Vestibular System - CN VIII Flashcards
The vestibular system consists of what 4 sections?
1) the membranous labyrinth and sensory receptor (endorgan)
2) cranial nerve VIII and its cell bodies (Scarpa’s ganglia)
3) vestibular nuclei which lie on the floor of the fourth ventricle at the junction of the medulla and pons, and
4) ascending and descending tracts.
What is the endorgan housed in?
the bony labyrinth (a series of cavities in the temporal bone)
What is the first role of the vestibular system? (3-fold)
1.As a sensory system, vestibular signals from the labyrinths, generated by head movement, regulate eye position in the orbit during head movements in order to assure a stable image on the retina (vestibulo-ocular reflex).
What is the second role of the vesitbular system? (3-fold)
Secondly, the vestibular system influences muscle tone in appendicular and axial muscles for control of postural support and balance (vestibulo-spinal and vestibulocollic reflexes).
What is the third role of the vestibular system? (3-fold)
The third role of the vestibular system is to provide conscious awareness of spatial orientation.
The peripheral endorgan in each bony labyrinth consists of a _______________________.
Membranous labyrinth
What is a membranous labyrinth?
a series of tubes made of fine membranes that contain the peripheral sensory receptors (hair cells) of the vestibular system.
The membranous labyrinth contains a fluid called:
endolymph
The membranous labyrinth is separated from the bone cavity within the ____________________________________________________by a fluid called __________________.
petrous part of the temporal bone (Bony labyrinth)
perilymph
The receptors of the vestibular apparatus are located in very specific sites within the ____________________.
membranous labyrinth
There are ______ receptor sites on each side, one in each of the three semicircular canals and two in the ____________ (otolith organs)
five
semicircular canals
vestibule
What are 2 otolith organs?
saccule and utricle
Semicircular canals =
three canals arranged at right angles to each other.
The horizontal canal is in a horizontal position when the head is:
flexed forward to 30 degrees.
The horizontal canal is activated with ________________ around the body axis.
rotation
The anterior and posterior canals are activated with rotation in an ______________________________ between the frontal and sagittal planes and work together on _____________ sides of body.
oblique orientation
opposite
Together, the semicircular canals perform the dynamic function of:
detecting angular velocity of the head in all planes
**especially important for stabilizing the eyes during head movement.
Function of semicircular canals: Canals are filled with?
enolylmph
Function of semicircular canals: Ampullae are located at the base of canals contain hair cells called?
crista
Function of semicircular canals: The hair cells are innervated by the peripheral ends of the:
vestibular nerve fibers
Function of semicircular canals: Hair cells protrude ______________ into gelatinous material called ______________.
upwards
cupula
Function of semicircular canals: Angular movement (rotation) causes the endolymph to lag behind (inertia) in the ______________ direction, causing displacement of the cupula, thereby ________________.
opposite
thereby moving the hair cells
Function of semicircular canals: Mechanical deflection of the hair cells produces a receptor potential that may either ________________________ or ______________________ the vestibular nerve that is ______________ active, with a resting discharge rate of ______________________________.
depolarize or hyperpolarize
tonically
100 to 300 spikes per second
Function of semicircular canals: The effect on the resting discharge rate depends on the _____________________________.
direction the hair cells bend
Function of semicircular canals: Each hair cell is made up of two types of projections ____________ (one) and __________(40-70).
kinocilium
stereocilium
Function of semicircular canals: Depolarization occurs when the stereocilium bend towards the ____________.
kinocilium
Function of semicircular canals: Hyperpolarization occurs when the stereocilium bend ______________ from the kinocilium.
away
Function of semicircular canals: Either an increase or a decrease in the firing of the already tonically active nerve therefore signals the direction of rotation. For example, with rotation around the body axis to the left, the hair cells in the left horizontal canal become ________________________________________________________.
more depolarized resulting in an increase in frequency of action potentials along the left vestibular nerve.
Function of semicircular canals: This left turning will also result in the hair cells in the right horizontal canal to become more ________________________________________________________________________
hyperpolarized resulting in a decrease in the frequency of action potentials along the right vestibular nerve.
