The Physiology of Hearing

Question 1

Describe the pathway of hearing

Answer 1

2 parts

Conductive:

• ear canal
• tympanic membrane
• ossicles

Sensorineural:

• cochlea
• cochlear nerve
• auditory cortex

Question 2

How do the cochlea help with hearing?

Answer 2

Hair cells within the Organ of Corti produce electrical activity (endolymph, perilymph)

This activity becomes a neural impulse and travels to the brain via the cochlear nerve VIII

Question 3

Explain the Vestibule and Semicircular Canals and their function

Answer 3

Balance

Semicircular canals:
-Lateral
-Posterior
-Superior
plus saccule, utricle

hair cells and otoconia produce electrical activity

This activity becomes a neural impulse and travels to the brain via the vestibular nerve VIII

Question 4

What two features combine to form sound?

Answer 4

Intensity (loudness)

Frequency (pitch)

Question 5

Describe the clinical significance of sound intensity

Answer 5

0 decibels is the quietest sound you should be able to detect between 18-20

Pain threshold:

• Threshold = 0db
• Pain threshold = 130 db

Question 6

Describe the clinical significance of sound frequency

Answer 6

Speech range is between 500Hz and 2000Hz

8000 outside human range e.g. dogs

Conductive losses tend to predominate in low frequencies

Sensorineural losses tend to predominate in high frequencies

Question 7

What parts of the Cochlea deal with high and low frequency?

Answer 7

Basal turn = high frequency

Apical turn = low frequency

Question 8

What is audiometry?

Answer 8

A subjective test involving the patient and audiologist

Measures amplitude or intensity of sound and frequency

Question 9

What is Tympanometry?

Answer 9

Measure of tympanic membrane compliance involving middle ear and ear canal pressure

Because of Eustachian tube function canal pressure should = middle ear pressure

Useful to detect:

• Eustachian tube dysfunction
• Middle ear effusion (glue-ear)

Question 10

Explain the importance of hearing in children

Answer 10

Key importance of sound input in development of auditory complex. Links to speech cortex.

Children “born” deaf in one ear will grow up with element of auditory cortex “adaptation”

Children born severely deaf will not be able to develop normal speech

If profoundly deaf then even if hearing restores will never speak unless it is achieved before the age of 4