The Auditory System

Question 1

what is compressed air?

Answer 1

air with dense particles.

Question 2

what is rarefied air?

Answer 2

air with less dense particles.

Question 3

what is frequency (waves)?

Answer 3

no. of compressed and rarefied patches of air pass by our ears each second, (Hz).

Question 4

what is low frequency?

Answer 4

fewer compressed and rarefied patches of air passing by our ears in a second.

Question 5

what is high frequency?

Answer 5

more compressed and rarefied patches of air passing by our ears in a second.

Question 6

what is intensity / amplitude (waves)?

Answer 6

the air pressure difference between peaks and troughs, (dB).

Question 7

what is low intensity?

Answer 7

a small difference in air pressure between the peaks and troughs (a quiet sound).

Question 8

what is high intensity?

Answer 8

a greater difference in air pressure between the peaks and troughs (a loud sound).

Question 9

what is the outer ear made up of?

Answer 9

Pinna,
Auditory canal,
Tympanic membrane.

Question 10

what is the middle ear made up of?

Answer 10

air-filled chamber,
Ossicles,
Oval window.

Question 11

what is the inner ear made up of?

Answer 11

Vestibular portion,
Cochlea,
Vestibulocochlear nerve (cranial nerve 8).

Question 12

what are the Ossicles?

Answer 12

the 3 tiniest bones in the body.

Question 13

name the 3 Ossicles:

Answer 13

Malleus,
Incus,
Stapes.

Question 14

what type of connection is between the Malleus and the Incus?

Answer 14

a rigid connection,

when the Malleus moves, the Incus moves.

Question 15

what type of connection is between the Incus and the Stapes?

Answer 15

a flexible connection,

when the Incus moves, the Stapes moves which causes the Oval window to move in and out.

Question 16

describe the process of the inward movement of the Tympanic membrane by the compression phase of a sound wave:

Answer 16

pushes the Malleus downwards,
the Incus moves up,
pushes the Stapes into Oval window,
fluid moves into the Cochlea.

Question 17

describe the process of the outward movement of the Tympanic membrane by the rarefaction phase of a sound wave:

Answer 17

moves Malleus into horizontal position,
moves Incus along with it,
pulls Stapes out so fluid moves outwards towards the middle ear.

Question 18

what is the overall shape of the cochlea / the drawn shape?

Answer 18

has a base and then it loops round like the spirals on a snail shell.

Question 19

how many fluid filled compartments are there in the cochlea?

Answer 19

3.

Question 20

what is the name of the fluid filled compartment that connects to the Oval window and runs all over the cochlea?

Answer 20

the Scala Vestibuli.

Question 21

what is the name of the other compartment that allows fluid to move in and out as it is being pushed by the Oval window?

Answer 21

the Scala Tympani.

Question 22

what is the name of the third compartment that is filled with endolymph?

Answer 22

the Scala Media.

Question 23

which 2 compartments are filled with perilymph?

Answer 23

the Scala Vestibuli and the Scala Tympani.

Question 24

how are the Scala Vestibuli and the Scala Tympani connected?

Answer 24

the helicotrema.

Question 25

where is the Organ of Corti located?

Answer 25

it is between the Scala Media and the Scala Tympani.

Question 26

what does the Organ or Corti contain?

Answer 26

hair cells.

Question 27

where do the hair cells sit, and what are they covered by?

Answer 27

hair cells sit on the basilar membrane and are covered by the tectorial membrane.

Question 28

what happens when fluid moves in and out of the Scala Vestibuli? (basic)

Answer 28

causes a ripple of movement in the Scala Tympani,
displacement of basilar membrane,
and hair cells to mechanically deflect (translated to electrical potentials in the cells).

Question 29

what specific parts of the hair cells are moved / deflected by the basilar membrane displacement?

Answer 29

hair bundles.

Question 30

describe the structure of the basilar membrane:

Answer 30

membrane is thinner, thicker in depth, and stiff at the base of the cochlea,
the membrane is wider and less stiff at the apex of the cochlea.

Question 31

different frequencies of sound will displace the basilar membrane to different extents:

Answer 31

high frequencies causes displacement at the base of the membrane,
whereas low frequencies cause displacement at the apex.

Question 32

how does the basilar membrane displacement affect hair cells? (rarefaction)

Answer 32

as the stapes move outwards,
the membrane moves upwards,
the tectorial membrane moves in one direction,
moves the hair bundles towards the longer stereocilia,
initiating depolarisation in the hair cells.

Question 33

how does the basilar membrane displacement affect hair cells? (compression)

Answer 33

as the stapes move inwards,
the membrane moves downwards,
the tectorial membrane is pulled in the other direction towards shorter stereocilia,
initiating hyperpolarisation.

Question 34

what structure connects the hair cells?

Answer 34

tip links.

Question 35

what happens to the tip links when the hair bundles are pushed and pulled?

Answer 35

the tip links mechanically open the channels to the hair cells causing K+ ions from the endolymph to enter.

Question 36

describe the process that occurs when the hair bundles are pushed towards the longer bundles:

Answer 36

the tip links tighten and the channels open,
K+ enters the cell increasing the positivity of the cell,
graded potential travels from the apex of the cell to the base of the cell,
causes Ca2+ channels to open,
Ca2+ causes the exocytosis / fusion of glutamate vesicles at the base of the cell.

Question 37

describe the process that occurs when the hair bundles are pushed towards the shorter bundles:

Answer 37

the tip links slacken and the channels close,
K+ cannot enter the cell so the cell becomes more hyperpolarised,
Ca2+ cannot enter the cell,
not glutamate released,
no firing of the afferent neuron.