Vestibular System Flashcards
Vestibular system function
Maintaining balance, posture and special orientation
Vestibular system 3 receptors
Eyes
General proprioceptive and cutaneous receptors
Vestibular receptors in ear
Spinothalamic
Crude touch
Pain
Temperature
Dorsal columns
Vibration
Proprioception
Discriminative touch
Membranous labyrinth
Inner ear Vestibular part (semi-circular canal) Auditory part (cochlea)
Endolymph
Fills membranous labyrinth
High potassium
Low sodium
–> Endocochlear potential, +ve voltage within ML
Perilymph
Within bony labyrinth surrounding membranous labyrinth
High sodium, low potassium
Semi-circular canals
Anterior Canal- Vertical
Lateral Canal- Horizontal
Posterior Canal- Vertical
Canals are at right angles of each other
Endolymph movement
When we move head, endolymph shifts within the canals
–> allows us to know which plane our head is rotating along
Speed/volume of endolymph gives us information of strength of rotation
Where do semi-circular ducts end
In Ampulla
Otolithic Organs
Utriculus
Sacculus
Hair cells within vestibular apparatus
Long kinocilium on top
–> when hair bends, either depolarises or hyperpolarises depending on direction
Depolarization- release neurotransmitter (glutamate) –> excites
Hyperpolarization- stops neurotransmitter release
Kinocilium MOA
Contain potassium channels that open in response to movement
Ampulla of semi-circular ducts
AKA Crista ampularis
Embedded in gelatinous gel
Senses angular acceleration and deacceleration
Utricular + Saccular maculae
Membranous sacs
Contain Otoliths- crystals that compress cilia continuously + responsive to gravitational forces
Striola
Curved ridge that runs through the middle of the macula
Orientate stereocilia
Utricles
Hair cells polarised (excited) towards striola
Striola divides macula into medial and lateral halves
Saccules
Hair cells polarised away from the striola
Striola divides each macula into anterior/posterior halves
Semi-circular hair cells
Kinetic sensitivity
Sensitive to head rotation
Angular acceleration
Complementary bilateral signalling
Otolithic Organ hair cells
Utriculus- horizontal Sacculus- vertical Gravity Tilt of head Linear acceleration
Vestibulo-Ocular reflex
Vestibular-nerve afferents –> central vestibular neurones –> extraocular motor neurones –> eye muscles
Move head to the right
Endolymph causes hyperpolarisation on left, which inhibits left medial rectus + right lateral rectus
Causes depolarisation on right, stimulating right medial rectus and left lateral rectus
–> eyes move left, staying on object they were fixed on
Nystagmus
Form of vestibulo-ocular reflex
Rapid and accurate eye movements
Initial slow rotation followed by fast flick back
Opokinetic (fixation) and rotational nystagmus
Normal
Spontaneous nystagmus
Abnormal
Damage to vestibular apparatus, brainstem or cerebellum
Superior vestibular and medial vestibular nucleus
Afferents from ampulla of semi-circular canals
Lateral vestibular and inferior vestibular nucleus
Afferents from ampulla of semi-circular canals
Ascending vestibular pathway
Ascending axons of neurones in SVN enter MLF rostral to abducens nucleus
Superior + Medial Vestibular Nuclei travel to..
Oculomotor and trochlear nucleus along the reticular formation
Lateral vestibulospinal tract
Antigravity muscles
Medial vestibulospinal tracts
Head/neck muscles
Sens of equilibrium
Depends on signal coming from vestibular apparatus
Kinetosis
Motion sickness
Meniere’s disease
Disease of inner ear
Episodes of vertigo
Otoliths go into semi-circular canals where they are not supposed to be
Benign paroxysmal positional vertigo
brief episodes of mild to intense vertigo
Balance disorders clinical exam
Eye movements
caloric testing
Hallpike manoeuvre- lower head to table + turn to one side, watch for nystagmus + dizziness–> if anything, ear pointing to floor is affected
