Physiology of hearing 21st july 11

PHYSIOLOGICAL BASIS OF HEARING

FUNCTION OF EXTERNAL EAR

FUNCTION OF MIDDLE EAR

FUNCTIONS OF MIDDLE EAR:1.IMPEDANCE MATCHING

• 1.Diameter of TM is 17 times• 2.ossicolar lever action increases the pressure

1.3 times• Total increase will be 22 times

2.ATTENUATION REFLEX

STRUCTURE OF INNER EAR

FUNCTION OF INNER EAR

• The inner ear has 2 main functions:

1. Mechanical frequency analysis:2. Sensory transduction:• Generated pressure waves which • are transformed into neural

impulse.

BASEMENT MEMBRANE

1.FREQUENCY ANALYSIS

PLACE PRINCIPLE

Reticular lamina

Rod of cortiPillar cell

2.SENSORY TRANSDUCTION IN INNER EAR

SENSORY TRANSDUCTION IN INNER EAR

• Kinocilia / Stereocilia are Linked

• Displacement Opens K+ Channels

• Depolarization → release of glutamate

• K+ flows through cell• Glutamate → increase spike

rate in auditory nerve

ENDOCOCHLEAR POTENTIAL

•Lesions of inner ear or cochlear nuclei ,pons willproduce total N deafness

•Lesions central ,cochlearNuclei primarily affect the ability to localize sound direction

Primary Auditory area 41,42Tranverse temporal gyri of Heschl

Pathophysiology of hearing

• Conduction deafness• Sensorineural deafness

Common tests differentiating b/w nerve & bone conduction

1.Rinnes 2.Webers3.Audiometer

Rinnes compares AC-BC

• Normal : AC>BC Rinnes + ve• Conductive deafness: BC>AC Rinnes – ve• Sensorinueral deafness: Reduced rinnes +ve AC>BC

Webers compares bone conduction of 2 ears,

• Normal : centralized• Conductive deafness: lateralized to diseased • Sensorinueral deafness:lateralized to normal

THANK YOU

TONOTOPICAL MAPPING

br of inf col

41,42

Loss of highfrequency tones in old age

stapedius

TT