Lecture 12

Question 1

Sound waves

Answer 1

Air condenses and rarefys

goas at 700mph

Amplitude = how loud

hz = pitch

human ears 20-20000 hz

Question 2

Timbre

Answer 2

Complexity of sound (like what instrument)

Question 3

Anatomy of ear

Answer 3

(1) sound funneled into pinnae (outer ear)
(2) sound coming down the ear canal vibrates the tympanic membrane
(3) Middle ear is comprised of 3 ossicles

Move the membrane behind the oval window

Go to cochlea

Question 4

Cochlea/basilar membrane

Answer 4

water runs around a central membrane in
Where it bends membrane = sound perception
Basilar membrane encodes high frequency notes at the beginning near the oval window and low frequency notes at the end

Question 5

Cochlea

Answer 5

Scala vestibuli (up) S
Scala tympani (below
Scala media has organ of corti

Question 6

Organ of corti

Answer 6

basilar membrane
Tectoral membrane
Hair cells

Question 7

Hair cells (inner and outer)

Answer 7

1:3 Inner:outer hair cells

Inner transduces signal

Outer, joint to both membranes and can contract therefore alters the shape of membranes and helps make it sensitive

No functional inner hair cells = totally deaf
No outer hair cells can hear but not well

Question 8

Hair cell cilia

Answer 8

On ends of inner hair cells and not joined to top membrane
Can move as water moves them
All joined together by tip links to insertional plaques
Mechanically pulls open ion channels when hair moved apart

Question 9

Loud noise

Answer 9

Easily break tip links
These grow back but takes a while
Probably protective as too much glutamate secretion causes excitotoxicity

When too much activity over a while = hair cells over stimulate nerve cells = excitotoxicity = cell death and permeant hearing loss

20% of 20 year olds have this

Also age related hearing loss

Question 10

Perception of pitch

Answer 10

Different frequencies produce maximal stimulation of hair cells at different points on the basilar membrane

Place coding

At very low frequencies, this does not work because the membrane bends over a large area so it switches to rate coding. How much NT is transmitted by low frequency hair cells

Question 11

Hair cell sensitivity

Answer 11

Respond best to a specific frequency
Will still respond to others but only if loud enough
High volumes cause multiple cells to fire but one will fire the most. This is the fundamental frequency and determines the pitch of the could we perceive. The number of cells that fire codes for the volume we perceive.

Question 12

Overtones

Answer 12

Natural sounds are composed of a fundamental frequency and a collection of overtones which are integer multiples of the fundamental frequency

Question 13

Timbre

Answer 13

The lowest and most intense frequency of a sound is the fundamental frequency
Sounds basic pitch is perceived from this

Overtones are sound frequencies that occur at multiples of the same fundamental frequency

Timbre of sound is the fundamental frequency and overtones mixed. Different instruments produce different overtones and thus timbres at the same notes. We analyze this over time and learn to interpret them as different,

Question 14

Cochlear implant

Answer 14

Often hair cells don’t work due to a defect in proteins
Person borne deaf
But the nerve still works
Implant 2024 electrodes in the cochlea
frequency patterns 250-6500hzHuman voice is 165-255 but implants cannot do this
By using overtones, can distinguish human voices

Not very good. Music is not pleasant. Very good overall

Question 15

Perception of spatial location (innate - 2 things)

Answer 15

Under 800Hz have half wavelengths larger than dimension of head so can note the different times it reaches the ear

High f - note the difference in loudness between the ears cos high f sounds are dampened as they pass through skull

Question 16

Perception of spatial location

Answer 16

Sound waves are altered by pinnae before they enter the ear canal
As this happens they are distorted depending on where they are coming from
We learn this pattern and associate it to a region
Blind ppl do not cos cannot look there

Question 17

From ear to primary auditory cortex

Answer 17

Cochlear nerve connects organ or corti to brain
Goes to cochlear nuclei in medulla where copies of the signal are made to be analyzed in parallel ascending paths
Axons from cochlear nuclei go to the inferior colliculi in the midbrain which help to localize sound source
Axons from inferior colliculi synapse in the medial geniculate nucleus of the thalamus which goes to the primary auditory cortex (in the temporal lobe)

Question 18

Tonatrophic Representation

Answer 18

Like basilar membrane, primary auditory cortex is organized by frequencies

Question 19

Auditory cortex pathways

Answer 19

Primary auditory cortex goes to association cortex

(1) Where posterior, dorsal, where parietal
(2) Anterior, what, temporal

Question 20

Auditory agnosia

Answer 20

Amazia

Cant perceive or produce melodic music

Cant sing or recognize songs

They can recognize emotions conveyed by songs (like soothing) but not the difference between consonant (nice) and dissonant (bad) music

Question 21

Vestibular system

Answer 21

Maintains upright position

Semicircular canals
Cupula are fluid in these
Move hair cells and break tip links like for sound

Question 22

Vestibular sac

Answer 22

Gravity

Utricle and saccule in the sac respond to the force of gravity and inform the brain about the heads orientation