DeLahunta Chapter 12 - Vestibular system Flashcards
What is the origin and content of the bony and membranous labyrinth respectively? What is the name and origin of the ear ossicles?
Bony labyrinth: mesodermal and contains perilymph
Membranous labyrinth: ectodermal (otic placode) and contains endolymph
stapes, malleus, incus - neural crest
What is the crista ampullaris?
receptor of denritic zone of bipolar cells of vestublar ganglion
=hair cells with microvilli (stereocilia) and a single modified cilium (kinocilium) in the ampulla
Responsible for rotation
What is the embryogenic origin of the neurons of the vestibulocochlear nerve?
The neurons of the vestibulocochlear nerve are derived from otic placode ectoderm. The dendritic zones of the neurons of the vestibular portion of the vestibulocochlear nerve are in synaptic contact with the base of the hair cells.
What is the macula? Where are the maculae located? What is their function?
The macula is the receptor found in each utriculus and saccule, which are located in the bony vestibule.
Macula utricle - horizontal
Macula sacculi.- vertical
Both have hair cells
Both have statoconia (otoliths)
Utricle –> changes in head posture
Sacule –> vibrational stimuli and loud sounds
These structures are responsible for the sensation of the static position of the head and linear acceleration or deceleration. They function in static equilibrium. The macula of the utriculus may be more important as a receptor for sensing changes in head posture, whereas the macula of the saccule may be more sensitive to vibrational stimuli and loud sounds.
Where does the lateral vestibulospinal tract course and what is the clinical effect of stimulation of neurons with axons coursing through this tract?
Is a motor pathway starting for the lateral vestibular nuclei
in the ventral funiculus of whole spnal cord
synapses with interneurons in ventral grey column –>
-fascilitatory of ipsilateral a-GSE and g-GSE –> ipsilateral extensors
-inhibitory to a-GSE to flexors ipsiltaeral
-contralateral inhibition of a gSE of extenrso
–> ispilateeral extnesor tone and contralateral inhibition of tone
Which are the three possible terminations of neuronal cell bodies in the vestibular nuclei in the brainstem? (where are going the vestibular nuclei in the brainstem)?
1) MLF (rostrally) –> CN VI, III,IV
2) ARAS (vomiting centre)
3) conscious perception of balance to cerebrocortex (mibrain, contralateral MGN –> Thalamus–>temporal cortex)
What muscle is responsible for the simultaneous eyelid movement seen in some
patients with vestibular disturbance?
Levator anguli oculi medialis muscle (LAOM muscle) - because vestibular nuclei had interconnections wwith facial nuclus
In a recent paper on vestibular disease in dogs, what percentage of dogs
diagnosed with a peripheral lesion based on neurological examination had a
consistent lesion on MRI?
a- 98.4%
b- 88.4%
c- 77.4%
d- 67.4%
c
What is the proposed mechanism for the head tilt and loss of balance being
contralateral to the side of the lesion in cases of paradoxical (central) vestibular
system disease?
Paradoxical (central) vestibular disease is a unique syndrome in which the head tilt and loss of balance are directed toward the side opposite to the central lesion, which usually involves the caudal cerebellar peduncle. An explanation for this paradox in the direction of the clinical signs of vestibular system dysfunction is based on the rule that the direction of the head tilt and balance loss is toward the side of the least vestibular system activity. The description of the physiologic anatomy of the cerebellum in Chapter 13 explains that the Purkinje neurons that form a single layer of cells in the cerebellar cortex are the only neurons that project their axons from the cerebellar cortex. These neurons are all inhibitory neurons that release γ- aminobutyric acid at their telodendria. Most of these neurons terminate via their telodendria on neuronal cell bodies in the cerebellar nuclei, which are located in the central portion of the cerebellum known as the cerebellar medulla. The neurons in these cerebellar nuclei comprise most of the efferent axons that leave the cerebellum to terminate in various brainstem nuclei. An exception to this rule is a small population of Purkinje neurons, most of which are located in the cortex of the folia of the flocculus in the hemisphere and the nodulus in the vermis. The Purkinje neurons of these cortical areas have axons that leave the cerebellum directly as a component of the caudal cerebellar peduncle. Tey terminate in the vestibular nuclei, where they are inhibitory to the activation of these neuronal cell bodies. A lesion in the caudal cerebellar peduncle interferes with this inhibition, resulting in excessive discharge of vestibular system neurons on that side. The imbalance in vestibular system activation between the two sides is recognized as a head tilt and loss of balance to the side opposite to this lesion because as a rule the direction of the head tilt and balance loss is toward the side with the least activity of the vestibular system. This paradoxical syndrome is in contrast to lesions that cause a loss of activation of the neuronal cell bodies in the vestibular nuclei, as seen in disorders of the peripheral components of the vestibular system or within the vestibular nuclei themselves. In clinical practice, the side of this unilateral lesion will be determined on neurologic examination by the side of the postural reaction deficit or the side of the hemiparesis and ataxia, which is ipsilateral to the lesion. The caudal cerebellar peduncle lesion is contralateral to the direction of the head tilt in paradoxical (central) vestibular syndrome. The caudal cerebellar peduncle lesion that causes the paradoxical (central) vestibular syndrome also interferes with GP afferents that are entering the cerebellum. Their interruption causes ipsilateral ataxia and a deficit in postural reactions.
Older age was associated with which cause for peripheral and central vestibular
syndrome respectively based on two recent studies?
(Harrison2021 https://doi.org/10.1002/vetr.61
Orlandi2020 https://doi.org/10.1186/s12917-020-02366-8 )
Central: ischaemic infarct
Peripheral: idiopathic vestibular
Which has been reported as the most commonly isolated pathogen from cats
diagnosed with otitis media-interna? In which percentage of these cats may
otoscopic examination be found normal?
(Moore2018 https://doi.org/10.1177/1098612X187645 )
At total of 19 cats were identified. Sixty-three percent had no previous history of ear infection. Otoscopic examination was normal in 47% of cases. The most common bacterial isolate was Pasteurella multocida, which was identified in 24% of cases. Outcome was successful for 83% of cats managed with ventral bulla osteotomy (VBO) and in 66% of cats managed without surgical intervention.
Which commonly used antibiotic has been associated with neurotoxicity
exhibited with vestibular signs, and what is the reported median time for
resolution of the clinical signs following treatment discontinuation?
(Tauro2018 https://doi.org/10.1111/avj.12772 )
Metronidazole – 3d
Please name some common breeds for congenital peripheral vestibular disease.
These breeds include the German shepherd dog,48 doberman pinscher, Akita, beagle, English cocker spaniel,3 and Burmese and Siamese cats
What unique disorder often accompanies otitis in horses especially if they have
exhibited a brief period of dysphagia?
Temporohyoid osteopathy
Which are the vestibular nuclei and where are they located?
4 - medulla oblongata
-Rostral vestibular nucleus
-Medial and lateral vestibular nucleus
-Caudal vestibular nucleus )
State one category of ototoxic drugs that can cause vestibular signs and why?
Degeneration of the vestibular or cochlear labyrinthine receptors or both may occur with high levels of aminoglycoside antibiotics. These drugs include streptomycin,
amikacin, kanamycin, neomycin, gentamicin, and vancomycin.
