Vestibular System Flashcards
Fluid in bony labyrinth
perilymph (ECF and CSF)
Fluid in membranous labyrinth
endolymph (ICF)
Membranous labyrinth is housed in
bony labyrinth
functions of vestibular system
position and movement of head, eye movements, equilibrium
Damage to vestibular system =
nausea, vomiting, dizziness, vertigo
Vertigo
sensation of movement when none is occurring
Bony labyrinth is housed in
the petrous portion of the temporal bone
Vestibule function
detects linear acceleration
Fluid does not mix between
bony and membranous labyrinths
Membranous Labyrinth is composed of
VESTIBULE and SEMIcircular canals
Vestibule function
linear acceleration
Semicircular canals function
rotational acceleration
Vestibule is composed of
saccule and utricle
Saccule’s function
to detect up/down, forward/backward movement of the head (linear acceleration in the (horizontal or vertical) A/P axis)
Saccule location
dilated portion of vestibule
macula is located on floor
1st order neuron: sensory end organ hair cells
Utricle location
dilated portion of vestibule
macula is located on wall
1st order neuron: sensory end organ hair cells
What is contained in Scarpa’s ganglion
SENSORY first order neuron
Utricle’s function
detects side-to-side linear acceleration (lateral plane)
How are the semicircular canals and the cochlea connected
utricle is connected to the semicircular canals and saccule is connected to the cochlea
How do the utricle and saccule work?
Hair cells embedded in an otolithic membrane with calcium carbonate crystals
When the head moves then
crystals move –> otolithic matrix moves –> hair cells deflect –> nerves fire
Semicircular canals function
angular acceleration and head rotation
Semicircular canals work in pairs
R horizontal- L horizontal
R Anterior - L Posterior
Horizontal canals are oriented
tilted 30 degrees posteriorly
Ampulla
dilated portion of the duct that containes the crista ampullaris
Crista ampullaris
1st order sensory end organ hair cell with kinocilia
kinocilia
the longest cilia that determines firing of nerve
Kinocilia orientation
in any given crista - orientation of the kinocilia is always the same and is CLOSEST to the MIDLINE
kinocilia in the horizontal duct is oriented
toward midline
Anterior and posterior ducts are oriented in
vertical plane
The semicircular canals are able to detect any head movement because
the ducts are positioned at 90 degree angles to one another
What causes movement of the kinocilia?
Movement of the endolymph
Endolymph moves opposite to head rotation so
it deflects the kinocilia of the same side as movement towards midline and cause increased firing rate
Kinocilia movement towards midline causes
increased firing rate
Kinocilia movement away from midline causes
decreased firing rate
Neuron firing rate at rest
90 spikes/second
primary sensory neuron cell body’s are located
in the vestibular/Scarpa’s ganglion
Primary sensory neurons and ganglion cells are
BIPOLAR
Turn your head left then the ______ side has increased AP
LEFT
Peripheral process of primary sensory neuron in vestibular system
synapses on receptor hair cells
Cell body of primary sensory neuron in vestibular system
Scarpa’s/Vestibular ganglion
Central process primary sensory neuron in vestibular system
Pontomedullar junction in the pontocerebellar angle
Central process primary sensory neuron in vestibular system synapse with
IPSILATERAL vestibular nuclei and vestibulocerebellum
Vestibulocerebellum Function
Maintain equilibrium and coordination of eye movements with head, neck, and body
Vestibulocerebellum structures
flocculonodular lobe and fastigial nucleus
Vestibulocerebellum received input from
IPSILATERAL vestibular ganglion OR IPSILATERAL vestibular nuclei
Pathway from vestibular ganglion to vestibulocerebellum
enters through brainstem and through juxtarestiform body on the inferior cerebellar peduncle
MOST primary sensory neurons terminate
IPSILATERALLY in the vestibular nuclei
Vestibular nuclei are located in
rostral medulla and caudal pons
There are 4 vestibular nuclei
Lateral, Medial, Inferior, Superior
Lateral (Deiter’s) Vestibular Nucleus gives rise to
Lateral Vestibulospinal Tract (LVST)
LVST function
IPSILATERAL innervation to EXTENSOR axial musculature for balance and postural changes
LVST projects to
ALL levels of spinal cord
Medial Vestibular Nucleus gives rise to
Medial Vestibulospinal Tract (MVST)
MVST function
BILATERAL innervation neck muscles for control and stabilization of head
MVST projects to
Cervical levels Only
Inferior vestibular nucleus
afferents project to juxtarestiform body to vestibulocerebellum
Superior vestibular nucleus
afferents project to juxtarestiform body to vestibulocerebellum
Which vestibular nuclei are composed of myelinated axons mixed with cell bodies giving them a “salt and pepper” appearance?
Lateral and Inferior
Extensive commissural connections between vestibular nuclei on opposite sides of the brian allow
direct comparison and coordination
Medial longitudinal fasciculus (MLF) contains
fibers projecting from ALL the vestibular nuclei to the EOM
Paramedian Pontine Reticular Formation (PPRF) contains
fibers projecting from the CONTRALATERAL vestibular nuclei
Paramedian Pontine Reticular Formation (PPRF) function
center for horizontal gaze; activation of IPSILATERAL abducens and CONTRALATERAL oculomotor
IF PPRF is stimulated on the Left then the _________ abducens and the _________ oculomotor is activated
Left; right; to produce a gaze to the side of the stimulated PPRF
Ascending portion of MLF function
connect vestibular nuclei with motor nuclei of EOM (lateral and vertical gaze)
descending portion of MLF function
MVST tract connections
What is the fluid flowing through the semicircular canals?
Endolymph
