Auditory System I And Ii

Front 1

What is the equation for decibel scale of pressure?

What do the variables stand for?

Back 1

dB = 20 * log(P/P0)

P = amplitude of the pressure
P0 = Reference pressure = human threshold for hearing = 0.0002 dynes/cm^2

Front 2

What is SPL?

Back 2

Sound pressure level

Notation to indicate P0 = reference pressure is set at 0.0002

Front 3

What is the relationship between pressure and loudness?

Back 3

Not 1:1, but rather an equation with an exponent of 0.4-0.6

10 fold increase in pressure (20dB) increases loudness only 2.5-4 fold

Front 4

What is an equal loudness curve?

Where is there a dip and what does it correspond to?

Back 4

A plot of various intensities vs. frequencies that give the same loudness

Dip at 3,000-5,000 Hz corresponds to human voice --> we can hear this at few dBs

Front 5

What does a frequency reading at "0" spl mean?

What does the lowest curve on an equal loudness curve show?

Back 5

Defined as the threshold for hearing a 1,000 Hz sound

Lowest curve = threshold for hearing different frequencies

Front 6

How does pitch relate to frequency?

Back 6

Correlated, but not the same

2 fold increase in pitch results from a 3 fold increase in frequency

Front 7

What is the relationship between pitch and amplitude of sound?

Back 7

Pitch depends on amplitude, but less than it does on frequency

When volume increases from 40dB to 110 dB at 500 Hz, 4% decrease of pitch

Front 8

What two types of cues are used to localize a sound source?

Back 8

Temporal (phase) and intensity (amplitude)

Front 9

What is the function of the pinna and head?

When does it work and why?

Back 9

Cast a shadow that gives an intensity difference for spatial resolution

Works at high frequency tones because wavelengths are smaller than the head

Front 10

What is the function of the Pinna and Concha?

When does this work?

Back 10

Resonator, can amplify intensity by 10 dB

Works between 2,000-5,000 dB

Front 11

What does the tympanic membrane serve as a boundary for?

Back 11

Outer and middle ear

Front 12

What is the middle ear composed of?

Back 12

Malleus
Incus
Stapes

Front 13

What is the function of the middle ear bones, in tandem with the tympanic membrane? (2)

Back 13

Transfer sound energy from a low (air) to high (liquid) impedance medium

Amplification

Front 14

How does amplification occur in the middle ear? (2)

Back 14

1. Focus of force on the tympanic membrane (large diameter) to the oval window (small diameter) --> 17x increase

2. Lever action of bones --> 1.3x increase

Front 15

What 2 muscles are activated in the reflex to a loud sound?

What do they do?

Back 15

1. Tensor Tympani --> increased stiffness of the tympanic membrane

2. Stapedius --> causes stapes to retract from the oval window

Front 16

To what structures do the tensor tympani and stapedius connect?

Back 16

tensor tympani to malleus

Stapedius to stapes

Front 17

What is the eustachian tube?

How can it cause pain and difficulty hearing?

Back 17

connects pharynx, below bones of middle ear

If pressure differences or tube is blocked, can cause pain

Front 18

What are the three chambers of the cochlea?

Back 18

Scala vestibuli
Scala tympani
Scala media

Front 19

Where does the organ of corti sit?

What makes it up?

Back 19

Sits at the base of the scala media

Includes structures from tectorial to the basilar membranes, place where hair cells are located

Front 20

What is the oval window?

Back 20

Basal entrance to the cochlea

Attaches to the stapes

Front 21

What is the helicotrema?

Back 21

Ends the division of the cochlear partition at the extreme apex

Front 22

Where is the round window?

Back 22

At the basal end on the other side of the cochlear partition from the oval window

Front 23

Where does the wave go once compression hits the tympanic membrane?

What does it do to the basilar membrane?

Back 23

Stapes pushes oval window --> signal travels around helicotrema to round window

Basilar membrane

Front 24

What is rarefaction?

Where does it travel?

Back 24

Rarefaction = opposite of compression, making wave less dense

Pulls stapes back --> fluid travels toward the vacuum from round to oval window

Front 25

What are the two kinds of hair cells?

Roles?

Back 25

Inner and outer

Inner hair cells send afferent projections to brain

Outer hair cells receive efferent feedback signals from brain, may sharpen resolution frequency

Front 26

What do hair cells contain at their apex?

Back 26

Stereocilia

Front 27

What are tip links?

Back 27

Connections between stereocilia at the apex of hair cells

Amplify the forces in the area of the molecular sensors

Front 28

Where do hair cells sit?

What stimulates them?

Back 28

Sit between tectorial and basilar membranes

Stimulated by sheering force between the two

Front 29

How does solution bathing the apical portion of the of the hair cell different from that at the base of the hair cell?

Back 29

Apex bathed in endolymph, which is K rich (+80)

base bathed in perilymph, which is K poor

Front 30

What happens when Mechanosensitive channels are stimulated to open in hair cells?

Back 30

K flows into cell --> depolarize --> opens Ca channels at basal end --> vesicular release of NTs

Also causes opening of Ca-dependent K channels at basal end --> K flows out --> repolarize cell

Front 31

What type of response to stimulation do hair cells give?

What does this allow for?

Back 31

Can depolarize or hyperpolarize in response to a given stimulus --> No APs

This allows for full sinusoidal curve for the stimulus, but only correlation at lower frequencies

Front 32

What is phase locking?

Back 32

Sinusoidal curve from hair cell --> firing of auditory neurons synchronously with sound wave --> 1:1 correspondance between sound wave and neuronal firing

Front 33

What is volley theory?