Function of semicircular canals: The signal from the hair cells is temporary because of a __________________ action of the cupula, which restores it to its resting position. Therefore, the semicircular canals are ______________ receptors, with a response lasting 20 sec. or less.
spring-like
rapidly adapting
Function of semicircular canals: The semicircular canals are ___________ threshold (___________sensitive receptors), responding to very ______________ angular changes
low (HIGHLY sensitive receptors)
small
Function of semicircular canals: The response from the receptor is _____________.
graded
Graded =
as velocity increases, more hair cells are activated each to a greater degree.
Otolithic organs =
The utricle and the saccule make up the otolithic organ.
The function of the otoliths is to detect linear _______________________________________ of the head as well as encoding the ______________________ of the head with respect to gravity.
acceleration and deceleration
static position
The important role of the utricle and saccule then is to maintain the head ______________ in space and to modulate postural ________________ relative to the position of the ______________.
upright
muscle tone
head
Structurally, the utricle and saccule are two large chambers located between the _____________________ and _____________________.
semicircular canals and the cochlear duct.
Both ends of the semicircular canals are continuous with the ___________.
utricle
The utricle and saccule are also filled with _______________.
endolymph
Overproduction of endolymph results in:
- auditory disturbances
- severe vertigo
- nausea and
- nystagmus
nystagmus is also know as:
a condition known as Meniere’s disease
What is the sensory organ on the wall of the utricle and saccule is called?
macula
The macula is covered with a _______________ layer with embedded small crystals of calcium carbonate called _______________.
gelatinous
otoconia
Hair cells project into the _____________________.
gelatinous layer
As with the hair cells in the ampulla of the semicircular canals, these hair cells synapse at their __________ with the _______________________________.
base
sensory axons of the vestibular nerve
The macula of the utricle is positioned in the __________________ plane when the head is upright, while the macula of the saccule is ________________.
horizontal
vertical
The hair cells in both organs (utricle and saccule) are arranged such that head tilt will result in _______________ discharge from specific parts of the _____________ and ______________ discharge from other parts of the ____________________________.
increased
macula
decreased
same macula
This complex arrangement allows for the utricle and saccule to be sensitive to _______________________. Therefore, these receptors are _____________________ and continue to respond at all times.
static head tilt in multiple planes
nonadapting
The anatomical relationship between the utricle, the macula, and the semicircular canals is clinically significant in a condition called:
benign paroxysmal positional vertigo (BPPV).
In BPPV, otoconia from the macular organs ______________________ into the semicircular canals, most commonly the ____________ canal.
break loose and float
posterior
With specific head motions, this “debris” stimulates (______________________________) the hair cells in the _____________ and produces symptoms of ______________.
(increases the inertia of the cupula)
ampulla
vertigo [characteristic nystagmus (see below), and may also be accompanied by nausea]
The vestibular portion of the 8th cranial nerve is a ___________ nerve with the cell bodies forming ________________ near the ____________ auditory meatus.
bipolar
Scarpa’s ganglion
internal
After leaving the ganglion, the central processes of the vestibular nerve fibers join with ______________ fibers and travel in the internal auditory canal, along with the ____________ nerve, passing through ________________ bone into the posterior fossa, entering the brainstem at the ____________________ junction.
cochlear
facial
temporal
pontomedullary
Primary vestibular afferents synapse on _________________________ in the vestibular nuclei of the brainstem and in the ____________________.
second order neurons
cerebellum
The vestibular nuclei form a ________________ shaped complex located in each side of the brainstem in the _________________________.
diamond
floor of fourth ventricle
The vestibular nuclei are surrounded by the ___________________ laterally, the ____________________ medially, the _______________________ rostrally, and the _________________________________ ventrally.
inferior cerebellar peduncle
pontine reticular formation
middle cerebellar peduncle
nucleus and spinal tract of the trigeminal nerve
The four main vestibular nuclei are the: .
