chapter 12-spatial orientation and the vestibular system Flashcards
problems with the vestibular system can lead to peculiar sensations
spatial disorientation, dizziness, vertigo, imbalance, blurred vision, illusory self-motion
spatial disorientation
any impairment of spatial orientation (sense of linear motion, angular motion, or tilt)
dizziness
nonspecific spatial disorientation; no specific direction
vertigo
sensation of rotation or spinning
vestibular organs/vestibular system
the set of five organs (3 semicircular canals and two otolith organs) located in each inner ear that sense head motion and head orientation with respect to gravity
vestibular organs help us in many ways, for instance; provide a sense of spatial orientation consisting of
linear motion, angular motion, tilt
spatial orientation
a sense comprised of three interacting sensory modalities; our sense of linear motion, angular motion and tilt
angular motion
rotation; can be sense when rotating head from side to side as if to say “no”; fluid motion
linear motion
sensed when accelerating or decelerating in a car; motion of hard substance/intertia
tilt
can be sensed when nodding head up and down as if to say “yes”; gravity
fluid and inertia processes what
acceleration, changes in velocity; starting and stopping motions
gravity processes what
acceleration force, constant acceleration
spatial orientation coordinates system for classifying direction on how many axes that are relative to what
3 axes; defined relative to the head of the person, independent of gravity
x axis
points forward, in the direction the person is facing; forward and backward
y axis
point laterally, out of the persons left ear; left and right
z axis
point vertically, out of the top of the persons head; up and down
linear motion-translation of movements
represented in terms of changes in the x y and z axes; any arbitrary linear motion can be represented as a change along these three axes
linear motion; vector
amplitude (degree of acceleration and velocity, size of head movement), direction (line one moves along)
three directions for sense of rotation
roll, pitch, yaw
roll
rotation around the x axis (maybe)
pitch
rotation around y axis (yes)
yaw
rotation around z axis (no)
tilt
more of a constant position vs a motion
tilt is in regard to 2 axes
x and y
semicircular canals
the three toroidal tubes that sense angular acceleration, a change in angular velocity;
otolith organs
mechanical structures that sense both linear acceleration and gravity
otolith organs offer sense of
linear velocity and tilt; hard structure inside that gets shifted within
semicircular canals source of
our sense of rotation; slosh fluid back and forth
semicircular canals have how many directions
3; anterior, posterior, horizontal
otolith organs are more localized; __ of them
2; utricle and saccule
hair cells are in semicircular canals and otolith organs
support the stereocilia that transduce mechanical movement in the vestibular labyrinth into neural activity sent to the brain stem
mechanoreceptors are in semicircular canals and otolith organs
sensory receptors that are responsive to mechanical stimulation (pressure, vibration, movement)
hair cells act as ____ in each of the five vestibular organs
mechanoreceptors
head motion causes hair stereocilia to ___, causing a change in hair cell ___ and altering ___ release (___ response)
deflect, voltage, neurotransmitter, gradient
degree to which stereocilia are bent determine how much ____ is released
neurotransmitter
hair cell responses; in the absence of stimulation
hair cells release neurotransmitter at a constant rate
hair cell responses; increase firing to rotation
in one direction and decrease firing to rotation in the opposite direction
hair cells have a ___ constant rate
high; ~100 spikes/sec vestibular nerve fibers
convey info by
increase or decreasing firing rate
depolarization
increase action potential rate
hyperpolarization
decrease action potential rate
amplitude
coded here in response rate; larger amplitude is depolarization
stereocilia not all the same height; bend to tallest
depolarization
stereocilia not all the same height; bend away from tallest
hyperpolarization
semicircular canals are filled with fluid and are what shaped
three-fourths of a toroid (donut shape)
ampulla
cross section of each canal swells substantially near where the canals join the vestibule
base area of semicircular canals is the
ampulla; hair cells that get activated by movement
edolymph
fluid thats moving around
semicircular canals are more sensitive to
certain areas; ex. horizontal semicircular canal responds to yaw rotation
push pull symmetry
hair cells in opposite ears respond in a complementary fashion to each other; when hair cells in the left ear depolarize, those in the analogous structure in the right ear hyperpolarize; overall activation is different between the 2 ears
tallest stereocilia located in the back; fluid in both ears moves
in the opposite direction of head motion, increase in one ear and decrease in the other ear
horizontal canal responds to what rotations
yaw
left posterior canal and ___ paired together
right anterior canal
right posterior canal and ___ paired together
left anterior canal
semicircular canal dynamics (fluid movement); neural activity is sensitive to
changes in rotation velocity
constant rotation of semicircular canal lead to decreased
responding from the canal neurons after a few seconds
semicircular canal dynamics have a burst of activity at ____; fluid stops moving with ____ ____; when you stop moving the fluid moves ____
acceleration; constant movement; backward
otolith organs sense what
acceleration and tilt
two otolith organs in each ear
utricle and saccule
utricle has how many hair cells
30,000
saccule has how many hair cells
16,000
hair cells in otolith organs are encased in what
otoconia
otoconia
gelatinous structure that contains calcium carbonate crystals
hair cells in otoconia have similar push pull symmetry because the stereocilia
converge
coding of amplitude in the otolith organs; larger accelerations move
the otolith organs otoconia more, and leads to greater deflectin of the hair cell bundles
response from tilt
substained
response from rotational and linear
transient
directional coding in the otolith organs arises from
anatomical orientation of the organs
directional coding in the utricular macula
horizontal plane; tilt side to side
utricular macula movement is sensitive to
horizontal linear acceleration and gravity
directional coding in the saccular macula
vertical plane; tilt vertical
saccular macula movement is sensitive to
vertical linear acceleration and gravity
rotation perception
at first, constant rotation in the dark is perceive accurately. soon subjects feel as though they are slowing down. after 30 seconds, they no longer feel as if they are rotating.
velocity storage
time course habituation for perceived velocity is slower than time course of habituation for velocity neurons
tilt perception
accurate for perceiving tilt for angles between 0 degrees (upright) and 90 degrees (lying down)
tilt perception illusion
if you roll tilt your head to the left or right while looking at a vertical streak of light, the light appears to tilt in the opposite direction
sensory integration
the process of combining different sensory signals; leads to more accurate information than obtained from individual senses alone
visual vestibular integration
vection
vection
illusory sense of self motion produces when you aren’t actually moving
sensory integration; observers looking at a rotational display report
rotational vection; subjects have the illusion of tilt but still feel vertical
why don’t people feel as if they are turning upside down
the vestibular systems sense of gravity stops the illusion
vestibulo-ocular reflexes (VORs)
counter rotating the eyes to counteract head movements and maintain fixation on a target; keep eyes fixated on stimuli by moving them in the opposite direction of the head
vestibulo-autonomic responses include
motion sickness, vertigo
motion sickness
results when there is a disagreement between the motion and orientation signals provided by the semicircular canals, otolith organs, and vision; could be an evolutionary response to being poisoned
vertigo
distorted perception of orientation relative to vertical, or motion relative to the environment, accompanied by dizziness, nausea, vomiting, and postural instability; height vertigo and postural alcohol mystagmus
blood pressure is regulated by
vestibulo autonomic responses
height vertigo
body movement size no longer matches the visual angle changes
postural alcohol mystagmus
alcohol changes the density of semicircular canals
