PSYC 212 Lecture Notes - Lecture 17: Angular Acceleration, Cerebral Hemisphere, Proprioception
6 Nov 2018
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The vestibular system and our sense of equilibrium
An overlooked sense
"sixth sense"?
○
Modalities and qualities of spatial orientation
Sense of linear motion: the perceptual modality that senses
translation
§
Sense of angular motion: the perceptual modality that sense
head rotation from side to side (as if to say 'no')
§
Sense of tilt: the perceptual modality that sense head
inclination with respect to gravity
§
○
These are considered different senses (like audition and vision) and
not different qualities of the same sense because they transduce
different energies
Linear acceleration
§
Angular acceleration
§
Gravity
§
○
•
Sense of equilibrium
Our sense of equilibrium is composed of multiple reflexes and
multiple perceptual modalities that begin with the vestibular organs
in the inner ear
○
Equilibrium reflexes include:
Vestibulo-ocular reflexes, that rotate our eyes to help
compensate for head motion
§
Balance reflexes that help us stand (with proprioception)
§
Autonomic reflexes that help maintain blood flow to our brain
when we rise to a standing position
§
○
•
Modalities and qualities of spatial orientation
All bodies moving in 3D have 6 'degrees of freedom'
3 are translational (x, y, z)
§
3 are rotational (roll (x-axis), pitch (y-axis), yaw (z-axis))
§
○
•
The mammalian vestibular system
The main peripheral component of the vestibular system is the
labyrinth: an elaborate set of interconnected chambers
○
The labyrinth is buried deep in the temporal pole and is located just
before the cochlea
○
The labyrinth has many things in common with the cochlea (hair
cells, endolymph, etc.)
○
The labyrinth consists of two otolith organs, the utricle and saccule,
and three semicircular canal
○
Hair cells are located in the utricle and saccule, and are tree
ampullae located at the basis of the semicircular canal
○
In the utricle and saccule, the sensory epithelium, or macula,
consists of hair cells and associated supporting cells
○
Overlaying the hair cells in a gelatinous layer
○
Above this layer is a fibrous membrane, the otolithic membrane, in
which are embedded crystals of calcium carbonate called otoconia
(otolith is Greek for 'ear stones')
○
Because the otoconia are heavier than the surrounding structure,
when the head tilts, gravity causes the membrane to shift relative to
the sensory epithelium
○
The displacement of hair bundles generate an action potential that
is dependent upon the direction of the tilt
○
Movement in the direction of the kinocilium (the tallest hair cell),
depolarizes the cell increased action potential rate), resulting in
excitation of the vestibular nerve
○
Movement away from the kinocilium hyperpolarizes the cell
(increased action potential rate), resulting in excitation of the
vestibular nerve
○
Movement away kinocilium hyperpolarizes the cell (decreased
action potential rate), resulting in inhibition of the vestibular nerve
○
The orientation of the kinocila relative to the stereocilia, is such that
given the utricle and saccule on each side of the body, there is
representation of all body movement
○
Population-level patterns of vestibular nerve activity can
unambiguously encode head position and the forces that influence
it
○
Except rotation
○
Note: with the head upright, utricule is sensitive to earth-horizontal
acceleration, and the saccule to vertical acceleration
○
Coding of amplitude in the otolith organs is proportional to
magnitude of linear acceleration of gravitational shear
○
Opposite coding on each side of the utricule/saccule
○
Semicircular canals sense head rotation
○
The ampulla at the base of each canal has a sensory epithelium, or
crista, that contains the hair cells
○
The hair bundles extend into a gelatinous mass, the cupula, that
separates the ampulla in two sections
○
When the head turns 'in-plane' of one semicircular canals, the
inertia of the endolymph produces a force across the cupula,
distending it away from the direction of the movement
○
Each canal works in pair when the equivalent canal on the other
side (when one is excited the other one is inhibited)
○
Neural activity in semicircular canals is sensitive to changes in
rotation velocity
○
Constant rotation leads to decreased responding from the canal
neurons after a few seconds (~15 s)
○
•
Rotation perception
Participant is placed on a stool in the dark, the stool starts rotating1.
