Physiology of Hearing

Question 1

What are the functions of hearing?

Answer 1

• Alerts us to danger
• Recognition
• Communication
• Localising objects

Question 2

What are the two attributes of sound that can be measures, and what are their units?

Answer 2

Frequency (Hz)

Intensity (dB)

Question 3

From what intensity of sound upwards can permanent hearing damage occur?

Answer 3

> 90dB

Question 4

What makes up the peripheral auditory system?

Answer 4

• Outer ear
• Middle ear
• Cochlea
• CN VIII

Question 5

What are the 3 bones of the middle ear, and what is their location to each other?

Answer 5

Malleus (lateral)

Incus (middle)

Stapes (medial)

Question 6

What is osteoclerosis, its cause, and treatment?

Answer 6

Osteoclerosis is hearing loss caused by the fusion of the stapes to the oval window.

It can be fixed through surgery

Question 7

What is otitis media, and what population is it most common in (and also type of infection it often arises from)?

Answer 7

Inflammation or infection of the middle ear.

Most common in children and usually arises from respiratory tract infections

Question 8

What is adhesive otitis sometimes referred to as?

Answer 8

Glue ear

Question 9

What is adhesive otitis, what can it lead to if chronic, and what can it be treated with?

Answer 9

The filling of the middle ear with secreted fluids and when chronic it can lead to hearing loss.

Treated with via grommets (draining of the ear via tube that passes through the eardrum to reach middle ear).

Question 10

What region the ear is the cochlea in, what shape is it, and what are its two ends?

Answer 10

Cochlea is in the inner ear and is a coiled structure

Has an apical end and a basal end.

Question 11

What is the function of the apical and basal ends of the cochlea?

Answer 11

Apical end is tuned to low frequency sounds

Basal end is tuned to high frequency sounds

Question 12

Where is the cochlear duct and what is its shape?

Answer 12

Found within the cochlea and it runs throughout the cochlea

Question 13

What are the 3 parts of the cochlear duct and what type of fluid do they contain?

Answer 13

Scala vestibuli (perilymph)

Scala media (endolymph)

Scala tympani (perilymph)

Question 14

What are the contents of perilymph and endolymph?

Answer 14

Perilymph (high Na+ and low K+)

Endolymph (low Na+ and high K+)

Question 15

Where is the organ of corti found, and what does it detect?

Answer 15

Found within the Scala media

Detects the sound-induced movements of the basilar membrane (which it is next to)

Question 16

What are the 2 types of sensory hair cells within the organ of corti, and what type of fibres are they innervated with?

Answer 16

Inner hair cells (sensory fibres)

Outer hair cells (mainly motor fibres but also some sensory fibres)

Question 17

How many hair cells are in each cochlea, and can they be regenerated?

Answer 17

15000 in each cochlea

Can’t be regenerated once they die

Question 18

What are the 2 membrane ends of the hair cells found in the organ of corti, and what fluid are they bathed in?

Answer 18

Apical end (bathed in endolymph)

Basolateral end (bathed in perilymph)

Question 19

What are the stages of mechanotransduction in hair cells?

Answer 19

1) Deflection of hair cells lead to non-selective cation channels opening (which are found between hair cells)
2) Since K+ is the major cation of endolymph, it enters and depolarises the hair cells
3) Voltage-gated Ca2+ channels then open and the influx of Ca2+ activates vesicle release
4) Afferent fibres then get activated

Question 20

What is electromotility, and what are the two types that can occur to hair cells?

Answer 20

Movement of hair cells which is caused by changes in electrical charge.

Shortening of hair cells which is caused by depolarisation

Lengthening of hair cells which is caused by hyperpolarisation

Question 21

What is protein is able to modify the length of outer hair cells, and what type of protein is it?

Answer 21

Prestin (modified transmembrane anion transporter)

Question 22

What are the 2 types of afferent fibres that innervate the hair cells, and what do they detect?

Answer 22

Type I which innervates inner hair cells and detects sound over a wide range of intensities

Type II which innervates outer hair cells and detects painfully loud sounds

Question 23

How are inner and outer hair cells innervated by efferent fibres?

Answer 23

Inner hair cells: Efferent fibres from the lateral olive synapse onto Type I spiral neurons, which then synapse onto inner hair cells

Outer hair cells: Efferent fibres from the medial olive directly synapse onto them

Question 24

What are the medial and lateral Oliver from?

Answer 24

Arise from the superior olivary complex (which is a collection of brainstem nuclei)

Question 25

What are the functions of the outer and middle ear?

Answer 25

Outer ear collects sound and funnels it onto the tympanic membrane

Middle ear transmits the vibrations of the tympanic membrane onto the oval window of the cochlea

Question 26

What is the eardrum also known as?

Answer 26

Tympanic membrane

Question 27

What nerve do Type I and II spiral neurons neurons arise from, and what structure do they from?

Answer 27

Arise from the vestibulocochlear nerve

Form the cochlear ganglion

Question 28

What are some factors that can cause sensorineural hearing loss?

Answer 28

• Noise
• Ageing
• Ototoxic drugs (e.g. some antibiotics and loop diuretics)
• Genetic mutations (half are gap junction mutations)

Question 29

What are cochlear implants and some of their limitations?

Answer 29

Electronic devices that can provide a sense of sound to those who can’t hear.

1) Expensive (so limited to western world)
2) Speech sounds robotic

Question 30

What is the route of auditory information form the cochlea to the brain?

Answer 30

1) Cochlear nucleus
2) Superior olivary nucleus
3) Nuclei of lateral lemniscus
4) Inferior colliculus
5) Medial geniculate
6) Primary auditory complex

Question 31

On what lobe is the primary auditory complex found?

Answer 31

Upper surface of temporal lobe

Question 32

What is sensory and motor aphasia?

Answer 32

Sensory aphasia: Difficulty understanding written and spoken language

Motor aphasia: Difficulty speaking or facilitating motor movements of speech