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Neuroscience - Physiotherapy > Module 30 - Eye movements & Reflexes > Flashcards

Module 30 - Eye movements & Reflexes Flashcards

1
Q

Based on the lesion in red, what would be the consequence of horizontal eye movements?

A

Answer

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2
Q

Based on the lesion in red, what would be the consequence of horizontal eye movements?

A
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3
Q

Identify the cranial nucleus in the image.

A

Answer

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4
Q

Based on the lesion in red, what would be the consequence of horizontal eye movements?

A
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5
Q

Based on the lesion in red, what would be the consequence of horizontal eye movements?

A

Answer

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6
Q

Based on the lesion in red, what would be the consequence of horizontal eye movements?

A

Answer

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7
Q

Which muscles are responsible for moving the eyes?

A
  • Lateral Rectus
  • Medial Rectus
  • Superior Rectus
  • Inferior Rectus
  • Superior Oblique
  • Inferior Oblique
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8
Q

What is the function of the lateral and medial rectus?

A

They are responsible for horizontal eye movements

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9
Q

What is the function of the superior and inferior rectus function?

A

They are responsible for vertical eye movements

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10
Q

What is the function of the superior and inferior oblique function?

A

They are responsible for Intorsion and extortion of the eye

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11
Q

What is the origin and insertion of the superior oblique? Explain its function.

A
  • Its origin is on the sphenoid bone.
  • And it inserts on the superior surface of the eye
  • It moves the upper pole of the eye inwards
  • It creates a little bit of rotation
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12
Q

What is the origin and insertion of the inferior oblique? Explain its function.

A
  • Its origin is on the medial orbital wall
  • And it inserts on the inferior surface of the eye
  • It moves the upper pole of the eye outwards
  • It creates a little bit of rotation
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13
Q

Associated with each direction of movement a specific muscles.

A

Answer = image

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14
Q

What are the brainstem gaze centers?

A
  • Supra-nuclear centers (above the level of the oculomotor nucleus)
  • Located in the brainstem, the cerebellum, the basal ganglia, and the cerebral cortex
  • Direct the movements of the eyes
    • Coordinate eye movements and control the response of the eyes to changes in target speed and position, and head position.
    • The function of each of these structures has been inferred from the effects of their destruction.
  • Connected to output nuclei by inter-nuclear pathways
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15
Q

Where are the brainstem gaze centers located?

A
  • Located in the brainstem
  • The cerebellum
  • The basal ganglia
  • The cerebral cortex
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16
Q

What does it mean when we explain that the brainstem centers are responsible to coordinate eye movements and control the response of the eyes to changes in target speed and position, and head position?

A
  • What this means is that if we are focusing on an object that is moving these brainstem gaze centers allow our eyes to work together to follow or track that object.
  • Conversely, if we are moving, for example, if we are in a car or on a train, and we are focusing on a single point, the brainstem gaze centers will also direct eye movements and it looks like the object is still and we can focus on it.
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17
Q

What does it mean when we explain that the brainstem centers are responsible for the function of each of these structures has been inferred from the effects of their destruction?

A

What this means, is either experimentally or as a result of a disease, these supranuclear centers have been abolished and so that is how we found out really what they were for, to begin with.

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18
Q

What are the three dedicated circuits of the brainstem gaze centers and pathways?

A
  • Horizontal eye movements
  • Vertical eye movements
  • Vergence eye movements
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19
Q

What is vergence eye movements?

A
  • It is when your eyes come in together towards focus.
  • Both eyes come medially, for example
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20
Q

What are the three dedicated circuits comprised of?

A

Comprised of a brainstem gaze center + inter-nuclear pathway (connects the center to output nuclei)

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21
Q

What is the function of all three dedicated circuits?

A
  • Yoke eye movements together
  • It makes sure that our right and left eye move together in a synchronous fashion
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22
Q

What is horizontal eye movements? What is it control by? Which muscles and to which corresponding nuclei?

A
  • When we move our eyes horizontally, it is controlled by both:
    • The lateral rectus
    • The medial rectus
  • The lateral rectus → is controlled by the abducens nuclei = CN VI
  • The medial rectus → it is controlled by the oculomotor nuclei = CN III
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23
Q

If we wanted to look to the left which muscles of each eye would we need to activate?

A
  • We would need to activate the lateral rectus on the left
  • We would also need the medial rectus on the right
  • Therefore, you need both the abducens nerve from the left eye, as well as the oculomotor nerve to be working from the right eye to be activating the lateral rectus of the left eye and medial rectus of the right eye respectfully.
  • *it is important to note that not only is the abducens nerve connected to the lateral rectus directly, but you can see on the image that it crosses over the midline and is connected to the oculomotor nerve, CN III, of the opposite side. = it is the medial longitudinal fasciculus
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24
Q

What is the medial longitudinal fasciculus (MLF)?

