FE: Lecture 3: Cranial Nerve 8

Question 1

Where do the vestibular and cochlear nerve originate?

Answer 1

the inner ear

auditory- cochlea
vestibule and semicircular ducts- vestibular

Question 2

What does the cochlea detect?

Answer 2

sound or vibrations in the ear

20-20,000 Hz- human

Question 3

What does the canals and semicircular ducts detect?

Answer 3

vibrations of the head, 0-10 Hz

static tilt

dynamic movements like linear and angular acceleration

Question 4

What are the three main features of the external ear?

Answer 4

Pinna- concentrates sound and direction filter

External auditory meatus

tympanic membrane- first to vibrate (external ear ends here)

Question 5

What is the name of the air filled chamber in the middle ear?

Answer 5

eustachian tube- fills with fluid when you have a cold due to pressure

Question 6

What bones and muscles comprise middle ear?

Answer 6

malleus, incus and stapes- bones

muscles- tensor tympani cn 5, stapedius cn 7 these both decrease vibration

damage to either nerve cause hyperacusis

Question 7

What are the two windows of the inner ear?

Answer 7

oval window- pushes air in (hydraulic like)

round window- allows relief out

they both transmit sound mechanically

Question 8

What is the bony labyrinth in the inner ear?

Answer 8

spaces in the bone that contain vestibule, semicircular canals and cochlear

filled with perilymph

Question 9

What is the membranous labyrinth in the inner ear?

Answer 9

sacs inside the spaces- utricle, saccule, semicircular ducts, cochlear ducts

these contain endolymph and contain receptor cells

Question 10

What is the cochlea?

Answer 10

spiral chamber in the petrous temporal bone

Question 11

How does sound pressure wave move in cochlea?

Answer 11

sounds enters oval window and down the scala vestibuli

sound exits via round window though scala tympani

Question 12

What is in the cochlear duct?

Answer 12

endolymph and organ of corti sensory receptor

Question 13

Describe the organization of the Organ of Corti?

Answer 13

hair cells are in basilar membrane which also contact tectorial membrane which amplifies movement of endolymph

Question 14

Describe of hair cells are depolarized in organ of corti?

Answer 14

any type of vibration depolarizes these hair cells and action potentials can be created and sent to spiral ganglia via primary afferent fibers

Question 15

Hair cells or stereocilia are what type of gated channels?

Answer 15

mechanical that make synaptic contact with primary afferent fibers

AP encode amplitude of sound as frequency of firing

Question 16

What is the pathway of an AP from the stereocilia?

Answer 16

1. hair cell receptors to spiral ganglia to cochlear nuclei (dorsal and ventral rostral medulla)

Question 17

How are low and high frequencies discriminated?

Answer 17

due to tonotopic receptive fields- place theory

based on where it is detected in organ of corti

high freq- base of organ

low- apex of organ

Question 18

What is the definition of deafness?

Answer 18

loss or reduction of hearing

due to loss of amplitude, can be specific to frequency

high frequency loss is common from rock music (loss of hairs)

Question 19

What different pathologies can cause deafness?

Answer 19

CVA (labyrinth artery), trauma, infections, toxins (penecillin)

Question 20

What is conduction deafness?

Answer 20

unable to transmit sound energy due to external ear or middle ear damage therefore no AP is ever created

Question 21

What is sensorineural deafness?

Answer 21

1. damage to cochlea/organ of corti- total, high end or notch hearing loss
2. acoustic neuropathy- damage to auditory part of CN 8

Question 22

What is central deafness?

Answer 22

damage to cochlear nuclei

Question 23

What is the pathway of auditory info from cochlear nuclei to cerebral cortex?

Answer 23

1. cochlear nuclei of medulla to inferior colliculus (some fibers )via lateral lemniscus, others may go to superior olive or nucleus of LL first then IC
2. inferior colliculus to medial geniculate nucleus of thalamus
3. MGN to primary auditory cortex areas 41/42 in the superior temporal gyrus

Question 24

Where does info from the left cochlea go?

Answer 24

both sides of cortex

Question 25

Where are the only two places in the pathway that if damaged will produce ipsilateral deafness?

Answer 25

labyrinth/ cochlear nerve or cochlear nuclei

Question 26

What type of auditory problems will you have with ipsilateral deafness?

Answer 26

sound localization, problems detecting complex sounds like speech

Question 27

Where are the auditory cortical areas?

Answer 27

1. primary auditory - 41, tone, intensity and localization
2. Auditory association cortex- 42, 22, memory of music speech and noise
3. speech sensory association cortex- 22, 39, 40 wernike’s area, comprehension of language

Question 28

What is the one major difference between auditory and vestibular hair cells?

Answer 28

vestibular hair cells have a kinocilia

if flow is toward kinocilia then the cell is depolarized and an AP is created (increased number of AP)

if flow is away then cell is hyperpolarized (decreased number of AP)