Ch 15: Vestibular system Flashcards
what does the vestibular system consist of?
receptors located in the inner ear on both sides of the head
peripheral nerve fibers of the vestibular division of CN 8
central connections that analyze information about the position and movement of the head in space
what are the functions of the vestibular system?
maintain body balance
coordinate eye, head and body movements
permit the eyes to remain fixed on a point in space as the head moves
what structures mediate the functions of the vestibular system?
commissural connections between the vestibular nuclei
vestibulocerebellar tracts
vestibulospinal tracts
vestibulo-ocular tracts
thalamocortical tracts
the thalamocortical pathway to the parietal lobes serves as:
the conscious sense of head position and acceleration
the inner ear (labyrinth) consists of:
bony labyrinth:
-consists of a series of interconnected cavities in the petrous portion of the temporal bone
membranous labyrinth (lies inside the bony)
- a system of tubes and sacs of fine membranes
- contains 5 compartments: utricle, saccule and 3 semicircular canals
what is perilymph?
a fluid that fills the space between the bony and membranous labyrinth
the perilymphatic space of the vestibular part of the bony labyrinth is continuous with the perilymphatic spaces of the cochlea: the scala vestibule and scala tympani
what is endolymph?
fills the membranous labyrinth
communicates through a small channel with that in the cochlear duct
what are the peripheral receptors of the vestibular system? where do they reside? what do they do?
the vestibular hair cells
reside in specialized receptor areas within the membranous labyrinth
dynamic functions:
detect both linear (translational) and angular (rotational) motion of the head in space
static functions:
allow detection of the position (tilt) of the head
what requires all components of vestibular function?
the control of posture, locomotion and eye movements
what are the 2 swellings within the membranous labyrinth?
utricle
saccule
what does the floor of the cuticle house?
what is on the apical surface of (the above)?
a specialized receptor region= macula
the macula contains hair cells that synapse on the distal branches of vestibular ganglion cells
the apical surface of each hair cell bears numerous STEREOCILIA and on each side of the stereocilia, a single KINOCILIUM
macula hairs extend upward into an overlying gelatinous substance containing ____?
otoconia - consists of calcium carbonate crystals
how does the macula lie when the head is in an erect position? what happens to the gelatinous matrix?
the macula of the utricle lies in the horizontal plane
the gelatinous matrix with its otoconia rests directly on the hair cells
what happens to the otoconia if the head tilts or accelerates in the horizontal plane?
the inertia of the otoconia causes the gelatinous matrix to lag behind the movement of the skull and thereby bends the hairs of the receptor cells
how does head movement change the membrane potential of the receptor cells?
when the force on a hair cell bends the sterocilia toward the kinocilium, the cell becomes DEPOLARIZED
when the stereocilia en away from the kinocilium, the cell becomes HYPERPOLARIZED
this results in a corresponding increase or decrease of activity at the synapses between the hair cells and the peripheral processes of the vestibular ganglion cells
the macula of the utricle responds to:
changes in head position with respect to gravity or tilt and to each-horizontal linear acceleration
the arrangement of hair cells in the macula creates a response to acceleration in any diretion
what is the stroll?
a specialized strip through the middle
defines the site of change in orientation of the hair cells
each hair cell is oriented with the kinocilium toward the stroll. thus the hair cells on either side of the stroll are organized as mirror images
the saccule contains a macula of similar structure, but..
responds to?
it is oriented vertically
thus linear acceleration in the vertical direction stimulates the macula. this occurs in response to gravity or against gravity, as when we accelerate or decelerate in an elevator
how are the semicircular canals arranged?
anterior/ superior
lateral /horizontal
posterior
arranged in 3 planes that lie roughly at R angles to one another
what is the ampulla?
what resides in it?
the enlarged end of each semicircular canal
within the ampulla resides the ampullary crest (Crista ampullaris) - a ridge that bears hair cells like those of the maculae
what covers the ampullary crest?
what affect does it have?
a gelatinous capsule termed the CUPULA covers the ampullary crest and extends upward to the roof of the ampulla.
this gelatinous matrix has the same specific gravity as the endolymph and therefor can’t sense the effects of gravity, but when the head undergoes angular acceleration or rotation, the viscous endolymph in the semicircular ducts lags behind as a result of inertia and pushes on the cupola
distortion of the cupola during angular acceleration evokes a receptor potential in the hair cells on the ampullary crest, and this alters the level of activity in the vestibular fibers of VN 8 which the hair cells synapse.
the afferent nerve fibers from each crista amullaris respond with an increase in impulse frequency to rotation in one direction and with a decrease in impulse frequency to rotation in the opposite direction.
these increases and decreases modify a baseline tonic level of vestibular activity that balance input from the 2 ears.
what does damage to the inner ear or vestibular nerve on one side cause?
an imbalance that can produce nausea, vertigo, postural imbalance, and abnormal eye movements
the afferent fibers of the vestibular nerve have cell bodies in:
the vestibular ganglion
axons of bipolar cells of the vestibular ganglion pass:
through the internal auditory canal and reach the upper medulla in company with the cochlear nerve