Vestibular Apparatus

Question 1

Vestibular system components

Answer 1

1.vestibular apparatus (peripheral sensory organ)
2.CN 8- vestibulocochlear nerve
3.Vestibular nuclei (medulla)
4.VVestibulocerebellum (flocculonodular lobe)

Question 2

Vestibular apparatus parts

Answer 2

-paired structure (right and left)
-membranous labyrinth (inner ear)
>semi-circular canals
>utricle
>saccule
-sensory structure (hair cells)

Question 3

What does vestibular apparatus detect?

Answer 3

-static position
-linear and rotational motion of the head

Question 4

Where is the vestibular apparatus?

Answer 4

-located inside the petrous part of the temporal bone
-near the brain

Question 5

Vestibular apparatus embryological origin

Answer 5

-From the otic vesicle (vestibular apparatus and cochlea)

Question 6

Lymph of vestibular apparatus

Answer 6

-Perilymph= CSF near brain and surrounding endolymph
-Endolymph= sitting within semi-circular canals

Question 7

Hair cells

Answer 7

-the sensory structures inside the vestibular apparatus and cochlea which convert peripheral sensations to nerve impulses (transmitted via CN VIII)

Question 8

Membranous labyrinth

Answer 8

-system of soft tissues and receptors

Question 9

Cristae ampullares (x3)

Answer 9

-located at base of each semicircular duct and are responsible for detecting rotational changes
>each of the 3 are positioned slightly different so they can detect change
>Cupula (protein -rich structure that is neutrally buoyant) surrounds the cristae ampullares

Question 10

Maculae (x2)

Answer 10

-paired structures
-otoliths (stones) floating inside endolymph in the walls of the utricle and saccule
-detect static and linear movement and pass on to hair cells and eventually CN VIII

Question 11

Cranial Nerve VIII

Answer 11

-vestibulocochlear nerve
-inputs information into medulla
-pathway is very short because vestibular apparatus is near the brainstem

Question 12

Where does Cranial nerve VIII travel?

Answer 12

-sensory axons enter medulla, and synapse mostly on vestibular nuclei within the medulla
-sometimes axons synapse directly within the cerebellum (vestibulocerebellum/ flocculonodular lobe)

Question 13

Where does vestibular nuclei go?

Answer 13

1.LMN of neck/limbs/trunk
2.LMN of extrinsic ocular muscles (CN III, IV, VI)
3.Cortex (via thalamus)=conscious awareness of head movement
4.Medulla at emetic centre= nausea/motion sickness

Question 14

Vestibular nuclei neurons and tract

Answer 14

-UMN running along vestibulospinal tract

Question 15

Vestibular nuclei effect on head/limbs/trunk

Answer 15

-input to LMN of head/limbs/trunk resulting in:
>increased ipsilateral extensors
>decreased ipsilateral flexors
>decreased contralateral extensors

Question 16

Vestibular nuclei effect on ocular muscle

Answer 16

-through CN III, IV, VI
-ocular muscles need to work together in synchrony where left and right eye movements are coordinated by opposite muscle activation/inhibition

Question 17

Nystagmus

Answer 17

-rapid, involuntary movements of the eyes (horizontal, rotational, vertical)
>coordinated movements between left and right eyes (will include inhibition of some parts of eye to allow movement with the head)
>eyes don’t move smoothly with re-positioning of the head (step-wise movements)

Question 18

Slow-phase eye movements

Answer 18

-eyes move away from the direction of the head movements

Question 19

Saccade

Answer 19

-fast-phase coordinated movement of eyes moving towards the direction of the head movement
>delay in eye movement compared to head movement

Question 20

Vestibular disease

Answer 20

-can affect anywhere within the vestibular system
>vestibular apparatus
>vestibular nuclei
>CN VIII
>flocculonodular region of cerebellum
-Lesions will result in reduced activity of the vestibular system on the ipsilateral side

Question 21

Lesions of vestibular Disease

Answer 21

1.Asymmetric head/body position (towards the side of the lesion) = head tilt, body leaning/falling, rolling
2.Ataxia= Vestibular ataxia= circling or falling towards the side of the lesion (staggering)
3.Pathological nystagmus (spontaneous)- occurs at rest; horizontal, vertical (if central lesion), rotary. Peripheral lesion would result in same type of nystagmus no matter the body position
>imbalance between L and R vestibular systems, and reduced input to medial longitudinal fasciculus
>fast phase away from the lesion (towards the more active side of the body)
4.Positional strabismus
>abnormal eye position when the head is moved/rotated
>ipsilateral ventral or ventrolateral strabismus when he is moved dorsally

Question 22

Resolution of vestibular disease

Answer 22

-lots of compensation mechanisms, so most clinical signs will resolve over time
>nystagmus and strabismus resolves most rapidly
-sometimes if you suspect vestibular disease but there is no nystagmus, it could be that it has resolved already. Can try re-positioning them and then spontaneous nystagmus may return

Question 23

Peripheral Vestibular Disease

Answer 23

1.head tilt towards side of the lesion
2. nystagmus (horizontal or rotary; but no change in direction with head position)
3. normal postural reactions
4.concurrent facial nerve (VII) damage or Horner’s syndrome (ipsilateral)

Question 24

Central vestibular disease

Answer 24

1.head tilt towards vs away (paradoxical)
2.Nystagmus (horizontal, rotary, or vertical; direction of nystagmus can change with head position)
3. Postural deficits
4. Multiple Cranial nerve deficits (ipsilateral or bilateral; can also see Horner’s syndrome)

Question 25

Paradoxical Vestibular disease

Answer 25

-lesions that effect connections at cerebellar peduncles (connection between vestibular nuclei and cerebellum)
-head will tilt away from lesion side because inhibitory neuron at cerebellar peduncles will be turned off resulting in that side being the most excitatory so animal will tilt away from lesion