Part 2 Flashcards
who is the judge
the vestibular system
can the vestibular system be consciously controlled
no
responsibilities of the vestibular system
assess movement of the head relative to gravity and the horizon to maintain posture control
stability of images on fovea during head motion
resolves inter-sensory conflicts
components of vestibular system
sensorial organs
vestibular nuclei
cerebellum (supervisor)
projections to brainstem, inner ear and cortex
what are the sensorial organs
utricle, saccule, Semi-circular canals
what motions of head can vestibular system encode
acceleration, decelerations and tilt
why are inner ears the judge
because they are internally referenced and don’t rely on the environment to determine since they are incased by bone and only are influenced by gravity
when do the otic placodes develop from germinate epithelium
22 days of embryonic life
explain anteroventral part of otocyst development
first utricle maculae (week 5E) then Saccule maculae (late week 5E) then cochlear fields are segregated (week 6E)
what are maculae used for?
they are used to encode information
what part is developed first vestibular or hearing
vestibular
how many sensors are on each ear and explain
- Each ear has 1 ampullae for each of the 3 SCC, 1 utricle and 1 saccule
how do vestibular hair cells work
they convert mechanical displacement into electrical signals which are transmitted by vestibular afferent nerves
50-100 stereocilia and a kinocilium extend into either the otolithic membrane or the cupula
- mechanic deflection opens channels at tip of sterocilia creating depolarizing potential
what are kinocilium
tallest filament in bunch
- disappear in hair cells after birth but vestibular hair cells keep them
vestibular hair cells are activated
when tip links bend towards kinocilium
vestibular hair cells are inhibited when
tip links bend away from kinocilium
Type 1 afferent nerve ending
flask shaped (chalice shaped)
1-4 hair cells per nerve ending
irregular afferents: rapid detection of head motion, Vestibular ocular reflex initiation and angular vestibular ocular reflex
Type 2 afferent nerve ending
Cylindrical (Button shaped)
- multiple hair cells per nerve ending
regular afferents senstive to a broad spectrum range of motion
what is the resting firing rate of type I and II afferent nerve endings
70-100 spokes/ second
what is the excitation rate of type I and II afferent nerve endings
400 spikes/sec
what is the inhibition rate of type I and II afferent nerve endings
0
anatomical components of semi-circular canals
filled with endolymph
each has own ampulla (sensor/detector of motion)
ampulla contains crista ampullaris
cupula itself is the gelatinous component of crista ampullaris
- ampulla connects utricle with SCC
what are the angular acceleration pairs
superior/anterior
posterior/inferior
lateral/horizontal
superior/anterior
look towards front 45 degrees and highest
posterior/inferiror
look towards back 45 degrees and lowest (gravity wise)
lateral/horizontal
almost horizontal 30 degrees
what are the vertical canals
posterior/ inferior and superior/anterior
- they are perpendicular to each other
what canal encodes axial rotation
lateral
what canal encodes flexsion/extension
anterior duct
what canal encodes lateral bending
posterior duct
what direction does fluid move compared to motion
opposite direction of motion due to inertia
when are hair cells activated
when endolymph fluid is in motion
location of ampula for anterior scc
at front
location of ampula for posterior scc
back
what is crus communae
where the anterior SCC canal back and front of posterior SCC are fused together
- open together towards inner ear close to utricle
why are static postion changes not encoded by cupula
bc cupula spefic gravity is = to endolymph and only acceleration or deceleration is coded
- in gravitational fields not responsive to static postion changes of the head
location of ampula for horizontal SCC
is at front and opens independently at inner ear
- no crus communae
when is motion of liquid (gel) and activation of HC maximal
when SCC rotate around perpendicular axis
when is motion of liquid (gel) and activation of HC minimal
when SCC rotate around longitudinal axis
how do we get the perception of head rotation
from integrating info from all 6 SCC and nerve centers analyzing activations and inhibitions, encoding head motion in 3 planes of space
Edwald’s second law
In Horizontal SCC: displacement towards the ampulla= greater VOR response than by acceleration which causes displacement away from ampulla
ampullopetal
towards ampulla
ampullofugal
away from ampulla
Edwalds third law
Vertical SCC: displacement away from ampulla= Greater VOR responses produced than by acceleration which causes displacement towards the ampulla
