vestibular system Flashcards
what type of cells are found in the
vestibular apparatus of the inner
ear
hair cells
what is the vestibular apparatus
a connected series of
ENDOLYMPH-FILLED,
membranous tubes that also
connect with the cochlear duct
what do hair cells in the vestibular apparatus do
detect changes in the motion and position of the head by a stereocilia transaction mechanism
what does the vestibular apparatus consist of
- 3 membranous SEMICIRCULAR
CANALS - 2 saclike swellings
- the UTRICLE
- the SACCULE
all of which lie in the temporal bone on either side of the head
what do semicircular canals do
Detect angular acceleration during the ROTATION of the head along three
perpendicular axes
what activates semi circular canals (3)
- nodding the head up and down
- shaking the head from side to side
- tipping the head so that the ear
touches the shoulder
what do receptor cells of semicircular canals contain
stereocilia
what are semi circualr canals stereocilia encapsulated in
within a gelatinous mass - the CAPULA
it extends across the lumen
of each semicircular canal at the
ampulla (a slight bulge in the
wall of each duct)
what happens whenever the head moves
the semicircular canal within its bony
enclosure and the attached bodies of the hair cells all move with it
BUT the fluid (endolymph) filling the duct is not attached to the skull,
so due to inertia it doesn’t movie
so the moving ampulla is pushed against the stationary fluid which in
turn causes bending of the stereocilia and the alteration in the rate of
release of glutamate from the hair cells
what does glutamate do
crosses the synapse and activates neurones associated with the hair cells, initiating the propagation of action potential towards the brain
what do the speed & magnitude of rotational head movements determine
the direction in which the stereocilia are bent and which hair cells are stimulated
what do the hair cells release at rest
glutamate
the release increases or decrease from the resting rate according to the direction in which the hairs are bent
what causes depolarisation and hyperpolarisation of each hair cell receptor
each hair cell receptor has one direction of maximum neurotransmitter release so when its stereocilia are bent in this direction, the
receptor cell depolarises.
When the stereocilia are bent in the opposite direction the cell hyperpolarises
what happens when the head continuously rotates at a steady velocity
the duct fluid begins to move at the same rate as the rest of the head and the stereocilia slowly return to resting position - thus hair cells are only stimulated during acceleration or deceleration
what causes nystagmus
- damage to the canals of one side
- with the slow phase towards the
damaged side and the rapid reset away from the damaged side - Pouring ice cold water into the external auditory meatus can cause
convection currents in the semicircular calls
what do the Utricle & Saccule (Otolithic organs) do
provide information about linear acceleration of the head, and about the
changes in head position in relation to gravity
when do hair cells in the utricle respod
they point nearly straight up when standing and they respond when the the head is tipped away from the horizontal plane or to linear accelerations in the horizontal plane
when do hair cells in the saccule respond
they project at right angles to those of the utricle and they responded when you move from lying to a standing position or to vertical accelerations like those produced when jumping on a trampoline
what are the stereocilia projecting from the hair cells covered by
a gelatinous substance in which tiny stones known as otoliths are embedded
what do the stereocilia of hair cells project into
into the otolithic membrane
what makes the gelatinous substance heavier than the surrounding endolymph
The otoliths with are calcium carbonate crystals
what does the gelatinous otolithic material do in response to a change in position
it moves according to the forces of gravity and pulls against the hair cells so that the stereocilia on the hair cells bend and the receptor cells are stimulated and the action potential is propagated via the VESTIBULAR NERVE
(branch of the vestibulocochlear nerve (CNVIII))
3 uses of vestibular information
- Control of eye muscles so that in spite of changes to head position, the
eyes can remain fixed on the same point. Nystagmus is a large,jerky,
back-and-fourth movement of the eyes that can occur in response to
unusual vestibular input in healthy people, but can also be used as a sign of pathology - Reflex mechanisms of maintaining upright posture & balance. The
vestibular apparatus plays a role in the support of the head during
movement and orientation of the head in space - Conscious awareness of the position & acceleration of the body,
perception of the space surrounding the body and memory of spatial
information - i.e PROPRIOCEPTION
where do the central processes of vestibular fibres mostly end
in the vestibular nuclei of
the rostral medulla
