Neuropathology of the inner ear

Question 1

What are the three small bones found in the middle ear?

Answer 1

• malleus
• incus
• stapes

Question 2

What is the dorsal chamber called?

Answer 2

scala vestibuli

Question 3

What is the ventral chamber called?

Answer 3

scala tympani

Question 4

How does albinotic deafness occur

Answer 4

The stria vascularis produces endolymph and melanocytes
= less stria vascularis = deafness

Question 5

What is the 8th cranial nerve?

Answer 5

Vestibulocochlear nerve

Question 6

What is the descending pathway auditory reflex?

Answer 6

• Turning of the head in response to sound
• The medial tectospinal tract descends to the LMN in the brain stem and spinal cord to turn the head eyes and body

Question 7

What is the most common way of investigating deafness?

Answer 7

Headphones with click generator in the ear
* headphones detect the potential difference across nerve cells in the brain when they polarise
* place an active electrode midway between the external occipital protuberance and medial canthus eye
* reference = electrode dorsal spine T1
* should ground the election dorsal midline (midcervical)

called BAER

Question 8

What is Conductive deafness?

Answer 8

• Obstruction passage sound/ obstruction of mechanical energy

e.g due to wax in the ears

Question 9

What is sensorineural deafness?

Answer 9

• abnormality in receptor organ or neurons of the cochlear division
• Can be congenital- albinotic, abiotrophic
• Can be acquired- inflammation/ infection or exposure to loud sounds

Question 10

What is a myringotomy?

Answer 10

A surgical procedure used to relieve pressure or drain fluid

creates a hole in the ear drum

Question 11

What is a Eustachion tube

Answer 11

Balances the pressure either side of the by draining the middle ear

Question 12

What causes primary secretory otitis media and what is it?

Answer 12

• BAER slope shifted to the right
• characterised by thick fluid in the middle ear space behind the ear drum

shift = conductive hearing loss

Question 13

What is congenital inherited sensorineural deafness?

Answer 13

Eventual collapse of the entire cochlear duct

Question 14

What is abiotropic inherited sensorineural deafness?

Answer 14

• Born with the ability to hear then they slowly lose it over time
• Directly affects hair cells
• ocassionally affects the vestibular apparatus
• deafness at a few weeks old

In CKCS it occurs at 3-4 years

Question 15

What can cause acquired sensorineural deafness?

Answer 15

• Temporal bone neoplasia
• Ototoxicity (aminoglycosides, ear-cleaning agents, chemotherapy agents)
• Presbycusis ( age-related deafness)

Question 16

What are the three main functions of the vestibular system?

Answer 16

• Maintain eye position despite head position
• Maintain head position relative to the horizon
• maintain body posture relative to the horizon

Question 17

What can lesions of the vestibular system result in?

Answer 17

• Falling
• Rolling
• Head tilting
• Nystagmus
• Ataxia
• Vomiting

Question 18

What is the function of the middle ear?

Answer 18

To protect the inner ear sensory cells from loud noise

Question 19

What muscles contract in reflex to loud noise to limit the movement of the ossicles?

Answer 19

• Stapedius
• Tensor tympani

Question 20

What is BAER and how does it work?

Answer 20

Brainstem Auditory Evoked response
* clicks between electrodes, electrodes pick up the brains response to these clicks

Question 21

What is the auditory reflex?

Answer 21

Turning head in response to sound (brainstem reflex)

Question 22

What is the function of the middle ear?

Answer 22

Protects the inner ear sensory cells from loud noise
* Stapedius and tensor tymapani muscles contract in reflex to loud noise limiting movement of ossicles

Question 23

When can the dog tympanic membrane and ossicles detect sound?

Answer 23

30-35,000Hz

Question 24

When are the horse tympanic membrane and ossicles most efficient?

Answer 24

1000-4000Hz

Question 25

What is the function of the spiral ganglion?

Answer 25

• Carries frequency, timing and sensory information about the sound stimulus from the hairs to the CN

Question 26

What happens to sterocillia once they are damaged?

Answer 26

They do not regenerate

Question 27

What is the order of the brain parts on the BAER graph?

Answer 27

1. Cochlear nerve inner ear
2. Intracranial cochlear nerve
3. Dorsal nucleus of the trapezoid body
4. lateral lemniscus pons
5. caudal colliculus
6. medial geniculate nucleus

Question 28

What are the neurologic components of peripheral vestibular disease?

Answer 28

• Peripheral receptor of CN VIIII
• Axons in the peripheral nerve of CN VIIII

Question 30

What are the anatomic components of peripheral vestibular disease?

Answer 30

• Middle ear
• Inner ear

Question 31

What does central vestibular disease result from?

Answer 31

• Vestibular nucleus
• Cerebellum
• Connecting pathways between the cerebellum and the brainstem

Question 32

What are the clinical signs of central vestibular disease?

Answer 32

• Proprioceptive defiicts
• Paresis
• Altered mental status

Question 33

What are the clinical signs of peripheral vestibular disease?

Answer 33

• Vestibular signs
• Normal proprioception
• Normal strength
• Normal mental status
• Cranial nerve deficits

Question 34

What does paradoxical vestibular disease lead to?

Answer 34

lesions result in a loss of inhibitory influence of teh cerebellum

Question 35

What are the clinical signs of bilateral vestibular disease?

Answer 35

• More likely to be metabolic over inflammatory
• Wide, searching head movements,
• Low body carriage/ posture
• Positional nystagmus