Physiology of Hearing

Question 1

What are mechanoreceptors?

Answer 1

• a somatosensory receptors
• relay extracellular stimulus to intracellular signal transduction through mechanically gated ion channels
• external stimuli are usually in the form of touch, pressure, stretching, sound waves, and motion

Question 2

The normal range of sound that humans can hear is measured in decibels (DB) and is approximately 50-60DB. What can happen if our ears are repeatedly exposed to high amount of DB?

Answer 2

• high DB, which is pressure can damage hearing

Question 3

Label the 3 parts of the outer ear in the image below, numbered 1-3 using the labels below:

• pinna/auricle
• tympanic membrane
• external auditory canal

Answer 3

1 - pinna/auricle
2 - external auditory canal
3 - tympanic membrane

Question 4

Label the 2 parts of the middle ear in the image below, numbered 1-2 using the labels below:

• ossicles (MIS = Malleus, Incus and Stapes)
• eustachian tube

Answer 4

1 - ossicles (malleus, incus and stapes)

2 - eustachian tube

Question 5

Label the 2 parts of the inner ear in the image below, numbered 1-2?

vestibule (with semi-circle canals)
cochlea

Answer 5

1 - cochlea

2 - vestibular apparatus (vestibular and semi-circle canals)

Question 6

The ossicles in the middle ear are important for transmitting the vibrations from sound waves from the outer ear to the inner ear. What is the malleus and the stapes connected to?

Answer 6

• malleus = tympanic membrane (tympanic muscle)

- stapes = oval window (stapedius muscle)

Question 7

There are 2 labyrinths in the inner ear, and both contain fluid. What are the names of the labyrinths and what fluid is contained within each?

Answer 7

• bony labyrinth = perilymph

- membranous labyrinth = endolymph

Question 8

There are 2 labyrinths in the inner ear, the bony and membranous labyrinth, which contain perilymph and endolymph, respectively. What is the Na+ and K+ concentrations in these fluids?

Answer 8

• perilymph = high Na+ and low K+ similar to extracellular fluid
• endolymph = low Na+ and high K+ similar to intracellular fluid

Question 9

Which nerve is in direct contact with the cochlea, and which cranial nerve (CN) is this a branch of?

Answer 9

• cochlea nerve

- branch of CN VIII (8) the vestibulocochlear nerve

Question 10

Which spongy bone does the cochlea nerve and the spiral ganglion sit inside?

1 - modiolus bone
2 - temporal bone
3 - zygomatic bone
4 - mandiubular bone

Answer 10

1 - modiolus bone

Question 11

The tubes of the cochlea are actually composed of 3 separate tubes. Label the tubes and the membrane using the labels below and what they contain (fluid wise).

• Scala vestibuli (perilymph)
• Scala media/cochlear duct (endolymph and the organ of Corti)
• Scala tympani (perilymph)
• basilar membrane

Answer 11

1 = scala vestibuli (perilymph)
2 = scala media/cochlear duct (endolymph and organ of Corti)
3 = scala tympani (perilymph)
4 = basilar membrane

Question 12

What is the spiral ganglion?

Answer 12

• group of cell bodies
• neurons axons supply the hairs of the organ of corti
• synapses with the cochlea nerve

Question 13

Of the 3 parts of the cochlea below, which 2 are are directly connected to the middle ear?

• scala vestibuli (perilymph)
• scala media/cochlear duct (endolymph and organ of Corti)
• scala tympani (perilymph)

Answer 13

• scala tympani connects with round window

- scala vestibuli connects with oval window

Question 14

When we look at the middle tube of the cochlea, the scala media/cochlear duct, there are 2 membranes, one above and one below. What are these called?

Answer 14

1 - top membrane = vestibular membrane (close to scala vestibuli)
2 - bottom membrane = basilar membrane

Question 15

The organ of corti contains mechanoreceptor hair cells, which include an inner and outer layer. Which of there layers is important for the following:

• sensory nerve fibres in charge of auditory transduction
• motor nerve fibre from the brain to contract or loosen the basilar membrane

Answer 15

• inner = sensory nerve fibres in charge of auditory transduction
• outer = motor nerve fibre from the brain to contract or loosen the basilar membrane (if its a loud noise then this is loosened so we don’t hear as much, but if its a whisper it tightens to accentuate the sound)

Question 16

What is the tectorial membrane?

1 - gel like membrane attached to the modiolus at one end and free on the other end
2 - gel like membrane between basilar membrane and the hair cells
3 - gel like membrane surrounding the organ of corti

Answer 16

1 - gel like membrane attached to the modiolus at one end and free on the other end

• runs parallel to the basilar membrane throughout the cochlea with hair cells between the 2
• in direct contact with the stereocilia (cilia) of hair cells contained within the organ of corti

Question 17

When vibrations move through the perilymph contained within the scala vestibuli and scale tympani they create movement to the basilar membrane, which causes what to happen?

