Auditory pathway
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The auditory pathway begins with hair cells in the inner ear that transmit signals through the vestibulocochlear nerve to the cochlear nuclei in the brainstem. These signals then travel to the superior olivary nuclei, lateral lemniscus nuclei, and medial geniculate bodies of the thalamus. Finally, auditory radiation fibers carry the signals to the temporal lobes of the cerebral cortex where sounds are perceived and analyzed in areas 41, 42, and Wernicke's area.
Auditory pathway
- 2. INTRODUCTION Higher center for hearing is in temporal lobe. The fibers of auditory pathway (Vestibulocochlear Nerve, VIII Cranial Nerve) terminates in temporal lobe.
- 3. RECEPTORS The hair cells in organ of corti are the receptors of the auditory sensations. Two types of hair cells, each hair cells are innervated by afferent and efferent nerve fibers.
- 5. FIRST ORDER NEURONS The bipolar cells form the spiral ganglion situated in the modiolus of cochlea represents the first order neurons. These neurons enters the medulla oblongata. After entering the medulla oblongata, the fibers divide into two groups which end on ventral cochlear nucleus and dorsal cochlear nucleus of the same side in medulla oblongata.
- 7. SECOND ORDER NEURONS The neurons of the dorsal and ventral cochlear nuclei in the medulla oblongata form the second order neurons of auditory pathway. The axons of the second order neurons pass through a complex pathway, which runs in four different directions.
- 9. First Group Nerve fibers cross the midline and run to the opposite side to form trapezoid body go to the superior olivary nucleus.
- 11. Second Group Second group neurons terminate at the superior olivary nucleus of same side via trapezoid body of the same side.
- 13. Third Group Neurons It runs in the lateral lemniscus of the same side and terminate in the nucleus of lateral lemniscus of same side.
- 15. Fourth Group It runs into the reticular formation, cross the midline as intermediate trapezoid fibers and finally join the nucleus of lateral lemniscus of opposite side.
- 17. THIRD ORDER NEURONS Third order neurons are in the superior olivary nuclei and nucleus of lateral lemniscus. The third order order neurons end in medial geniculate body which forms subcortical auditory center. Fibers from the medial geniculate body go to the temporal cortex, via internal capsule as auditory radiation. The fibers of auditory radiation are involved in reflex movement of head in response to auditory stimuli.
- 18. CORTICAL AUDITORY CENTERS It is present in the temporal lobe of the cerebral cortex. The auditory areas are area 41, area 42 and wernicke’s area.
- 20. FUNCTIONS OF CORTICAL AUDITORY CENTERS Perception of auditory impulses. (Area 41 & Area 42) Analysis of pitch and intensity of sound. (Wernicke’s area) Determination of source of sound. (Wernicke’s area)