Lecture 4: The Auditory Pathway (unfinished) Flashcards Preview

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Flashcards in Lecture 4: The Auditory Pathway (unfinished) Deck (30):
1

Why is the middle ear a 'high risk space'?

- Connected to nasopharynx - prone to infection
- Connected to mastoid air cells - infection may spread to middle cranial fossa
- Internal jugular vein lies inferior - thrombosis risk
- Internal carotid artery lies anterior - link to pulsatile tinnitus
- Traversed by chorda tympani and facial canal - infection risk

2

What is the inner ear filled with?

Perilymph - like extracellular fluid i.e. high in Na, low in K

3

Name the cavities in the petrous part of the temporal bone?

Vestibule
Semicircular canal
Cochlea

4

What is the cochlear duct?

Closed tube within the cochlea.

5

What is the cochlear duct filled with?

Endolymph

6

Where is the inner ear located?

Within the petrous part of the temporal bone.

7

What is the function of the external ear?

To transmit sound waves.

8

What is the function of the middle ear?

To convert sound waves to mechanical energy.

9

What is the function of the inner ear?

To convert mechanical energy into electrical energy (i.e. action potential).

10

What two chambers are formed within the cochlea by the cochlear duct.

- Scala vestibuli
- Scala tympani

11

Where are the scala tympani and scala vestibuli continuous?

The helicotrema

12

How does the cochlea work?

Hydraulic pressure created in the perilymph, by the vibrations of the stapes pass to the apex via the SV. Pass through the helicotrema and descend via the ST to the round window. As the fluid moves around the cochlea it deforms the fluid, endolymph, in the cochlear duct.

13

What forms the roof and floor of the cochlear duct?

Roof - Vestibular membrane

14

What is the name of the auditory receptor?

The Spiral organ of Corti

15

What is contained within the spiral organ of Corti?

Hair cells

16

What are hair cells embedded in?

Tectorial membrane

17

How is the spiral organ stimulated?

The spiral organ is stimulated by the deformation of the cochlear duct by the perilymph in the surrounding SV and ST

18

What are the features of primary auditory fibres?

- Axons of bipolar neuron in
spiral ganglion
- Forms the cochlear nerve which
becomes part of vestibulocochlear nerve (CNVIII)

19

Where does the vestibulocochlear nerve (CNVIII) enter the brainstem?

Cerebellopontine angle

20

Where do the primary auditory fibres synapse with secondary neurones?

In dorsal and ventral cochlear nuclei

21

What are the auditory centers in the brainstem?

- Medial geniculate nucleus of thalamus
- Inferior colliculus
- Superior olivary nucleus
- Cochlear nuclei

22

Which two inputs does the auditory pathway have to compare?

- Timing
- Loudness

23

What name is given to the primary auditory cortex?

Heschl's gyrus

24

What are the secondary auditory areas?

Broca's area - anterior (parietal), involved in motor/production of words

Wernicke's - posterior (temporal), sensory/understanding

25

Which division of the MCA supplies Broca's area?

Upper division

26

Which division of the MCA supplies Wernickes's area?

Lower division

27

What are the functions of the descending auditory pathways?

- Reflex head and eye movements (CN III(3), IV(4) and VI(6)) ie in reaction to sound.

- To stapedius via CN VII(7) and tensor tympani via CN V3. Prevents damage during loud noise.

28

What effect does a unilateral lesion have on hearing?

Little. The ability to localise sounds may be impaired.

29

What is conductive deafness?

Defect of sound transmission up to spiral ganglion

30

What is sensorineural deafness

Defect in function of spiral ganglion or cochlear nerve