12. Vestibular system Flashcards
What are the 5 components of the vestibular system?
- peripheral receptor apparatus
- central vestibular nuclei
- vestibuloocular network
- vestibulospinal network
- vestibulothalamocortical network
The _______ ______ ________ is the inner ear and is responsible for transfusing head motion and position
Peripheral receptor apparatus
The ______ ______ ______ is involved in integrating and distributing information that controls motor activities and spatial orientation
Central vestibular nuclei
The ________ _______ is involved in the control of eye movement
vestibuloocular network
The _____ ______ coordinates head movements, axial musculature and postural reflexes
Vestibulospinal network
The _________ ______ is involved in conscious perception of movement and spatial orientation
vestibulothalamocrotical network
What are the receptor organs that are involved with rotational head movements?
Semicircular canals
What are the receptor organs that are involved with translational head movements and linear accelerations
otolith organs and the utricle and saccule
What are the receptor cells in the vestibular organs innervated by?
Primary afferent fibers of the vestibular organ
_______ is located between the membranous and the bony labyrinths and is similar in composition to CSF
Perilymph
_______ is in the membranous labyrinth and bathes the receptors of the auditory and vestibular systems
Endolymph
What is the cause of a vestibular disease?
The disturbance in volume or ionic concentration of the endolymph
Describe the blood supply to the vestibular system
Via the labyrinthine artery form the AICA that entires the temporal bone through the internal acoustic meatus
What is the function of the stylomastoid artery in the vestibular system?
Feeds the semicircular canals but is NOT the primary source
If there is a decrease or interruption in blood flow to the vestibular system, what happens?
Vertigo, nystagmus, and unstable gait
What is the cause of Meniere’s disease?
Disruption of the endolymph volume which results in an abnormal distension of the membranous labyrinth
When this happens, it leads to vertigo, vomiting, tinnitus, and make head movements difficult with association fluctuating hearing loss
What is the treatment of Meniere’s disease?
Diuretic and salt restricted diet to decrease the hydrops
small shunt into the endolymphatic sac
What is the purpose of hair cells?
To register positional changes of the head and respond by moving in a way that will depolarize or hyper polarize the cell; they are organized how they are going to move
If the hair cells move toward the kinocilium, what happens?
The cells are depolarized
If the hair cells move away from the kinocilium what happens?
The cells are hyper polarized
Differentiate between type 1 and type 2 hair cells
Type 1 hair cells are innervated by a nerve calyx which is like a cup like thing at the bottom of the cell
Type 2 hair cells are innervated by boutons
What is the ampullae?
semicircular ducts that have hair cells embedded in the cristae and extend into the cupula
Notices rotational acceleration
Describe how the ampullae are activated
rotational acceleration causes displacement of endolymph and causes the cupula to bend to one side or another and the stereo cilia are displaced
If the cilia move towards the kinocilium then an action potential will occur
What is the maculae?
Utricle and saccule are involved with otoconia involvement (ear stones)
Notices gravity/linear acceleration
Describe how the maculae are activated?
Gravity and linear accelerations displace the otoconia and bend the underlying hair cells stereo cilia
Describe the vestibular afferents
The primary afferents are from CN VIII from the semicircular duct or the otoliths enter at the pontomedullary junction and project to the vestibular nuclei
_______ ______ are directionally selective and encode direction, speed of movement, and head position
Vestibular nuclei
What do the secondary afferent neurons target?
CN III, IV, VI, vestibulocerebellum, SC, reticular formation, and thalamus
________ _______ are reciprocal connections with analogous contralateral nucleus
If you turn your head to the right side, the right side is activated and the left side is inhibited so that you dont get dizzy
Vestibulovestibular fibers
______ _____ arise from all SC levels to provide proprioceptive input
Head involved with posture
Spinovestibular fibers
The _______ _______ is the only sensory organ body that sends direct fibers to the cerebellum
Vestibulocerebellar fibers
These fibers course through the juxtarestiform body and part of the inferior cerebellar peduncle
Vestibulocerebellar fibers
What do the primary vestibulocerebellar fibers target? Where do they terminate?
Target the dentate nucleus and terminate as the mossy fibers
What do the secondary vestibulocerebellat fibers target?
Target the flocculonodular lobe and the fastigial and dentate nuclei
What do the reciprocal cerebellovestibular fibers target?
