Physiology of Hearing

Question 1

What is the membrane between the scala vestibuli and scala media?

Answer 1

reissner’s membrane

Question 2

What is the membrane between the scala tympani and scala media?

Answer 2

basilar membrane

Question 3

The scala vestibuli is associated with what structure in the inner ear?

Answer 3

oval window

Question 4

The scala tympani is associated with what structure in the inner ear?

Answer 4

round window

Question 5

OTITIS MEDIA

Answer 5

Infection or inflammation of middle ear
Usually self-limiting

Common in children
Often from upper respiratory tract infection

Secretory form with effusion
“Glue ear”
If chronic causes a conductive hearing loss
May need draining
Grommets

Question 6

OTOSCLEROSIS

• cause
• treatment

Answer 6

• Fusion of stapes with oval window

- Can be fixed by surgery

Question 7

Cochlear Nucleus (CN)

Answer 7

– parallel processing starts here

• Auditory nerve fibres from cochlear ganglion innervate many types of neuron
• Neurons extract information about level, onset and timing of sounds

Question 8

Superior Olivary Complex (SOC)

Answer 8

– uses inter-aural time differences and inter-aural intensity differences for localization

• Interaural level differences are detected in the lateral superior olive (LSO)
• Interaural time differences are detected in the medial superior olive (MSO)

Question 9

Inferior Colliculus (IC)

Answer 9

• layers
• combines spatial analysis from SOC with information from dorsal CN, and directs auditory reflexes

-encodes complexity and localization of sound
Auditory reflex centre; reflexive orientation to stimuli

Question 10

Auditory Cortex (AC)

Answer 10

many functions including the analysis of complex sounds (eg speech) and sound localization

Question 11

Outline the central auditory system

Answer 11

Cochlear nucleus
Then project ipsilaterally and contralaterally to SOC 
Nuclei of lateral leminiscus 
Inferior colliculus 
Medial geniculate body 
primary auditory cortex

Question 12

What does the Medial Superior Olivary complex respond to?

Answer 12

responds to arrival time differences

i.e interaural time differences

Question 13

What does the lateral Superior Olivary complex respond to?

Answer 13

responds to amplitude differences

i.e interaural level differences

Question 14

Where is the inner ear located?

Answer 14

in the petrous part of the temporal bone

Question 15

What type of innervation do inner hair cells receive?

Answer 15

afferent innervation

Question 16

What type of innervation do outer hair cells receive?

What are their main functions

Answer 16

efferent innervation

-amplify basilar membrane motion

Question 17

What kind of fluid of fluid is contained within scala vestibuli and scala tympani?
Describe this fluid

Answer 17

perilymph

high in Na+
low in K+

Question 18

What kind of fluid of fluid is contained within scala media?

Describe this fluid

Answer 18

endolymph

low in Na+
high in K+

Question 19

What is the function of hair cells in organ of corti?

Answer 19

move with the movement of the fluid and the stereocilia set up an action potential within the cochlear nerve

Question 20

Describe the mechanism of mechanotransduction in hair cells

Answer 20

movement of hair buncle opens non-selective cation channels

• K+ enters
• depolarisation
• Ca2+ enters
• triggers vesicle release
• Afferent nerver fibres activated

Question 21

What type of cells are inner hair cells

Answer 21

sensory

Question 22

What types of cells are outer hair cells

Answer 22

sensori-motor

Question 23

Afferent innervation of the cochlear

Answer 23

Inner hair cells innervated by type 1 spiral neurons

outer hair cells innervated by type II spiral neurons

Question 24

Efferent innervation to the cochlear

Answer 24

efferent fibres from medial olive innervate outer hair cells directly

efferent fibres from lateral olive synapse on Type 1 afferent
-Activation of efferent system modifies the sensitivity of the cochlea

Question 25

Conductive Hearing Loss

Answer 25

sound can’t pass from outer or inner ear to the cochlea

Question 26

Sensorineural Deafness

Answer 26

due to a fault in the inner ear or the cochlear nerve