12. Vestibular system

Question 1

What are the 5 components of the vestibular system?

Answer 1

1. peripheral receptor apparatus
2. central vestibular nuclei
3. vestibuloocular network
4. vestibulospinal network
5. vestibulothalamocortical network

Question 2

The _______ ______ ________ is the inner ear and is responsible for transfusing head motion and position

Answer 2

Peripheral receptor apparatus

Question 3

The ______ ______ ______ is involved in integrating and distributing information that controls motor activities and spatial orientation

Answer 3

Central vestibular nuclei

Question 4

The ________ _______ is involved in the control of eye movement

Answer 4

vestibuloocular network

Question 5

The _____ ______ coordinates head movements, axial musculature and postural reflexes

Answer 5

Vestibulospinal network

Question 6

The _________ ______ is involved in conscious perception of movement and spatial orientation

Answer 6

vestibulothalamocrotical network

Question 7

What are the receptor organs that are involved with rotational head movements?

Answer 7

Semicircular canals

Question 8

What are the receptor organs that are involved with translational head movements and linear accelerations

Answer 8

otolith organs and the utricle and saccule

Question 9

What are the receptor cells in the vestibular organs innervated by?

Answer 9

Primary afferent fibers of the vestibular organ

Question 10

_______ is located between the membranous and the bony labyrinths and is similar in composition to CSF

Answer 10

Perilymph

Question 11

_______ is in the membranous labyrinth and bathes the receptors of the auditory and vestibular systems

Answer 11

Endolymph

Question 12

What is the cause of a vestibular disease?

Answer 12

The disturbance in volume or ionic concentration of the endolymph

Question 13

Describe the blood supply to the vestibular system

Answer 13

Via the labyrinthine artery form the AICA that entires the temporal bone through the internal acoustic meatus

Question 14

What is the function of the stylomastoid artery in the vestibular system?

Answer 14

Feeds the semicircular canals but is NOT the primary source

Question 15

If there is a decrease or interruption in blood flow to the vestibular system, what happens?

Answer 15

Vertigo, nystagmus, and unstable gait

Question 16

What is the cause of Meniere’s disease?

Answer 16

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

Question 17

What is the treatment of Meniere’s disease?

Answer 17

Diuretic and salt restricted diet to decrease the hydrops

small shunt into the endolymphatic sac

Question 18

What is the purpose of hair cells?

Answer 18

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

Question 19

If the hair cells move toward the kinocilium, what happens?

Answer 19

The cells are depolarized

Question 20

If the hair cells move away from the kinocilium what happens?

Answer 20

The cells are hyper polarized

Question 21

Differentiate between type 1 and type 2 hair cells

Answer 21

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

Question 22

What is the ampullae?

Answer 22

semicircular ducts that have hair cells embedded in the cristae and extend into the cupula

Notices rotational acceleration

Question 23

Describe how the ampullae are activated

Answer 23

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

Question 24

What is the maculae?

Answer 24

Utricle and saccule are involved with otoconia involvement (ear stones)

Notices gravity/linear acceleration

Question 25

Describe how the maculae are activated?

Answer 25

Gravity and linear accelerations displace the otoconia and bend the underlying hair cells stereo cilia

Question 26

Describe the vestibular afferents

Answer 26

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

Question 27

_______ ______ are directionally selective and encode direction, speed of movement, and head position

Answer 27

Vestibular nuclei

Question 28

What do the secondary afferent neurons target?

Answer 28

CN III, IV, VI, vestibulocerebellum, SC, reticular formation, and thalamus

Question 29

________ _______ 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

Answer 29

Vestibulovestibular fibers

Question 30

______ _____ arise from all SC levels to provide proprioceptive input Head involved with posture

Answer 30

Spinovestibular fibers

Question 31

The _______ _______ is the only sensory organ body that sends direct fibers to the cerebellum

Answer 31

Vestibulocerebellar fibers

Question 32

These fibers course through the juxtarestiform body and part of the inferior cerebellar peduncle

Answer 32

Vestibulocerebellar fibers

Question 33

What do the primary vestibulocerebellar fibers target? Where do they terminate?

