralis ossea and it contains mainly bipolar neurons (only 10 % are pseudounipolar neurons) – 1. N of the acoustic tract. Their dendrites surrounds bases of inner and outer hair cells together with axons of the controll acoustic pathways. Their axons (cochlear nerve) run from the cochlear ganglion through the modiolus (canales longitudinales modioli) to lower anterior part of the fundus of internal acoustic meatus (tractus spiralis foraminosus) and they joint the vestibular nerve to form the vestibulocochlear nerve.

Brainstem and origin of vestibulocochlear nerve

Dorsal aspect of brainstem

Microscopic section through brainstem at the level of cochlera nuclei

Microscopic section through pons-midbrain junction at th elevel of inferior colliculus, Nissl staining

Lateral aspect of the hemispere with the cortical representation of auditory areas

The video demonstrates the first part of auditory pathway

Videodemonstration of 2nd and 3rd neurons of auditory pathway

Videodemonstration of auditory pathway

Lateral aspect of brainstem and geniculate bodies