Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Neuroscience Unit 1 > Central Control of Visual Reflexes and Eye Movements > Flashcards

Central Control of Visual Reflexes and Eye Movements Flashcards

1
Q

Where are pupillary constriction and vertical eye movements organized?

A

The pretectal level, level of posterior commissure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where are accommodation and convergence organized?

A

Rostral midbrain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where are horizontal eye movements organized?

A

Caudal pons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the order of neurons in the pupillary constriction (miosis) pathway, and what type of reflex is it?

A

Subcortical reflex controlled at the pretectal level

  1. Axons from ipRGCs project to ipsilateral (or bilateral, if on nasal side of retina) pre-tectal nucleus.
  2. Pretectal nucleus sends axons bilaterally, some through pretectal/posterior commissure and some to ipsilateral Edinger-Westphal nucleus
  3. Edinger-Westphal nucleus is origin of preganglionic PANS cellbodies for pupillary constrictor, axons follow CN3
  4. Synapse in ciliary ganglion, send axons to to pupillary contrictor muscles.

Reflex will be bilateral due to pretectal nucleus sending to both sides, but even if one pretectal nucleus was knocked out, it would still be bilateral since light is sent to both pretectal nuclei from one eye if the whole eye is illuminated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is the pupillary light reflex useful and what does it test?

A

Can be used when patient is unconscious. Since it is subcortical, it tests CN2/CN3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a Marcus Gunn pupil?

A

Relative afferent pupillary defect -> shining light in eye does not produce direct or consensual light reflex, but the opposite eye will. Indicates CN2 damage to the affected eye (Afferent)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the pathway for pupillary dilation (mydriasis)? What type of reflex is this?

A

Also subcortical. Triggered by SANS.

  1. Hypothalamus, passes through reticulospinal tract (close to ALS) all the way to T1, synapse on lateral horn (preganglionic SANS in ILC at T1).
  2. Preganglionic axons enter sympathetic chian ganglionic, synapse in superior cervical ganglion
  3. Superior cervical ganglionic cells send axons to synapse on pupillary dilator muscle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What causes anisocoria and what typically accompanies it?

A

Typically a CN3 lesion, causing ipsilateral mydriasis (loss of PANS). May also have exotropia and ptosis (loss of levator palpebrae superioris, CN3).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does Horner’s syndrome cause and why?

A

Interruption of SANS pathway anywhere past SCG. Causes ipsilateral miosis (loss of SANS), ptosis (loss of SANS to tarsal muscle), loss of sweating on ipsilateral face

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the vergence eye movements?

A

Convergence - bringing the eyes towards midline, happens with accommodation
Divergence - bringing them back to straight ahead position

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the convergence, accommodation, pupillary constriction pathway and what type of reflex is it? (near-point response)

A

Cortically-dependent since it uses area 17 (occipital cortex), all organized at rostral midbrain level

  1. RGCs in the fovea are activated by an image, synapse on ipsilateral and contralateral LGN because image falls on both sides of vertical meridian
  2. LGN neurons project to area 17 as usual via optic radiations
  3. Cortical fibers travel via superior longitudinal fasciculus to vergence center (supraoculomotor area)
  4. Vergence center neurons synapse on E-W nucleus
  5. E-W axons have many fates
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where is the vergence center located?

A

Superior to the oculomotor complex, in the reticular formation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the fates of the axons in the E-W nucleus for the accommodation-convergence reflex?

A
  1. One set of axons synapses in ciliary ganglion, postganglionic PANS head to ciliary muscles for accommodation (PANS)
  2. One set of axons synapses in ciliary ganglion,
    postganglionic PANS head to pupillary constrictor muscle of iris (PANS)
  3. Final set of axons synapse on oculomotor nucleus, cause ipsilateral somatomotor neuron activation, activating medial rectus muscles on each side.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the Argyll-Robertson pupil? (Prostitute’s pupils)

A

During CNS syphilis, there is no pupillary light reflex constriction, but the accommodative-convergence constriction remains the same. Probably due to lesion of pretectal nucleus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is required for initial eye movement? What disease is this relevant in?

A

Motor release from basal ganglia. In Parkinson’s, this release never happens.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are conjugate / version eye movements, and what is this in contrast to?

A

When eyes move in the same direction. This is in contrast to vergence movements, in which eyes move in opposite directions (converging or diverging)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the two stabilizing eye movement types, and what is their control?

A

Vestibulo-ocular reflex (VOR) - subcortical

Optokinetic reflex (OKR) - cortically dependent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the VOR?

A

Vestibulo-ocular reflex “Doll’s eyes”, tests CN 3,6,8. Initiated by signals from semicircular ducts. Don’t do with C-spine patients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the OKR?

A

Optokinetic reflex - initiated by visual signals, works together with VOR to stabilize the visual field. Involved when the semicircular ducts cannot detect the subtle changes in visual field

20
Q

What are foveating eye movements?

A

Movements which shift the fovea to a new object or follow an object continuously

21
Q

What are saccadic movements? What is saccadic suppression?

A

Very rapid eye movements that shift fovea to a new target, cortically mediated, via FEF / PPRF / superior colliculus pathway

Saccadic suppression - no image is seen during saccades

22
Q

What are pursuit eye movements?

