Physiology of Ear

Question 1

State the basic functions of the external, middle and inner ear

Answer 1

External: collect sound
Middle: amplify sound
Inner: sound transduction

Question 2

What does sound “frequency” dictate? What frequency of sound can humans perceive?

Answer 2

Frequency = pitch of sound

Humans perceive between 20 and 20,000 Hz

Question 3

What does sound “amplitude” dictate?

Answer 3

Amplitude = intensity/loudness of sound

Question 4

How does the auricle/pinna of the external ear aid sound collection?

Answer 4

Concave cartilaginous structure directs sound into the ear canal

Question 5

The inner ?/3 of the ear canal is embedded in the temporal bone

Answer 5

The inner 2/3 of the ear canal is embedded in the temporal bone

Question 6

Where does airborne sound travel towards in the ear canal?

Answer 6

Towards the tympanic membrane (eardrum)

Question 7

What is the function of the tympanic membrane (eardrum)?

Answer 7

Separates external + middle ear
Transmits airborne sound from external ear to middle ear through vibration
Protects middle ear structures

Question 8

Where (anatomically) is the middle ear cavity located?

Answer 8

Mastoid process of temporal bone

Question 9

List the main structures of the middle ear

Answer 9

Tympanic membrane
Malleus
Incus
Stapes
Oval window
Eustachian tube

Question 10

What makes up the ossicular chain?

Answer 10

Incus
Malleus
Stapes

Question 11

The malleus is attached to the tympanic membrane. True/False?

Answer 11

True

Question 12

At how many decibels does the ossicular chain amplify sound?

Answer 12

25 decibels, depending on frequency of sound transmitted

Question 13

What is meant by “impedance matching” of sound in the middle ear?

Answer 13

When sound in air strikes fluid, there is a loss of sound energy and thus intensity which would be detected by a listener;
to compensate, the middle ear concentrates sound on the small SA of the stapes to result in proportional amplification (SA eardrum 21x greater than stapes), thus overcoming loss of decibels due to liquid interface

Question 14

What is the function of the Eustachian tube?

Answer 14

Air pressure equaliser + ventilator for middle ear mucosa

Question 15

At rest, the Eustachian tube is closed. True/False?

Answer 15

True

Question 16

Which muscles open the Eustachian tube?

Answer 16

Tensor veli palatini

Levator palatine

Question 17

What are the two openings from the middle ear to cochlea (inner ear)?

Answer 17

Oval window

Round window

Question 18

What are the 2 main components of the inner ear?

Answer 18

Cochlea

Vestibular system

Question 19

What is the collective term for the cochlea + vestibular system?

Answer 19

Otic capsule

Question 20

What is the fluid system that suspends the otic capsule?

Answer 20

Perilymph (connected to cerebrospinal fluid)

Question 21

The perilymph system is located within the membranous labyrinth of the inner ear. What are the 6 specialised receptor organs found within the membranous labyrinth?

Answer 21

Organ of Corti
Maculae of utricle + saccule
Cristae of the 3 semicircular canals

Question 22

What 3 chambers make up the cochlea?

Answer 22

Scala vestibuli
Scala tympani
Scala media

Question 23

The scala media is filled with endolymph/perilymph and the scala tympani + vestibuli are filled with endolymph/perilymph

Answer 23

The scala media is filled with endolymph and the scala tympani + vestibuli are filled with perilymph

Question 24

What is the function of the Organ of Corti?

Answer 24

Sensory organ for hearing

Contains hair cells that convert mechanical bending force (caused by sound waves) into electrical impulses

Question 25

Outline the process of hearing sound!

Answer 25

1. Sound wave enters inner ear via oval window
2. Transmitted through cochlear fluid
3. Basilar membrane deflects in response to waves in inner ear
4. Motion of basilar membrane bends hair cells resulting in sound transduction into electrical impulse
5. CN VIII carries impulse from Organ of Corti to brainstem

Question 26

The basilar membrane is “tonotopically organised” - what does this mean?

Answer 26

Each part responds to specific sound frequency
Apex = curly part of cochlea = low frequency
Base = high frequency

Question 27

Where is the auditory cortex in the brain located (where electrical sound impulses arrive)?

Answer 27

Superior temporal gyrus, Broadmann area 41/42

Question 28

List the central pathways for sound (ECOLI)

Answer 28

Eighth cranial nerve
Cochlear nucleus
Olivary complex
Lateral lemniscus
Inferior colliculus

Question 29

What is the function of the vestibular system?

Answer 29

Maintain balance regardless of head position or gravity in conjunction with eye movement + somatosensory input

Question 30

What are the 5 specialised receptor organs within the membranous labyrinth of the inner ear related to balance?

Answer 30

Maculae of utricle + saccule

Cristae of the 3 semicircular canals

Question 31

What is another term for the utricle + saccule?

Answer 31

Otolith organs

Question 32

Outline the function of the maculae of the otolith organs

Answer 32

Sensory part with upward-projecting cilia covered in gelatinous mass + calcium carbonate
Brain perceives linear movement due to firing of cilia when head is tilted

Question 33

What is the degree of orientation of the otolith organs?

Answer 33

360’

Question 34

Outline the function of the cristae of the semicircular canals

Answer 34

Sensory part with hair cells embedded in a cupula that depolarise/hyperpolarise depending on fluid inertia created by head angulation

Question 35

What is the degree of orientation between the semicircular canals?

Answer 35

90’