AV Flashcards
What are the two functions of CN VIII?
cochlear: sound
vestibular: head position and mvmt
Where are the semicircular canals located?
attached the vestibule
What are the two main divisions of the inner ear?
vestibule (semicircular canals) and cochlea (swirly thing)
What are the two enlargements of the membranous labyrinth in the vestibule?
utricle – semicircular canals attached here
saccule – connects cochlear duct and utricle
Where would you find perilymph?
fills the bony labyrinth
Where would you find endolymph?
fills membranous labyrinth
What keeps perilymph and endolymph from mixing?
tight junctions in hair cells
What are the causes and symptoms of Meneiere’s disease?
causes: not sure why but swelling of membranous labyrinth fucks with the endolymph
symptoms: vertigo, nausea, tinnitus
Describe a hair cell.
polarized cell: has specialized stereocilia on the top, connections to CN VIII on bottom
tallest of the stereocilia (called kinocilium) is embedded in a gelatinous structure, who’s name and components change based on where the hair cell is located
Do cochlear hair cells have kinocilia?
no
Where are hair cells with kinocilia located?
semicircular ducts, utricle, saccule
Hair cells in the organ of corti
part of labyrinth?
gelatinous material?
stimulus transmitted?
part of labyrinth: cochlea
gelatinous material: tectorial membrane
stimulus: sound
Hair cells in the cristae
part of labyrinth?
gelatinous material?
stimulus transmitted?
part of labyrinth: semicircular ducts
gelatinous material: cupula
stimulus: angular acceleration
Hair cells in the maculae
part of labyrinth?
gelatinous material?
stimulus transmitted?
part of labyrinth: utricle, saccule
gelatinous material: otolithic membrane
stimulus: linear acceleration
How do hair cells work?
all use same basic mechanism: deflection of stereocilia initiated by gelatinous material causes action potential
What happens if there is deflection towards the tallest stereocilia?
cell depolarized (action potential)
What happens if there is deflection away from the tallest stereocilia?
cell is hyper polarized (no action potential)
What happens if there is deflection perpendicular to the tallest stereocilia?
nothing
When the stapes strikes the round window, is endolymph or perilymph directly affected?
perilymph, because perilymph is in the bony labyrinth
What is the function and innervation of the stapedius muscle
pulls stapes away from oval window of cochlea (blocks sound of own voice)
CN VII
What is the function and innervation of the tensor tympani muscle
pulls malleus in toward middle ear (adding tension to tympanic membrane (blocks chewing sounds)
CN V
What are the three channels of the cochlea?
scala vestibuli
scala media
scala tympani
Whats inside the scala vestibuli, and what is it continuous with?
filled with perilymph
continuous with vestibule
Whats inside the scala media?
endolymph, spiral organ of corti
Whats inside the scala tympani and what is it continuous with?
filled with perilymph
ends blindly at round window
Where are the primary afferent fibers of cochlear division of CN VIII?
inside the modiolus (spongy bone at center of cochlea)
How does the spiral organ of corti work?
has inner hair cells and outer hair cells
inner hair cells are stimulated by endolymph mvmt
outer hair cells are stimulated by vibrations of the basilar membrane (which is what the SOC lies on)
What is the path of vibrations as the enter the cochlea?
- vibrations begin as stapes hits the oval window
- vibrations travel through perilymph in the scala vestibule
- vibrations pass through the scala media (cochlear duct)/endolymph and stimulate the spiral organ of corti
- vibrations continue through the perilymph of the scala tympani, where they end blindly at the round window
How is the auditory system tonotopically arranged?
different parts of the basilar membrane are stimulated by different tones
the different tones are sent to specific relax nuclei and cortex
Would a cochlear implant help someone who’s CN VIII endings are destroyed?
no, it only helps those who have intact nerve endings but dead hair cells
What is the primary ascending auditory pathway and is it contra, ipsi or bilateral?
lateral lemniscus
bilateral (info from both ears)
mostly info from dorsal cochlear nucleus
What is the auditory relay nuclei of the thalamus?
MGN
If you have a stroke in your brainstem, are you likely to become totally deaf?
no because the auditory pathway is very bilateral
How does auditory info get from the inferior colliculus to the MGN?
inferior brachium
Where is the primary auditory cortex located?
transverse temporal gyrus of Heschl
superior surface of temporal lobe
How does the CNS locate where sound is coming from?
sound from the left would reach left ear first (compare arrival times)
superior olivary nucleus important to sound localization
What does the superior olivary nucleus do and how
compares arrival times
info enters from both cochlear nuclei, crossing milline at trapezoid body
medial sub nuclei of superior olivary nucleus compares times, who the fuck knows what the lateral sub nuclei is doing
What is the role of the vestibular division of CN VIII?
detect linear and angular acceleration of head
regulate posture, coordinate head and eye mvnts
Where are cristae located?
at the end of each semicircular duct, there is an ampules (thickening) and the cristae is located here (cristae is just a ridge with hair cells)
Where is the cupula located?
kind of sits like a really tall hat on top of the cristae (like an upwards extension of cristae), extends across the ampulla
How does the cupula work?
- the semicircular duct rotates in a perpendicular direction the cupula
- if you rate the duct to the right, the endolymph inside the duct will travel the opposite way due to inertia
- if the stereocilia located in the cupula are bent towards the tallest stereocilia, an AP will be recorded
(each channel responds to changes of speed in a given plan)
What is a macula?
a patch of hair cells located in the utricle and saccule
In the utricle, which way do the macula face when the head is upright?
macula is horizontal
stereocilia are facing up
In the saccule, which way do the macula face when the head is upright?
macula is vertical
stereocilia are facing laterally
What type of movement do the hair cells in the utricle detect?
forward and backward
side to side
What type of movement do the hair cells in the saccule detect?
forward and backward
up and down
What is the otolithic membrane?
gelatinous membrane of macula
has crystals to increase its density
Where do the vestibular primary afferent cell bodies project to?
vestibular nuclei of rostral medulla, caudal pons
some to cerebellum via juxtaform body
Where do the vestibular nuclei get inputs from?
each of the semicircular ducts
cerebellum, spinal cord, contralateral vestibular nuclei
Where do the vestibular nuclei of the brainstem project to?
spinal cord
CN III, IV, VI (eye movements)
contralateral vestibular nuclei
thalamus (VPL)
visceral nuclei of brainstem (adjust cardiovascular system for laying down/sitting up, sea sickness)
What does the lateral vestibulospinal tract do?
excitatory projections to ipsilateral antigravity muscles (changes posture in response to tilting)
spin around on a baseball bat? you’ve just over excited your LVST congrats
What does the medial vestibulospinal tract do?
extends to cervical cord via the MLF
stabilizes head mvmts as we walk, coordinates head and eye mvmts
Describe the vestibuloocular reflex (VOR)
afferent limb: VIII (vestibular division)
efferent limb: III, IV, VI (eye mvmt)
has connections with MLF and reticular formation
purpose is to keep retina focused on object while you are moving
How does your VOR work if you spin to the left while looking at something?
- your left semicircular duct gets excited (CN VIII)
- right lateral rectus muscles and left medial rectus muscles contract to keep you looking to to the right
- your left lateral rectus and right medial rectus are inhibited
What is nystagmus?
rapid back and forth eye movements
Why does drinking alcohol give you nystagmus?
alcohol increases and decreases the density of your endolymph, making your semicircular canals sensitive to gravity
What are the three things that give you positional sense?
vestibular
proprioceptive from spinal cord
visual systems
What does romberg’s sign test?
romberg: ask pt to close eyes, see if they sway
tests whether your proprioception from spinal cord is intact
