Lecture 12 9/8/23 Flashcards
What are the two functions of the vestibular system?
-maintain upright posture
-coordinate head movement with eye movement
How do the eyes move in relation to head movement?
when the head moves, the eyes will move in the opposite direction in order to maintain a steady image
Where are the sensory organs of the vestibular system?
inner ear
What parts of the inner ear are important for the vestibular system?
-utricle and saccule
-3 semicircular canals
What do the utricle and saccule sense?
linear acceleration and gravity
What do the semicircular canals detect?
rotary acceleration
How do the hair cells of the vestibular system work?
-the cells are tonically active
-bending one way increases activity
-bending another way decreases activity
What is important about the way the semicircular canals are arranged?
-one is in each dimension
-can detect movement in all three planes
Why are the cilia able to detect movement?
fluid lags with movement and will flow over the cilia, causing them to bend
What is the cupula?
a jelly-like substance over the hair cells that bends around them
What are the utricle and saccule?
ridges filled with hair cells
Why are the otoliths on the on the surface of the cupula important?
they provide weight to help bend the hair cells
What are the two paths of the vestibular system?
-path rostrally that makes the eyes move
-path to the spinal cord and LMNs to maintain posture
What is the role of the vestibular nuclei?
take inner ear input and compare the two to detect rotation and gravity
What happens when the head is level and not rotating?
there is equal electrical activity and exert equal extensor muscle messages
What happens when the head leans to the left?
-greater elec. activity on the left
-more extensor messages and muscle activity on left side
What happens when there is a lesion on the left inner ear?
-there is no elec. activity on the left, only the right
-extensor muscle signals only on right side
-patient leans left towards lesion
What are the rotation-induced eye movement?
-eyes move in an equal and opposite direction
-forebrain induces corrective movement towards direction
How do the eyes move when there is a lesion on the left inner ear?
-eyes move to the left towards lesion
-corrective phase to the right, away from lesion
What is spontaneous nystagmus?
-eyes drift towards lesion
-quickly correct away from lesion
-eyes move when patient is not rotating
What is pendular nystagmus?
-eyes moving equal speed in each direction
-congenital abnormality
-NOT vestibular
What is the role of the cerebellum?
inhibit the vestibular nuclei
What happens when there is a left cerebellar lesion?
-left vestibular has no inhibition
-increased activity and extensor tone on left side
-animal leans to the right side, away from lesion
What occurs in bilateral vestibular disease?
-animal will stay in a crouched position
-head will dramatically move from side to side
Would animals with bilateral vestibular disease have physiologic nystagmus?
no, because their brain cannot sense if they are rotating
