Auditory / Vestibular System Flashcards
What is conductive deafness?
Deafness from obstruction or altered transformation of sound to the tympanic membrane or through the middle ear
What causes conductive deafness?
Occlusion of meatus, otitis media, otitis externa, otosclerosis, fracture of temporal bone (damage to ossicles or bleeding into middle ear)
What is sensorineural (nerve) deafness?
Deafness ( / tinnitus) from damage to nervous tissue
What are causes of sensorineural deafness?
Lesion of the cochlea, lesion of cochlear portion of CN VIII, prolonged loud noise exposure, treatment with certain antibiotics, infections, tumors
What is labrynthitis (or otitis interna)?
Deafness from infection or inflammation (sensorineural)
Central lesions rarely cause ________
complete deafness in one ear
What is otosclerosis?
Conductive hearing loss that occurs in 50% of cases where tissue overgrowth fixates the stapes in the oval window
Do hair cells regenerate?
HELL. NO.
How is the Rinne Test done?
1) Place vibrating tuning fork on mastoid process (tests BONE CONDUCTION) and hold until sound is not perceived any longer
2) Tuning fork is placed just outside the pinna for AIR CONDUCTION and hold until sound is no longer perceived
How do you interpret results of the Rinne Test?
- If sound heard via bone and NOT air: NEGATIVE Rinne Test (conductive deafness)
- If sound heard via air and NOT bone: POSITIVE Rinne Test (sensorineural deafness)
How is Weber’s Test done?
A vibrating tuning fork is placed in the midline of the skull (conduction should be done by both air and bone)
How is Weber’s Test interpreted?
- Normal: sound perceived equally in both ears
- Conductive loss: GREATER net vibration on AFFECTED side (louder in affected ear)
- Sensorineural loss: sound LOUDER in NORMAL ear
What is the stria vascularis?
Vascular supply within the spiral ligament (site of endolymph production)
What happens with damage to the stria vascularis?
Loss of endolymphatic potential –> failed mechanoelectrical transduction
How do cochlear implants work?
Electrodes tuned to broad frequency bands connected to an electrical receiver; input of electrodes must be at the correct tonotopic point along the spiral organ (for sensorineural hearing loss)
What is monaural deafness?
Deafness on one side (unilateral lesion of cochlear nerve or nucleus)
What does a lesion at or above the superior olive cause?
Not deafness! (due to binaural pathway, the trapezoid body)
Inattention to stimuli on CONTRALATERAL side or inability to follow convos in a crowded room (cocktail effect)
When higher centers impacted, the result is typically info disruption from BOTH ears.
What can occlusion of AICA cause? (labyrinthine a.)
- Monaural hearing loss
- Ipsilateral facial paralysis
- Inability to look TOWARD side of lesion (pontine gaze center)
- Also: vertigo, oscillopsia, nystagmus, ataxia
How is a lesion experimentally located in the auditory system?
Auditory Evoked Responses. Activity within structures correspond to specific waves on auditory brainstem response recording - shifts in latency indicate lesion/swelling
What is central deafness?
Results from damage to cochlear nuclei or central pathways relaying auditory information to auditory cortex
What do central lesions cause?
Deafness (infrequently though). More often altered perceptions of sound (brainstem/diencephalon/cortex).
What is pontine auditory hallucinosis?
Orchestra sound out of tune, buzzing insects, strands of music heard. Accompanied by other pontine lesions (CN deficits or long tract signs).
What is Wernicke Aphasia?
Damage to Area 22 on superior temporal gyrus (occlusion of branches of MCA) –> impaired comprehension of speech and difficulty in producing coherent speech
What is Broca Aphasia?
Damage to Area 44, 45 of pars opercularis and triangularis of inferior frontal gyrus (occlusion of branches of MCA) –> nonfluent, difficult speech (comprehension intact)
Broca’s area is connected to the primary visual cortex via _______
the arcuate fasciculus
What is the purpose of the middle ear reflex?
Activate the stapedius (VII) and tensor tympani (V) to affect conduction in middle ear by impeding ossicles and tympanic membrane, respectively. Protection against loud sounds with long duration and dampening background sounds (speaker’s voice).
How does the middle ear reflex work?
- Bipolar afferents first synapse in anterior cochlear nucleus
- Second neurons in chain synapse in superior olives (bilateral)
- Interneurons synapse in facial motor nucleus (stapedius) and trigeminal nucleus (tensor tympani)
- Efferents to mm.
A BILATERAL reflex
What is the acoustic startle reflex?
It is sensory-motor integration to turn head TOWARDS sound.
What does the acoustic startle reflex work? (generally)
Two ways.
1) Reticulospinal neurons sample the lateral lemniscus and lead to a very rapid response
2) Superior colliculus integrates info from the inferior colliculus and auditory cortex and projects via tectobulbospinal fibers.
Acute vestibular disorders can disrupt vestibular autonomic response, leading to…
Orthostatic hypertension, postural tachycardia, frequent falls, motion sickness, and emesis (vomiting)
This is from damage to the medial and inferior vestibular nuclei connecting to the solitary tract and ventrolateral medullary reticular area.
What is BPPV? (Benign Paroxysmal Positional Vertigo - and no, that’s not the answer)
Tilting of the head in a certain way lead to vertigo, commonly a result of cupulolithiasis or canalithiasis.
Speaking of which…what is cupulolithiasis?
Otolith breaks off of utricle and lodges in cupula. This is longer-lasting and resistant to maneuvers (fixing is 50% success rate).