L15 - Vision & Balance(LA) Flashcards
T/F: Visual system has direct access to vestibular nuclei (involved in balance)
T
Vection is an illusion of self-motion while stationary caused by? What types?
Moving visual scenes
Liner: like in a train
Circular: sitting in a rotating cylinder
What happens when we rotate at a constant velocity?
The sense of rotation is gradually replaced by a sense that the world is rotating around us.
If you place someone in a centrifuge - what do they associate verticality with? Gravity, centrifugal force, resultant force?
Resultant
*It is not gravity but FORCE in general with which we align our notion of what is “vertical”
!How do we sense force? (4)
- Pressure on feet
- Other body parts may take weight
- Muscle reactions to maintain uprightness
- MAJOR SOUCE: vestibular apparatus inside inner ear
!What are the 3 main sources of orientation info?
1) Visual orientation info
2) Proprioceptive info (joint position, muscle force (via sensors in tendons))
3) Vestibular system
_ semicircular canals that sense? _ otolith organs that sense? Both in inner ear (each side of the head) found in?
3 - Rotation, angular acceleration
2 - Linear acceleration
Petrous portion of temporal bone (hardest bone in skull - but still vulnerable to infection)
!How can vestibular system be disrupted?
Deaf people lack the system, may be destroyed by gentamycin or related antibiotics, viruses
What is affected if vestibular system is disrupted?
Swimming (disrupts proprioceptive and visual sources of “up” info), standing on one foot, walking in the dark
What is presbycusis?
Hearing loss
What happens to vestibular organs when excessive physical activity occurs?
Damage to vestibular organs. High impact aerobics can injure otoliths
Bony labyrinth of vestibular system contains?
Perilymph
Membranous labyrinth of vestibular system contains?
Endolymph
Vestibular nerve is part of CN_
8 - same as auditory nerve but different termini
Where do hair cells of all the labyrinth organs send their output to?
Vestibular nuclei in brainstem
Cell bodies of vestibular nerve cluster in?
Vestibular ganglia of Scarpa (a swelling of the vestibular nerve within the internal auditory meatus)
Where does vestibular nerve send efferent input to?
Hair cells
The 2 otolith organs (fluid filled sacs) are called?
- Utricle is joined to the 3 semicircular canals
- Saccule is a separate little pouch
- Oto (ear) lith (stone) - they are crystals of Ca2CO3
Sensory hair cells embedded into otolith organs where the otoliths are embedded on top of it
Sensory hair cells embedded into otolith organs where the otoliths are embedded on top of it
Auditory transduction
Bending towards kinocilium - depol
Away - Hyperpol
Auditory transduction
Bending towards kinocilium - depol
Away - Hyperpol
Responses of kinocillium saturate when cilia are bent more than _ microns?
0.5 microns - about the width of a cilium
What happens to otolith organs when airplane loses altitude in downdraft suddenly?
- Saccular up/down otoliths stimulated
- Utricular otoliths no longer press on hair cells
Where are endolymph found?
Semicircular canals are filled with endolymph
Each semicircular canal has a bulge called?
Ampulla
Hair cells detect inertia of? Otoliths? Canals?
Hair cells - Internal contents
Otoliths - otoliths itself
Canals - Endolymph
Cupula
Gelatinous mass on top of crista (thickened zone of epithelium) that contains hair bundles in the same orientation. Bending one direction hyperpol (away from kinocilium), other direction depol (towards kinocilium).
During head rotation, the endolymph pushes on the?
Cupula
Vestibular nerve transmits info about head rotation to vestibular nuclei in the medulla ipsilaterally or contralaterally?
Ipsilaterally
Vestibulo-ocular reflexes
Keep eyes still when head moves
Vestibulo-spinal reflexes
Enables skeletomuscular system to compensate for head movement and for head to be kept still while body moves
!3 Different Vestibular-ocular reflexes (VOR) - what do they compensate for? Input from? Walking involves which ones?
1) Rotational (most important one) - compensates for head rotation. Canal input
2) Translational - Compensates for linear head movement. Otolith input
3) Ocular counter-rolling - compensates for head tilt in the vertical. Otolith input
Walking involves rotational and translation
When the canals sense rotation in one direction, the eyes slowly rotate in the same/opposite direction? Does this occur in the dark?
Opposite, yes
In horizontal rotation - what drives the slow phase? Fast phase?
Slow - vestibular signals
Fast - brainstem circuits
What phase - slow or fast in horizontal rotation do comatose patients don’t have?
Fast
3 neuron arc of horizontal VOR
1) Ear to vestibular nucleus
2) To eye movement nuclei
3) To eye
Theories of motion sickness (2)
1) Sensory mismatch - e.g. reading book in car, your ear says moving but eyes say stationary. Drivers can anticipate motions, giving less mismatch
2) Poisons (e.g. alcohol) tend to produce mismatch between vision and balance by upsetting viscosity of ventricular endolymph - hence vomiting may be an adaptive response to ingesting poison
No explanation fits all the data
Is Vection influenced by eye movements?
No
What is better for predicting sickness - VA or duration of eye movements?
VA
