Midterm Vestibular System Flashcards
What happens to vestibular info
output of vestib system goes to cerebal cortex (interpretation of what has been done) ocular motor muscles (vestibulo-ocular reflex) spinal cord (connects info from inner ears to spine, vestibulo-spinal reflex cerebellus (main function- distance, direction, force, etc. controlled here)
Why do we need the vestibular system
- maintain posture
- maintain equilibrium & ocular stability during movement
- maintain muscle tone
What do cranial nerves do
give sensory or motor info to head
What do spinal nerves do
give info to everything below head
Moro reflex
protect oneself when falling (arms go out, eyes open, neck tenses) for vertical drop or fall
How is our equilibrium & posture maintained
- multiple sensory inputs (visual, vestibular, somatosensory (touch/pressure), propriceptive (knowledge of self), central integration, auditory, etc.)
- adaptive control (what needs to be done to correct equilibrium)
Why do Au.Ds do audio & vestib evals
- scope of practice
- proximity of vestib system to cochlea
- hair cells (same cells as in cochlea) both are affected by the same things
- history (audiologist have since beginning)
People who made contributions to our knowledge of vestib system (8)
- Erasmus Darwin
- Jan Evangelista Purkyne
- Marie Jean Piere Flourens
- Prosper Meniere
- Ernst Mach
- Robert Barany
- Joseph Breuer
- Alexander Crum-Brown
What is Jan Evangelista Purkyne best know for
his discovery of Purkinje cells & Purkinje fibers, first to use microtome & discovered sweat glands
What similar conclusion did Ernst Mach, Joseph Breuer, and Alexander Crum-Brown come to
attributed the sensation of angular movement to the semicircular canals & linear movement to the otoliths
what is the vestib system responsible for
detection of acceleration, not velocity, of head/body & maintenance of gaze
development of vestib system
19-21 days: oticplacode 21-23 days: otocyst 5 weeks: folding of otocyst 6.5 weeks: formation of super-structures 8 weeks: morphologic changes 7-15 weeks: formation of micro-structures
4 regions of temporal bone
Squamous (forms middle cranial fossa)
Tympanic (forms anterior, inferior & part of posterior EAC)
Mastoid (forms majority of posterior portion of EAC)
Petrous (encases the inner ear)
hardest part of temporal bone
petrous
orientation of posterior canal
45 degrees off sagital plane
orientation of horizontal canal
30 degrees from horizontal plane
orientation of anterior canal
45 degrees from coronal plane
where is bony labyrinth located
in petrous portion of temporal bone
2 portions of bony labyrinth
vestibule & canals
vestibular hair cells
have kinocilium where the basal body is in the auditory system
-1 per cell
what does kinocilium do
increases sensitivity to stimulation
Type 1 hair cells
globular shape
surrounded by nerve endings
synapse with calyceal dendritic endings
Type 2 hair cells
column shape
innervated by Bouton dendrite nerve endings
Cylindrical in shape
Ampullae
contains Crista
Crista
sensory organ of semicircular canals
Components of Crista
hair cells
supporting cells
cupula
cupula
attaches at top & bottom of ampulla
2300 cells between all 3 cristae
type 1 hair cells predominate the crista
function of semicircular canals
movement of head causes relative movement of fluid
types of cupular movement
utriculopetal (Ampullopetal)
utriculofugal (ampullofugal)
Utriculopetal (ampullopetal)
toward utrical (toward ampulla)
utriculofugal (ampullofugal)
away from utrical (away from ampulla)
orientation of steriocilla in horizontal SCC
toward utricle (utriculopetal)
orientation of steriocilia in posterior and anterior SCC
away from utricle (utriculofugal)
Hair cell stimulation
Depolarization- Steriocilia deflect toward the kinocilium
Hyperpolarization- steriocilla deflect away from kinocilium
100 spikes per second when nothing is happening, after depolarizing the fire rate increase, when hyperpolarized the firing rate decreases
Ewald’s Laws of canal function
- the eye and head movement always occur in the plane of canal being stimulated
- ampullopetal flow of HSCC induces greater movement than ampullofugal
- ampullofugal flow of ASCC and PSCC induces greater movement than ampullopetal
Cupular biophysics
“pendulum model” cupula is attached at top, not free moving
what do otoliths do
detect linear acceleration
orientation of otoliths
30 degrees off the horizontal plane
what is the maculae
sensory organs of otoliths
components of the maculae
hair cells
supporting cells
otoconial membrane
otoconia
location and orientation of Utricle
located at lower boarder of HSCC
roughly parallel to HSCC
otoconia
calcium carbonate
originate early in vestibular development from dark cells of vestibule
crystals that sit on top of the otoliths
more dense than endolymph, so gravity can pull on them making them a gravitational sensor
Otolithic arrangement
utricle and saccule between 68 and 84 degrees apart
striola- region with no hair cells underneath, otoconial concentration more dense
hair cell arrangement: Uticle- arranged with kinocilia toward the striola, Saccule- arranged with kinocilia away from striola
blood supply of cochleo-vestibular complex
vestibular artery
labyrinthine artery
anterior inferior cerebellar artery
how does blood supply leave the cochleo-vestibular complex
anterior vestibular vein
posterior vestibular vein
a few others
labyrinthine fluids
Perilymph
Endolymph
Cerebrospinal Fluid
vestibular fluids
Perilymph (a filtrate of cerebrospinal fluid, blood) endolymph (a secretion of stria vascularis, vestibular dark cells) endolymph resorption (occurs in endolyphatic sac)
theories of endolymph resorption
longitudinal- created above and pushed through
radial- circulation
dynamic- mixture
firing rates in the cristae ampullaris
neurons have spontaneous firing rate of 70-90 s/s
when depolarized, they increase up to 400 s/s
when hyperpolarized, they decrease to near 0 s/s
firing rates in the maculae
neurons have spontaneous firing rate of approx 65 s/s
types of primary afferents
irregular
regular
irregular and regular primary afferents in the cristae ampullaris
irregular- most sensitive to motion, responds to HF accelerations
regular- less sensitive to motion, more responsive to lower accelerations
irregular and regular neurons in the maculae
irregular- adapt rapidly, wide response range, sensitive to small changes in accelerations
regular- maintain consistent firing rate during tilt, sensitive up to 1kHz, act as a low pass filter
synaptic connections of primary afferent neurons in cristae
connections made via calyceal, bouton, or combo
can have up to 3 calyceal endings per neuron
calyceal found near center of crista (type 1)
boutons found near periphery (type 2)
synaptic connections of primary afferent neurons in maculae
calyceal found near center of striola (type 1)
boutons found near periphery (type 2)
distribution of CN 8
- vestibu meet and form their branch of the CN 8 at the scarpa ganglion
- vestib=superior part of CN 8 (lateral- superior & utricle of superior part, posterior canal & saccule on inferior part)
- cochlear- inferior part of CN 8
