Auditory Pathway Physiology

1. 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)