Efferent Lecture 5 The Ways The Eyes Move And Pathways For Control

Front 1

what are two examples of fast eye movements

Back 1

saccades
quick phase of nystagmus

Front 2

what are 4 examples of slow eye movements

Back 2

pursuit
vergence eye movement
vestibular eye movement
optokinetic eye movement

Front 3

what is the main reason for eye movements which is common in all movement,

Back 3

to keep object on the fovea
and stereo/binoularity
enlarged field of vision

Front 4

what is the function of vestibular eye movement

Back 4

to hold image steady during brief head rotations

Front 5

what are saccades

Back 5

quick eye movements of both eyes in the same direction

Front 6

where are saccades initiiated

Back 6

frontal lobe broadmans area 8

Front 7

saccade function

Back 7

to maintain fixation
to refixate

Front 8

how is the amplitude of a saccade measure

Back 8

it is the angular distance that the eye needs to travel during the movement

this is linear for amplitudes up to 60 degrees

for larger than 60 degrees the peek velocity remains constant at the max velocity that is attainable

Front 9

wha is saccade latency

Back 9

defined as the delay encountered between the presentation of the stimulus and the onset of the saccade
averges about 200 ms

Front 10

what are microsaccades

Back 10

tiny eye movement, how we look at the world. cannot perceive them under normal circumstances they are roughly 60 arc seconds in excursion

Front 11

what would happen if we didnt have micro-saccades

Back 11

vision would cease after a few seconds since photoreceptors only respond to changes in luminance

Front 12

how fast are saccadic eye movements

Back 12

600-700 degrees per second, but can go up to 1000

Front 13

what are examples of non-voluntary saccadic eye movements

Back 13

fast phase of nystagmus
rem sleep

Front 14

what is nystagmus

Back 14

rhythmic back and forth of the eyes. fast in one direction slow in another

Front 15

what is the frontomesencephalic track

Back 15

the visual pathway for saccades

Front 16

what is the pathway for saccades

Back 16

originates in broadmans 8 decends as the frontomesencephalic tract to the upper end of the midbrain where it splits into two different pathways one for vertical another for horizontal

Front 17

pathway for horizontal eye movements

Back 17

originates in broadmans 8 decends as the frontomesencephalic tract to the upper end of the midbrain decends through corticospinal tract of the midbrain. it then crosses at the level of cn iv (so its contralateral horizontal haze centers in the pons which are nea the 6th nerve nucleus (PPRF)

8->PPRF-> LR of one eye amd MR of the other because the 6th sends msg to the third subnucleaus of the other eye

Front 18

how are vertical saccades stimulated

Back 18

they are initiated in the frontal lobe and need bilateral stimulation in oder for them to be produced

Front 19

how are vertical centers organized

Back 19

fibers end up on the same side in the medial posterior commissure for UPGAZE
and the rostal interstitial nucleus fo the MLF for DOWNGAZE

Front 20

which gaze is associated with the interstitial nucleus of Cajal associated with but is poorly understood

Back 20

vertical movement pathway

Front 21

how is vision maximized during saccadic eye movement

Back 21

they are fast so vision is not blurred

Front 22

how many action potentials are produced in saccadic eye movement

Back 22

up to 1000 AP's

Front 23

what are three types of neurons which are associated with saccades and where are they found

Back 23

1.burst
2.pause
3.tonic

in the PPRF

Front 24

when do burst cells fire

Back 24

right before a saccadic eye movement

Front 25

tonic cells function

Back 25

hey discharge in relation to eye position, provides step to hold eye in position

Front 26

explain pause cell firing

Back 26

they fire continuouslyc but pause during a saccade

Front 27

what is cerebellar function in saccadic eye movement

Back 27

it calibrates and coordinates them

Front 28

how fast are pursuit eye movement

Back 28

20 to 50 degrees per second

Front 29

when is a target too fast for pursuits

Back 29

40 degrees per second, you would get a saccade eye movement in this case

Front 30

where is the center for smooth pursuits

Back 30

brodmanns 19,37,39

Front 31

wich eye movement is the occipitomesncephalic tract associated with

Back 31

pursuits

Front 32

when does the pursuit tract splin into horizontal and vertical pursuit movements

Back 32

upper area of the midbrain

Front 33

describe vertical pursuit eye movement !!!!!!!!

Back 33

originates in the POT and hey mix with saccade fibers from the frontal lobe which travel through the tegmentum of the midbrain

Front 34

does the pursuit system cross in the brain

Back 34

it either double decussates or doesn't at all so either way the system reamains ipsilateral

Front 35

what is cogwheeling

Back 35

catch up saccades

Front 36

will a pure occipital lobe lesion impair pursuit eye movement

Back 36

no you only need half the macula to achive fixation and pursue a target (as this type of lesion will cause a homonymous hemianopia)

Front 37

what type of movement would you get with and OKN drum to the right

Back 37

pursuit right
saccade left

Front 38

what does a normal symmetric OKN drum indicate

Back 38

verifys the sensory visual pathway, saccadic and pursuit system and connections to visual cortex are well functioning

Front 39

what are 2 main stimuli to make a vergence movement

Back 39

retinal blur
or location disparity so diplopia

Front 40

what does the vergence system stimulate

Back 40

accommodation and fusional movement

Front 41

how is accommodative vergence stimulated

Back 41

loss of focus , so retinal blur occurs with association of the full near triad (lens, puipilar costriction, convergece)

Front 42

can accommodative effort alone produce convergence

Back 42

yes. example if one eye is covered the eye uncovered changes fixation and shifts from distance to near

Front 43

what does putting a minus lens do

Back 43

converge through accomodation stimulation

Front 44

what part of the visual system is the slowest

Back 44

vergence eye movement at 20 degrees per second

Front 45

where do vergence movement originate

Back 45

brodmanns area 19 the pathway travels to the pretectal area and midbrain tegmentum