At first, constant rotation is perceived accurately2.
Soon, however, semicircular canal response decreases and subjects
fell as if they are slowing down
3.
After 30 s, they no longer feel as if they are rotating4.
When rotation stops, subjects feel as if they are rotating in the
opposite direction
5.
Note: time course of habituation for perceived velocity is slower
than time course of habituation for velocity neurons: 'velocity
storage'
○
•
The mammalian vestibular system
Neural activity in semicircular canals is sensitive to changes in
rotation velocity
○
Constant rotation leads to decreased responding from the canal
neurons after a few seconds (~15 s)
○
Canal afferent neurons are sensitive to back and forth rotations of
the head, as well
○
Greatest sensitivity to rotations at 1 Hz or less
○
Decomposition by frequency can simplify the coding of complex
movements (as for vision or audition)
○
•
Translation perception
When people are passively translated in the dark, they are able to
use a joystick to reproduce the distance they traveled quite
accurately
○
Interestingly, they also reproduce the velocity of the passive-motion
trajectory
○
The otolith organs register acceleration, and our brain
mathematically integrate the acceleration and turn it into the
perception of linear velocity
○
•
Tilt perception
We are very accurate when perceiving tilt for angles between 0
degrees (upright) and 90 degrees (lying down)
○
•
Sensory integration
Sensory integration: the process of combining different sensory
signals
Typically leads to more accurate information than can be
obtained from individual senses alone
§
○
Visual-vestibular integration
Vection: an illusory sense of self motion produced when you
are not, in fact, moving
Example: being stopped in your car at a light next to a
semi. The semi begins to roll forward and you press on
the brake because you feel as if your are rolling
backwards
□
Rotational vection
Subjects have the illusion of tilt but do not feel as
if they are upside down
®
The vestibular system's sense of gravity stops the
illusion
®
□
§
○
•
Active sensing
Our sensory systems must simultaneously integrate changes in
sensation due to our own actions and changes in the external world
○
Sensory reafference: change in afference caused by self-generated
activity
E.g. moving our head
§
○
Sensory exafference: change in afference caused by external stimuli
E.g. being pushed
§
○
•
Vestibulo-ocular reflexes
VORs: counter-rotating the eyes to counteract head movements and
maintain fixation on a target
○
Angular VOR: the most well studied VOR
Example: when the head turns to the left, the eyeballs are
rotated to the right to partially counteract this motion
§
○
VORs are accomplished by the 6 oculomotor muscles that rotate the
eyeball
○
The 'gain' of VORs decreases for lower frequencies <0.02 Hz
○
The reflex is more sensitive that its input (analogous to velocity
storage)!
○
In some sense, the reflex is therefore more accurate than its input!
○
Motion sickness: results when there is a disagreement between the
vestibular system and vision
Could be an evolutionary response to being poisoned
§
○
Blood pressure is regulated by vestibulo-autonomic responses
○
Patients with vestibular damage don’t re-adjust their pressure as
well, suggesting that the vestibular system helps maintaining
constant pressure
○
•
Vesitulo-spinal reflexes
A whole family of reflexes that work together to keep us from falling
over
○
Without vestibulo-spinal responses, we would be unable to stand
up in the dark
○
Patients with vestibular loss do not compensate for body sway
○
•
Thursday, March 22, 2018
1:05 PM
Lecture 17(18)
The vestibular system and our sense of equilibrium
An overlooked sense
"sixth sense"?
