vestibular system Flashcards
anatomy of the ear
role of vestibular system
- not prominent conscious sensation
- reflexes evoked (equilibrium/balance & stabilization of visual field)
2 suborgans of vestibular system
- semicircular canals
- otolith (macular) organs
semicircular canals function
- sense angular acceleration (turning head)
- inertial mechanism
- rapidly adapting (phasic) receptors
otolith (macular) organs
- sense linear acceleration and static position of the head
- gravitational mechanism
- slowly adapting (tonic) receptors
semicircular canals structure
- filled with endolymph
- ampulla
- crista ampullaris
- hair cells
- cupula (watertight seal)
each canal has an expansion called
ampulla which contain the endolymph
hair cells are located within
the ampulla of the semicircular canals
ampulla is innervated by
CN VIII
cupula extends to
the top of the ampulla to divide the sides from each other
- important to only allow hair cells to go side to side
hair cells
- flask (I) and tube (II) shapes
- 1 kinocilium (larger)
- 100 stereociia (smaller)
- synaptic vesicles
depolarization and hyper polarization of hair cells
- to depolarize: kinocilium pushed away from stereocilium (then release neurotrasnmitter) because open channels
- to hyperpolarize: kinocilium pushed toward the stereocilium (less transmitter release) beacuse closed channels
hair cells have ________ firing rate
high
signaling to release neurotrasmitters of hair cells
- the kinocilium pulls away from the sterocilia
- the mechanically gated channels open up
- K+ to flow in >
- depolarization >
- Ca2+ flows in >
- synaptic vesicles release transmitter into
synaptic cleft > - activation of afferent nerve (CN VIII)
vestibular afferents
- vestibular branch of CN VIII
- cell bodies in vestibular (Scarpa’s) ganglion
- have high firing rate
endolymph - relative motion
- head moves to the right
- canal moves in that direction
- endolymph is fluid so it stays put by inertia
differential movement - pushes cupula in that direction
orientation of sterocilia - horizontal canal
I = inhibition
E = excitation
each semicircular canal transduces
angular velocity in plane of duct
there is no signal if movement is
normal to plane of duct
if rotation is at an angle to plane of duct
signal is a vector fraction
otolith organs structure
- macula is a patch of hair cells
- covered by gelatinous mass
- otoconia embedded in mass
- otoconia are CaCO3 crystals
otolith organs orientation
- located in saccule and utricle
- utricular macula is horizontal
- saccular macula is vertical
otolith organ physiology
- shearing forces act on otoconia
- otoconial movements cause stereocilia to be deflected
shearing forces are produced by
- linear acceleration or deceleration
- tilting of the head
reflexes evoked by vestibular stimulation
- maintenance of equilibrium
- stabilization of visual orientation
maintenance of equilibrium afferent fibers connect to
lateral vestibulospinal tract (extensor muscles of the eye)
- abducens, oculomotor, trochlear nuclei
stabilization of visual orientaiton afferent fibers connect to
medial longitudinal fasciculus (MLF)
- this binds the 3 nuclei of eye movement
vestibular afferents terminate in
- vestibular nuclei (border between medulla and pons)
- cerebellum
vestibular nuclei
#? projects down what tract? CN?
- 4 total (superior, lateral, inferior, medial)
- lateral = projects down through spinal cord (LVST)
- CN VIII distributes to all 4 nuclei
vestibular nuclei efferents
- to abducens, trochlear, oculomotor nuclei via ascending MLF
- to neck motor neurons via descending MLF
- to limb and trunk motor neurons via LVST
- to cerebellum
- to reticular formation
- to VPM and cerebral cortex
loss of vestibular function symptoms
- difficulty maintaining balance
- visual disturbances while walking
- nystagmus
- vertigo
- nausea
vestibular system disorders
- Benign positional vertigo
- meniere’s disease
- acoustic neuroma
- ototoxic drugs
- trauma
motion sickness occurs when
motion signals transmitted by the eyes, vestibular system, and proprioceptors are at a variance with one another or with what is expected from previous experience
motion sickness evokes what?
- autonomic reactions (nausea, vomiting, pallor, sweating, hypersalivation, stomach awareness)
- drowsiness
- fatigue
continued exposure of motion sickness leads to
disappearance of reactions
- “sensory conflict and neural mismatch” theory
