Physiology of auditory system

References:

Guyton & Hall

Review of medical physiology (Ganong)

Dr. Mohammadi

The EarThe Ear

Houses two senses

Hearing

Equilibrium (balance)

Receptors are mechanoreceptors

Anatomy of the EarAnatomy of the Ear

The External EarThe External Ear

Middle EarMiddle Ear

Two tubes are associated with the inner ear

The opening from the auditory canal is covered by the tympanic membrane

The auditory tube connecting the middle ear with the throat (Eustachian tube)

• Allows for equalizing pressure during yawning or swallowing

Impedance matching

↑17 times in force

↑1.3 times in force

Total: 17 × 1.3 = 22

AmplificationAmplification

Attenuation reflex

Contraction of the stapedius muscle pulls the handle of

the stapes outward

Contraction of the tensor tympani muscle pulls the

malleus inward

Increase in ossicular system rigidity

Reducing the ossicular conduction of low frequency

sound

Function (Protection & Masking)

Inner EarInner Ear

Sound

Range: 20 Hz to 20,000 Hz Pitch: High pitch = high frequency; low frequency = low pitch Intensity: High intensity louder than low intensity

Tonotopic maps on the basilar membrane

Travelling wave in the basilar membrane

Organ of Corti

n = 12000

n = 3500

Transduction by hair cells

Central auditory system

Mechanisms of sound localization

Localization of sound in vertical plan

Mechanisms of sound localization (continued)

Superior olivary complex

Medial superior olive (Time delay)

Lateral superior olive (Intensity difference)

Auditory cortex

Superior temporal gyrus (Brodmannś area 41)

Complete bilateral removal of the auditory cortex: Detection of sounds remains intact Greatly reduce ability to discriminate different sound pitches and specially patterns of sound Loss of almost all ability to detect the sounds direction Greatly reduces one's sensitivity for hearing Destruction of one side: Only slightly reduces hearing in the opposite ear Loss of ability to detect the sounds direction Lesions that affect the auditory association areas: Loss of ability to interpret the meaning of the sound

Damage to the cochlea Drug sensitivity of the organ of Corti

Otosclerosis

Audiogram in nerve deafness Audiogram in conduction deafness

Ludwig van Beethoven

Around 1796, by the age of 26, Beethoven began to lose his hearing.By 1814 however, Beethoven was almost totally deaf.