Auditory and Vestibular System - Benifla Flashcards
What are the two components of the bony labyrinth?
Cochlea (changes mechanical waves to electrical)
Semicircular canals
Filled with perilymph
What are the components of the membranous labyrinth?
Utricle
Saccule
Filed with endolymph (suspended within perilymph)
How is sound transmitted across the cochlear duct?
Hair cells are attached to the basal membrane in the cochlear duct.
At the end of the hair cells there are cilia which are attached to the tectorial membrane.
Movement of the tectorial membrane moves hair cells which stretch and release and cause K+ to leak from the endolymph.
Increased K+ causes changes of electricity of hair cells which causes release of Ca2+ vesicles within the hair cells.
The hair cells release neurotransmitters in response to calcium which stimulate bipolar cells.
Bipolar cells go from the hair cells to become the cochlear nerve
Changes in the bipolar nerve cell voltage in the spiral ganglion and then many spiral ganglia join the vestibular part of the vestibulocochlear nerves.
The cochlear nerve goes to the cochlear nuclei to the lower part of the pons.
How is a delay in sound caused by fibers through the trapezoid body?
Fibers reaching cochlear nuclei reach anterior cochlear nucleus and pass fibers to the superior olive (ipsilateral and contralateral).
Contralateral fibers to the olive go through the trapezoid body.
From the olives it goes to the lateral lemnisci, to the inferior colliculi, through the inferior brachia to the MGBs to the auditory cortex (superior temporal gyri/gyri of Heschel).
What does the Rinne test distinguish between ? What is the difference?
What does the test entail?
Nerve deafness vs. Conduction deafness
Tuning fork on bone behind the ear indicates conduction through bone. Then, after sound can no longer be heard on bone, transferred to in front of ear to detect conduction through air. Normally should be able to hear through air better.
Nerve deafness
Can’t hear well normally, but normal Rinne test (can hear better through air).
Conduction deafness:
Can hear through bone but not through air.
What is the Weber test and what is it used to distinguish?
Tuning fork on forehead.
In normal patient sound is equal in both ears.
Tests which side patient has deafness AND neural versus conduction deafness.
In conduction deafness: Conduction of deaf side better than hearing side (because no interference through ear)
In neural deafness: Conduction of hearing side better than deaf side.
Need to combine with Rinne test to determine whether worse in one side or better in the other.
What is a vestibular schwanoma?
Tumor in Schwann cells in the vestibulocochlear nerve at the cerebellar-pontine angle.
As the tumor grows there is deafness from pressure, peripheral facial nerve paralysis, loss of balance (first sign), ipsilateral discoordination (from pressure on cerebellum).
Not rare.
Can cause death if moves to block the AICA.
What is the BAER (brainstem auditory evoked response) exam?
Put electrodes on skull and play sound and check at each station.
Test frequency to detect sound response based on time delay.
Measure wave at each station. If a station disappears we know the auditory component before it is defective.
Flatline at points after the injury.
In reality irrelevant, just do an MRI and audiogram.
What are the components of the otolithic organ and what do they do?
Linear acceleration (movement of the head)
Utricle (forward/backward, horizontal acceleration, eye movement) and Saccule (side/side, posture muscles, vertical acceleration)
Within the vestibule of bony labyrinth
Where are the vestibular nuclei?
What is their input?
Where do they project to?
In the floor of the 4th ventricle from the hypoglossal nucleus and the abduscent nucleus (medulla and pons).
Four nuclei.
• From semicircular ducts to the sup. And
medial Nuc.
• From utricle to lateral nuc.
• From saccule to inf. Nuc.
• Receive input from- floculonodular lobe
and uvula’ vermis’ contra lateral vestibular
nuclei
• Project fibers to- flocculonodular lobe and
uvula, contralateral vestibular nuc., inferior
olivary nuc., III,IV,VI cranial nerves,MLF,
ventral horn of gray matter in spinal cord,
thalamus
What is the vestibuloocular reflex and when is it used?
Examined in patients suspected to be braindead.
Head should move before eyes then follow slightly delayed in a normal patient.
In a braindead patient eyes can be locked and not follow the head and stay stable OR they follow head without lagging.
