Eye and head movements Flashcards Preview

Neuroscience > Eye and head movements > Flashcards

Flashcards in Eye and head movements Deck (28):
1

What are the components that control gaze and stabilise an image on the retina?

Oculomotor system: moves eyes in orbit whilst head is still

Head-movement system: moves eye sockets as a whole whilst head moves

2

Describe the different types of eye movements?

Saccadic: shift fovea rapidly to new visual target

Smooth pusruits: keep image of a moving target on fovea

Vergence: moves eyes in opposite directions

Vesticular ocular: holds image still on retina during brief head movements

Optokinetic: holds image stationery during sustained head rotation or translation

3

Describe the extraocular muscles?

4 rectus muscles: superior, inferior, lateral, medial

2 obliques: inferior, superior 

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4

Describe the movements that can be performed by the eye?

Elevation/depression

Abduction/adduction

Intorsion/extorsion 

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5

What determines the actions of the rectus muscles?

 

Their insertion onto the eyeball

6

Describe the primary actions of the rectus muscles?

 

SR: elevation

IR: depression

MR: adduction

LR: abduction

7

Describe the insertions of the oblique muscles?

 

Insert a long way down the back of the eyeball

SO: well behind equator at an oblique angle close to LR (tendon runs through trochlea)

IO: behind equator close to LR

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8

Describe the primary actions of the oblique muscles?

SO: torsion (also involved in depression)

IO: torsion (also involved in elevation)

9

How can each of the six eye muscles be tested in isolation?

 

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10

Which lower motor neurons are involved in the neural control of eye movements?

 

Oculomotor nerve (CN III): SR, IR, MR, IO

Abducens nerve (CN VI): LR

Trochlear nerve (CN IV): SO

11

Describe the neural control of eye movements?

 

Hierarchical control of eye movement involving:

LMNs (CNs)

Brainstem centres (reticular formation)

Higher cortical areas

 

12

How does the neural supply of CN IV to the SO muscle differ to the innervation of the other extraocular muscles?

 

CN IV innervates contralateral SO

Others all have ipsilateral innervation

13

Which structures are responsible for coordinating the movements from one eye with the other?

Medial longitudinal fasiculus

Reticular formation: PPRF (pontine paramedian reticular formation) and MPRF (mesencephalic paramedian reticular formation)

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14

What is the MLF?

Medial longitudinal fasiculus

White matter tract that connects the various cranial nerve nuclei

 

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15

What is the function of the pontine paramedian reticular formation?

Horizontal gaze centre

Coordination of MR and LR of each eye (CN III and CN VI)

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16

What is the function of the mesencephalic paramedian reticular formation?

Vertical gaze centre 

Coordination of SO and SR of each eye (CN IV and CN III)

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17

Where is a patient's lesion if they cannot coordinate horizontal movement of the eyes?

Pons

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18

Where is a patient's lesion if they cannot coordinate vertical movement of the eyes?

Midbrain 

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19

Describe the neural control of horizontal saccades?

Requires simultaneous excitation of burst neurons and inhibition of omnipause neurons 

 

Message from cortex > excites burst neurons > stimulates ipsilateral abducens > contraction of ipsilateral LR

At same time, activates neuron in MLF > stimulates part of contralateral oculomotor nucleus > contraction of contralateral MR 

 

Communication from PPRF inhibits contralateral abducens nucleus > contralateral LR inhbited 

At same time, via MLF, inhibitory signal from contralteral abducens nucleus to ipsilateral oculomotor nucleus > ipsilateral MR inhibited

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20

Describe the function of burst neurons in the PPRF?

Fire at high frequency just before movement

Two types: excitatory and inhibitory

Excitatory: provide excitatory connections with ipsilateral abducens

Inhibitory: suppress activity of contralateral abducens 

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21

Describe the function of omnipause neurons in the MPRF?

Fire continuously during the saccade, excpet when the eyes move (tell eyeballs when to stop moving)

Project to contralteral abducens nucleus 

 

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22

Which neurotransmitter do omnipause neurons in the MPRF use?

GABA

23

What drives saccadic eye movements?

Higher cortical processing

Frontal eye fields, superior colliculus and basal ganglia play important roles 

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24

How is the abducens nucleus connected to the contralteral oculomotor nucleus?

MLF

25

How are we able to maintain focus on a stationary object while moving our heads, without loss of visual focus or dizziness?

Input from vestibular system 

26

How does the vestibular system help us to maintain focus on a stationary object when our head is moving?

Three semiciruclar canals provide information about the head in space (fluid movement across hair cells > neural signal)

In addition, otolith organs give information about linear acceleration 

 

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27

How does neural signalling within semicicrcular canals alter eye movements?

When fluid goes in one direction through the semicircular canal > increase in AP firing

At the same time, fluid going through the oppsoite ear will cause a decrease in AP firing

This signalling goes to the vestibular nucleus in the brainstem > integrates with eye movement system (CN III, CN VI nuclei)

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28

Describe the vestibular-ocular reflex?

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