Mechanics Of Hearing

Front 1

What do the sensory receptor cells in the ear act as?

Back 1

Transducers which convert external sound signals into electrical impulses.

Front 2

Back 2

1. Semicircular ducts

2. Vestibular nerve

3. Cochlear nerve

4. Cochlea

5. Auditory tube

6. Inner Ear

7. Middle ear

8. Tympanic cavity

9. Eardrum

10. Auditory canal

11. Outer ear

12. Earlobe

13. Auricle

14. Stapes

15. Incus

16. Malleus

17. Temporal bone.

Front 3

What are the 3 main areas of the ear?

Back 3

1. Outer ear

2. Middle ear

3. Inner ear

Front 4

Describe the process of mechanotransduction.

Back 4

1. Sound waves indue vibrations in the tympanic membrane

2. Mechanical vibration in middle ear transmitted to cochlear in inner ear

3. Vibrations in cochlear fluids transmitted to sensory hair cells

4. Sterocilia deflect, transduction channels open, leading to K+ influx

5. Receptor potential triggers glutamate release, leading to action potential in cochlea nerve

Front 5

What is the consistency of the air in a sound wave?

Back 5

Zones of molecular compression - zones of compression and zones of low compression - zones of rarefraction

Front 6

What range of frequencies can the human ear hear?

Back 6

20 - 20,000 Hz

Front 7

What is amplitude in terms of compression and rarefraction zones?

Back 7

Difference between area of compression and area of rarefraction

Front 8

What are the main functions of the middle ear?

Back 8

1. Transmits sound vibrations from the tympanic membrane to the oval window and the middle ear.

2. Amplifies sound waves by 15-20x

3. Converts sound waves into mechanical vibrations

Front 9

What are the two main components of the inner ear?

What is each filled with?

Back 9

Two fluid filled labyrinths

1. The Osseus labyrinth - contains perilymph

2. Membranous labyrinth - contains endolymph

Front 10

Back 10

1. Cristae within ampullae

2. Utricle

3. Saccule

4. Vestibulocochlear nerve

5. Cochlea

6. Tympanic duct

7. Cochlear duct

8. Vestibular duct

9. Posterior semicircular duct

10. Lateral semicircular duct

11. Anterior semicircular duct

12. Semicircular ducts

Front 11

What component(s) of the inner ear make up the vestibular system?

Back 11

1. Semicircular ducts

2. Utricle

3. Saccule

Front 12

What component(s) of the inner ear make up the auditory system?

Back 12

The cochlear duct

Front 13

What is the cochlea?

Back 13

The cochlea is the organ of hearing. It is anatomically a tube within a tube.

Front 14

How are sound signals amplified from the middle to inner ear?

Back 14

The oval window is far smaller than the tympanic membrane. This amplifies the sound waves.

Front 15

Describe the sound transmission to the cochlea.

Back 15

1. Sound waves coming through the external auditory canal move the tympanic membrane.

2. Middle ear bones move

3. Vibrates the membrane in the oval window

4. Causes oscillation of specific regions of the basilar membrane

5. Pressure bends the membrane of the cochlear duct at a point of maximum vibration for a given frequency, causing hair cells in the basilar membrane to vibrate.

Front 16

Back 16

1. Outer Hair Cell stereocilia

2. Outer Hair Cell lateral membrane

3. Tectorial membrane

4. Auditory nerve

5. Inner hair cell

6. Outer hair cells

7. Deiter's cell / supporting cells

8. Basilar membrane

Front 17

What is the fluid which surrounds the organ of corti called?

What is its ionic makeup?

Back 17

1. Endolymph (within the cochlear duct)

2. Low Na+ and high K+

Front 18

How many rows of outer hair cells are there?

Inner hair cells?

Back 18

3 rows of outer, 1 row of inner

Front 19

What is the function of supporting / deiters' cells?

Back 19

Support hair cells and connect them to the basilar membrane. This ensures efficient transmission of mechanical vibrations to the hair cells.

Front 20

How does the cellular composition of supporting cells support its function?

Back 20

Contain large transcellular cytoskeletal arrays.

Made up of:

i) microtubules

ii) actin filaments

iii) intermediate filaments

Front 21

What is the area which hair cells sit on called?

How does its structure support its function?

Back 21

The cuticular plate.

Strong actin network which serves as an anchor for stereocilia.

Front 22

Describe the basic morphological hallmarks of a stereocilia.

Back 22

1. Modified giant microvilli

2. Bundle of actin filaments which are interconnected by tip links.

Front 23

Describe briefly, a tip link.

Back 23

Two helically intertwined protofilaments which link the top of a stereocilium to an adjacent stereocilium. Tip links are involved in opening and closing of ion channels.

Front 24

Describe the process of stereocilia deflection.

Back 24

1. Mechanical vibrations in the basilar membrane.

2. Transmitted to the hair cells via the supporting cells

3. Shearing forces between stereocilia

4. Stereocilia deflection

Front 25

How do stereocilia become excited?

Back 25

1. Stereocilia deflect

2. Tip links become stretched - opening K+ ion channels

3. Depolarisation of stereocilia

4. Generation of receptor potential.

5. Release of neurotransmitter

Front 26

How do stereocilia become inhibited?

Back 26

1. When tip links become compressed K+ and Ca++ channels close.

2. Hyperpolarisation - K+ exit via basolateral channels

3. Inhibition of neurotransmitter release

Front 27

In which direction does stereocilia deflection occur towards?

Back 27

Always occurs towards the tallest stereocilia.

Front 28

Why does K+ enter the stereocilia when the channels open?

Back 28

K+ influx is driven by electrical potential differences. The endolymph has a potential of +85 mV and the hair cells -40mV

Front 29

What channel in hair cells pumps K+ out of the cell?

When is it activated?

Back 29

The KCNQ4 channel which is activated on hair cell depolarisation.

Front 30

What nerve carried nerve impulses for hearing and balance to the brain?

Back 30

Vestibulocochlear cranial nerve

Front 31

What neurotransmitter is associated with hair cell depolarisation?

Back 31

Glutamate