Vestibular System Flashcards
Where is the vestibular system located?
In the inner ear
What is the vestibular system responsible for?
The body’s equilibrium
What does it use to transduce physical motion into neural impulses?
Specialized sensory (hair) cells
The vestibular labyrinth is composed of what two organs?
otolith organs (utricle & saccule) and the semicircular canals (superior, posterior & horizontal)
What are the two types of vestibular hair cells?
Sterocilia, kinocillum (longest process)
How does the movement of the hair cells change the membrane potential?
When the stereocilia move toward the kinocillum ==> it depolarizes (excitation) and vice-versa
What is the post-synaptic neuron of the hair cells?
The vestibular nerve
What are the two otolith organs?
Utricle and saccule
What do the otolith organs do?
detect linear movement (translational head movements and head tilts)
Each otolith organ contains what?
sensory epithelia (macula), gelatinous layer (hair bundles), fibrous layer (otolithic membrane), otoconia (embedded crystals of calcium carbonate
What do the otoconias do?
they make the otolithic membrane heavier than the structures and fluid surrounding it. When the head moves it causes a shift in the membrane relative to the macula which causes the hairs to be displaced and a potential to be generated
The utricle detects what kind of translational movements of the head?
The horizontal movements
The saccule detects what kind of translational movements of the head?
the vertical movements
What is the orientation of the hair bundles present in the utricle?
hair bundles are directed toward the striola and positioned horizontally
What is the orientation of the hair bundles present in the saccule?
hair bundles are directed away from the striola and positioned vertically
What is the function of the semicircular canals?
specialized for responding to rotations of the head
What are the three semicircular canals?
Horizontal (turning left and right), superior ( nodding up and down), posterior (tilting to a side)
What are the components of the semicircular canals?
ampulla, cupula, endolymph fluid
What is the ampulla?
enlargement at the base of each semicircular canal. Houses the hair cells
What is the cupula?
gelatinous mass that the hair bundles extend out into
What is the endolymph fluid?
fluid that circulates in the canals. It is through its movement that the hair cells get displaced
How do each semicircular canal work in relation to its partner on the other side? How does right work with left?
they work in opposite manner. For example, a head tilt to the right activates the hair cells in the right activates the right posterior canal but inhibits the hair cells in the left posterior canal
What are some of the rapid motor movements the vestibular system contributes to?
reflexive eye movements that stabilize gaze, rapid postural adjustments to maintain balance, help with sense of spatial orientation and self-motion
Why is the central vestibular processing multisensory?
because it receives visual, cerebellar and proprioceptive inputs
What does the vestibular nerve project to?
projects its fibers to the vestibular nucleus in the brainstem which in turn send projections to several brain regions
What does the vestibulo-ocular reflex (VOR) do?
VOR produces eye movement that counters head movement to allow the gaze to remain fixed on a particular point
What happens to the eyes when the heads turns to the side (left in this case)?
left horizontal canal nerve send signal to vestibular nucleus which sends out two projections: one excitatory to the right abduces nucleus and one inhibitory to the left abduces nucleus. The right abduces nucleus sends an excitatory impulse to the lateral rectus muscle of the right eye and to the medial rectus muscle of the left eye. The left abduces nucleus inhibits the lateral rectus m. of the left eye and the medial rectus m. of the right eye.
What does the vestibulo-cervical reflex (VCR) do?
regulates head position by reflex activity of neck muscles in response to stimulation of the semicircular canals following head movement
What is the neural pathway in the VCR?
superior canal ==> medial vestibular nucleus ==> medial vestibulospinal tract ==> cervical lower motor neurons ==> activates head/neck muscles
What does the vestibulospinal reflex (VSR) do?
initiated by the VCR, VSR causes the extension of the forelimb and the flexion of the hindlimb to stabilize the body and protect against a fall
Information from the otolith organs project mainly to what?
to the lateral vestibular nucleus
Where do the axons from the lateral vestibular nucleus go?
they descend in the lateral vestibulospinal tract to terminate at the medial levels of spinal cord. They then excite the ipsilateral lower motor neurons and inhibit the contralateral lower motor neurons
What does the vestibular-cerebellar pathway do?
plays a critical role in integrating and modulating vestibular signals to enable adaptive changes to VCR, distinguish head tilts from translational movement and distinguish passive movement of head and body from those that are self generated
What happens to a blindfolded subject on a rotating chair?
he will perceive that the rotation is slowing and after about 30 seconds, that it has stopped completely even though the chair is still rotating thanks to the desensitization of the hair cells
What causes motion sickness?
brain receives conflicting info from the vestibular system, eyes and muscle nerves. Vestibular system reports rocking back and forth while the car seems perfectly stable based on the two other system inputs
What is oscillopsia?
condition in which a person with vestibular damage finds it difficult or impossible to fixate on visual targets while the head is moving. Illusion that the environment in moving when head is moving
