Vestibular system Flashcards
what did the organs of balance originate from ?
lateral line organs
small pits along the animals side which contain hairlike sensory cells
the cilia project into a gelatinous substance and detect vibrations
what is the function of the vestibular system ?
monitors position, movements of the head, helps give us the sense of balance and helps us coordinate movements of the head and eyes
what are the 2 main structures of the vestibular labyrinth ?
otolith organs and semicircular canals
what do the otolith organs detect?
detect force of gravity and tilts of the head
what do the semicircular canals?
sensitive to head rotations
what makes up the otolith organs ?
saccule and utricle
what makes up the semicircular canals?
3 arcing structures lying in orthogonal planes
what is the macula ?
it is the sensory epithelium within the otolith organs
it is vertically orientated in the saccule
it is horizontally orientated in the utricle
they contain hair cells lying along a bed of supporting cells and projecting into a gelatinous cap
on top of the gelatinous cap are otoliths which are tiny crystals of calcium carbonate which are very sensitive to tilting of the head
what the process that occurs when the head angle changes or accelerates?
forces is exerted on the otoliths
force exerted in the same direction on the gelatinous cap causing it to move slightly
this causes the cilia to bend
bend towards the kinocillium it causes depolarisation but when they bend away from the kinocillium it causes hyperpolarisation
what happens to the otolith organs on each side of the head?
they are mirror images of each other so head movement excites hair cells on one side and inhibits hair cells in corresponding location on the other side
what acceleration is detected by the otolith organs and the semicircular canals?
otolith organs- angular acceleration
semicircular canals- linear acceleration
where are the hair cells in the semicircular canals ?
clustered in sheets of cells called crista
crista is in a bulge of the canal called the ampulla
hair cells project into the gelatinous cupula
kinocillium ampulla are all orientated in the same direction
when do the cilia bend in the semicircular canals?
when the semicircular canal is rotated
the movement of the endolymph exerts forces onto the cupula which causes the cilia to bend causing either excitation or inhibition
what is the acitvity like in the vestibular axons at rest ?
fire a lot at rest so activity of the semicircular canals increases/decreases the activity of the axons
what is the central vestibular pathway ?
otolith organs of the vestibular labyrinth projects to the lateral vestibular nucleus and this projects to the cerebellum and spinal motor neurons which control the leg muscles-this projection occurs in the vestibulospinal tract
semicircular canals of the vestibular labyrinth project to the medial vestibular nucleus and this projects to the VP nucleus of the thalamus and then onto the cortex, it also projects to the extraocular motor neurons and motor neurons of the trunk and neck muscles to orientate the head (in medial longitudinal fasiculus)