A
  • Connects CN VI and CNIII nuclei
  • Function: conjugate gaze in ALL directions
  • It gives the ability for the eyes to work together synchronously or in unison = it refers to the motion of both eyes looking in the same direction at the same time.
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25
Q

What is the pontine reticular formation (PPRF)?

A
  • Provides input from the cortex
  • We see connections from higher brain centers to the MLF
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26
Q

What type of functional deficits will happen with a lesion on the right abducens nerve? (Lesion 1)

A
  • A pure functional deficit in the right eye looking right
  • No impairments in the left eye
27
Q

What type of functional deficits will happen with a lesion to the right abducens nucleus? (Lesion 2)

A
  • Right lateral gaze palsy
  • Neither eye is able to move to the right
  • No deficits when looking to the left
28
Q

What type of functional deficits will happen with a lesion to the right PPRF? (Lesion 3)

A
  • Right lateral gaze palsy
  • Neither eye is able to move to the right
  • No deficits when looking to the left
29
Q

What type of functional deficits will happen with a lesion to the left MLF? (Lesion 4)

A

Lose a contralateral control
Nystagmus (on the left eyeball) when looking to the right
No functional deficits to looking to the left

30
Q

What type of functional deficits will happen with a lesion to the left MLF and left nucleus (1 ½ syndrome)? (Lesion 5)

A
  • Lose a contralateral control
  • Nystagmus (on the left eyeball) when looking to the right
  • Deficits to the leftwards gaze
31
Q

What muscles of the eye are innervated by the abducens nerve?

A

Lateral rectus

32
Q

What muscles of the eye are innervated by the trochlear nerve?

A

Superior oblique

33
Q

What muscles of the eye are innervated by the oculomotor nerve?

A
  • All other eye muscles
    • Superior rectus
    • Medial rectus
    • Inferior rectus
    • Inferior oblique
34
Q

What is a helpful mnemonic for remembering extraocular eye muscle innervation?

A

LR6SO4 - all the rest are 3

35
Q

In order to coordinate synergistic eye movements, the nuclei of cranial nerves _____, ______, and ________ need to communicate with one another both ipsilaterally and contralaterally.

A

In order to coordinate synergistic eye movements, the nuclei of cranial nerves III, IV, and VI need to communicate with one another both ipsilaterally and contralaterally.

36
Q

Where are the vertical gaze centers located?

A

It is in the midbrain, specifically the midbrain reticular formation and pretectal area.

37
Q

Where are the horizontal gaze centers located?

A

It is located in the pons, specifically in the paramedian pontine reticular formation (PPFR)

38
Q

What are the 4 distinct types of eye movements

A
  • Smooth pursuits
  • Saccades
  • Opto-kinetic Nystagmus (OKN)
  • Vestibular Occular-reflex (VOR)
39
Q

What are the saccadic eye movements?

A
  • A key part of visual exploration
  • Rapid eye movements
  • Saccades are rapid, simultaneous movements of the eyes that redirect the gaze between different fixation points.
  • In this way, saccadic eye movements allow us to scar our environment by directing our gaze to objects of interest so that they will be projected onto the fovea (area of the retina with the highest visual acuity)
40
Q

What is the function of saccadic eye movements?

A
  • Bring targets of interest in the field of view
  • Refocus image on the fovea (remember that the fovea is the part of the eye that has the highest level of acuity)
  • They are ballistic (very rapid) conjugate eye movements
    • These ballistic eye movements cannot respond to changes in the position of a target during the course of a movement.
    • Missile = if you shoot a missile, once you shoot a missile, it can’t change direction – similar with saccades you can’t actually change in the middle of a saccade, but these movements are so quick, that we don’t notice that.
41
Q

What controls saccadic eye movements in the horizontal gaze center?

A

PPRF and the abducens nucleus

42
Q

What controls saccadic eye movements in the vertical gaze center?

A

iMLF (near the oculomotor nucleus)

43
Q

What are the two major types of saccades? Describe them.

A

Reflexive saccades - visually guided saccade in response to external cues (prosaccade)
Volitional saccades - voluntary eye movements, independent of any visual stimulus.

44
Q

What is the origin of a reflexive saccadic eye movement?

A

Superior colliculus

45
Q

What is the origin of a voluntary saccadic eye movement?

A

Frontal eye fields

46
Q

Both the superior colliculus and frontal eye fields communicate with which structures?

