Vestibular System Flashcards
what does the vestibular apparatus consist of?
3 semi-circular canals
the utricle
the saccule
which of the ampulla, utricle and saccule contains sensory hair cells?
all of them
what are the otolith organs?
the utricle and saccule
what are the functions of the otolith organs?
> detect linear acceleration
> encode information about the position of the head in space
what does the utricle detect?
back and front tilt
what does the saccule detect?
vertical movement
what do the semicircular canals detect?
rotational acceleration
where are the sensory cells of the semi-circular canals located?
in the swellings at the base of the semi circular canals: ampulla
what is in the ampulla?
sensory receptors called cristae that consist of flexible gelatinous structures called cupula that stretch across the entire width of the ampulla
what do the cristae respond to?
movement of the endolymph fluid within the canals
what are imbedded in the cupula?
cilia of hair cells
what does the hair cell cilia in the cupula synapse with?
directly to the sensory neurons of the vestibular nerve CNVIII
name the two types of hair cells
> Kinocilium
> stereocilia
describe the kinocilium
single and very large
describe the stereocilia
smaller and multiple
distortion of cilia away from the kinocilium leads to…..
hyperpolarisation and decreased discharge of action potentials in the vestibular nerve
distortion of cilia towards the kinocilium causes….
depolarisation and increased discharge of action potentials in the vestibular nerve
what are maculae?
the sensory apparatus of the utricle and saccule
are the macula in the utricle in the horizontal and vertical plane?
the horizontal
are the macula in the saccule in the horizontal and vertical plane?
the vertical
what do the maculae cilia protrude into?
a gelatinous mass, the otolith membrane
what are otoliths?
CaCO3 crystals embedded in the otolith membrane
what has a greater density, otoliths of endolymph?
otoliths
what do the vestibular nuclei project via?
the thalamus to the cerebral cortex
what do tonic labyrinthine reflexes do?
they keep the axis of the head in a constant relationship with the rest of the body using information from the maculae and neck proprioceptors
what are dynamic righting reflexes?
rapid postural adjustments made to stop you from falling when you trip, these are long reflexes involving extension of all limbs.
why do the semi circular canals have a strong influence on eye movement?
because the afferents from the semi-circular canals project and connect, within the vestibular nuclei) to afferent fibres travelling to the extra ocular nuclei.
describe the static reflex
when you tilt your head the eyes intort/extort to compensate over a certain range, keeping the image the right way up
what is dynamic vestibular nystagmus?
a series of saccadic eye movements that rotate the eye against the direction of rotation so the original direction of gaze is preserved. when the eyeball comes to the end of its range of movement it rapidly flicks back to the zero position.
in post rotatory nystagmus, at the end of left rotation during deceleration what nystagmus will you get?
right nystagmus due to endolymph catching up and pushing the cupula in the opposite direction
in caloric stimulation does the warm or the cold fluid cause nystagmus towards the affected side?
warm
what can powerful maintained stimulation of the vestibular system give rise to?
kinetosis: motion sickness
what is vertigo?
perception of movement in the absence of movement
what is menieres disease?
> vertigo, nausea, nystagmus and tinnitus
> overproduction of endolymph causing increased pressure
what is used to compensate in chronic vestibular impairment?
visual system
what can lead to nystagmus at rest?
brain lesions
