auditory pathway ppt

description of auditory pathway,types
of deafness,tests of 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 8 th 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.

7. 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.

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

9. 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

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

11. SENSORINEURAL HEARING LOSS: results from lesions of cochlea/8 th 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.

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

13. 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-

14. 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.

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

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

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

18. 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