1 - basilar membrane moves and pushes hair cells into the tectorial membrane
2 - vestibular membrane pushes tectorial membrane down into hair cells
3 - basilar membrane tightens and tectorial membrane will move down into the hair cells
4 - basilar membrane loosens and tectorial membrane will move down into the hair cells

Answer 17

1 - basilar membrane moves and pushes hair cells into the tectorial membrane
- stereocilia at top of hair cells and the organ of corti are pressed into the tectorial membrane

Question 18

When vibrations move through the perilymph contained within the scala vestibuli and scale tympani they create movement in the basilar membrane, causing the stereocilia of the hair cells and the organ of corti to press against the tectorial membrane. What does this do to the stereocilia of the hair cells?

1 - as soon as hair cells touch tectorial membrane, Na+ channels open
2 - hair cells trigger and intracellular pathway that will lead to an electrical signal
3 - tip link between adjacent stereocilia lean against one another opening mechanical gated K+ channels to open

Answer 18

3 - tip link between adjacent stereocilia lean against one another opening mechanical gated K+ channels to open

Question 19

When vibrations move through the perilymph contained within the scala vestibuli and scale tympani they create movement in the basilar membrane, causing the stereocilia of the hair cells and the organ of corti to press against the tectorial membrane. This causes the tip link between 2 adjacent stereocilia to lean against one another and open the mechanically gated K+ channels to open. What then happens to the stereocilia of the hair cells?

1 - endolymph, high in K+ runs down concentration gradient into hair cells causing depolarisation
2 - endolymph, high in Na+ runs down concentration gradient into hair cells causing depolarisation
3 - endolymph, high in K+ means K+ will leave the hair cell causing depolarisation
4 - endolymph, high in Na+ runs down concentration gradient into hair cells causing depolarisation

Answer 19

1 - endolymph, high in K+ runs down concentration gradient into hair cells causing depolarisation

• K+ concentration is higher in endolymph than in the cells
• K+ rushes inside the cells and depolarises
• Ca2+ channels open increasing Ca2+
• neurotransmitter glutamate is then released into synaptic space

Question 20

Once a hair cell has depolarised in the organ of corti due to the influx of K+, what must then happen at the basilar end, which is where the pre-synaptic membrane is located in order for this to create a neuronal signal along the cochlea branch of the vestibulocochlear nerve (CN VIII)?

1 - depolarisation of hair cells release Ca2+ signalling the release of dopamine
2 - depolarisation of hair cells release Ca2+ signalling the release of glutamate
3 - depolarisation of hair cells release Ca2+ signalling the release of serotonin
4 - depolarisation of hair cells release Ca2+ signalling the release of acetylcholine

Answer 20

2 - depolarisation of hair cells release Ca2+ signalling the release of glutamate
- neurotransmitter glutamate is then released into synaptic space

Question 21

When we look at the stereocilia, they are able to move laterally, which signals K+ influx and depolarisation. What does medial movement of the stereocilia of the hair cells cause?

1 - hyperpolarisation and must stronger action potential and glutamate release
2 - hyperpolarisation, K+ efflux from the cell, no Ca2+ channels open and no glutamate released
3 - hyperdepolarisation and must stronger action potential and glutamate release

Answer 21

2 - hyperpolarisation, K+ efflux from the cell, no Ca2+ channels open and no glutamate released

Question 22

In addition to causing the binding of vesicles containing glutamate with the pre-synaptic membrane for the release of glutamate, what else does the release of Ca2+ do to the hair cell?

1 - maintains depolarisation ensuring signal is constant
2 - can lead to excitotoxicity of the organ of corti
3 - induce hyperpolarisation of the hair cell due to an efflux of K+

Answer 22

3 - induce hyperpolarisation of the hair cell due to an efflux of K+

Question 23

On the hair cells there are 2 types of hair. What are these called?

Answer 23

1 - steriocilia

2 - kinocilia

Question 24

In the organ of corti there are inner and outer hair cells. Do they both transmit afferent and efferent nerve impulses?

Answer 24

• no
• inner = afferent neurons (sensory information) which signal auditory transduction
• outer = afferent and efferent which change the stiffness of basilar membrane as required

Question 25

How is the organ of corti connected to the vestibulocochlear nerve (cranial nerve 8 (VIII))?

Answer 25

- hair cells send action potential to spiral ganglion - spiral ganglion (bipolar) synapses with the cochlear nerve - cochlear nerve merges into the vestibulocochlear nerve (cranial nerve VIII (8)).

Question 26

Once the vestibulocochlear nerve (cranial nerve VIII (8)) has received an action potential the afferent signals synapse at the ventral and dorsal cochlea nucleus in the brain stem. From here the afferent signals will go to 3 different places, what are they?