Vestibular nuclei in the juxtarestifrom body
________ is a nonspecific term that means spatial disorientation and may or may not involve feelings of movement, accompanied with nausea or instability, and may not be secondary to a vestibular issue
Dizziness
______ is an illusion of body motion, spinning, turning sensation when it is not actually occurring
Vertigo
Differentiate between subjective and objective vertigo
Subjective vertigo is when the patient experiences the sensation of spinning when things are not actually moving (I am spinning in the room)
Objective vertigo is the sensation of objects moving when the patient is not (the room is spinning)
This is one of the most common vestibular disorders and is characterized by brief episodes of vertigo that coincide with changes in body position (getting out of bed, bending over, etc)
Benign paroxysmal positional vertigo
This disorder can be secondary to the otoconial crystals from the utricle becoming dislodged and lodged into the cupula of the semicircular canal, which results in abnormal cupula deflections with head positional changes
Benign paroxysmal positional vertigo
What is a vestibular schwannoma
Benign tumor of the schwann cells of the vestibular root that impinges on everything that is going through the internal acoustic meatus
CNVII CNVIII labyrinthine artery to the vestibular organ (from AICA)
Where are vestibular schwannomas typically found? What are the sx?
in the cerebellopontine angle
hearing loss, gait abnormalities, and tinnitus
If a patient presents with severe vertigo, nausea, vomiting, but no hearing loss, including a recent viral infection what is the possible diagnosis?
Vestibular neuritis
involves edema of the vestibular system and the vestibular nerve
What is the treatment for vestibular neuritis
Antiemetics, vestibular suppressants, corticosteroids, and antiviral agents
the ______ ________ ______ arises from the lateral and inferior vestibular nuclei and project to the ipsilateral SC
This is a powerful control of extensors for maintenance of posture
Lateral Vestibulospinal tract
The _____ ______ _____ has fibers that descend bilaterally through the MLF and terminate on the cervical SC stabilizing the neck flexor and extensor musculature
Medial vestibulospinal tract
critical in the vestibulocolic reflex that stabilizes the head via activation of the neck musculature
What are the cortical areas that are targeted by the thalamocortical pathways?
Primary somatosensory cortex
Parietoinsular vestibular cortex
Posterior parietal cortex
What will lesions in the parietoinsular vestibular cortex result in?
vertigo, unsteadiness, and loss of visual vertical
What will lesions in the posterior parietal cortex result in?
Confusion and spatial awareness
Describe the vestibuloocular reflex
Stabilizes retinal images during head movements through vestibular input
helps you to be able to read things while walking, and adjust to head movements with eye movements to accompany so that you are able to focus
Describe the eye position during the VOR
saw tooth position with a slow phase and a fast phase
If you rotate your head to the right, then the ocular muscles are activated to move the eyes to the left in the slow phase, activating the right vestibular apparatus and the left lateral rectus and right medial rectus
The quick phase takes the eyes back to the right with the head, to offset the slow phase
______ is the combo of a slow phase punctuated by fast return phase
Nystagmus
How is nystagmus named?
For the direction of the fast phase
Describe what happens when you move your head to the right
The fluid in the semicircular duct moves and causes an activation of the right afferent fibers
This alerts the right vestibular nuclei and the left CN VI nucleus and the right CN III nucleus
The left lateral rectus is linked with the right medial rectus
Describe what happens with the VOR with a rightward rotation of the head
Right vestibular afferents are activated
Eyes rotate slowly to the left
Abrupt shift back to the right (right beating nystagmus)
decreased activity of the left vestibular afferents
Right lateral rectus and left medial rectus relax
Describe spontaneous nystagmus
Unilateral damage to the vestibular system
The output of the damaged side is silenced causing differences in the firing rates of CN VIII which can cause nystagmus
What can peripheral damage lead to?
Vestibular labyrinth and/or CN VIII
imbalance between left and right vestibular input causes nystagmus
Does not affect voluntary saccades and smooth pursuit
What does central damage of the brainstem or cerebellum lead to?
Nystagmus with impaired voluntary saccades
Involvement of multiple pathways
Describe the caloric test
Tests the vestibular labyrinth system and the VOR without moving the head
water is used to alter the convection currents in the endolymph which alters the CN VIII firing rate
When warm water is used in the caloric test, what happens?
Currents are generated that mimic the head turning to the irrigated side; nystagmus will beat toward the irrigated ear
When cold water is used in the caloric test, what happens?
Currents are generated toward the opposite side; nystagmus does the same
What is the oculocephalic reflex?
Rotating the head back and forth horizontally induces eye movements that are dependent on the visual and vestibular function
The reflex occurs when the patients eyes move in the opposite direction of the head movements
When is the oculocephalic reflex tested?
in a comatose patient; to assess brainstem function; if it is intact, then the brainstem is fine and vice versa
