Vestibular System Flashcards
What is the vestibular system responsible for
Maintaining balance, posture and spatial awareness
What are the 3 receptor systems involved in vestibular system
The eyes
General proprioceptive
Vestibular receptors in the inner ear
What 2 apparatus are in the ear
Vestibular apparatus
Cochlear apparatus
In what structure are the cells and the mechanics of the vestibular system contained
The labyrinth
What is found inside the labyrinth
Fluid
Is the fluid in auditory or vestibular part
Both
What is the inner fluid called
Endolymph
What is the outer fluid called
Perilymph
What are the electrolyte levels in perilymph
High sodium
Low potassium
What are the electrolyte levels in endolymph
High potassium
Low sodium
What is the advantage of there being different electrolyte levels in the 2 fluids
Provides an ionic gradient (endocochlear potential)
When the head is in neutral position, how are the circular ducts positioned
Vertical to eachother
Anterior ventral
Posterior ventral
Lateral horizontal
What happens if you turn your head
The fluid moves in the same direction as you turn your head
What is found next to semicircular duct
Utriculus and Sacculus
What cells are found in utriculus and sacculus
Vesicle protrusions
Where are the vestibular signalling cells sitting
Vesicle protrustion
Which cells are activated by the slushing on fluid, and what information can be gathered from this
Vestibular signalling cells
The semilunar ducts being activated and whether utriculus and sacculus
What kind of cilia are found in vestibular signalling cells
Sterocillia
Short
What happens when endolymph bends the stereocilia
Bends towards the kinocilium is depolarisation
Causes release of glutamate
What happens when glutamate is released
Vestibular system nerve fibres are activated
What happens when cells are hyperpolarised
Hyperpolarisation
Glutamate release ceases
What kind of cells modulate neurotransmitter release
Cholinergic cells
What are the hair cells embedded in and why
Gelatatinous fluid called pupillae
Allows for proper bending
What accompanies activation of one semi-circular duct
Deactivation of the other one
What kind of encoding does utricular provide
Horizontal (lying down vs standing up)
What kind of encoding does saccular provide
Vertical
What is nystagmus
Involuntary movement of the eye
Form of vestibulo-ocular reflex
Combination of initial slow rotation followed by fast flick back
2 types of nystagmus
Horizontal and vertical
How are the nerves involved in eye movement connected
Medial longitudinal fasciculus
What sensory organs respond to angular acceleration
Semicircular ducts
How is head movement (angular acceleration) detected
Turning the head excites receptors in one ampulla and inhibits receptors on the other side
How to kinocilium in the otoliths differ from in the semicircular ducts
They are not orientated in a consistent direct
How do kinocilium point in the saccule
Away from striola in the middle
How do kinocilium point in the utricle
Towards the striola in the middle
Where do the otoliths lie
Against the wall of the inner eye between the semicircular ducts and the cochlear
What is the function of the vestibulo-occular reflex
Controls eye mvoement to stabilise images during head movements
How many neurones are involved in the arc of the vestibulo-ocular reflex
Oculomotor nuclei
Vestibular nuclei
Vestibular ganglion
Which cranial nerve is responsible for rotating the eye laterally
Abducens
What cranial nerve is responsible for rotating the eye medially
Occulomotor
What happens when head turns to the left
- Eyes turn to the right by contraction of right lateral rectus and left medial rectus
- Flow towards utricle causes depolarisation
- Abducens excites contralalteral occulomotor nucleus
Why does spontaneous (pathological) nystagmus occur
Damage to vestibular apparatus/ brainstem/ cerebellum
What structures detect linear acceleration
The otoliths
What is a normal nystagmus
Optikokinetic and rotational nystagmus
What 4 major nuclei are involved in the central pathway
Superior nucleus
Medial nucleus
Lateral nucleus
Inferior nucleus
What part of the cerebellum is connected to vestibulo system
Flocculoodular node
What is the oldest part of the cerebellum
Flocculoodular node
What does lateral vestibulospinal tract control and where does it start
Control limbs
Lateral vestibular nucleus
Where does lateral vestibular nucleus receive information from
Utriculus
What information travels through medial vestibulospinal tract
Information to the eye muscles
Name some symptoms of vestibular system pathologies
- Nystagmus
- Nausea
- Dizziness
- Disequilibrium
- Vertigo
What does the macula innervate and what tract does this give rise to
Inferior and lateral nuclei giving rise to ateral vestibulo spinal tract
What does medial vestibular nucleus allow
Ability to rotate body without confusing the head
What is Kinetosis
Motion sickness
Causes of vestibular problems
Nerve/ inner eye infections Tumours Vascular insufficiency Trauma Endolymph imbalance
Name 3 major peripheral vestibular pathologies
Kinetosis
Menieres diseases
Benign paroxysmal positional vertigo
Name the test for BPPV
Hallpike manoeuvre
Describe the hallpike manoeuvre
`-Lower head to table and turn to one side, watching eyes for nystagmus
- If patient gets dizzy and exhibits nystagmus, ear pointed to floor is affected ear
- If nothing happens repeat test on other side
What is thought to cause BPPV
Due to damaged otoconia from utricle being displaced into semilunar canal
