Hearing

Question 1

Define ‘hearing’

Answer 1

Distinguishing different sounds and localisation of the sounds (capture/avoidance)

Question 2

What is the function of the outer ear?

Answer 2

Detects air vibration and is involved in protection, localisation and amplification

Question 3

What is the function of the middle ear?

Answer 3

Impedence matching and sound amplification

Question 4

What is the function of the inner ear?

Answer 4

Splits complex sounds into simple components, outer hair cells amplify sound signals, transduction of mechanical signals by opening (depolarisation) or closing (hyperpolarisation) potassium channels

Question 5

What is the function of the central auditory nervous system?

Answer 5

Receives electrochemical signals and is involved in information processing

Question 6

What is impedence matching?

Answer 6

Involves the Eustachian tube due to a difference in area between the eardrum and the oval window, it works to compensate for the impedance mismatch between the air and cochlear fluid

Question 7

Describe the flow of vibration in the inner ear

Answer 7

Stapes –> oval window –> periplymph in cochlear –> round window

Question 8

How does the endolymph of the ear differ from the perilymph?

Answer 8

Endolymph is high in potassium and perilymph is high in sodium

Question 9

What are the three canals within the cochlea?

Answer 9

Scala vestibule, scala tympani and scala media

Question 10

Describe the scala vestibule and scala tympani of the cochlea

Answer 10

Both canals within the cochlea of the air that contain perlymph (has higher sodium levels than endolymph)

Question 11

Describe the scala media of the cochlea

Answer 11

Contains the organ of Conti and endolymph (has higher potassium levels than perilymph)

Question 12

What forms 95% of the cochlear nerve?

Answer 12

Inner hair cells from the organ of Conti

Question 13

Describe the structure of the organ of Conti

Answer 13

Hair cells are present between the (upper) tectorial membrane and (lower) basilar membrane and these play a large role in the transmission of sound

Question 14

Describe the inner hair cells of the organ of Conti

Answer 14

The inner hair cells (inner one layer of cells) form 95% of cochlear nerve and are involved in auditoy discrimination

Question 15

Describe the outer hair cells of the organ of Conti

Answer 15

Outer hair cells (arranged in 3 outer rows), have cilia embedded in the tectorial membrane, and are involved in frequency tuning (they amplify the basilar membrane vibrations, enhancing sensitivity and frequency selection)

Question 16

How do we differentiate sounds at different frequencies?

Answer 16

Vibration of perilymph –> reaches organ of Conti –> movement of basilar and tectorial membranes –> stimulates and depolarises certain hair cells –> stimulates cochlear aspect of CN VIII and specific hair cell stimulated allows the brain to relay that a different pitch is being received

Question 17

How do we localise sound direction?

Answer 17

The superior olivary nucleus use interaural time differences (ITF - difference in time of sound reaching the two ears) and interaural level differences (ILD, using pressure) to localise sound cues.

Question 18

Define pitch/frequency

Answer 18

Number of oscillations per second

Question 19

Define intensity/loudness

Answer 19

Height of soundwave in dB

Question 20

In the auditory pathway, what occurs at the ventral cochlear nucleus in the medulla?

Answer 20

Involved in the location and intensity of the sound

Question 21

In the auditory pathway, what occurs at the dorsal cochlear nucleus in the medulla?

Answer 21

Involved in the pitch and quality of the sound

Question 22

In the auditory pathway, what occurs at the superior olivary nucleus in the pons?

Answer 22

Involved in spatial localisation of sound

Question 23

Describe the passage of the cochlear nerve in the auditory pathay

Answer 23

Primary cochlear nerve afferent –> internal auditory meatus –> synapses at cochlear nucleus in medulla –> second order neurone –> superior olivary nucleus in pons OR to inferior colliculus in midbrain –> then synapse at inferior colliculus –> medial geniculate nucleus in midbrain –> primary auditory cortex in cerebrum

Question 24

What is conduction deafness?

Answer 24

Air conduction is impeded such as damage to the ear itself

Question 25

What is sensorineural deafness?

Answer 25

Nerve damage (brain or cochlear nerve for example), or if you damage cochlear

Question 26

How can Rinne’s test be used to test for deafness?

Answer 26

Vibrating tuning fork placed on mastoid process on both sides; should have better air conduction but in conduction deafness there is better bone conduction on affected side and in sensorineural deafness air conduction is normal in affected ear but sound is loudest in unaffected ear

Question 27

How can Weber’s test be used to test for deafness?

Answer 27

Tuning fork in middle of forehead; should hear sound the same on both sides, in conduction deafness there is louder sound in the affected ear, in sensorineural deafness the sound is louder in the unaffected ear

Question 28

What are the consequences of middle ear disorders and give examples

Answer 28

Conduction deafness e.g. perforated of tympanic membrane, glue ear or otosclerosis

Question 29

Describe a vestibular schwannoma

Answer 29

Benign neoplasm arising from sheaths of cranial nerve (CN VIII) which causes unilateral hearing loss, tinnitus and disequilibrium

Question 30

Describe a meningioma

Answer 30

Second most common mass in cerebellopontine angle and arise from arachnoid layer of meninges

Question 31

What is the purpose of auditory reflexes?

Answer 31

To prevent damage to the eardrum (tympanic membrane) and also to distinguish sounds from the background

Question 32

Describe the attenuation reflex

Answer 32

Reflex is stimulated by low pitch (allows higher pitch to be discerned more easily, such as your own voice)
• In this reflex there is a delay between 50-100ms from the onset of the stimulus, and therefore doesn’t offer much protection from very sudden loud sounds

Question 33

What is the function of the attenuation reflex?

Answer 33

Involves the contraction of the muscles in the ear to dampen the transmission from the middle to inner ear when exposed to loud sounds or own voice, in order to prevent damage to tympanic membrane

Question 34

Describe the startle/blink reflex

Answer 34

Rapid reflex involving the facial nerve and reticular formation and it functions to protect the back of the neck (whole body startle) or the eye (blink)

Question 35

What results if there is a faulty attenuation reflex?

Answer 35

Hyperacuity

Question 36

Why doesn’t the attenuation reflex offer much protection from very sudden loud sounds?

Answer 36

There is a delay between 50-100ms from the onset of the stimulus