A

Used for following objects, a foveating eye movement, cortically dependent - input from visual cortex to pontine nucleus to cerebellum to vestibular nucleus to eye muscles. Not well understood.

23
Q

Where is the frontal eye field located?

A

In the posterior part of the middle frontal gyrus

24
Q

What is the function of the FEF?

A

they choose which objects in the visual field to look at, involved primarily with saccades. They have a very low threshold for eye movements

25
Q

What will irritating stimulation to the FEF on one side cause?

A

Conjugate / version eye movement away (contra) the side that was stimulated

26
Q

What happens if there is destruction of a FEF?

A

Transient ipsilateral deviation to the affected side (they work in equilibrium like the vestibular nuclei)

27
Q

Where do the FEF synapse?

A

Ipsilateral superior colliculus / basal ganglia

28
Q

How does FEF action differ for horizontal vs vertical eye movements?

A

Both FEF must fire for vertical, only one side must fire for horizontal (moves eyes towards contralateral side)

29
Q

What is the function of the superior colliculus? Where is it located?

A

Located in rostral midbrain, calculates the precise coordinates for moving the eyes so that the foveas register the important object of interest (as determined by FEF)

30
Q

What are the three layers of the superior colliculus?

A
  1. Superficial - receives input from optic tract directly, and also area 17.
  2. Middle - receives input from FEF and other sensory modalities (i.e. auditory)
  3. Deep - contains premotor neurons which receive input from upper layers which send motor axons to midbrain (vertical), PPRF (horizontal), and tectospinal tract (neck)
31
Q

What type of movements does FEF stimulation of superior colliculus produce?

A

Volitional / conscious eye and head movements

32
Q

What type of movements does sensory stimulation of superior colliculus produce?

A

Reflexive eye and head movements

33
Q

Where does stimulation of the superior colliculus cause the eyes and neck to move?

A

Via tectospinal tract -> contralateral neck movements

Via PPRF -> movement of eyes towards contralateral side

34
Q

Where is the PPRF and what does it do? What does PPRF stand for?

A

Paramedian pontine reticular formation, located near the abducens nucleus at the level of the caudal pons.

It functions to speed the signal from the superior colliculus and stimulate the ipsilateral abducens nucleus for version eye movement towards that side

35
Q

How does the superior colliculus communicate with the PPRF?

A

Sends axons across midline to stimulate PPRF. PPRF will stimulate the ipsilateral abducens nucleus

36
Q

What does the abducens nucleus do when stimulated by PPRF?

A
  1. Sends motor axons to activate lateral rectus of ipsilateral eye
  2. Sends internuclear neuron axons via MLF on contralateral side to synapse in contralateral oculomotor complex, ultimately activates medial rectus of contralateral eye
37
Q

Is convergence preserved in abducens nerve palsy? What is the primary clinical symptom?

A

Yes, because control centers near the oculomotor nucleus are unaffected by the lesion.

If right CN6 palsy, then there will be an RET at rest, and right eye will rest at midline in right gaze.

38
Q

What causes lateral gaze paralysis? Is convergence preserved?

A

Lesion of abducens nucleus where both eyes do not move to ipsi side because the internuclear neurons to nucleus 3 are also destroyed. Will still be an RET at rest.

Convergence is preserved (nucleus of 6 not leaded for near point reflex)

39
Q

What happens when you knock out the left MLF between CN6 and CN3? Is convergence preserved?

A

Internuclear ophthalmoplegia, patient will have problems with their left eye turning to the right (medial rectus paralysis of eye in right gaze)

Yes, convergence is preserved, MR is used in that pathway via a different pathway (E-W nucleus)

40
Q

What is one and a half syndrome and what causes it?

A

Lesion of PPRF or abducens nucleus, with ipsilateral lesion of MLF (controls MR in opposite gaze).

Will be combined lateral gaze syndrome and internuclear ophthalmoplegia in opposite gaze. All the patient will be able to do abduct the eye on the unaffected side.

41
Q

Where is vertical gaze controlled?

A

Vertical gaze center (VGC), most rostral part of rostral midbrain, dorsomedial to red nucleus at midbrain-diencephalic junction.

42
Q

Where does the VGC project? How is it it innervated?

A

Superior and inferior recti, + superior and inferior obliques.

Innervated by Superior colliculi. To work correctly, FEFs, superior colliculi, VGCs, and oculomotor complexes must fire bilateral and simultaneously

43
Q

What is Parinaud’s syndrome?

A

Pineal tumors of pretectal area and rostral midbrain. First symptom is problems with vertical eye movements. Later: pupillary light reflex problems (pretectal nucleus), ptosis (CN3), impaired convergence

44
Q

What is meant by “down and out” of CN3 lesion?

A

Eyes deviated laterally and downward due to knockout of everything but SO / LR

45
Q

Why will patients with CN4 lesions have problem walking down stairs?

A

Vertical diplopia happens when looking down (controlled by SO)

46
Q

What is cavernous sinus syndrome?

A

CN 3, 4, 6 not working properly, causes ophthalmoplegia of 1 or more eye muscles

47
Q

What disease often causes eye muscle weakness?

A

Myasthenia gravis

Neuroscience Unit 1 (20 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions