Vestibular and Visual Systems Flashcards
(33 cards)
The vestibular system is important in perceiving self-motion. What other sense is its functioning vital to and why?
Vision. It helps stabilize the head and field of vision during motion.
What is VOR? What does it contribute to?
Vestibulo-ocular reflex; stabilization of gaze.
One of 3 contributing to postural control.
What are the 3 components to the vestibular system and their features?
- Peripheral sensory apparatus
- semicircular canals
- otoliths (stones within) - Central processor
- in rostral medulla and caudal pons
- vestibular nuclei - Motor output
- vestibulo-ocular for gaze stabilization
- vestibulospinal for posture, balance
The membranous labyrinth is a membrane-lined chamber that houses the peripheral vestibular apparatus and cochlea? What bone are they located in?
The petrous portion of the temporal bone.
The cochlea is located anterior to the vestibular apparatus. Describe their anatomy.
Vestibular apparatus:
- semicircular canals (ant, post, lat)
- otoliths (succule and utricle; have slightly different functions than canals)
- all parts connected
The vestibular apparatus is contained within a cave of bone and is surrounded by membranes (2). Describe each.
Endolymph
- fills membranous labyrinth chamber
- viscous fluid
Perlymph
-fills space between membrane and bone
All semicircular canals are open at both ends to the utricle. What planes are the 3 semicircular canals in and what are their functions?
ANT and POST: oblique plane between sagittal and coronal.
-at 90* to each other
Work in complimentary pairs:
-anterior on R in same plane as posterior on L and visa versa
LATERAL
- 30* elevated from horizon
- lateral axial rotation
ANT
-flexion / extension
POST
-lateral side bending
Ampulla are bulb-like objects located on one end of each canal and have hair receptors located on a bump called the “crist”. Describe their anatomy.
- Contain hair cells which are the receptors
- Stereocilia protrude from hair cells
- Longest = kinocilium, all arranged in same direction in each canal
- Covered by gelatinous cupula, exposed to endolymph
Does the cupula (and hair cells within) move in the same direction as head motion?
No, it’s opposite: rightward rotation gives leftward movement of endolymph.
Endolymph lags behind with head motion and will apply a force to the cupula once it is in motion.
Through receptor potential summation, neurotransmitter is released at the base of the hair cell and picked up by CNVIII causing AP. What is the baseline nerve firing rate bilaterally, and what happens when this rate is increased or decreased? What is the mechanism?
80-100 spikes / sec.
DEPOLARIZATION (+)
- occurs when stereocilia move toward kinocilium
- increase in firing rate
- excitation
HYPERPOLARIZATION (-)
- stereocilia move away from kinocilium
- decrease firing rate
- inhibition
Which way does the cupula move with left head motion?
Cupula bends to the left because endolymph push is coming from the right.
The push-pull arrangement is a bilateral stereocilia reference. What happens with right axial rotation at the lateral canal cupula on the right and left side? Kinocilium closest to midline.
RIGHT
- endolymph moves left
- stereocilia move toward kinocilium
- excitation and depolarization
LEFT
- endolymph moves left
- stereocilia move away from kinocilium
- inhibition and hyperpolarization
If the canals detect angular acceleration, what do the utricle and saccule detect? What is their detection orientation? The receptor area is called macula.
Linear acceleration and head position relative to gravity, due to movement of calcium carbonate crystals called otoconia (analogous to cupula).
UTRICLE
-horizontal
SACCULE
-vertical
Regarding head motion, what is something the otoliths can do that the canals cannot?
Detect static head position relative to gravity.
In central processing, CNVIII relays information to the vestibular nuclei. Describe its anatomy and the significance?
Superior
Inferior (descending)
Medial
Lateral (Deiter’s)
-Each have different afferent and efferent connections
What is the purpose of the vestibular nuclei and where are they?
Vestibular nuclei integrate visual and somatosensory with vestibular information.
Rostral medulla and caudal pons.
By what pathway does the vestibular system communicate with motor (eye movement) output after central processing?
Down spinal cord through vestibulospinal tracts, up to eye movement via medial longitudinal fasiculus (MLF).
When perceiving self-motion, ___ in unconscious and ___ is conscious.
Postural control
Information projected to cortex
The VOR is heavily myelinated and has the least lag of any reflex in the body. What CN’s does it recruit for motor action?
VI - abducens
III - oculomotor
T/F: Coordinated eye movements are equal and opposite to head movements.
True. Keep visual targets on the fovea (point of fixation with highest visual acuity).
What is unique about vertigo?
Sense of movement typically with acute unilateral lesions.
What is oscillopsia?
Visual field is moving, unstable.
What is the most common type of vestibular system tumor?
Acoustic schwannoma.
What happens at the optic chiasm? What about the lateral geniculate nucleus?
Crossing of axons.
Relay nucleus of thalamus.