Answer 26

1 - nerve decussates to opposite side with inferior colliculus 2 - nerve decussates to opposite side with superior olivary complex 3 - superior olivary complex on the same side

Question 27

Which bone is the auditory cortex located within in the brain? 1 - zygomatic bone 2 - temporal bone 3 - parietal bone 4 - occipital bone

Answer 27

2 - temporal bone

Question 28

The the auditory cortex is located below the temporal bone. What are the broadman areas responsible for the auditory cortex? 1 - 41 and 41 2 - 4 3 - 1, 2 and 3 4 - 17

Answer 28

1 - 41 and 41

Question 29

Although Wernicke’s area and Broca’s area are secondary auditory areas, they are involved in speech. Why are these 2 areas important for the auditory system?

Answer 29

- Wernicke’s area (BA 22) = important for our interpretation - Broca’s area (BA 44) = important for speech development BA = Broadmann Area

Question 30

Hearing loss can be subdivided into different categories. What is conductive hearing loss? 1 - disease/impairment of inner ear 2 - disease/impairment of outer ear canal or in the middle ear 3 - disease/impairment of middle ear 4 - disease/impairment of cochlear duct

Answer 30

2 - disease/impairment of outer ear canal or in the middle ear

Question 31

Hearing loss can be subdivided into different categories. What is sensorineural hearing loss? - sensor= sensory - neural = neurons 1 - disease/impairment of inner ear 2 - disease/impairment of outer ear canal or in the middle ear 3 - disease/impairment of middle ear 4 - disease/impairment of cochlear duct or neural pathway

Answer 31

4 - disease/impairment of cochlear duct or neural pathway | - neural pathway from the cochlea to the brain is impaired

Question 32

Hearing loss can be subdivided into different categories. What is occupational hearing loss?

Answer 32

- noisy work environment can cause deterioration of the organ of corti - organ of corti becomes less sensitive to vibrations

Question 33

Hearing loss can be subdivided into different categories. What is Ototoxic hearing loss?

Answer 33

- oto = ear - toxic = dangerous causing toxicity to tissue - drug induced damage to hearing

Question 34

Hearing loss can be subdivided into different categories. What is infectious hearing loss?

Answer 34

- destruction of the cochlea (mumps or rubella virus), cytomegalovirus

Question 35

Hearing loss can be subdivided into different categories. What is Tinnitus?

Answer 35

- hearing of a sound that has no external source

Question 36

Hearing loss can be subdivided into different categories. Conductive hearing loss, which is a disease affecting the outer ear canal or in the middle ear. What are some of the most common causes of this?

Answer 36

- earwax - outer ear infection - middle ear inflammation – Otitis media - perforated eardrum (due to high pressure sounds) - tumour in the ear canal or middle ear

Question 37

Hearing loss can be subdivided into different categories. Conductive hearing loss, which is a disease affecting the outer ear canal or in the middle ear. One such disease is Otosclerosis, what is this?

Answer 37

- oto = ear - sclerosis = hard - hard and abnormal bone growth in the ear (Pagets disease) - can be genetic or external factors, such as viral infection - temporal bone sclerosis affects the stapes that becomes fixed to the oval window and impair vibrations

Question 38

Hearing loss can be subdivided into different categories. Conductive hearing loss, which is a disease affecting the outer ear canal or in the middle ear. One such disease is Otosclerosis, which is abnormal bone growth in the ear and can cause the temporal bone sclerosis affects the stapes, which becomes fixed to the oval window. How can this be treated?

Answer 38

- external hearing aids (amplify sounds) - bypasses the need to be dependent on the stapes - surgery: stapedectomy that involves the use of an implant

Question 39

Cochlear implants can be used to treat people with hearing loss. What are cochlear implants?

Answer 39

- an electronic device that provides a sense of sound to someone with severe hearing loss - needs to be surgically implanted - contains a microphone, speech processor, transmitter, receiver an array of electrodes

Question 40

Cochlear implants can be used to treat people with hearing loss. How do cochlear implants improve hearing?

Answer 40

- the microphone detects sounds arranged by the processor as the external ear would - electrodes transform the sounds to nerve stimulations bypassing external, middle and inner ear - they do not completely restore hearing

Question 41

What is the most common genetic defect that causes non-syndromic hearing loss?

Answer 41

- gene GJB2 encodes for protein connexin 26 - this is involved in the inner ear K+ homeostasis - there is now a genetic test that can be done on babies

Question 42

Otosclerosis is abnormal bone growth in the temporal bone, which can cause the stapes to fuse with the oval window and impair vibrations and therefore sound. Patients can have surgery called a stapedectomy, which is removal of the stapes. This can damage one specific nerve that runs through the nerve. Which nerve is this and what can happen to the patients sensory information?

Answer 42

- chorda tympani, part of the mastoid nerve of cranial nerve VII (7) the facial nerve runs through the middle ear - if damaged this can affect the patients sense of taste on anterior 2/3rds of the tongue