The vestibular system Flashcards
What is the vestibular system?
Provides information about balance and positioning
What are the major anatomical structures of the vestibular system? (2)
- Semi-circular canals
- Otolith organs
What is the function of the semi-circular canals?
3 different types detect different types of head rotation
What are the ampullas and what is their function?
- Wide openings at the ends of the semi-circular canals
- Contain the hair cells (transducers)
What are the 2 Otolith organs?
- Utricle
- Saccule
What is the function of the Otolith organs?
Detect linear motion
What kind of motion does the saccule detect?
Linear motion in the vertical plane (up and down)
What kind of motion does the utricle detect?
Linear motion in the horizontal plane (backwards and forwards)
How many semi-circular canals are there?
3
How many Otolith organs are there?
2
Which fluid is inside the semi-circular canals?
Endolymph
What is the composition of endolymph?
High K+ content
Which fluid is inside the Otolith organs?
Endolymph
Which neurotransmitter is used in the vestibular system?
Glutamate
How does the function of hair cells in the vestibular system differ from the auditory system?
Exactly the same function but vestibular hair cells respond to lower frequencies
What range of frequency can the vestibular hair cells respond to?
0 - 20 Hz
How does the structure of hair cells in the vestibular system differ from the auditory system?
- More rows of stereocilia in the hair bundle in the vestibular system
- Vestibular hair cells keep their kinocilium throughout their life but auditory hair cells don’t
What is the kinocilium?
A special cilium which determines the polarity of the hair bundle
What are the 2 types of vestibular hair cells?
- Type 1
- Type 2
What is the difference between type 1 and type 2 vestibular hair cells?
- Type 2 has a normal synapse to afferent neuron
- Type 1 has expanded calyx afferent neuron
What are macula?
Sensory patches containing hair cells inside the Otolith organs
What lies on top of the hair cells in the Otolith organs?
Gelatinous otolithic membrane
What are the otoconia?
Calcium carbonate crystals on top of the gelatinous otolithic membrane in the Otolith organs
What is the striola?
- A line separating the hair cells in half in the Otolith organs
- The hair cells are positioned in opposite directions on either side so when one side is activated, the other is inhibited
How is motion detected in the Otolith organs?
- Otoconia pull on the otolithic membrane due to gravity when there is movement
- Hair bundles are in contact with the otolithic membrane which pulls the stereocilia towards the tallest/shortest one, causing depolarisation/hyperpolarisation
- Half the hair cells are depolarised, half are hyperpolarised
Which fluid is inside the ampulla?
Endolymph
What is the cupula?
Gelatinous membrane in the ampulla into which hair cells project their hair bundles into
How is motion detected in the ampulla?
- The higher inertia of the endolymph than the solid structures pushes the cupula during rotation
- This pushes the cupula and the hair bundles in the opposite direction to motion
How are the hair cells orientated in the ampulla?
In both ears, the hair cells are orientated with the tallest stereocilia towards the front (the face)
How do the semi-circular canals work in pairs?
- The hair bundles are orientated in the same way which means that during motion, the hair cells in one ear are activated while the other ear is inhibited
- The endolymph is moving in the same direction in both ears
Which part of the brain is highly involved in motor coordination?
Cerebellum
What is the vestibulo-ocular reflex?
Communication from the vestibular system to the visual system to keep the eyes stabilised during head movement
What is vestibular nystagmus?
- Mechanism which enables the resetting of eye position during prolonged head rotation
What are the phases of vestibular nystagmus?
- Slow phase where eyes rotate in the opposite direction to head movement
- Quick phase where eyes are rapidly reset to the centre of the gaze
