Vestibular System Flashcards
What is the function of the vestibular system?
Essential in producing motor responses; necessary for daily funciton
What are the 5 components of the vestibular system?
Peripheral receptor apparatus Central vestibular nuclei Vestibulo-ocular network Vestibulo-spinal network Vestibulo-thalamic cortical network
Where is the peripheral receptor apparatus?
What is the function of it?
Inner ear
Transduces head motion/position
Where is the central vestibular nuclei?
What is their function?
Brainstem
Integrates and distributes info that controls motor activities and spatial orientation
Where is the vestibule-ocular network?
What is its function?
Vestibular nuclei
Controls eye movements
What is the function of the vestibulo-spinal network?
Coordinated head movements, axial musculature, and postural reflexes
What it’s he function of the vestibule-thalamic cortical network?
Conscious perception of movement/spatial orientation
What the the vestibular receptor organs?
Semicircular canals
Otoliths organs (utricle and saccule)
What kind of movement does semicircular canal detect?
Rotational head movements
Angular accelerations
What kind of movement do otoliths organs detect?
Linear accelerations
Translation head movements
What are the receptors of vestibular organs innervated by?
Primary afferent fibers of vestibular ganglion (Scarpa ganglion)
Where do central porcesses vestibular ganglion enter and terminate?
Enter brainstem
Terminate in ipsilateral vestibular nuclei and cerebellum
Where is perilymph?
B/w membranous and bony labyrinths
Where is endolymph found?
Membranous labyrinth, bathing receptors of auditory and vestibular system
What maintains the ion concentrations of peri and endolymph?
Concentrations maintained by secretory cells in membranous labyrinth and endolymphatic sac
What is a vestibular disease caused by?
Disturbances in volume or ionic content of endolymph
What is the blood supply to the vestibular system?
Labyrinthine a. (Branch of AICA)
Stylomastoid a.
How does the labyrinthine a. Enter temporal bone
Via IAM
What happens if the labyrinthine a. Is compromised?
Compromised vestibular and cochlear funciton
Vertigo, nystagmus and/or unstable gait
What do type 1 and 2 hair cells contain?
Contain 60-100 stereocilia
1 kinocilium
What innervates
Type 1 hair cells?
Type 2?
Cn 8 via nerve calyx
Cn 8 via boutons
What does movement of stereocilia toward kinocilium cause?
Depolarization and AP
What does movement of stereocilia away from kinocilium cause?
Hyperpolarization
What is the ampullae?
How are the hair cells distributed in it?
Semicircular ducts
Hair cells in cristae across base of ampulla and extending into cupulla
What is the function of the ampulla?
Rotational and angular accelerations
How do angular accelerations act on the ampulla?
Displace endolymph
—>
Bends cupulla
—>
Displace stereocilia
What does the macula consist of?
Utricle and saccule
How are hair cells organized in the macula?
Hair cells’ stereocilia extends into gelatinous otoliths membrane covered by otoconia
What is the function of the macula?
Detect gravity/linear accelerations
How does gravity/linear accelerations act on the macula?
Displace otoconia
—>
Bend underlying hair cell stereocilia
Where do the priamry afferent of the vestibular system come from and enter at?
Primary aff. = cn 8
From ampullae or macula
Thru scarpa ganglion
Enter at pontomedullary junction
Where do primary afferents of the vestibular system project to?
Vestibular nuclei (superior, medial, later, and inferior) IPSILATERALLY
What do the vestibular nuclei encode?
Direction, speed of movement, and head position
What do the 2nd order nuerons coming from vestibular nuclei target?
CNs 3,4, 6 nuclei
And Vestibulocerebellum SC RF Thalamus
Where do the vestibular nuclei project to?
Ventral posterior nuclear complex in thalamus
Where do thalamic nuclei go to?
What are they conveying?
To cortical regions of S1, Parietoinsular vestibular cortex, posterior parietal cortex
Relay vestibular input needed for processing motion and body orientation
What happens if the Parietoinsular vestibular cortex is lesioned?
Vertigo
Unsteadiness
Loss of visual vertical
What happens if the posterior parietal cortex is lesioned?
Confusion in spatial awareness
What are vestibulovestibular fibers?
Reciprocal connections b/w R and L vestibular nuclei
R side activ. —> L side inhibited
Where are spinovestibular fibers from?
What do they provide?
From all SC levels
Provide proprioceptive input
What are the vestibulocerebellar fibers?
Where do they project to ?
Fibers thru juxtarestiform body
Sends DIRECT projection to cerebellum
(Only sensory organ body that does this)
What do primary vestibulocerebellar fibers target?
What kind of fibers are these?
Dentate nucleus of cerebellum
Mossy fibers
What do the secondary vestibulocerebellar fibers target?
Flocculonodular lobe - fastigial and dentate nuclei
What do the reciprocal cerebelli vestibular fibers provide?
Regulatory mechanisms for coordinating eye movements, head movements, and posture
What nuclei does the lateral vestibulospinal tract come from?
Inferior and lateral nuclei
Where does the lateral vestibulospinal tract project to?
What does it control?
