Vestibular System Flashcards
What is postural equilibrium ?
Think balance
Static-when the body is not moving
Dynamic-moving…applied and internal forces acting upon the body are balanced (no acceleration)
What is postural orientation?
The relative position of body segments with respect to each other and to the environment (think proprioception)
3 sensory sources used to maintain balance
- vision
- somatosensory
- vestibulary
All work together to maintain balance
Vestibular system
Tell us about head acceleration:
1-angular (nodding head)
2-linear (gravity)
Angular vs. linear accelerations
Angular-nodding Pitch-yes Roll-maybe Yaw-no Linear Medial-lateral Anterior-posterior Inferior-superior
8th cranial nerve
Vestibulocochlear nerve
Contains all the vestibular afferents
Transmits vestibular signals
Two types of hair cells
1-kino ilium (1 per cell)
2-sterlcilia (40-70)
increase in length until they reach the kinocilium
are cilia are attached to each other
Bending of the stereocilia towards the kinocilium cause the hair cell to depolarize…opening potassium channels, increasing firing rate of 8th cranial nerve
Bending of the stereocilia away from the kinocilium cause the cell to hyperpolarize (decrease firing rate)
At rest the channels are not completely shut, constant influx of K+, so 8th cranial is always firing (100hz)
Hair cells and Semicircular canals & otoliths organs
Semicircular canals-hair cells lie within the ampullae, face one direction
Otoliths-hair cells found on the maculae, face opposite directions
Otolith organs
Respond to LINEAR acceleration. Hair cells within the macula project into gelatinous layer (otolithic membrane)
Otoconia (small crystals) are embedded on top of this membrane. Shearing of this membrane causes cilia to bend
How to generate shear force? Linear accelerations, Head tilts (muscle spindle changing)Saccule:(vertical)kinocilia point AWAY from striola
Utricle:(horizontal)kinocilia point TOWARDS striola
Together they can code for 3 dimensions
Semicircular canals
Sensitive to ANGULAR acceleration
All of the hair cells are oriented in the SAME direction (all depolarize or hyperpolarize)
All 3 semicircular canals are located ORTHOGONALLY (90 degrees) to each other to pick up accelerations in each direction
Vestibulo-ocular reflex
➡️accelerations are picked up by the SCC, and activate pathway to rotate eyes
➡️this occurs in complete darkness, does not depend on vision at all
Vestibulo-somatosensory integration
➡️not as obvious as the connection between vistubular system and vision
➡️vestibular and neck spindles/skin feedback, provide information on head on body proprioception
➡️research done in lambs lab has showed that removal of skin feedback has effected vestibular response to perturbation
Galvanic vestibular system
⭐️has been used for a very long time
➡️can be used to determine the function of the vestibular system
➡️determine pathways
➡️examine how the body uses this information
➡️and how the body integrates this information with other information (sensory sources)
➡️pass an electrical current behind the ears (mastoid process) to activate the 8th cranial nerve
➡️increase firing on Cathodal side, decrease anodal..However, turn towards the anode, but think you are turning towards cathode .
⭐️increasing firing of peripheral afferents on (right) Cathodal side, decrease on anode
Advantages of GVS
➡️able to control the magnitude and duration of stimulus
➡️creates a temporary but distinct perturbation , a useful indicator of vestibular function.
GVS causes two distinct responses
1⃣reflexive muscle response
2⃣postural sway
