Week 5.3 Flashcards
What are the three major types of eye movements?
- saccades
- smooth pursuit
- vestibulo-ocular
What are saccades?
quick step changes in eye position as the visual field is scanned
What is the neural pathway for voluntary saccades?
- frontal eye fields
- superior colliculus
- reticular formation
- oculomotor nucleus
- eye muscles
What are reflex saccades?
saccades in response to novel stimuli appearing in the visual field
What is the neural pathway for reflexive saccades?
- retinal ganglion cells
- superior colliculus
- reticular formation
- oculomotor nucleus
- eye muscles
Voluntary saccades are mediated by the ___ while reflexive saccades are mediated by the ___.
- frontal eye fields
- superior colliculus
What are smooth pursuit eye movements?
those used to track an object through the visual field with the head stationary
Smooth pursuit eye movements are limited in what way?
they are limited to 30 degrees per second
Smooth pursuit eye movements are triggered by what?
slip of the image on the retina
What is the neural pathway for smooth pursuit eye movements?
- retinal ganglion cells
- LGN
- visual cortex
- reticular formation
- oculomotor nucleus
- eye muscles
What is the vestibulo-ocular reflex?
the compensatory adjustment of gaze when the head moves
What is the maximum velocity of saccades, smooth pursuit movements, and the vestibulo-ocular reflex?
- saccades: 400-700 degrees/second
- smooth: 30 degrees/second
- VOR: 300 degrees/second
What is the neural pathway for the vestibulo-ocular reflex?
- vestibular hair cell
- vestibular nerve
- vestibular nucleus
- oculomotor nucleus
- eye muscle
What brain structure primarily mediates voluntary saccades, reflexive saccades, smooth pursuit, and the vestibulo-ocular reflex?
- voluntary saccades: frontal eye fields
- reflexive saccades: superior colliculus
- smooth pursuit: visual cortex
- VOR: vestibular nucleus
Describe the layers of the vestibular apparatus.
temporal bone surrounding perilymph surrounding membranous labyrinth surrounding endolymph
Name the two vestibular organs.
- semicircular canals
- otolith organs
What are the otolith organs?
utricle and saccule
What are the adequate stimuli for the kinetic labyrinth?
- rotational forces
- head acceleration and deceleration
What are the adequate stimuli for the static labyrinth?
- maintained head tilt
- translational forces, horizontal displacement
The semicircular canals send impulses along the ____ division of the ___ nerve to the ____.
- superior division
- vestibular nerve
- central vestibular pathways
What is a functional pair within the semicircular canals?
two canals within the same plane but in different sides of the head
The horizontal semicircular canals are actually in what plane?
one thirty degrees below horizontal
The semicircular canals are attached to what structure?
the utricles
Where in the semicircular canals are the vestibular hair cell receptors?
the ampulla
What is the cupulla?
a gelatinous mass into which the cilia of vestibular hair cells are inserted
What is scarpa’s ganglion?
the cell bodies of the 8th nerve vestibular afferents
What is a kinocilium?
the single long cilium of a vestibular hair cell
Describe the orientation of kinocilium.
- near the utricle in the horizontal canals
- away from the utricle in the anterior and posterior canals
Vestibular hair cells use what NT to affect the 8th nerve afferents?
glutamate
What causes depolarization of vestibular hair cells?
bending of the stereocilia toward the kinocilium
Describe the flow of endolymph through the horizontal canals as you move your head from side to side.
- initially, endolymph moves relatively slower than hair cells and thus “opposite” head movement
- later, inertia causes endolymph to continue moving relative to hair cells and therefore in the direction of herd movement
Describe 8th nerve activity in response to the three phases of rotation to the right.
- acceleration to the right: increased right nerve activity, decreased left nerve activity
- constant velocity: tonic activity (endolymph is equilibrated)
- deceleration: decreased right nerve activity, increased left nerve activity
In the post-rotational phase of the Barany chair test, you expect a person to fall in which direction?
fall in the direction of rotation
Describe the neural pathway that causes one to fall in the direction of rotation during the post-rotational phase of the Barany chair test.
- decreased 8th nerve firing on rotational side
- decreased firing rate of vestibulospinal neurons
- inhibition of extensors on the right
- flexion to the right (aka fall/tilt)
What eye movements are expected in the post-rotational phase of movement?
slow movement in the direction of rotation followed by a fast rest in the opposite direction
Falling and the typical eye movements in the post-rotational phase of movement are mediated by output from the vestibular nucleus to where?
the vestibulospinal tract and oculomotor nuclei, respectively
What are the features of internuclear ophthalmoplegia?
- inability to adduct affected eye
- nystagmus in the unaffected eye
Internuclear ophthalmoplegia is the result of a lesion to what?
the medial longitude fasciculus, which contains the abducens interneurons that transmit signals to the 3rd nerve nucleus for contraction of the medial rectus
What are the expected effects of a cold and hot caloric test?
- cold: nystagmus toward the contralateral side
- warm: nystagmus toward the ipsilateral side
- COWS (cool opposite, warm, same)
In someone with a unilateral lesion of the vestibular nerve, what symptoms can be expected?
- fall toward the ipsilateral side
- nystagmus to the contralateral side
