Neuropathology of the inner ear Flashcards
What are the three small bones found in the middle ear?
- malleus
- incus
- stapes
What is the dorsal chamber called?
scala vestibuli
What is the ventral chamber called?
scala tympani
How does albinotic deafness occur
The stria vascularis produces endolymph and melanocytes
= less stria vascularis = deafness
What is the 8th cranial nerve?
Vestibulocochlear nerve
What is the descending pathway auditory reflex?
- 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
What is the most common way of investigating deafness?
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
What is Conductive deafness?
- Obstruction passage sound/ obstruction of mechanical energy
e.g due to wax in the ears
What is sensorineural deafness?
- 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
What is a myringotomy?
A surgical procedure used to relieve pressure or drain fluid
creates a hole in the ear drum
What is a Eustachion tube
Balances the pressure either side of the by draining the middle ear
What causes primary secretory otitis media and what is it?
- BAER slope shifted to the right
- characterised by thick fluid in the middle ear space behind the ear drum
shift = conductive hearing loss
What is congenital inherited sensorineural deafness?
Eventual collapse of the entire cochlear duct
What is abiotropic inherited sensorineural deafness?
- 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
What can cause acquired sensorineural deafness?
- Temporal bone neoplasia
- Ototoxicity (aminoglycosides, ear-cleaning agents, chemotherapy agents)
- Presbycusis ( age-related deafness)
What are the three main functions of the vestibular system?
- Maintain eye position despite head position
- Maintain head position relative to the horizon
- maintain body posture relative to the horizon
What can lesions of the vestibular system result in?
- Falling
- Rolling
- Head tilting
- Nystagmus
- Ataxia
- Vomiting
What is the function of the middle ear?
To protect the inner ear sensory cells from loud noise
What muscles contract in reflex to loud noise to limit the movement of the ossicles?
- Stapedius
- Tensor tympani
What is BAER and how does it work?
Brainstem Auditory Evoked response
* clicks between electrodes, electrodes pick up the brains response to these clicks
What is the auditory reflex?
Turning head in response to sound (brainstem reflex)
What is the function of the middle ear?
Protects the inner ear sensory cells from loud noise
* Stapedius and tensor tymapani muscles contract in reflex to loud noise limiting movement of ossicles
When can the dog tympanic membrane and ossicles detect sound?
30-35,000Hz
When are the horse tympanic membrane and ossicles most efficient?
1000-4000Hz
What is the function of the spiral ganglion?
- Carries frequency, timing and sensory information about the sound stimulus from the hairs to the CN
What happens to sterocillia once they are damaged?
They do not regenerate
What is the order of the brain parts on the BAER graph?
- Cochlear nerve inner ear
- Intracranial cochlear nerve
- Dorsal nucleus of the trapezoid body
- lateral lemniscus pons
- caudal colliculus
- medial geniculate nucleus
What are the neurologic components of peripheral vestibular disease?
- Peripheral receptor of CN VIIII
- Axons in the peripheral nerve of CN VIIII
What are the anatomic components of peripheral vestibular disease?
- Middle ear
- Inner ear
What does central vestibular disease result from?
- Vestibular nucleus
- Cerebellum
- Connecting pathways between the cerebellum and the brainstem
What are the clinical signs of central vestibular disease?
- Proprioceptive defiicts
- Paresis
- Altered mental status
What are the clinical signs of peripheral vestibular disease?
- Vestibular signs
- Normal proprioception
- Normal strength
- Normal mental status
- Cranial nerve deficits
What does paradoxical vestibular disease lead to?
lesions result in a loss of inhibitory influence of teh cerebellum
What are the clinical signs of bilateral vestibular disease?
- More likely to be metabolic over inflammatory
- Wide, searching head movements,
- Low body carriage/ posture
- Positional nystagmus