SUPERIOR, LATERAL, MEDIAL, and DESCENDING (inferior or spinal) nuclei.
Nucleus Y is important from an _________________ point of view. There are actually a number of others we won’t deal with. There is ____________________ of sensory input from multiple vestibular receptors (e.g. canals and otolith) onto __________________ order neurons in some areas of the nuclei, while in other locations there is clear _________________ organization of input from specific endorgans to specific nuclear areas.
integrative
convergence
second
topographic
For example, the projections to the superior nucleus are primarily from the _______________________ and terminate in the _______________ in a topography specific to the canals.
semicircular canals
nucleus
Surrounding brainstem areas support the vestibular nuclei in the task of controlling:
eye movements in the horizontal and vertical planes
For the most part, each nucleus receives input from both the __________________________________.
The exception is the lateral nucleus that receives the majority of its vestibular input from the _____________.
semicircular canals and the otoliths.
utricle
Fibers from the cerebellar ________________ lobe and ________________ nucleus (discussed with Cerebellum) terminate in _________________________.
floculonodular lobe and
fastigial nucleus
all four vestibular nuclei
Afferents to the vestibular nuclei from the eyes as well as from the neck and limbs are relayed through the _________________ and help modulate _______________________________________ reflexes.
cerebellum
vestibulo-OCULAR, vestibuloCOLLIC and vestibuloSPINAL
For example, the cerebellum exerts influence on limb extensor tone ________________ through tonic inhibition of the _________________
indirectly
lateral vestibular nucleus.
The vestibular nuclei are extensively connected to each other and to adjacent and distant structures along the ______________.
neuraxis
Ascending projections to the motor nuclei of the extraocular eye muscles in the ___________ and ___________ travel ______________________________ that runs in the floor of the fourth ventricle.
pons and midbrain
via the medial longitudinal fasciculus (MLF
Projections also descend in the MLF, as well as in the lateral vestibulospinal tract _________________, and in the medial vestibulospinal tract to _______________________ of the spinal cord.
IPSILATERALLY
BOTH SIDES
The fastigial nuclei and flocculonodular lobe of the cerebellum _________________ extensive input from the vestibular nuclei. The entire _________________, receives input from the vestibular nuclei where it is integrated with somatosensory mapping from the _______________________.
receive
vermis
limbs and trunk
What is the vermis?
a principal region of the spinocerebellum
Ascending vestibulo-thalamo-cortical projections serves the third function of the vestibular system involving ___________________________.
perception of self in space
Traveling in the reticular formation adjacent to the MLF and the __________________ (auditory pathway), _____________ fibers from the lateral and superior vestibular nuclei terminate in the thalamus.
lateral lemniscus
secondary
Thalamocortical projections to regions of the parietal lobe (association areas) produce a __________________________________________. This does not project to _________________________cortex therefore there is no perception of specific location in space (proprioception).
subjective sensation of rotation and body displacement.
primary somatosensory
The peripheral vestibular endorgan is supplied by the ________________ artery, which most often is a branch of the ___________________________________, but occasionally branches directly off of the basilar artery.
labyrinthine
anterior inferior cerebellar artery (AICA)
The labyrinthine a. has no anastomotic network and is highly susceptible to ________________.
ischemia
Ischemia of the labyrinthine a. results in:
hearing loss and sudden onset of vertigo.
The area of the brainstem containing the vestibular nuclei is supplied by the:
posterior inferior cerebellar artery (PICA) (caudal aspects) and the anterior inferior cerebellar artery (AICA) (rostral aspects).
Specific clinical syndromes with symptoms of vestibular system involvement occur with occlusions of the _______________ artery, the ________________ artery, AICA and PICA.
basilar, labyrinthine and AICA, PICA
The purpose of the vestibulo-ocular reflex (VOR) is to:
maintain stable vision during head motion
When the head is turned to the left, the _____________ vestibular nerve ______________ firing and the ________________________ firing (as explained above).
When the head is turned to the left, the LEFT vestibular nerve INCREASES firing and the RIGHT DECREASES firing (as explained above).
