Vestibular Flashcards
What are the different regions of the membranous labyrinth?
tube containing receptors for head movement/position and is subdivided into: Semicircular ducts (within the semicircular canals) Saccule & Utricle (within the vestibule)
Where are the Perilymph and endolymph.
Endolymph • secreted by cochlear duct • drains into dural sinuses via endolymphatic duct Perilymph • secreted by periosteum • drains into CSF via perilymphatic duct
What is Meniere’s disease and what causes it?
Transient vertigo & dizziness, nausea, vomiting and
abnormal saccadic eye movements (nystagmus).
• Excess endolymph & fluid pressure affect receptor functions.
Describe the structure and function of the crista.
Receptor in the ampulla of each semicircular canal
Epithelium of receptor (hair) cells and supporting cells that make the gelatinous mass (cupula). Hair cells have a single kinocilium and several stereocilia which project into the gelatinous mass (cupula).
What is detected by the semicircular ducts?
Differential endolymph flows in all three ducts generates patterns of neural activity in the vestibular nerve
. Describe the structure and function of the saccule and utricle.
Macula receptor system inside of these chambers .Epithelium with receptor cells and that produce the
gelatinous layer, i.e. the otolithic membrane.
Otoliths: calcium carbonate stones embedded in gelatinous layer
What do saccule and utricle respond to and what is the mechanism?
Macula is in a vertical plane, utricle is mostly
horizontal. Each hair cell responds optimally to
acceleration in the direction of its alignment,
increasing firing rate when the stereocilia are
deflected toward the kinocilium,
decreasing away from the kinocilium
Movement of otoliths (due to gravity or head movement)
embedded within the gel bend the cilia of the hair cells
generating receptor potentials
Briefly describe acoustic neuromas and their impact on vestibular function.
benign tumor of the myelin-forming cells of the inferior vestibular nerve, part of CN VIII
• Ipsilateral sensorineural deafness or tinnitus
• Vestibular disturbance : unstable gait, vertigo , nausea and vomiting
What causes benign paroxysmal positional vertigo?
Otoliths (otoconia) from utricle fall into semicircular canals and trigger apparent motion from the crista
To what structures do the vestibular nuclei project vestibular information?
Vestibular nuclei in brain stem
– Project to thalamus and cortex, spinal cord for postural control, brain stem nuclei for eye movements, autonomic centers for vascular control
Describe the VOR in terms of actions.
Vestibulo-Ocular Reflex
Adjusts eye movements to rotation of head to fix gaze on a visual object.
Rightward rotation of head stimulates horizontal semicircular ducts. Vestibular
nerve –>abducens and oculomotor nuclei–>eyes to the
left.
How does the cerebellum impact the VOR?
vestibulo-cerebellum for precision of VOR
What is Nystagmus? Does it occur normally or just pathologically?
involuntary saccadic movements when the eyeball is moving (physiological) or at rest (pathological)
What does the vestibule-sympathetic reflex do?
VSR enhances vasoconstriction to protect against syncope during postural changes or emotional stress.
VSR increases skin vasoconstriction (pallor) and sweating during nausea
RVLM mediated
Where is the vestibular cortex? How does it relate to other sensory modalities?
Vestibular input ascends from the vestibular nuclei to the thalamus (VPL). Thalamus projects TPJ (temporal parietal junction SELF LOCATION) and parietal areas, and the insula
