Lecture 49: Vestibular System Flashcards
(23 cards)
What are the functions of the vestibular system?
- Reports on linear and angular acceleration of the head, but not velocity
- Stimulus is change in head position and is reliant on gravity
- Balance, controlling eye movements, and
reflexes
Name the 2 compartments of the vestibular system:
- Semicircular canals
- Otoliths
What are the otoliths?
- Sense linear acceleration and sustained tilt
- Two otoliths (utricle and saccule)
- Fluid filled
What are the semicircular canals?
- Sense rotational acceleration
- Fluid filled (endolymph)
- 3 orthogonal channels (canals)
- Ampullae
Describe the axes of the semicircular canals:
- Aligned in 3 axes: Each most responsive to acceleration around its preferred plane
- Z axis (yaw): Turning of head left/right; lateral canal (horizontal plane)
Describe the pairing of semicircular canals:
- Works in pairs: one set in each ear (coplanar pairs)
- Left <-> right horizontal
Where are the ampulla located?
Each of the 6 semicircular canals have an ampulla
Describe the structure of the ampulla:
- Hair cells and endolymph
- Crista ampullaris: membrane containing hair cells
- Cupula: gelatinous matrix embedded around vestibular hair cells (bathed in endolymph) - endolymph flow displaces cupula and causes deflection of stereocilia
What is direction-dependent hair cell discharge?
- Vestibular hair cells signal movement in 2 directions
- Release of neurotransmitter onto afferent axon
- Rate of discharge depends on direction of hair deflection
What is the vestibulo-ocular pathway?
- Vestibular afferent nerves form the vestibular nerve
(part of cranial nerve VIII) - Axons enter brainstem and synapse in vestibular
nuclei - Projections from vestibular nuclei to oculomotor cranial nerves
- Inhibitory and excitatory pathways
What is the role of the vestibulo-ocular pathway?
Stabilises gaze during movement
What is the vestibular-cerebellar pathway?
Projections from vestibular nuclei to cerebellum
What is the role of the vestibular-cerebellar pathway?
Balance coordination
What is the vestibulo-thalamo-cortical pathway?
- Projections from vestibular nuclei to contralateral thalamus
- Thalamus to various cortical regions that make up the “vestibular cortex”
* Vestibular cortex is not a single region but a number of regions - includes parietal cortex
What is the role of the vestibulo-thalamo-cortical pathway?
Conscious perception of motion, orientation, and multisensory integration
How is tilt detected?
- Initially detected by semicircular canals
2.Endolymph flow will cease when tilt is sustained - Loss of hair cell displacement in semicircular canals
What 2 structures make up the otolith organ?
Utricle and saccule
What does the otolith organ detect?
Linear acceleration and sustained tilt
Describe the structure of the otolith organ:
- Hair cells and endolymph
- Otolithic membrane: getatinous matrix embedded around hair cells
- Otoconia: Calcium carbonate crystals embedded within top layer of otolithic membrane (added gravitational mass)
What effect does shear force from gravity and/or inertial force have on stereocilia?
Causes deflection of stereocilia
What is vertigo?
Caused by diseases affecting the vestibule or its afferent nerves
* Illusion of movement, dizziness, nausea
What is motion sickness?
Caused by mismatch between visual and vestibular information
* Improved if horizon visible
What are bedspins?
Caused by alcohol which lowers density of cupula (more buoyant)
* Get sleep
