Vestibular System Flashcards
What is the function of the vestibular system?
it reflexively controls the eye and body position in response to change in head position
What do vestibular nuclei send information to?
medial longitudinal fasciculus and vestibulospinal tract
Where does the medial longitudinal fasciculus send the information that it received from the vestibular nuclei to?
the motor nuclei of III, IV, and VI
Where does the vestibulospinal tract send the information that it recieved from the vestibular nuclei to?
the skeletal muscles associated with eye and body position
What type of neuron is the vestibular neuron?
a bipolar sensory neuron
Where is the vestibular organ located?
in the petrous portion of the temporal bone
What are the two labryinths associated with the vestibular organ?
membranous and osseous
What is the osseous labyrinth filled with?
perilymph
What is the membranous labyrinth filled with?
endolymph
Where is endolymph produced?
in the cochlea
What are the structural units of the vestibular organ?
three semicircular ducts, utricles, and saccules
What are the sensory receptors for the utricle and saccule?
the macula
What is the sensory receptor associated with the ampulla?
the crista ampullaris
What are the names of the semicircular ducts?
lateral, posterior, and anterior
What sensory structures are located in the sensory cells of the crista ampullaris?
one kinocilium and multible stereocilia
What do the supporting cells of the crista ampullaris produce?
cupula - gelatinous substance
Where is the cupula located?
it is attached to the roof of the ampulla
What does the cupula cover?
it encapsulates the stereocilia
Where is the macula located?
in the utricle and the saccule
What do the supporting cells of the macula produce?
statoconial membrane
What is the statoconial membrane made up of?
gelatinous substance and statoconia (Ca carbonate crystals)
What is the function of the sensory cells in the vestibular system?
they generate spontaneous firing of vestibular axons
What does the firing rate of vestibular axons reflect?
the deflection of stereocilia
If the stereocilia move towards the kinocilium what happens to the firing rate?
it increases (depolarization)
If the stereocilia move away from the kinocilium what happens to the firing rate?
it decreases (hyperpolarization)
What moves the sterocilia in the semicircular duct and crista ampullaris?
the endolymph moves due to a turning motion of the head which pushes the cupula to move the sterocilia
In the semicircular duct and crista ampullaris, what does the firing rate reflect?
the direction of angular motion
In the utriccle/saccule and ampulla, what does the firing rate reflect?
the direction of linear motion and head tilt
What occurs to the statoconial membrane during linear movement?
the statoconial membrane lags behind the linear motion or displaces towards the tilted side by the force of gravity
What semicircular duct detects angular motion in the horizontal plane?
the lateral duct
What semicircular duct detects angular motion in the vertical plane?
the anterior and posterior ducts
If the head turns counter clockwise on the horizontal plane, what is the firing rate like on the left and the right side?
the firing rate is increased on the left side and decreased on the right side
If the head turns clockwise on the horizontal plane, what is the firing rate like on the left and the right side?
the firing rate is increased on the right side and decreased on the left side
Where do the vestibulospinal tracts run?
in the ventral funiculus
Where do the vestibulospinal tracts terminate?
in the motor nucleus of the accessory nerve and the spinal motor neurons
How many vestibulospinal tracts are there?
4: there are both medial and lateral tracts on both sides
What muscles does the vestibulospinal reflex work with?
the extensor muscles
What semicircular canals are associated with the vestibulospinal reflex?
anterior and posterior
What is the function of the vestibulospinal reflex?
to maintain posture
In the vestibulospinal reflex, if the head rotates to the left, what happens to the firing rate on the left and right side?
the firing rate increases on the left side and slows down on the right
In the vestibulospinal reflex, if the head rotates to the right what happens to the firing rate on the left and right side?
the firing rate slows down on the left side and increases on the right
What is the purpose of the vestibulo-ocular reflex?
to change eye position in response to change in head position
What does rotation of the head trigger in the vestibulo-ocular reflex?
physiological nystagmus
What is physiological nystagmus?
a combination of slow and quick eye movements in response to continued head rotation
What occurs during the quick phase of nystagmus?
eyes turn quickly towards the direction of the head turn
What occurs during the slow phase of nystagmus?
eyes turn slowly away from the direction of the head turn
A cat presents with abnormal right nystagmus, what side is the lesion/head tilt on?
the left side
What structures are associated with the vestibulo-ocular reflex?
vestibular receptors, vestibular nerve, vestibular nuclei, medial longitudinal fasciculus, motor nuclei of CN III, IV, and VI, the flocculonodular lobe of the cerebellum, and the reticular formation