How fast can neurons firing?

Back 33

Encoding pitch at low frequency by phase locking sound wave and neuronal firing

Neurons can fire at about 1000 impulses/sec

Front 34

What properties of the basilar membrane allow for tonotopic encoding?

Back 34

Basilar membrane becomes thicker and wider further from the oval and round windows, so different sets of neurons are stimulated as the wave passes

This encodes the frequency of mid- and high level frequencies

Front 35

Where does the tonotopic map of frequencies exist?

Back 35

On the basilar membrane all the way to the primary auditory cortex

Front 36

Low frequency stimuli
a. Spatial localization
b. Frequency encoding

Back 36

a. Phase shift
b. Volley theory

Front 37

High frequency stimuli
a. Spatial localization
b. Frequency encoding

Back 37

a. Intensity (shadowing)
b. Tonotopic map

Front 38

What are 3 mechanisms in which sound intensity is encoded?

Back 38

1. Recruitment of more neurons
2. Increasing the probability of firing of recruited neurons
3. Loss of spatial resolution from loud stimuli (more areas on the tonotopic map stimulated at higher frequencies than at lower frequencies)

Front 39

What is the pathway of air conduction of sound?

What is it called if there is damage to the pathway?

Back 39

Sound waves from air --> tympanic membrane --> 3 ossicles of middle ear

If damage: conduction deafness

Front 40

What is the pathway of sound conveyed by bones?

What is it called when there is damage to the pathway?

Back 40

Vibration in contact with skull or bones --> cranial bones --> CN 8

If damage: sensorineural deafness

Front 41

What is Rinne's Test?

What is a normal response?

Back 41

Hold a tuning fork to head until patient can no longer hear it (bone conduction), then hold up to ear (air conduction)

Normal response = air conduction better than bone conduction

Front 42

What is the response in Rinne's test to conduction deafness?

To sensorineural deafness?

Back 42

Conduction deafness = bone conduction is better than air conduction (b/c there is a deficit with bones of the middle ear)

Sensorineural deafness = air conduction better than bone conduction (but both forms are diminished because problem with nerve)

Front 43

Weber's test:
a. Method
b. Normal results

Back 43

a. Base of vibrating tuning fork placed at middle of forehead --> see whether sound is heard in midline or in one ear

b. normal: sound heard in midline

Front 44

Weber's test
c. Conduction deafness result
d. Sensorineural deafness result

Back 44

c. Sound louder in abnormal ear (even though air conduction is decreased, bone conduction may be increased as compensation)

d. Sounds louder in normal ear (problem with bone conduction in bad ear)

Front 45

What is the nature of afferent innervation of brain from auditory complex?

Back 45

Tonotopic, carried by inner hair cells

Front 46

What is the role of efferent innervation in auditory complex?

Back 46

Efferents --> outer hair cells, sharpen acuity and improve frequency resolution

Front 47

What are otoacoustical emissions?

Back 47

Acoustic energy recorded from the cochlea produced by efferent innervation to outer hair cells

Front 48

What is the pathway of afferents from the ear?

Back 48

Cochlear nuclei --> superior olive --> lateral lemniscus (brainstem) --> inferior colliculus(medulla) --> medial geniculate (thalamus) --> auditory cortex (superior temporal gyrus)

Front 49

What is the general effect of CNS lesions beyond the cochlear nuclei?

Back 49

General deficits rather than deafness in one ear because about half the fibers cross at the superior olive

Front 50

What is the role of the medial superior olive?

How does it do this?

Back 50

Plays a role in sound localization by computing interaural time differences


Compares inputs from left and right anterior ventral cochlear nuclei to determine phase shifts

Front 51

What is required of the medial superior olive?

Back 51

Requires phase locking (because it determines sound localization based on phase shifts)

Works at low frequency (<3000 Hz)

Front 52

What is the role of the lateral superior olive and the medial nucleus of the trapezoid body?

Back 52

Sound localization

Brain integrates input from the left and right anterior ventral cochlear nuclei to determine intensity differences

Front 53

What are the properties of the processing done by the lateral superior olive and the medial nucleus of the trapezoid body? (3)

Back 53

1. Major cue is the shadowing by Head and Pinna
2. Works at higher frequency
3. Cells stimulated by ipsilateral input, inhibited by contralateral input

Front 54

What is the role of the lateral lemniscus?

What does it receive?

Back 54

Processes onset and offset of sounds

Receives input from contralateral cochlear nuclei

Front 55

What does the inferior colliculus process?

Back 55

Auditory space map for localization of sounds, differentiates important sounds like 'speech'

Front 56

Medial geniculate complex
a. Input
b. Role

Back 56

a. Inferior colliculus
b. Frequency comparison, temporal comparison

Front 57

What is the structure of cells within the primary auditory complex?

Back 57

Columnar organization of cells receiving input EE (excited both ears) and EI (excited by one, inhibited by the other)

Columns are orthogonal to tonotopic map

Front 58

Where is the secondary auditory complex?

What does it process?

Back 58

Inferior on the temporal lobe from the primary auditory complex

Processes more complex sounds

Front 59

Where are the speech recognition centers

Back 59

Posterior to the primary cortex

Front 60

What is the role of speech recognition centers in the left or dominant hemisphere?

Right or non-dominant hemisphere?

Back 60

Process speech

Process emotional tone and inflections

Front 61

What is word salad?

Back 61

Incomprehensible speech caused by lesion in Wernicke's area --> difficulty conveying an idea