○
Modalities and qualities of spatial orientation
Sense of linear motion: the perceptual modality that senses
translation
§
Sense of angular motion: the perceptual modality that sense
head rotation from side to side (as if to say 'no')
§
Sense of tilt: the perceptual modality that sense head
inclination with respect to gravity
§
○
These are considered different senses (like audition and vision) and
not different qualities of the same sense because they transduce
different energies
Linear acceleration
§
Angular acceleration
§
Gravity
§
○
•
Sense of equilibrium
Our sense of equilibrium is composed of multiple reflexes and
multiple perceptual modalities that begin with the vestibular organs
in the inner ear
○
Equilibrium reflexes include:
Vestibulo-ocular reflexes, that rotate our eyes to help
compensate for head motion
§
Balance reflexes that help us stand (with proprioception)
§
Autonomic reflexes that help maintain blood flow to our brain
when we rise to a standing position
§
○
•
Modalities and qualities of spatial orientation
All bodies moving in 3D have 6 'degrees of freedom'
3 are translational (x, y, z)
§
3 are rotational (roll (x-axis), pitch (y-axis), yaw (z-axis))
§
○
•
The mammalian vestibular system
The main peripheral component of the vestibular system is the
labyrinth: an elaborate set of interconnected chambers
○
The labyrinth is buried deep in the temporal pole and is located just
before the cochlea
○
The labyrinth has many things in common with the cochlea (hair
cells, endolymph, etc.)
○
The labyrinth consists of two otolith organs, the utricle and saccule,
and three semicircular canal
○
Hair cells are located in the utricle and saccule, and are tree
ampullae located at the basis of the semicircular canal
○
In the utricle and saccule, the sensory epithelium, or macula,
consists of hair cells and associated supporting cells
○
Overlaying the hair cells in a gelatinous layer
○
Above this layer is a fibrous membrane, the otolithic membrane, in
which are embedded crystals of calcium carbonate called otoconia
(otolith is Greek for 'ear stones')
○
Because the otoconia are heavier than the surrounding structure,
when the head tilts, gravity causes the membrane to shift relative to
the sensory epithelium
○
The displacement of hair bundles generate an action potential that
is dependent upon the direction of the tilt
○
Movement in the direction of the kinocilium (the tallest hair cell),
depolarizes the cell increased action potential rate), resulting in
excitation of the vestibular nerve
○
Movement away from the kinocilium hyperpolarizes the cell
(increased action potential rate), resulting in excitation of the
vestibular nerve
○
Movement away kinocilium hyperpolarizes the cell (decreased
action potential rate), resulting in inhibition of the vestibular nerve
○
The orientation of the kinocila relative to the stereocilia, is such that
given the utricle and saccule on each side of the body, there is
representation of all body movement
○
Population-level patterns of vestibular nerve activity can
unambiguously encode head position and the forces that influence
it
○
Except rotation
○
Note: with the head upright, utricule is sensitive to earth-horizontal
acceleration, and the saccule to vertical acceleration
○
Coding of amplitude in the otolith organs is proportional to
magnitude of linear acceleration of gravitational shear
○
Opposite coding on each side of the utricule/saccule
○
Semicircular canals sense head rotation
○
The ampulla at the base of each canal has a sensory epithelium, or
crista, that contains the hair cells
○
The hair bundles extend into a gelatinous mass, the cupula, that
separates the ampulla in two sections
○
When the head turns 'in-plane' of one semicircular canals, the
inertia of the endolymph produces a force across the cupula,
distending it away from the direction of the movement
○
Each canal works in pair when the equivalent canal on the other
side (when one is excited the other one is inhibited)
○
Neural activity in semicircular canals is sensitive to changes in
rotation velocity
○
Constant rotation leads to decreased responding from the canal
neurons after a few seconds (~15 s)
○
•
Rotation perception
Participant is placed on a stool in the dark, the stool starts rotating1.
At first, constant rotation is perceived accurately2.
Soon, however, semicircular canal response decreases and subjects
fell as if they are slowing down
3.
After 30 s, they no longer feel as if they are rotating4.
When rotation stops, subjects feel as if they are rotating in the
opposite direction
5.
