L10 Auditory System

Question 1

Wave amplitude defines __________

Answer 1

Loudness

Question 2

Wave frequency defines _________

Answer 2

Pitch

Question 3

External ear, parts and function

Answer 3

Pinna and external auditory canal funnel sound waves onto the tympanic membrane.

Question 4

Middle ear, parts and functions

Answer 4

Vibration of the tympanic membrane causes movement of the auditory ossicles that then vibrate the oval window.

Question 5

Auditory ossicles

Answer 5

Malleus, incus, stapes.

Question 6

Flexion of the tensors tympani

Answer 6

Attenuates vibration of the tympanic membrane
Cranial nerve V

Question 7

Flexion of the stapedius muscle

Answer 7

Reduces movement of the stapes, reduces sound transmission
Cranial nerve VII

Question 8

Acoustic reflex

Answer 8

Flexion is automatically triggered by loud noises via cranial nerves (V - tensor tympani, VII - stapedius)

Question 9

Three chambers of the cochlea

Answer 9

Scala vestibuli - perilymph
Scala tympani - perilymph
Scala media - endolymph

Question 10

Location of the organ of corti

Answer 10

Within the scala media on top of the basilar membrane, lots of sensory receptors

Question 11

Organ of corti structure

Answer 11

Hair cells with stereocilia make contact with the tectorial membrane. Hair cells are divided into a row of inner cells and three rows of outer cells. These cells synapse onto afferents of primary sensory neurons. Axons of these neurons format he cochlear portion of the vestibulocochlear nerve.

Question 12

Sound transmission: basilar membrane

Answer 12

Displacement of the basilar membrane, high pitches at the stiff base, low pitches at the floppy apex.

Question 13

Sound transmission organ of corti

Answer 13

Hair cells move whilst the tectorial membrane is immobile, upward deflection causes stereocilia to be bent away and downward causes them to bend in the other direction. Vibration is a back and forth motion.

Question 14

Sound transduction: receptor potentials

Answer 14

Membrane depolarisation increases with increased deflection of the cilia NO ACTION POTENTIALS.

Question 15

Molecular mechanism of sound transduction

Answer 15

Mechanically gated K+ channels depolarise the membrane, triggering the opening of VGSC2+ which then triggers the release of glutamate on to sensory afferents for APs.

Question 16

Inner hair cells

Answer 16

Receive 95% of the innervation from sensory neurons bulk of information.

Question 17

Outer hair cells

Answer 17

Sensory neurons contact many outer hair cells. Recieve efferents from the super olivary complex in the brainstem. Can rapidly change length and amplify movements of the basilar membrane.

Question 18

Otoacoustic emissions

Answer 18

Vibrations generated by outer hair cells that generate sound

Question 19

Conductive hearing loss

Answer 19

External and middle ear, due to canal occlusion, tympanic membrane rupture, arthritic ossification of the bones.

Question 20

Sensorineural hearing loss
Congenital
Acquired

Answer 20

Due to an inner ear defect such as cell death
Defects in essential genes
Acoustic trauma, too toxic drugs, prebycusis

Question 21

The auditory pathway

Answer 21

Cochlea - spiral ganglion of the auditory nerve - cochlear nuclei(superior olive) - inferior colliculus - medial geniculate nucleus - auditory cortex

Question 22

What determines frequency sensitivity of the neuron

Answer 22

Location of the innervated hair cell on the basilar membrane characteristic frequency and tuning curve.

Question 23

Phase locking

Answer 23

Low frequency-tuned neurons carry exact information in their firing pattern. High frequency sounds are too fast, so the information is only via tonotopy. Intermediate neurons don’t fire every cycle but are still phase locked.

Question 24

Location for sound localisation

Answer 24

Occurs in the superior olive (first center in the auditory pathway to recieve input from both ears), then relayed by the dorsal cochlear nucleus to the inferior colliculus.

Question 25

Horizontal localisation of low frequency sounds

Answer 25

Temporal comparison.

Question 26

Vertical localisation of low frequency sounds

Answer 26

Comparison of intensity coming from either ear. Head casts a sound shadow.