The auditory pathway consists of relay stations from the inner ear hair cells through the spiral ganglion, cochlear nuclei, superior olivary nucleus, lateral lemniscus, inferior colliculus, medial geniculate body, and auditory cortex. Sound is transmitted through these relay stations with the first order neurons in the spiral ganglion and higher order neurons at each subsequent station. There are three main types of hearing loss - conductive, sensorineural, and mixed. Conductive hearing loss interferes with sound conduction to the cochlea, sensorineural involves lesions of the cochlea/vestibulocochlear nerve, and mixed has both conductive and sensorineural components. Hearing

1. HEARING

2. AUDITORY PATHWAY
RELAY STATIONS:
spiral ganglion
superior olivary nucleus
,trapezoid n
 nucleus of lateral
lemniscus
 inferior coliiculus
 medial geniculate body
 auditory cortex
 from hair cells through cochlear division of
8th cranial nerve

3. SPIRAL GANGLION:
first order neurons –bipolar cells of spiral
ganglion.
dendrites of bipolar cells constitute afferent
fibres innervating the hair cells.
axons form the cochlear division of eight
cranial nerve
cochlear nerve ends in cochlear nuclei in
medulla.

4. COCHLEAR NUCLEI:
second order neurons
two cochlear nuclei-dorsal and ventral
axons pass medially in pons.
most of them cross to opposite side, some
remain uncrossed.
the crossing fibres of two sides form –
trapezoid body

5. SUPERIOR OLIVARYNUCLEUS,TRAPEZOID
NUCLEUS :
third order neurons
s o n-recieves large majority of fibres from
cochlear nucleus. form as ascending bundle
of lateral lemniscus.
few fibres relay in trapezoid nucleus before
reaching lateral lemniscus.
fibres of lateral lemniscus ascend in midbrain
to terminate in inferior colliculus.

6. INFERIOR COLLICULUS:
fourth order of neurons.
fibres terminate in medial geniculate body.
MEDIAL GENICULATE BODY:
FIFTH ORDER OF NEURONS
fibres form acoustic radiationsend in
auditory cortex.

10. AUDITORY CORTEX:
temporal lobe
 primary auditory cortex(41,42)
 auditory association area(22,21,20)
PRIMARY AUDITORY
AREA/AUDIOSENSORY AREA:
centre of hearing
location:middle of superior temporal gyrus on
upper margin on its deep insular aspect.

11. APPLIED PHYSIOLOGY
 :
 HEARING LOSS :IMPAIRMENT OF
HEARING
 DEAFNESS:LITTLE OR NO HEARING
 TYPES OF HEARING LOSS:
 conductive
 sensory
 mixed

12. 1.CONDUCTIVE HEARING LOSS:
interferes with conduction of sound from
external ear to cochlea.
CAUSES:
external ear
tympanic membrane
middle ear cavity
ear ossicles
eustachian tube obstruction

13. CHARACTERISTIC FEATURES:
never complete ,partial hearing loss present
speech discrimination is good
MANAGEMENT:

14. SENSORINEURAL HEARING LOSS:
results from lesions of cochlea/8th nerve and
its central connections.
causes:
congenital and acquired
acquired hearing loss later in life
infection of labyrynth,injury to labyrynth,noise
trauma,ototoxicity,acoustic neuroma,d m
,htn,senile degeneration of hair cells-
presbycusis, meniers disease.

15. LOSS OF HEARING –complete
speech discrimination –poor
management:
treat the underlying cause
hearing aids-cochlear implants
3.MIXED TYPE:

16.  TINITUS:
 Ringing sensation in ears caused either due to
irritative stimuli to inner ear or vestibulocochlear
nerve.
 HEARING TESTS:
 TO ASSESS THE TYPE OF HEARING
LOSS,DEGREE,SITE OF LESION, CAUSE OF
HEARING LOSS
 TWO TYPES
 CLINICAL TYPES AND AUDIOMETRIC TYPES.
 CLINICAL TYPES:
 1.FINGER FRICTION TEST-

17. 2.WATCH TEST-
3.SPEECH TEST-
4. TUNING FORK TEST-
RINNE TEST-AC >BCPOSITIVE-
NORMAL & SENSORINEURAL DEAFNESS.
BC>AC-NEGATIVE RINNE TEST-
CONDUCTIVE DEAFNESS.

18. WEBER TEST:
CONDUCTIVE DEAFNESS –LATERALISED
TO WORSE EAR
SENSORINEURAL DEAFNESS –
LATERALISED TO BETTER EAR

19. SCHWABACH TEST:BC OF PATIENT AND
EXAMINER
REDUCED IN SENSORY NEURAL
DEAFNESS

20. AUDIOMETRIC TESTS:
ASSESMENT OF HEARING USING
ELECTRONIC EQUIPMENT.
PURE TONE AUDIOMETRY
SUBJECTIVE TEST.
AUDIOMETER –MACHINE
AUDIOGRAM –RECORDING
TO DETECT OR RULE OUT CONDUCTIVE
DEAFNESS

21. 2.SPEECH AUDIOMETRY:
.
3.TONE DECAY TEST:
4.BRAIN STEM EVOKED RESPONSES:
POTENTIALS RECORDED FROM
AUDITORY PATHWAY IN RESPONSE TO
BRIEF AUDITORY STIMULATION.
ASSESS FUNCTIONAL STATUS OF
AUDITORY PATHWAY UPTO MID BRAIN