Answer 33

Target the dentate nucleus and terminate as the mossy fibers

Question 34

What do the secondary vestibulocerebellat fibers target?

Answer 34

Target the flocculonodular lobe and the fastigial and dentate nuclei

Question 35

What do the reciprocal cerebellovestibular fibers target?

Answer 35

Vestibular nuclei in the juxtarestifrom body

Question 36

________ 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

Answer 36

Dizziness

Question 37

______ is an illusion of body motion, spinning, turning sensation when it is not actually occurring

Answer 37

Vertigo

Question 38

Differentiate between subjective and objective vertigo

Answer 38

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)

Question 39

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)

Answer 39

Benign paroxysmal positional vertigo

Question 40

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

Answer 40

Benign paroxysmal positional vertigo

Question 41

What is a vestibular schwannoma

Answer 41

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)

Question 42

Where are vestibular schwannomas typically found? What are the sx?

Answer 42

in the cerebellopontine angle hearing loss, gait abnormalities, and tinnitus

Question 43

If a patient presents with severe vertigo, nausea, vomiting, but no hearing loss, including a recent viral infection what is the possible diagnosis?

Answer 43

Vestibular neuritis involves edema of the vestibular system and the vestibular nerve

Question 44

What is the treatment for vestibular neuritis

Answer 44

Antiemetics, vestibular suppressants, corticosteroids, and antiviral agents

Question 45

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

Answer 45

Lateral Vestibulospinal tract

Question 46

The _____ ______ _____ has fibers that descend bilaterally through the MLF and terminate on the cervical SC stabilizing the neck flexor and extensor musculature

Answer 46

Medial vestibulospinal tract critical in the vestibulocolic reflex that stabilizes the head via activation of the neck musculature

Question 47

What are the cortical areas that are targeted by the thalamocortical pathways?

Answer 47

Primary somatosensory cortex Parietoinsular vestibular cortex Posterior parietal cortex

Question 48

What will lesions in the parietoinsular vestibular cortex result in?

Answer 48

vertigo, unsteadiness, and loss of visual vertical

Question 49

What will lesions in the posterior parietal cortex result in?

Answer 49

Confusion and spatial awareness

Question 50

Describe the vestibuloocular reflex

Answer 50

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

Question 51

Describe the eye position during the VOR

Answer 51

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

Question 52

______ is the combo of a slow phase punctuated by fast return phase

Answer 52

Nystagmus

Question 53

How is nystagmus named?

Answer 53

For the direction of the fast phase

Question 54

Describe what happens when you move your head to the right

Answer 54

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

Question 55

Describe what happens with the VOR with a rightward rotation of the head

Answer 55

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

Question 56

Describe spontaneous nystagmus

Answer 56

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

Question 57

What can peripheral damage lead to?

Answer 57

Vestibular labyrinth and/or CN VIII imbalance between left and right vestibular input causes nystagmus Does not affect voluntary saccades and smooth pursuit

Question 58

What does central damage of the brainstem or cerebellum lead to?

Answer 58

Nystagmus with impaired voluntary saccades Involvement of multiple pathways

Question 59

Describe the caloric test

Answer 59

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

Question 60

When warm water is used in the caloric test, what happens?

Answer 60

Currents are generated that mimic the head turning to the irrigated side; nystagmus will beat toward the irrigated ear

Question 61

When cold water is used in the caloric test, what happens?

Answer 61

Currents are generated toward the opposite side; nystagmus does the same

Question 62

What is the oculocephalic reflex?

Answer 62

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

Question 63

When is the oculocephalic reflex tested?

Answer 63

in a comatose patient; to assess brainstem function; if it is intact, then the brainstem is fine and vice versa