Vestibular System Flashcards by Sarah Heath

Conscious sensation

Vestibulothalamicocortical (ascending) pathway to cerebral cortex

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Reflexive postural movements in response to changes in head position

Vestibulospinal network

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Refined reflex movements in response to changes in head position

Vestibulocerebellar system

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Reflex mediating conjugate eye movements in response to changes in head position

Vestibuli-ocular

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What are the semicircular canals connected to

The utricle

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Each semi circular canal ends with a single prominent enlargement called the

Ampulla

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Sensory receptors of the semicircular canals reside in the _______

Cupola at the base of each ampulla

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What do the semicircular canals transduce

Rotational head movements (angular acceleration)

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Where are the otoliths organs located

Utricle and saccule

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What do the otolith organs respond to

Linear accelerations

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The horizontal semicircular canals are activated by

Movement in the horizontal plane

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Anterior and posterior semicircular canals respond to what

Movement in the vertical planes

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The two vertical canals sense what

Tilt in different directions

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Where do the sterocilia that project from

The apical surface of the cell

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What is the talles hair cell of the stereocilia

Kinocilium

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How are the stereocilia oriented

In rows of ascending height, with the tallest lying next to the lone kinocilium

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How do the stereocilia move

In a wave

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Within each ampulla, the hair cells and their supporting cells lie in a neuroepothelial ridge called the ______, which extends across the base of the ampulla

Crista

Sensory transduction here

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Endolymph motion

Flows in direction opposite of movement of head, warps cupula, warps cilia, gives electrophysical tranduction

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Rotational head movements produces _____________ that causes the endolymph in the membranous ducts to be displaced in ____________

Angular acceleration

In opposite direction

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Excitement or inhibition of receptor cells

Displacement in one direction activated (depolarization) the receptor cells, whereas displacement in the other direction inhibits (hyperpolarizes) the receptor cells

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What does linear accelerations result in

Produce displacements of the otoconia, resulting in bending of the underlying hair cell stereocilia

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Movement of the stereocilia toward the kinocilium

Cause the hair cell membranes to depolarize, whihc results in an increases rate of firing and release of NT

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If the stereocilia are deflected away from the kinoceilium

The hair cell is hyperolarized and the afferent firing rate decreases

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The vestibular hair cells lay in ____________ rich endolymph

Potassium

Deflection of stereocilia toward the kinocilium causes ____________ channels in the apical portions of the stereocilia to open, depolarizing the cell membrane

potassium

Left-ward head-turn

- left horizontal canal, endolymph flows in clockwise direction, opposite to the left-ward head turn, exciting hair cells of left horizontal canal - right horizontal canals, endolymph flows in a clockwise direction away from the kinocilium, inhibiting the hair cells of the right canal

Leftward turn of the head causes

A clockwise flow of endolymph in the left horizontal canal

Leftward turn of the head and the right horizontal canal

Inhibited

How do the left and right semicircular canals of each functional pair walkways respond

Oppositely, with one side excited and the opposite side inhibited

What do otolith organs respond to

Tilt, not turn

The receptor cells in each vestibular organ are innervated by

Primary afferent fibers that join with those from the cochlea to comprise the vestibulocochlear Cranial nerve

Cell bodies of the primary afferent fibers of the receptor cells in vestibular organs

Bipolar neuron, in the vestibular ganglion

Where do the central processes of the bipolar neurons of hot evestibular organs terminate

In the ipsilateral vestibular nuclei in medulla

Where are the vestibular nuclei

In the rostral medulla and caudal pons

The ___________ nucleus lies superolaterally in the central pons and is bordered by the restiform body and the fourth ventricle

Superior vestibular

The _________ nucleus lies in the lateral floor of the fourth ventricle trough most of its rostrocaudal extent

Medial vestibular

The _____ nucleus is lateral to the medial vestibular nucleus

Lateral vestibular

The ______ nucleus extends through much of hte medulla

Inferior vestibular

These are the afferent fibers in the vestibular apparatus project to the vestibular nuclei in the vestibulo-thalami-cortical pathway

1st order sensory neurons

2nd order neurons in the vestibulo-thalami-cortical pathway

2nd order neurons in the vestibular nuclei, project to thalamus bilaterally

3rd order neurons in the vestibulo-thalamo-cortical pathways

Project to several cerebral cortical regions

What does the diversity of the thalamic nuclei and cortical regions reflect

Multi sensory integration

Visual-spatial and vestibular integration

Posterior parietal cortex

Integration of sensation of acceleration with crude touch and pressure (feeling pressure in feet in elevator)

Somatosensory cortex

Upper motor neurons for voluntary eye movements

Frontal eye fields

Part auditory, part visual sensation

Posterior insular and parieto-temporal cortex

The vestibular system influences _____________ through the two descending medial and lateral vestibulospinal tracts

Muscle tone and produces reflexive postural adjustments of the head and body

What do the lateral and medial vestibulospinal tracts target

The LMN of the spinal cord serving muscles for the head and body movements.

Where does the medial vesticulospinal tract descend to

In the medial medulla and medial spinal cord

The medial vestibulospinal tract is synonymous with

Medial longtitudinal fasciculus (MLF)q

What descending tract is responsible for head and neck

Medial vestibulospinal tract

What descending tract is responsible for limbs

Lateral vestibulospinal tract

Where does the medial vestibulospinal tract terminate

Bilaterally in the cervical spinal cord

What is the MVST analogous to

Anterior corticospinal tract: both regulate axial musculature, not the extremities

How do fibers of the lVST course

Ipsilaterally through the lateral medulla, then ipsilaterally through the anterior funciculus of the spinal cord and exciting the tract to synapse ipsilaterally on LMNs

The LVST can exert an _______ on extensor muscle motor neurons

Excitatory

Unilateral lesions to the LVST system

Produce ipsilateral instability or falls

The LVST is analogous to the

Lateral corticospinal tract

The patient experiences the sensation of spinning while things in the environment are not moving

Subjective vertigo

The sensation is one of hte environment spinning while the patient is not moving

Objective vertigo

In this disease, there is an increases of endolymph volume, resulting in an abnormal distinction of the membranous labyrinth

Ménière's disease

Symptoms of Ménière's disease

Severe vertigo

One of the most common vestibular disorders observed clinically

Benign paroxysmal positional vertigo

Characterized by brief episodes of vertigo with coincide with particular changes in body postion

Benign paroxysmal positional vertigo

Otoconia lodged in cupula

Begging paroxysmal positional vertigo

Tumors on the vestibulocochlear nerve

Change normal firing rates , interpreted in the brain as head turning

How are tumors on the glomus or vestibular Schwann cells translate?

Interpreted as a head turn away from the side of the lesion

What happens if a tumor of the vestibulocochlear region expands from the bony canal of VIII to cerebellum-pontine angle-where cerebellum and pons-medulla border meet

It can affect the VII and V nerves, cerebellar function, lateral PNS/medulla

Patients often present with severe vertigo, nausea, and vomitting yet have no accompanying hearing loss or other central nervous system abnormalities

Vestibular neuritis

How is vestibular neuritis diagnosed

It is thought to involve edema of the vestibular nerve (or ganglion)

What is the most common cause of vestibular neuritis?

Acute viral infection such as herpes simplex

Unilateral CNS damage in the vestibular nuclei

Interpretation of head/body movement toward the intact side