L9 - Hearing

Question 1

What is vibration in air detected by?

Answer 1

Inner hair cells

Question 2

What range of vibration can be detected by the ear?

Answer 2

20 - 20, 000 Hz

Question 3

How sensitive is the ear?

Answer 3

picometers to 100 decibels

Question 4

Receptive field for the ear

Answer 4

Peak of travelling wave in the basalar membrane

Question 5

Function of external ear

Answer 5

Amplifies around 3000 HZ, some elevation enhancement of high freq

Question 6

Impedence mismatch

Answer 6

The way that energy flows through air is different to how it flows through water

Question 7

How is the impedence mismatch overcome in the ear

Answer 7

The middle ear bones transfer vibrations efficiently from the tympanic membrane (air) to the oval window (liquid) by amplifying pressure. The Eustation tube allows equalisation of pressure across the tympanic membrane.

Question 8

What makes up the middle ear?

Answer 8

MIS, Malleus, Incus, Stapes

Question 9

Where does spectral decomposition occur?

Answer 9

In cochlea, organ of corti, the basilar membrane has big fibres that vibrates in sympathy with low freq and small fibres with high freq.

Question 10

Kinocillium are connected to what membrane

Answer 10

Tectorial membrane

Question 11

Unlike the “usual” systems, is K+ found higher intra or extracellularly?

Answer 11

Extracellularly

Question 12

Scala vestibuli, tympani and media, which one is high in K+ extracellularly?

Answer 12

Scala media

Question 13

Auditory nerve is which CN

Answer 13

CN8

Question 14

Central auditory pathway

Answer 14

Sound enters cohlea -> travels bilaterally to superior olive -> thalamus (medial geniculate) -> cortex

Question 15

Is left ear leading neuron closest to left ear in the MSO (medial superior olive) or furthest away?

Answer 15

Furthest away

Question 16

Attenuation definition

Answer 16

Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances.

Question 17

What occurs in the LSO (Lateral superior olive)

Answer 17

Inhibition of sounds, where if one side is louder - the other side is inhibited, exaggerating relative loudness of sound.

Question 18

How do we know if something is infront or behind in cone of confusion?

Answer 18

Pinna tells you the relative position of it

Question 19

Whats unique about the cone of confusion?

Answer 19

If there is a cone next to someone’s ear and you release sounds from each different point of the cone - the sounds from the points have identical interaural time and level difference.

Question 20

500 Hz (low freq) responds to which part of cochlea

Answer 20

Apex

Question 21

16 000 Hz (high freq) responds to which part of cochlea

Answer 21

Base

Question 22

Belt areas is aka

Answer 22

Secondary auditory cortex

Question 23

Wernickes area is found in ___ and used for recognizing ___

Answer 23

It is found in the secondary auditory cortex aka belt areas and used for recognising lingustic objects

Question 24

Left side of belt area is for speech recognition where else right side is for

Answer 24

Music

Question 25

Structure of inner ear

Answer 25

Within the inner ear the coiled cochlea contains two liquid filled chambers, the scala vestibuli and scala tympani (low potassiumion concentration), separated by the cochlear duct (scala media – high potassium ion concentration) containing the basilar membrane. The Organ of Corti sits on top of the basilar membrane with many mechanically supporting cells. A single row of inner hair cells and three rows of outer hair cells are anchored to the basilar membrane with cilia of the outer hair cells contacting the tectorial membrane.

Question 26

What does the basilar membrane look like?

Answer 26

The basilar membrane is narrower and stiffer at the base and becomes wider and more elastic towards the apex so that high frequency sounds cause maximum vibration at the base end and low frequency sounds cause maximum vibration at the apical end. Thus hair cells and their innervating fibres have a corresponding tonotopic organisation (map of frequency space).

Question 27

Where does transduction occur? How?

Answer 27

Organ of Corti. Vibration of the ossicles leads to the oval window and round window vibrating in and out and causes the Organ of Corti to vibrate up and down. The basilar membrane and tectorial membrane have different ‘pivot points’ so that there is relative tangential motion between them, and therefore the cilia are bent forwards and backwards. When the stereocilia bend towards the kinocilium, the resulting tension in the “tip links” opens potassium ion channels causing depolarization or excitation and vice-versa.

Question 28

The apical surface of the hair cells is exposed to a ___ potassium ion concentration, the basal surface to a __ concentration, this allows potassium to flow into the cells at the apex when potassium channels are mechanically opened (which depolarises the cell), and out of the cells in the basal region due to the concentration gradient.

Answer 28

High, low