Auditory and Vestibular Pathways Flashcards
What is the afferent auditory pathway from the hair cells to the primary auditory cortex? How many neurons?
hair cells
thorugh aucitory nerve to cochlear nucleu
throuh trapeoid body to superior olivary complex
thoruhg lateral lemniscus to inferior colliculus
through brachium of IC to medial genicular nucleus
through internal capsule to the primary auditory cortex
6 neurons in total
What are the three efferent outputs in the auditory pathway?
from the superior olivary complex to the:
- hair cells
- tensor tympani
- stapedius
Through what nerve do the efferent fibers travel to reach the hair cells? The tensor tympani? The facial motor nucleus?
auditory nerve to hair cells
trigminal V3 to tensor tympani
Facial nerve to stapedius
What sort of sounds will the acoustic reflex protect the ear from?
it will protect the ear from loud, low frequency tones, but it won’t protect against high pitched, quick tones like gun shots - this is because it’s slow and won’t be able to activate in time to do any good
Because there is extensive bilateral connections int he auditory system, what is the only way to have an ipsilateral hearing loss form a single lesion?
you’d have to have a peripheral defect, like at the cochlea, auditory nerve or cochlear nucleus (the cochlear nucleus projects bilaterally, so anything after that would affect both sides)
Bilateral hearing loss from a single lesion has to be…
central
In the vestibular pathway, the hair cells project to what nuclei thorugh what nerve?
it’s easy…
to the vestibular nuclei via the vestibular nerve
How many vestibular nuclei are there?
4 on each side - superior, lateral, medial, and inferior
What part of the thalamus does the vestibular nulei project to? Through wha tpathway?
to the vetroposterior nucleus by the medial lemniscus
What are the three reflexes the vestibular pathway is involved in?
the vestibulo-occular reflex
the vestibulocerebellar reflex
the vestibulospinal reflex
What does the vestibulospinal reflex do?
It runs in the lateral vestibulospinal tract and the medial vestibulospinal tract
lateral is related to limb and trunk position in comparison to the head
medial is related to upper back and neck position in comparison to the head
What does the vestibulo-ocular reflex (VOR) do?
It’s what keeps your eyes focused on one thing while your head moves
What tract does the vestibulo-ocular reflex run through on its way to the oculomotor, abducens, and trochlear nuclei?
the medial lontiduinal fasciculus
What are 1 ,2 and 4
are they involved in the auditory or vestibular pathways
1 - medial geniculate of the thalamus
- branchium to the inferior colliculus
- inferiro colliculus
auditory
Where will the median and inferior vestibular nuclei be located in relation to other landmarks in the mid medulla?
it will be dorsal to the solitary tract/nucleus
lateral to the 4th ventricle
In the more rostral medulla, what nucleus will you be able to see very lateeral?
the cochlear nucleus
In the caudal pons, the facial nerve divides the facial nuclei and the abducens nuclei from what other nuclei involved in the vestibular system?
the superior vestibular nucleus
In the midbrain, what important auditory pathway structures are located laterally from the periaqueductal gray?
the inferior colliculus and brachium
Why is the auditory pathway especially myelinated?
It is highly concerned with temporal acuity, so it has to be precist
it only takes 10 mS between when a sound occurs and the nerve begins to conduct
The superior olivary nucleus is involved in the localization of sound by comparing the sound received by the two ears
more specifically, the lateral superior olive neurons localize ___ frequency stimuli by comparing interaural ___ differences
while
the medial superior olive neurons localize ___ frequency stimuli by comparing interaural ____ differences
lateral: compares interaural intensity differences to compare localize high frequency stimuli
medial: compares interaural timing differences to localie low frequency stimuli
When is the function of the vestibulospinal reflexes most evident?
decerebrate rigidity
How do the lateral vestibulospinal tract and medial vestibulospinal tract differ in terms of their afferent source?
the lateral gets afferents form the entire membranous labyrinth in the inner ear while the medial gets only from the semicircular canals
this means the lateral gets motion and gravity info while the medial gets only motion
Specifically for function, which vestibulospinal tract is in charge of posteural changes to compensates for tilts and movement of the body and which is responsible for stabilizing head position during walking?
lateral
medial
How do the efferent connections and functions differ between the lateral and medial vestibulospinal tracts?
lateral = ipsilateral connection, excitatory only
medial = bilateral connection, excitatory and inhibitory
The lateral vestibulospina tract causes adjustment of the proximal limbs and trunk musculature by ___ of the extensor msucles and ___ ____ of the flexor muscles.
contraction of extensors
indirect relaxation of the flexors
Conductive hearing loss is an issue with what part of the ear? Sensorineural?
conductive: external and middle
sensorineural: inner - usually the cochlea
In the Weber test, to what ears will the sound lateralize in conductive loss? sensorineural loss?
conductive = will lateralize to the affected side (don’t have air conduction masking anything on that side, so it’s louder)
sensorineural = will lateralize to the unaffected side
Talk about the signal pathway in the VOR if you turn you rhead to the left.
- turn head to the left
- left semicircular canal depolarizes, right hyperpolarizes
- activation of the left medial and superior vestibular nuclei with inhibition on the right
- the left vestibular nuclei project to the left eye medial rectus and the right eye lateral rectus, activating them. the right vestibular nuclei projects to the left eye lateral rectur and right eye medial rectus, inhibiting them
- the eyes turn to the right
In what tract do the neurons from the right and left medial nad superior vestibular nuclei cross to supply the extraoccular muscles?
the mediolateral funusculus
Nystagmus consists of a slow drift in one direction called the ___ followed by a rapid recobery in the opposite direction called the ____
pursuit
saccade
Which does the VOR control - the pursuit or the saccade? How about the cortex?
the VO controls the pursuit while the cortex controls the saccade
Which part, the pursuit or saccade, is the nystagmus named for?
the saccade (even though the issue is typically in the VOR, not the cortex)
so in a right horizontal nystagmus, the VOR pursuit is to the left and the cortex saccade correction is to the right