A
  • PPRF (Horizontal gaze center)
  • iMLF (Vertical gaze center)
47
Q

Why do both the superior colliculus and frontal eye fields communicate with the PPRF and iMLF?

A

They send motor commands to move eyes in magnitude and direction specified

48
Q

What is the result when both the superior colliculus and frontal eye fields communicate with the PPRF and iMLF?

A
  • Result = eye is moved to intend new position for foveation of visual stimulus
  • The eye is quickly moved and we can get this target into our fovea, our into the part of the idea has the highest acuity.
49
Q

How would you produce a rightward saccade?

A
  • There is descending control from the superior colliculus and the frontal eye fields.
  • We need activation of the right PPRF. The activation of pre-motor neurons in the right PPRF is increased. In the activity of the LMN associated with the right abducens nerve which innervates the lateral rectus of the right eye Is increased.
  • Activation of the right PPRF also increases the activity of the inner nucleus neurons in the right abducens nucleus, which sends their axons along the MLF to innervate the LMN in the left ocular motor nucleus, which in turns innervates the medial rectus of the left eye.
50
Q

How do the planning, programming, and execution happen for a saccade eye movement

A
  • Planning = happens in the frontal eye field
  • Programming = it is in the horizontal and vertical gaze centers
  • Execution = it is in cranial nerve III, IV and VI
  • ***Sometimes between planning and programming there is a bypass to the superior colliculus before going to the horizontal or vertical gaze centers
51
Q

Which specific structures have descending control on eye movements?

A

The superior colliculus (voluntary)
Frontal eye field (reflexive)

52
Q

What are smooth pursuit eye movements?

A
  • Require moving stimulus; cannot be carried out voluntarily without a stimulus
  • Require processing in visual cortex to analyze what an object is, whether it is of interest, direction, and speed of movement
  • Therefore requires a lot of neural processing and cannot follow a fast-moving stimulus (compared with VOR)
53
Q

Where does the descending input for the smooth pursuits come from?

A

ipsilateral parieto-occipito-temporal cortex

54
Q

Which eye movement requires a moving target/stimulus?

A

Smooth pursuit requires moving target
***we can smoothly follow a bird that is flying on by.

55
Q

What is the reason why smooth pursuits require a moving stimulus?

A

The reason they require a moving stimulus is that they are quite smooth and they require a higher up processing in the visual cortex.

56
Q

What is a Vestibulo-ocular reflex (VOR)?

A
  • Eye movements maintain fixation on target when the head moves so that the outside world looks stable
  • For any movement of the head (up/down, moving forward and down, etc.)
  • The VOR will program the precise eye movements in exactly the opposite direction
  • Stimulation of vestibular organs in any combination: leads to the correct excitation/inhibition of 6 eye muscles for each eye.
57
Q

What does the horizontal VOR involve?

A
  • Vestibular nucleus
  • Abducens motor neurons
  • Medial rectus
  • Lateral rectus
  • *This makes sense since these are the 4 centers required for eye movements.
58
Q

What happens when your head turns to the left? What is the final response of a VOR head turn to the left?

A
  • Your eyes turn to the right
  • Abduction of the right eye → comes from the lateral rectus
  • Adduction of the left eye → comes from the medial rectus
59
Q

Which nerves need to be activated in order to VOR head turn to the left and bring your eyes to the right?

A
  • The lateral rectus = abduction of the right eye → abducens nerve
  • The medial rectus = adduction of the left eye → oculomotor nerve
60
Q

Explain the step by step process of what happens when VOR head turns to the left. What is the final response?

A
  • Left semicircular canal excited (part of the audio-vestibular system is excited)
  • Left cranial nerve VIII afferents firing more
  • Recruit right abducens nerve (inhibit left abducens nerve)
  • Right CN VI and left CN III excited
  • Right lateral rectus & left medial rectus contract
  • Eye movements to the right oppose the head movement
61
Q

What are the 3 synapses in the CNS that explains the step by step process of what happens when VOR head turns to the left?

A
  • It excites the vestibular nucleus, the same side
  • It then excites the abducens motoneurons on the opposite side
  • It then excites the oculomotor motoneurons back on the original side
  • Also excites reciprocal inhibition of antagonists
62
Q

What is optokinetic nystagmus?

A
  • A combination of smooth pursuit and saccade like movement
  • Slow phase → in one direction = smooth pursuit
  • Fast phase → eye movements in the other direction = saccade like movement
63
Q

Explain “train nystagmus”

A
  • If you imagine your eyes following a train, you are doing a smooth pursuit following a train, and then all of a sudden you want to look back to the beginning of your vision again –> you look to know if the train is stopping for example.
  • This is an example of optokinetic nystagmus

Neuroscience - Physiotherapy (34 decks)

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