lecture 4

Question 1

reasons for making eye movements

Answer 1

to keep the images on the retinas relatively still - clearer

to position the images of interest onto the fovea- most sensitive regions of the retinas

Question 2

how to keep retinal images steady

Answer 2

keep the head still

Question 3

what is the VOR vestibular - ocular reflex

Answer 3

reflex involving the vestibular organs
sensory - vestibular organs - part of the inner ear
motor/response- eye/ocular

Question 4

without the VOR

Answer 4

clear vision would be impossible

Question 5

if the vestibular organs are lost

Answer 5

balance is quickly recovered

Question 6

the VOR keeps your eyes

Answer 6

fixated on an area/ object of interest as your head moves

Question 7

the VOR is mediated by circuits which

Answer 7

do not involve the spinal cord , the BRAIN

not all reflexes are spinal

Question 8

eye movements bring the image onto the

Answer 8

FOVEA known as SACCADES

Question 9

saccades

Answer 9

rapid shift of eye position

they can be reflexive, voluntary or spontaneous

Question 10

an eye moves in two basic ways

Answer 10

very rapid shifts- saccades

much closer smooth movements - VOR

Question 11

Types of eye movements

Answer 11

conjugate or disconjugate

Question 12

conjugate

Answer 12

when the eye moves together in the SAME direction through the SAME ANGLE

Question 13

disconjugate

Answer 13

when the eye move together in OPPOSITE DIRECTIONS

Question 14

neural mechanisms of reflex saccades

to make a conjugate saccade to the left the

Answer 14

right oculomotor nuclei and left abducens nuclei need to be activated simultaneously

Question 15

interneurons in the abducens nuclei connect to the

Answer 15

contralateral oculomotor nuclei

Question 16

to make a left saccade activating signals are sent to the

Answer 16

left abducens nuclei which excites motor neurons and interneurons that carry the signal to the right oculomotor nuclei

Question 17

but contraction of the two muscles on the left side of the eyes is

Answer 17

NOT SUFFICIENT so the muscles on the right need to RELAX

Question 18

muscles on the right relax by

Answer 18

shutting off/ inhibiting excitation of these muscles

Question 19

additional nucleus contained

Answer 19

inhibitory interneurons

Question 20

what does the inhibitory interneurons do

Answer 20

shuts down the muscle activity on the right as it inhibits the contralateral abducens nucleus

Question 21

where does the command signals come from

Answer 21

from a region in the pons called the Paramedic Pontine Reticular formation PPRF

Question 22

what does the PPRF do

Answer 22

contains command signals

generates a burst of excitation that causes the eyes to move rapidly to a new position

Question 23

another signal is needed that holds

Answer 23

the eyes in their NEW POSITION. the signal is generated by the nucleus prepositus hypoglassi(NPH)

Question 24

the NPH contains

Answer 24

loops - feedback the output back into the nucleus

Question 25

the PPRF sends signals to

Answer 25

the motor neurones and interneurons and the NPH

Question 26

how does the circuit get activated so it produces a saccade

Answer 26

reflex saccades involve pathways from the sensory organs to the superior colliculi and then to the PPRF
The superior colluculi are midbrain nuclei

Question 27

saccades are also

Answer 27

voluntary -not initiated by stimulus - instead act of will

originates in the frontal lobe of the cerebral cortex

Question 28

when you make a voluntary saccade you often turn your head aswell but

Answer 28

it was previously sad that when you turn your head it will elicit the VOR response- trying to keep your eyes looking in the same direction

Question 29

so the VOR needs to be

Answer 29

turned off when you make a voluntary head turn to look in a new direction as it keeps your head fixated

Question 30

VOR responses depends on

Answer 30

your intent
to look in the SAME direction - VOR response
to look in a new direction = NO VOR response
= NOT REPEATABLE

Question 31

What would happen if the left abducens nuclei is damaged

Answer 31

it would not be able to transmit signals to the left lateral rectus causing it to contract and pull the eye left

Question 32

what would happen if the nucleus paragigantocelularis dorsals was damaged (NPD)

Answer 32

Purpose - neurons inhibit neurones in the abducens nuclei - responsible for transmitting signals to the muscles that move the eyes to the right - cause relaxation
so removing inhibition - muscles do NOT relax and will oppose leftward movements