Vestibular System 19 Flashcards
Def. Postural equilibrium (2 types)
How is it controlled?
Postural equilibrium = balance
Static: body is at rest (motionless)
Dynamic: applied and internal forces acting on body are balanced (no acceleration)
– control COM within COP
Def. Postural orientation
Relative positioning of the body segments with respect to “each other” and “the environment”
Sensory sources used in order to maintain balance?
Vision
Somatosensory
Vestibular
The vestibular system is not….
A major component of “consciousness”
When vestibular system fails, it can cause?
Also when receives a lot of input
Contradictory signals can make u very sick
What does the vestibular system tell us?
Head accelerations
Angular accel. - nodding
Linear accel. - gravity
Physical features that make up the vestibular system (aka labyrinth)
Peripheral apparati imbedded bilaterally in the head (one per ear)
3 planes of linear acceleration?
Medial-lateral
Anterior-posterior
Inferior-superior
3 types of angular accelerations
Pitch (yes)
Roll (maybe)
Yaw (no)
Vestibular organ location
Very close to the auditory system (cochlea)
Vestibular organ is made up of what two parts?
Where are they found?
Semicircular canals - found within the ampullae
Otolith organs - found on the macula
Nerve that transmits vestibular signals?
8th cranial nerve (aka vestibulochoochlear nerve)
- contains all the vestibular afferents
How does organ tell us about accelerations?
Tiny “hair” cells within each organ
Vestibular organ has two types of cilia (hair cells)
How many of each?
What’s their formation?
Kinocilium (1 per cell)
Stereocilia (40-70)
- increase in length from one end of cell to the
- cilia are attached to one another
How do hair cells respond?
Bending of the stereocilia towards the kinocilium cause “depolarization”
(Away from causes hyperpolarization)
How causes the response of the hair cells?
Gated channels open and close depending on direction of bending
- potassium enters cell causing depolarization
- depol opens voltage gated Ca channels
- Calcium increase potential towards -55, to generate AP
- Ca causes release of neurotransmitter
The hair cells are NOT completely shut. This means?
- there is a constant influx of potassium
- 8th cranial nerve is always firing
(Tonic firing rate of ~100Hz)
Orientation of hair cells is extremely important. What’s difference between semicircular canals and otolith organs?
Semicircular - hair cells found within the ampullae - all cells face 1 directions Otolith - found within maculae - multiple directions
Line in the middle of the macula is called?
Striola
- otolith organs hair cells face multiple directions
- kinocilia of hair cells either point towards or away from striola
Two types of macula?
What is the difference?
Utricle - horizontal acceleration - kinocilia face towards striola
Saccule - vertical accel. - kinocilia face away from striola
Otolith organs are sensitive to?
Linear acceleration
Hair cells of the otolith organs (macula) project into the …
Overlying gelatinous layer
“Otolithic Membrane”
Name of the small crystals imbedded in the otolithic membrane of the macula?
Otoconia
What recognizes linear accelerations of the head? (Head tilts)
Otolith organs (macula) - causes shearing of the otolithic membrane
How to tell the difference between acceleration (sitting in a car) and head tilt?
Use other sensory sources (receptors in the neck sense tilt)
Each otolith organ (utricle or saccule) codes…
Linear accelerations
In 2 dimensional plane
“Combined” utricle and saccule code
Linear accelerations
In all 3 dimensions
Semicircular canals hair cells are oriented ….
In the same direction
- all depolarize or hyperpolarize
Semicircular canals themselves are organized?
Parts of canal?
3 semicircular canals arranged ORTHOGONALLY (90 degrees to each other) - to pick up accel in each direction
- horizontal, posterior and superior canals organized as one SCC
Semicircular canals are sensitive to
Angular accelerations
Hair cells found in semicircular canals are found in?
The capula within the ampulla
- splits the ampulla into two
Semicircular canals are filled with what
This has what affect on hair cells?
Endolymph fluid
Rotation causes fluid to lag behind (inertia) - bends cilia opposite direction of the angular acceleration
Membranous ducts of semicircular canals work in pairs. What works with what?
Horizontal left works with horizontal right
Anterior canal of one side works with posterior of other side
Because semicircular canals are set up as mirror image, and kinocilia face same direction, head turn will cause the pair of canals to have what output response ?
Opposite
Depol (increase firing) in one side
Hyperpol (decrease firing) other side
Semicircular canals code for what acceleration? How many dimensions?
Angular acceleration
All 3 dimensions
Roles of the semicircular canals?
Helps control the eye in head (Gaze)
Also balance, head on body information
Only what type of movement changes firing rate of vestibular afferents?
Accelerations
Velocity does not change firing rate
Damage to the vestibular system, symptom may be irregular movements of the eyes called? What’s its definition? Experimentally induced? What is this reflex?
Nystagmus
Slow smooth movement of eyes in one direction followed by fast in the other direction
Experimentally induced by spinning in circle fast
Vestibulo-ocular reflex
Where does the 8th cranial nerve travel to?
Where does it go after?
Vestibular nuclei and cerebellum
Then sent down brain stem to vestibulospinal and reticulospinal tracts causing muscle contraction
Relation between vestibular and visual?
Directly connected
Work together to control “gaze”
Def. Vestibulo-ocular reflex
Accelerations picked up by SCC, activate pathways to rotate eyes
-works in darkness, does not require vision
Vestibular-somatosensory integration
Vestibular and neck spindles + skin feedback provide head on body Proprioception
Galvanic stimulation used to?
Determine pathways
How body uses information
How body integrates info with other sensory sources
GVS is?
Non invasive technique to test function of vestibular system
- pass electric current behind ear to stim 8th cranial nerve
- increases FR on cathode afferents and decrease anode side
Short latency response
Response SL
reflexive, hard to modulate
Medium latency response
Response ML
Occurs later in time, opposite response to SL, correlated to balance, easy to modulate
Postural sway
Movement of the COP to maintain whole body stability
- sensed by vestibular info about the head and somatosensory about spindles and skin of the neck
Highest contribution of vestibular system when walking?
During heal contact
*note vestibular system is used at different levels during gait
Lowest contribution from vestibular system during gait?
Initial toe off
Depression of the cerebellum causes? Significance?
Increased postural sway
- shows there is a role of the cerebellum
- explains ml response
Vestibular contributions when standing walking running?
Standing - Not much movement (use more visual somatosensory)
Walking - very important, particularly heal contact
Running - not as important - pre planned motor program
Gurfinkel paper purpose, results?
- determine if vestibulomotor response will adapt to changed perception of head position during prolonged status head turn
- direction of sway changed with perception of head location, over time thought returned to normal so returned to medial lateral sway
- perception of head wrt body, not actual position
