6.3.1 Ear Structure and Function

Question 1

What makes up the kinetic labryinth and what is the function?

Answer 1

• Semicircular Canals (three) and Crista Ampullaris
• Detect changes in rotational acceleration

Question 2

What is the sequence by which sound wave entering the ear result in 8th nerve activity?

Answer 2

Question 3

What are the peripheral components of the auditory system?

Answer 3

-external, middle, and inner ear

Question 4

What is the role of the vestibular system in regards to balance and movement?

Answer 4

• Hair cells provide info about motion and gravity from the left and right sides
• Brain compares the info from the two sides
• Information does not reach the cortex, but does interact with the motor system
• Other systems also provide info about position: Visual system and Proprioception (somatosensory)

Question 5

What are the 3 components of the cochlea?

Answer 5

• Inner: Scala Media filled with endolymph
• Outers: Scala Vestibuli and Scala Tympani filled with perilymph

Question 6

Both auditory and vestibular hair cells transduce energy via?

Answer 6

movement of their stereocilia

Question 7

What are the transducers for both the auditory and vestibular system?

Answer 7

Hair cells

Question 8

What is pressure equalization in regards to middle ear functions?

Answer 8

• Eustachian tube connects the middle ear and the nasopharynx
• Tensor veli palatini and salpingopharyngeous muscles open the Eustacian tube during swallow

Question 9

Describe the movement of the basilar membrane, is it uniform throughout?

Answer 9

Question 10

What is the role of the basilar membrane and how do hair cells affect this?

Answer 10

• Basilar membrane: floppy membrane receiving different frequencies at specific regions
• Hair cells sit atop of the basilar membrane within the scala media endolymph
• Tectorial membrane sits atop of the stereocilia of the hair cells
• As hair cells move, a shearing force is produced relative to the tectorial membrane
• Causes changes in AP firing rate

Question 11

What is the importance of the middle ear?

Answer 11

-filled with air; ossicles conduct vibrations from tympanic membrane to the oval window of the cochlea

Question 12

What is the mechanism by which the saccule and utricle detect changes in linear acceleration (gravity)?

Answer 12

• Stereocilia embedded in gelatinous glycoprotein matrix filled with otoliths
• Otoliths (calcium carbonate crytsals) shift during linear acceleration
• Results in bending of stereocilia

Question 13

Damage to auditory or vestibular nerve results in?

Answer 13

Hearing loss or balance disorders

Question 14

What is the importance of the inner ear?

Answer 14

-filled with fluid; where mechanical sound vibration or motion is transduced into neural activity

Question 15

What is the function of the auditory system how is this achieved?

Answer 15

provides information about sound in the environment

• Afferent info from CN VIII synapses on cochlear nuclei in brainstem
• Auditory information reaches the cortex

Question 16

How does the cochlea allow for transmission of sound?

Answer 16

• Entry: from stapedal vibrations at oval window through scala vestibuli
• Exit: at round window through scala tympani

Question 17

What is the mechanism by which the ampullae (semicircular canals) detech angular acceleration?

Answer 17

• Hair cells are located in ampullae on a ridge of tissue called the crista ampullaris
• Stereocilia are embedded in the cupula, a tall glycoprotein matrix mass
• Cupula is deflected by fluid flowing through the canal when the head turns
• Results in bending of stereocilia

Question 18

Stereocilia have what at their tips and what is this importance?

Answer 18

• Stereocilia have potassium channels at their tips
• Bending causes either opening/closing of channels, influx of K+ causes opening of Ca++ channels, changing amount of NT released
• Results in a change of AP frequency

Question 19

Describe the ionic composition of the endolymph vs the perilymph.

Answer 19

• Endolymph: low Na, Cl; High K
• Perilypmh: high Na, Cl; Low K

Question 20

The basilar membrane location that experiences the greatest displacement depends on?

Answer 20

Mechanical properties of the membrane and frequency of sound

Question 21

What are the characteristics of the Macular organs?