These changes in firing rates influence discharge from the medial vestibular nuclei, which in turn sends signals via the __________ to activate RIGHT _____________________ (right lateral rectus) and LEFT _______________________ (left medial rectus).
MLF
abducens nucleus
oculomotor nucleus
Inhibitory impulses are sent to nuclei that control the antagonistic muscles that result in a lateral __________________ eye movement towards the right called nystagmus.
compensatory
Nystagmus is characterized by:
a slow phase away from midline (caused by the vestibular input) and a fast phase (as the eyes rebound towards midline).
The direction of nystagmus is named by the direction of the _______ phase because it is more readily identified.
fast
For example, in the above case, nystagmus would be called left beating.
For example, in the above case, nystagmus would be called left beating.
Eye movements are parallel to the plane of the _________ that has been stimulated.
canal
Nystagmus is a normal response to ______________ head velocity. However there are also a whole host of nystagmus responses that are considered pathologic and relate to lesions either in the _________________ vestibular organ or the ______________ vestibular nuclei or pathways.
rotatory
peripheral
central
The vestibulo-spinal reflex Influences ____________ extensors, primarily of the ________________ musculature and the ___________________.
ipsilateral
axial
lower extremities
What give rise to the lateral vestibulospinal pathway?
Output of the lateral vestibular nucleus gives rise to the lateral vestibulospinal pathway.
Axons of vestibulospinal pathway are seen in cross section as they pass through the ____________________ nucleus.
inferior vestibular
Where does the vestibulocollic reflex get its name from?
the musculature of the neck.
Remember identifying longus colli muscles on the anterior surface of the cervical vertebrae. This is a _________________ pathway that is most active through the __________________________ regions of the spine.
bilateral
cervical AND thoracic
The primary source of these fibers is from the ________________________ of both sides.
medial vestibular nuclei
When considering the bilateral nature of this pathway, consider that while one side of the system is sending excitatory signals to the ______________ of the __________________________________ on both sides, the other side is carrying signals that are decreasing, but are also going to both sides. This is an important concept since the control of axial musculature is dependent on this balance of increasing and decreasing signals.
extensors
upper extremity and axial musculature
Major Inputs of superior vestibular nuclei =
semicircular canals
cerebellum
contralateral v. nuclei
Major Inputs of lateral (Deiter’s) vestibular nuclei =
cerebellum
utricle and saccule
semicircular canals
(minimal)
Major Inputs of medial vestibular nuclei =
semicircular canals
1o horizontal
utricle and saccule
cerebellum
contralateral v. nuclei
reticular formation
Major Inputs of inferior (spinal or descending) vestibular nuclei =
utricle and saccule
cerebellum
Major Inputs of Nucleus Y vestibular nuclei =
utricle and saccule
Major outputs of superior vestibular nuclei =
MLF to oculomotor nuclei
Cerebellum
dorsal pontine RF
adjacent RF
thalamus
Major outputs of lateral (Deiter’s) vestibular nuclei =
ipsilateral lateral vestibulo-spinal tract
thalamus
Major outputs of medial vestibular nuclei =
bilateral medial vestibulo-spinal tract
MLF to oculomotor nuclei
Cerebellum
adjacent RF
Major outputs of inferior (spinal or descending) vestibular nuclei =
Cerebellum
RF
contralateral v. nuclei
Major outputs of Nucleus Y vestibular nuclei =
RF
contralateral v. nuclei
Function of superior vestibular nuclei =
maintain eye position during head movement
arousal
conscious awareness of spatial orientation
Function of lateral (Deiter’s) vestibular nuclei =
facilitates antigravity limb tone through vestibulospinal reflexes
spatial orientation
Function of medial vestibular nuclei =
coordination of eye, head and neck movements
gaze holding in the horizontal plane
head control & stability – head turning and righting
Function of inferior (spinal or descending) vestibular nuclei =
integrates vestibular signals from two sides with signals from cerebellum and RF
Function of Nucleus Y vestibular nuclei =
integrates vestibular signals from two sides with signals from cerebellum and RF