Projects to ipsi SC at cervical and lumbosacral regions
Controls extensors for maintenance of posture
Where does the medial vestibulospinal tract come form?
What is the input to it?
Medial vestibular nucleus
Integrated input from vestibular receptors, cerebellum and PCMLS
What is the pathways of the medial vestibulospianl tract?
What is the function?
Medial vestibular nucleus —> MLF —> Cervical SC
Stabilize neck flexor and extensor musculature
What reflex is the medial vestibulospianl tract needed for?
Critical in vestibulo-colic reflex
Stabilizes head via activation of neck musculature
What is the Vestibulo-ocular reflex for?
Stabilizes images on retina during head movements thru vestibular input
Describe the vestibulo-ocular reflex
Head rotates —> endolymph moment in semicircular canals —> vestibular input about head motion —> drives COUNTER ROTATION of EYES
What is the slow phase of eyes characterized by?
Eyes move away from head motion
What is the fast phase of eyes characterized by?
Eyes snap black toward head motion
What is needed in order for the vestibulo=ocular reflex to occur?
Need activation of ocular muscle for slow phase via vestibular apparatus
In the vestibulo ocular reflex,
What happens when you turn your head to the right?
Fluid in right semicircular ducts—> activate right afferent fibers —> Right vestibular nuclei —> CN 6 — inter-nuclear neurons via MLF —>CN 3
—> Lateral rectus, Medial rectus
What links left lateral rectus with the right medial rectus?
Internuclear nuerons
Go from CN 6 —> CN 3 using MLF
What is the Vestibulo=ocular reflex?
Push pull mechanisms that unifies movements of eyes thru bilateral symmetry of VOR circuits
What will the left vestibular apparatus do when the head is rotated right?
Left vestibular afferents are inhibited
Cause complementary circuit to relax
(Via vestibulovestibular fibers)
What is physiological nystagmus?
Combo of slow phase punctuated by fast return phase
How do we name physiological nystagmus ?
For the fast phase
The direction he head is turning
What does unilateral damage to the vestibular system cause?
silences output from damaged side causing steady firing of intact side by CN 8
Causes spontaneous nystagmus, vertigo, falls, and vomiting
What will peripheral damage to vestibular labyrinth or CN 8 cause?
Imbalance b/w left and right vestibular input
Nystagmus
What happens if there is central damage to the brainstem or cerebellar strucutres ?
Nystagmus w/ impaired voluntary saccades and/or smooth pursuit
How do you test for nystagmus?
Caloric test
In the caloric test what will warm water cause?
Nsytagmus that beats toward irrigated ear
I.e. fast phase is toward ear irrigated
In the caloric test, what will cold water cause?
Nystagmus that beats AWAY from irrigated ear
If r. Ear done, fast phase will be toward the left
What is Ménière’s disease caused by?
Disruption of normal endolymph volume causing endolymphatic hydrops (distortion of membranous labyrinth)
What are the Sxs of Ménière’s disease?
What are the txs for Ménière’s disease?
fluctuating hearing loss Vertigo Positional nystagmus Nausea Tinnitus
Restrict salts and diuretics to reduce hydrops, implant shunt to endolymphatic sac
What is benign paroxysmal positional vertical characterized by?
Caused by?
Brief episodes of vertigo that coincide w/ changes in body position
Cupololithiasis
What is cupololiithiasis
Otonconia crystals lodged in cupola of semicircular changes that will change the movemnt of endolymph and cause feeling of motion when headchanges positions
What is vestibular schwannoma (Acoustic neuroma)
Benign tumor from Schwann cells in vestibular root
Where is a vestibular schwannoma?
What will it impinge on?
Within cerebellopontine angle
Structures traversing IAM
CN 7,8, labyrinthine a.
What are the symptoms of Vestbiular schwannoma?
Hearing loss, gait difficulties, tinnitus
What is vestibular neuritis caused by?
Edema of vestibular n. Or ganglion due to recent viral infection (i.e. herpes simplex)
What are the symptoms of vestibular neuritis?
What will patients report recent history of?
Txs?
Severe vertigo
Nausea
Vomiting
NO HEARING LOSS THOUGH
Recent Hx of URI, Cold, or influenza
Antiemetic, vestibular suppressants, corticosteroids, and antiviral agents
What is dizziness?
Non specific term for spatial disorientation
May or may not feel movement
Could have nausea or postural instability
NOT EXCL. Vestibular in origin
What is vertigo?
Illusion of body motion, often spinning
What is subjective vertigo?
Patient feels spinning while things in environment are not moving
What is objective vertigo?
Patient not moving but has sensation of object spinning
What is the oculocephalic reflex?
A head rotated back and forth will have yes that move in opposite direction
Do you see an oculocephalic reflex in conscious patients?
NO
Voluntary eye movements mask reflex
How can the oculocephalic reflex be used in comatose patients?
To asses brainstem function
If brainstem is intact, doll’s eye reflex is present
What happens if there is a lesion to MLF?
One eye = abducted
Other one does not move
INO
(Remember that the MLF is the tract for internuclear neurons)
