L25 The Vestibular System Flashcards
(25 cards)
What abilities does the vestibular system provide for us?
- They keep our eyes still when we move.
- They maintain our upright posture
- Our ability to perceive our own movement within space.
What is the vestibular system?
The vestibular system is a complex sensory system located in the inner ear that plays a crucial role in balance, spatial orientation, and the coordination of movement.
What sections are within the vestibular system?
- Otolith organs
- Semicircular canals
- Ampulla
- Vestibular nerves.
What does the Otolith organs do? And what are the two types?
They detect linear motions (acceleration) and head tilt
Utricle - horizontal
Saccule - vertical
What does the semicircular canals do?
They detect head rotations
Where does the hair cells in the vestibular system sit?
In the ampulla
What are the 2 types of liquids within the vestibular labyrinth?
Endolymph
Perilymph
What do vestibular hair cells have?
They have:
1. A hair bundle with stereocilia and tip links
2. A kinocilium throughout life.
What is the difference in terms of structure between Vestibular and Cochlear inner hair cells?
The vestibular hair cells have a kinocilium whereas the cochlear do not have kinocilium.
What frequencies does vestibular hair cells detect?
Vestibular hair cells respond to lower frequencies (0 to ~ 20Hz), less than hair cells of the auditory system
How is Type I different to Type II vestibular hair cell?
Type I has a calyx (a massive dendritic terminal which envelops around the whole of the hair cell - reliable transmission)
Type II has a normal afferent dendrite
Where is the cupula located?
In the semicircular canals.
How does the semicircular canals detect angular acceleration (rotation)?
- Semicircular canal is filled with endolymph (fluid)
- When head rotates, the inertia of the endolymph tends to lag behind the movement of the canal walls
- The relative motion between the endolymph and the canal wall creates a pressure difference across cupula
- Lagging endolymph pushes against cupula, causing it to deflect (bend) in the direction opposite to the head’s rotation
Which system is quicker in signalling - vestibular sytem or visual sytem?
Vestibular system is faster than the visual system
Which part of the inner ear does the vestibular system come after?
It comes after the cochlea
Give us an example of a vestibular reflex pathway
The vestibular-ocular reflex (VOR) that controls eye muscles to keep visual objects in focus whilst the head is moving. It does so by moving the eyes in the opposite direction as the head
When the stereocilia bends towards the kinocilium, is it excitatory or inhibitory?
Excitatory
When the stereocilia bends towards the kinocilium, how is it an excitatory process?
1) The bending actions puts tension on the tip links which mechanically pulls open the ion channels located at the tips of the stereocilia
2) Open channels allow K+ to rush the hair cell from endolymph
3) Influx of K+ makes the inside of hair cell more positive (depolarisation)
4) This depolarisation triggers the influx of Ca2+ then causes release of neurotransmitters from hair cell to afferent nerve fiber
5) This leads to an increase in the firing rate of action potentials that are sent to the brain
What is Otoconia?
Cilia of these cells are embedded in a gel-like layer sprinkled with calcium carbonate crystals called otoconia, commonly known as “ear rocks”. The crystals add weight to the layer, pulling it down with gravity.
What happens to the utricle when the head is in an upright position?
When the head is in upright position, the gelatinous layer bears down evenly on the cells of the utricle, the cilia remain straight and no signals are generated.
What happens to the saccule when the head is in an upright position?
On the vertical, saccule, heavy gel is pulled down by gravity at one end, bending the cilia, generating nerve impulses.
What is the utricle and saccule responsible for?
Together they are responsible for our sense of balance.
Utricle - Horizontal linear acceleration and horizontal head tilts
Saccule: Vertical linear acceleration and vertical head tilts
What is the vestibular nystagmus?
Vestibular nystagmus enables the resetting of eye position during sustained head rotation
What is the slow and quick phase of the vestibular nystagmus?
- Slow phase: Eyes rotate in the opposite direction to head movement
- Quick phase: Rapid resetting movement back to the centre of the gaze to regain focus
