The ear and auditory pathways

Question 1

What sort of waves are sound waves?

Answer 1

Transverse (compressions and rarefactions)

Question 2

What is the range of frequencies that can be heard by the human ear?

Answer 2

20-20,000Hz

Question 3

Recall the 2 main structures of the external ear

Answer 3

1. Pinna/auricle

2. External acoustic meatus (auditory canal)

Question 4

What are the 2 main functions of the auricle?

Answer 4

1. “Catching” sound waves

2. Indicating elevation of stimulus

Question 5

What are the 2 main functions of the external acoustic meatus?

Answer 5

1. Focus sound waves

2. Increase pressure at tympanic membrane

Question 6

What is the other name given to the middle ear?

Answer 6

Tympanic cavity

Question 7

Recall the 2 principle structures of the middle ear

Answer 7

1. Tympanic membrane

2. Auditory ossicles (malleus, incus, stapeus)

Question 8

What is the middle ear continuous with?

Answer 8

Eustacian tube

Question 9

What is the purpose of the eustacian tube?

Answer 9

Links middle ear and nasopharynx

Question 10

What are the 2 layers of the inner ear?

Answer 10

Bony labyrinth

Membranous labyrinth

Question 11

Recall the constituent parts of the bony labyrinth

Answer 11

Vestibule
Semi-circular canals
Cochlea

Question 12

What separates the bony and membranous labyrinths?

Answer 12

Perilymph

Question 13

Which auditory ossicle directly connects to the TM?

Answer 13

Stapeus

Question 14

Describe the basic structure of the cochlea

Answer 14

3 chambers: scala vestibuli/ media/ tympani
Basilar membrane between SM and ST
Organ of Corti on top of BM

Question 15

Recall the location and composition of the different lymphatic fluids in the inner ear

Answer 15

Endolymph: scala media - high K+, low Na+
Perilymph: scala vestibuli and tympani - low K+, high Na+

Question 16

What is the helicotrema?

Answer 16

Hole that allows passage of perilymph between SV and ST

Question 17

Recall the composition of the organ of corti

Answer 17

Inner and outer hair cells, neurons

Question 18

Where is the organ of corti located?

Answer 18

Between the basilar membrane and beneath the tectorial membrane

Question 19

Recall the differences in distribution between inner and outer hair cells

Answer 19

Inner hair cells found alone, outer hair cells found in groups of 3

Question 20

How does the function of inner and outer hair cells differ?

Answer 20

Inner = send afferents to brain
Outer = receive efferents

Question 21

Where are stereocilia located, and what is their function?

Answer 21

Inner hair cells: base in perilymph, respond to endolymph movement in SM
NO CONTACT WITH TM

Question 22

Recall the contacts of the hair cells with the TM

Answer 22

Inner hair cells = no contact

Outer hair cells = in contact

Question 23

Recall 3 functions of outer hair cells

Answer 23

1. Receive efferents from brain
2. Expand/ contract to amplift vibrations (due to electromotility)
3. Control inner hair cells

Question 24

What is the purpose of the auditory ossicles

Answer 24

Amplify pressure of sound waves in tympanic cavity so that they have enough energy to produce a pressure change in the fluid-filled inner ear

Question 25

Recall the 2 mechanisms by which the amplitude of sound waves is augmented in the inner ear

Answer 25

1. Auditory ossicles - stapeus vibration against superior oval window
2. TM - vibrations focused from large SA of TM to small SA of sup. OW

Question 26

Where is the round window located?

Answer 26

Just below superior oval window

Question 27

What is the function of the round window?

Answer 27

Pressure release - moves outwards to equalise pressure when stapeus pushes oval window into cochlear

Question 28

Summarise the pathway of sound transduction

Answer 28

Sound wave –> movement of fibres in BM –> movement of endolymph in SM –> inner hair cell change in polarity –> endocochlear potential

Question 29

Describe the relationship between hair cell movement and polarity

Answer 29

Upwards: K+ influx from endolymph, depolarisation
Downwards: K+ channels close, hyperpolarisation

Question 30

How is a concentration gradient maintained between the endolymph and perilymph?

Answer 30

Stria vascularis

Question 31

Recall the afferent neuronal pathway from the cochlear to the brain

Answer 31

Spiral ganglion
Ipsilateral cochlear nuclei
Superior olivary nucleus
Medial genticulate nucleus
Auditory cortex

Question 32

Explain the process of tonotropic mapping

Answer 32

Fibres longer as you go down BM
At base. short + stiff fibres respond to high frequency sounds. As you go towards end, longer and looser fibres detect lower frequencies
Generates a place code depending on time it takes to reflect sound

Question 33

Which muscles control ossicle movement

Answer 33

Tensor tympani

Stapedius

Question 34

Describe the auditory reflex

Answer 34

Muscles contrcat to reduce ossicle movement so that large noises cause less damage

Question 35

What is the difference between conductive and sensorineural deafness

Answer 35

Conductive: ossicle destruction prevents amplification
Sensorineural: cochlea/ cochlear nerve damage

Question 36

Recall 5 causes of conductive hearing loss

Answer 36

Wax
Otitis media
Otosclerosis of ossicles
Perforation of TM
Congenital