Lecture 23 Flashcards
What is the role of the vestibular system?
it provides the brain with information about head movement and location`
What does the vestibular system detect? (what is it stimulated by)
Angular and linear accelerations of the head
What is acceleration?
Rate of change of velocity
What is linear acceleration of the head?
Head movements with respect to gravity, body is moving backwards and forwards
What is angular acceleration of the head?
Movements of the head (e.g. nodding, stretching)
What does the vestibular system do in response to the stimuli?
- generates reflexes to compensate for head movement and the perception of movement in space
- provides information to help with maintain of right posture
- provides information for conscious awareness of position/movement/acceleration of the head and body
What are the two parts of the vestibular system?
- semi-circular canals
2. otolith organs
Where is the vestibular system located?
in the inner ear.
What are the semi-circular canals?
They are canals sensitive to angular acceleration during head rotation. they work in pairs, one set in each ear. the canals are aligned in three axes, each canal is most vigorously stimulated by acceleration in its performed plane.
what are the semi-circular canal filled with?
endolymph
What plane is the horizontal canal stimulated by?
Transverse plane (crossing a road)
What plane is the anterior canal stimulated by?
sagittal (nodding)
What plane is the posterior canal stimulated by?
coronal (head tilting)
What is the ampulla?
a structure at the bottom of the semi-circular canal where there are hair cells.
What is the structure of the ampulla?
There are hair cells, which from project cilia out to the duct of the semi-circular canal (lumen). The cilia sit in a structure called the cupula.
What is the effect of the ampulla’s structure on fluid movement?
fluid cannot move very freely
how does inertia occur in the cupula?
When the head moves, the fluid stays for a second longer before catching up with the movement. this causes inertia, which results in the cilia bending.
What does resting discharge rate mean?
It means that vestibular hair cells can detect movement in two directions
How does transduction occur in the vestibular system?
When head movement cause the bending of the longest hairs in the cupula, mechanically gated ion channels on the cilia open. this results in an influx of potassium, depolarising the cell. this leads to opening of voltage gated calcium channels, so there is an influx of calcium. there is release of neurotransmitter, and an increased firing rate.
if the hairs bend towards the short stereo cilia, the mechanically gated ion channels close.
What are the Otolith organs?
they are the utricle and the saccule, and they detect linear acceleration.
How is the Utricle structured?
It is approximately horizontal when standing (hair cells within it are oriented vertically)
How id the Saccule structured?
it is approximately vertical when standing (hair cells within it are oriented horizontally)
What is the anatomy of the otolith organs?
They have hair cells which sit inside a structure called the macula.
the otoconia is small stores of CaCo3, and it acts as wights on the otolith organs to prevent them from shifting too quickly.
Where are EPSPs transmitted from the otolith organs?
to the vestibular nuclei in the brainstem
What is the information from the vestibular system used for?
- stabilise eyes
- stabilise the head
- maintain balance
What is Vertigo?
Is it motion sickness (illusion of movement and dizziness) cause by disease affecting the vestibule or its afferent fibers
what is motion sickness?
it is caused by mismatch between visual and vestibular information
what can help motion sickness?
sea leg tablets - Meclozine Hydrochloride
What are bedspins?
It is motion sickness caused by alcohol. Ethanol infiltrates cupula, lower density and causes it to ‘float’, bending hairs on hair cells and creating perception of movement
What are ototoxic drugs?
they are medications which are harmful to hair cells (over 600). can result in temporary to permanent loss of hearing and balance.