Note: time course of habituation for perceived velocity is slower
than time course of habituation for velocity neurons: 'velocity
storage'
○
•
The mammalian vestibular system
Neural activity in semicircular canals is sensitive to changes in
rotation velocity
○
Constant rotation leads to decreased responding from the canal
neurons after a few seconds (~15 s)
○
Canal afferent neurons are sensitive to back and forth rotations of
the head, as well
○
Greatest sensitivity to rotations at 1 Hz or less
○
Decomposition by frequency can simplify the coding of complex
movements (as for vision or audition)
○
•
Translation perception
When people are passively translated in the dark, they are able to
use a joystick to reproduce the distance they traveled quite
accurately
○
Interestingly, they also reproduce the velocity of the passive-motion
trajectory
○
The otolith organs register acceleration, and our brain
mathematically integrate the acceleration and turn it into the
perception of linear velocity
○
•
Tilt perception
We are very accurate when perceiving tilt for angles between 0
degrees (upright) and 90 degrees (lying down)
○
•
Sensory integration
Sensory integration: the process of combining different sensory
signals
Typically leads to more accurate information than can be
obtained from individual senses alone
§
○
Visual-vestibular integration
Vection: an illusory sense of self motion produced when you
are not, in fact, moving
Example: being stopped in your car at a light next to a
semi. The semi begins to roll forward and you press on
the brake because you feel as if your are rolling
backwards
□
Rotational vection
Subjects have the illusion of tilt but do not feel as
if they are upside down
®
The vestibular system's sense of gravity stops the
illusion
®
□
§
○
•
Active sensing
Our sensory systems must simultaneously integrate changes in
sensation due to our own actions and changes in the external world
○
Sensory reafference: change in afference caused by self-generated
activity
E.g. moving our head
§
○
Sensory exafference: change in afference caused by external stimuli
E.g. being pushed
§
○
•
Vestibulo-ocular reflexes
VORs: counter-rotating the eyes to counteract head movements and
maintain fixation on a target
○
Angular VOR: the most well studied VOR
Example: when the head turns to the left, the eyeballs are
rotated to the right to partially counteract this motion
§
○
VORs are accomplished by the 6 oculomotor muscles that rotate the
eyeball
○
The 'gain' of VORs decreases for lower frequencies <0.02 Hz
○
The reflex is more sensitive that its input (analogous to velocity
storage)!
○
In some sense, the reflex is therefore more accurate than its input!
○
Motion sickness: results when there is a disagreement between the
vestibular system and vision
Could be an evolutionary response to being poisoned
§
○
Blood pressure is regulated by vestibulo-autonomic responses
○
Patients with vestibular damage don’t re-adjust their pressure as
well, suggesting that the vestibular system helps maintaining
constant pressure
○
•
Vesitulo-spinal reflexes
A whole family of reflexes that work together to keep us from falling
over
○
Without vestibulo-spinal responses, we would be unable to stand
up in the dark
○
Patients with vestibular loss do not compensate for body sway
○
•
Thursday, March 22, 2018 1:05 PM
Lecture 17(18)
Document Summary
The vestibular system and our sense of equilibrium. Sense of linear motion: the perceptual modality that senses translation. Sense of angular motion: the perceptual modality that sense head rotation from side to side (as if to say "no") Sense of tilt: the perceptual modality that sense head inclination with respect to gravity. These are considered different senses (like audition and vision) and not different qualities of the same sense because they transduce different energies. Our sense of equilibrium is composed of multiple reflexes and multiple perceptual modalities that begin with the vestibular organs in the inner ear. Vestibulo-ocular reflexes, that rotate our eyes to help compensate for head motion. Balance reflexes that help us stand (with proprioception) Autonomic reflexes that help maintain blood flow to our brain when we rise to a standing position. All bodies moving in 3d have 6 "degrees of freedom" 3 are rotational (roll (x-axis), pitch (y-axis), yaw (z-axis))
