Vestibular Flashcards
external auditory Meatus
The sound waves travel through this area and will cause vibrations to occur at the eardrum or the tympanic membrane
auditory ossicles
Malleus, incus, stapes
sound amplification
internal to the eardrum and pick up the movement of the tympanic membrane in response to the vibrations and transmits the sound waves to the oval window
There are muscles that attached to the ossicles that helps reflexively dampen the sound and as protection
Oval window
transmit sound vibrations into the lymph fluid inside the labyrinth, the cochlea
after the sound waves have been transmitted into the fluid of the cochlea,
There are hair cells that send signals to the cochlear nerve.
The pressure is then dissipated at the round window
The order of events of sound
auricle
External auditory canal
Tympanic membrane
auditory ossicles
oval Window
Fluid lymph in cochlea
hair cells
Cochlear nerve
Pressure dissipated at round window
labyrinth inner ear
Cochlea
Vestibule
Semicircular canals
bony labyrinth
within Compact bone
Contains perilymph suspends membranous labyrinth
membranous labyrinth
Cochlear duct
Utricle
Saccule
Semicircular canals
Filled with endolymph
Hair cell receptors -bend and send signal frequencies to cranial nerve eight
perilymph
Between the labyrinth and the bone
endolymph
Inside the membranous labyrinth
semicircular canals
Three hollow rings, perpendicular to each other
Anterior (superior)
Lateral (horizontal)
Posterior
receptors detect motion via movement of the endolymph
Only sensitive to rotational acceleration and deceleration
The canals open into the utricle (otolithic organ)
Before you get to the utricle, there is the ampulla which are swellings of each canal that contains a crista
crista ampullaris
ampullae contain cristae
supporting cells
Sensory hair cells
Embedded in gelatinous mass called cupula
Movement of the cupula causes hair cells to move and detect movement
Hair cells
translate, mechanical force into nerve impulses
Consist of sensory neuron
multiple small stereocilia
a single large kinocilium
when the lymph moves, and there is movement towards the kinocilium… along the hair cell
there is going to be an excitatory effect
increased discharge rate of the vestibular nerve
Depolarization happens at a faster rate
when the lymph moves away from the kinocillium… opposite direction
Theres going to be an inhibitory effect
Hyperpolarization
Discharge is significantly slow
cupula movement
Head moves one way, cupula moves the other
Head stationary, baseline rate of the cell firing
Head movement (cupula)
Head moves - fluid lag causes the cupula to bend and move the hair cells
Head movement slowing or stopping- cupula bends in opposite direction
Constant movement (cupula)
endolymph moves at the same speed so the hair cells fire at a constant rate
orientation of the semi circular canals
Are at 90° to each other
Relays movement from correct plane of motion
otolithic organs
utricle
saccule
do not respond to rotation
Respond to head position relative to gravity
Linear acceleration and deceleration
Each sack contains a macula
utricle in which plane
Horizontal plane
saccule in which plane
Vertical plane
Membranous sacs (utricle, saccule) are located between
cochlea And semicircular canals
otoliths in the lymph
The movement of the otolith in the lymph moves across the hair cells that causes the bending and the change in the firing rate from the hair cells
macula
Hair cells in the gelatinous membrane with calcium carbonate crystals on the top (otoconia)
Changes and head position tilt the macula
Hair bends due to otoconia displacing the gelatinous mass
Bending of the hair stimulates neural firing frequency in cranial nerve 8
utricular macula
resides in the floor of the utricle when head is upright
Oriented horizontally
Maximal response -head upright and bending forward
Also response to linear acceleration and deceleration
Sagittal plane movement
sacular macula
oriented vertically
Maximal response - from laterally flex position
sideline to standing
Frontal plane movement
Vestibular cochlear nerve portions
cochlear- portion hearing
Vestibular portion- postural control and control of eye movements
Vestibular nuclei reside in
brainstem at the Pontomedullary junction
contribute to
head movement
Head position relative to gravity
eye movement control when head moves, gaze stabilization
Postural adjustments
autonomic functions
lateral vestibular nucleus
Lateral vestibular spinal tract originates here (medial, postural, balance, tone)
Extends length of the spinal cord
Regulates lower motor, neurons to postural muscles and limbs and trunk
lateral vestibular nucleus
Regulates lower motor neurons to postural muscles and limbs and trunk
Medial vestibular nucleus
(and the small portion of the inferior vestibular nucleus)
Gives rise to medial vestibular spinal tract
Extends into the cervical region and controls the head and neck position (SCM , Traps)
The nucleus and the small portion of the superior vestibular nucleus
fibers ascend into the medial longitudinal fasciculus
oculomotor ,trochlear, abducens nuclei
superior colliculus and cranial nerve 11 nucleus
mediate vestibular ocular reflex VOR
VOR
eye movements adjust for changes and head position
Stabilizes images during head movement
dolls eyes
gaze stabilization
Head turns right - increase signal from right horizontal canal and decreases signal from left horizontal canal
Move eyes opposite to direction of the head movement to maintain the visuals stability
VOR order
rotational, acceleration or deceleration of the head
Receptors in semi circular canals
Vestibular nuclei
oculomotor nuclei
Extra ocular muscles
Face tilts down
Anterior Canal stimulated
First synapse in the vestibular nucleus is superior
Second synapse in the nucleus of cranial nerve three
Muscles activated, bilateral superior rectus, and contralateral inferior oblique
Movement of the eyes is up
Face turns right or left
Horizontal Canal stimulated
First synapse in vestibular nucleus is medial
Second synapse in nucleus of cranial nerve three and six
Bilateral medial and contralateral lateral rectus
eye moves horizontal
Face tilts up
Posterior canal stimulated
First synapse and vestibular nucleus as medial
Second synapse and nucleus of cranial nerve three and four
Ipsilateral superior oblique and contralateral inferior rectus
eyes Move down
medial longitudinal fasiculus
connections with extraocular nuclei (3, 4, 6)
Regulates eye movements in response to head movements
vestibulospinal tracts
postural regulation
vestibulocolic pathways
Of the spinal accessory nerve influencing head position
vestibulothalamocortical pathways
Conscious awareness of head position and movement
vestibulocerebellar
Controls magnitude of muscle responses to vestibular information
Vestibular reticular pathways
Influences reticular spinal tracts and autonomic centers for nausea and vomiting
semi circular canals are activated by
Rapid rotation
Can trigger loss of control, leaning or falling