Answer 21

• Saccule and Utricle
• Detect changes in linear acceleration (gravity)

Question 22

What is the Stria Vascularis?

Answer 22

lining of the scala media, secretes K+ ions to maintain potential

Question 23

What is the importance of the external ear?

Answer 23

-amplifies sound reaching the tympanic membrane

Question 24

What is the function of the vestibular system how is this achieved?

Answer 24

• provides information about motion and gravity
• Afferent info from CN VIII synapses on vestibular nuclei in brainstem
• Information does NOT reach the cortex

Question 25

What are the properties of the inner hair cells of the cochlea?

Answer 25

- Primarily responsible for sending info to the CNS via **CN VIII afferents** - Organized in a single row - Sensory transducers - **S****ingle CN VIII afferent contacts a single inner hair cell; one IHC receives several contacts**

Question 26

Hair cells within the cochlea sit on what?

Answer 26

They sit in a specific orientation on a structure called the basilar membrane.

Question 27

Describe the central auditory pathway.

Answer 27

Question 28

What are the peripheral components of the vestibular system?

Answer 28

Inner ear

Question 29

Shearing force against stereocilia with basilar membrane movement does what?

Answer 29

change in hair cell membrane potential causes release of neurotransmitter at the base.

Question 30

What are the characteristics of outer hair cells?

Answer 30

**-Change the stiffness of the basilar membrane** **-Damage changes thresholds and** - Organized in three rows - Modulate sensory transduction by IHCs - Synapse with **efferent fibers from the brain** - Originating in **superior olivary nucleus** - Amplify the transduction of quiet sounds and attenuate the transduction of loud sounds - Can create otoacoustic emissions

Question 31

Describe the wave displacement of the basilar membrane at the base and apex. Relate this to stiffness and frequency.

Answer 31

- Wave produced by stapes at oval window moves from base to apex of the basilar membrane - Stiffness of the membrane differs along its length * -Base: narrow and stiff * -Apex: wide and flexible -Amplitude of displacement at a given location of the membrane depends on the frequncy * -Base: high frequencies (stiff membrane ⇒ requires more energy to displace) * -Apex: low frequencies (flexible membrane ⇒ requires less energy to displace)

Question 32

How do the basilar membrane and cochlea act in tonotopic organization?

Answer 32

Question 33

How does the middle ear gain control of vibrations reaching the inner ear?

Answer 33

- **Tensor tympani and stapedius** muscles can change the **stiffness of the tympanic membrane** - Used to **dampen** the movement of the stapes - Increases the **dynamic range** of the inner ear and protects cochlear hair cells from loudness

Question 34

What are the two membranes of the cochlea?

Answer 34

- Vestibular: separates scala vestibuli from scala media - Basilar: separates scala media from scala tympani

Question 35

Describe the membrance potentials between the endolymph and the hair cell membrane and what the importance of this is.

Answer 35

- Endolymph: +80mV - Hair Cell Membrane: -40mV - 120mV membrane potential difference drives K+ ions from the endolymph into the hair cells

Question 36

How is sound information organized in the auditory system?

Answer 36

Auditory - frequency

Question 37

What is impedence matching in regards to middle ear functions?

Answer 37

-Ossicular chain and the size difference between the tympanic membrane and oval window prevent loss of pressure at the oval window

Question 38

Outer hair cells are innervated by?

Answer 38

Question 39

What does the cochlea do?

Answer 39

Produces nerve impulses in response to sound and vibration

Question 40

What are the two types of organs in the vestibular system?

Answer 40

Static Labyrinth (macular organs) Kinetic Labyrinth

Question 41

How does hair cell bending in regards to kinocilium alter the function of nerve conduction?

Answer 41

- Deflection of hair bundle toward kinocilium (tall side): **depolarization and excitation** - Deflection of hair bundle away from kinocilium (tall side): **hyperpolarization and inhibition**