Vestibular System Flashcards
Where is the vestibular labyrinth located? And what structures does it comprise of?
It is buried deep in the temporal bone
It has 2 otolith organs:
- utricle and saccule
- semicircular canals
Describe how the movement of vestibular hair cells initiates transduction.
Movement of stereocilia towards the kinocilium in vestibular organs opens the mechanically gated transduction channels located at the tips of the stereocilia, depolarising the hair cell and causing neurotransmitter release onto vestibular nerve fibres
Movement in the opposite direction results in the hyper-polarisation of the hair cells
What is the purpose of the striola?
It divides the hair cells into 2 populations with opposing polarities
What type of movements does the utricular macula respond to?
Responds to translational movements in the horizontal plane and to side ways head tilts
What type of movements does the saccular macula respond to?
Responds to vertical translational movements and to upward or downward head tilts
What is the sensory epithelium of the utricle and saccule called?
Macula
Describe the structures which lie internally of the utricle and saccule.
They both contain a sensory epithelium = macula
- macula consists of hair cells and associated supporting cells
- above the hair cells and their bundles is a gelatinous layer
- above that is a fibrous layer = otolithic membrane
Describe how the structures of the otolithic membrane allow for the function of the saccule and utricle.
The membrane is embedded with crystals of calcium carbonate = otoconia
- otoconia makes the membrane heavier than the structures and fluids surrounding it, therefore when head tilts, gravity causes the membrane to shift relative to the macula
- resulting shear motion between membrane and macula displaces the hair cells which then generates receptor potentials in hair cells
Describe the structures which lie within the ampulla.
Ampulla is a bulbous expansion which lies at the base of the semicircular canals. It houses the sensory epithelium (crista) that contains hair cells.
Hair bundle extend out of the crista into a gelatinous mass (cupula) that forms a barrier which the endolymph cannot circulate
What type of movements do the semicircular canals respond to?
Head movements arising either from self induced head rotations or from angular accelerations imparted by external forces
Outline the series of events which would need to occur to result in a displace of the hair cells within the crista.
Movements of endolymph fluid distorts the cupula when the head turns in directional plane of one of the semicircular canals - the inertia of the fluid produces a force across the cupula, distending it away from direction of head movement and therefore causing displacement of hair cells within crista
What is meant by spontaneous nystagmus?
Where the eyes move rhythmically from side to side in the absence of any head movements
- occurs when one of the canals or nerves are damaged
Which reflex is used for assessing physiological nystagmus?
Vestibulo-ocular reflex
- tenses for function of CN 3, 6 and 8
Detail the central pathways which carry vestibular information.
Fibres travel from lateral and superior vestibular nuclei at the pons
- these ascend to the ventral posterior nuclear complex of the thalamus
- projection multiple areas in the cortex - parietal insular vestibular cortex and visual posterior sylvian area
