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Neuroscience > Exam 3: Eye movement and Limbic system > Flashcards

Exam 3: Eye movement and Limbic system Flashcards

1
Q

6 fundamental tasks of ocular motor system

A
  • fixation
  • saccades
  • smooth pursuit
  • vestibule-ocular reflex (VOR)
  • optokinetic reflex (OKR)
  • vergence system
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1
Q

what is the main goal of eye movement?

A

alignment of the two foveae on objects of interest in the visual field
- The fovea is the part of the retina with the sharpest or best vision (cones)

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2
Q

Fixation

A

maintenance of focus on a particular spot in the visual world
- Your eyes need to stay motionless for a brief moment in order for you to see

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3
Q

Saccades

A

rapid conjugate shifts in gaze attention
- These are the fastest movements human muscles can make ⇒ 660-900 degrees/sec

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4
Q

smooth pursuit

A

fixation on slowly moving objects when head is stationary

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5
Q

vestibule-ocular reflex (VOR)

A

fixation on stationary objects during brief head movements
- It’s critical for this reflex to be in tact ⇒ the world will not look stable

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6
Q

optokinetic reflex (OKR)

A

lets you fixate your eyes on stationary images during sustained head rotations or track nearby moving images with the head fixed
- Lets you track moving images close to you

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7
Q

vergence system

A

fixation on near points in the visual world
To view stationary objects that are close to you with your head stationary

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8
Q

what is the goal of the 6 fundamental ocular motor tasks?

A

to ensure a stable image of the same part of the visual world on the same parts of the fovea of each retina

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9
Q

conjugate movements

A

eyes move in the same direction at the same time

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10
Q

which fundamental movements are conjugate? (4)

A
  • Saccades
  • Smooth pursuit
  • Vestibulo-ocular reflex
  • Optokinetic movements
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11
Q

disconjugate movements

A

the eyes move in opposite direction from each other at the same time

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12
Q

examples of disconjugate movements

A

Vergence movements ⇒ near vision

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13
Q

what are the 6 extra ocular muscles and what cranial nerves control them?

A

4 rectus muscles
- Superior ⇒ 3
- Medial ⇒ 3
- Inferior ⇒ 3
- Lateral ⇒ 6
2 oblique muscles
- Superior ⇒ 4
- Inferior ⇒ 3

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14
Q

agonist/antagonist pairs

A

the lateral and medial rectus muscles attached on either side of one globe ⇒ when one contracts the other relaxes

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15
Q

yoked muscle pairs

A

each pair of medial and lateral rectus muscles attached to the same side as the direction of movement in each orbit ⇒ both contract in unison

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16
Q

what are saccades used for? (5)

A
  • Gaze shift in response to a novel stimulus in the visual field
  • Gaze shift during reading
  • Searching novel scenes
  • Return gaze to remembered locations
  • Quick reset phase of VOR and - OKR ⇒ head movements, eyes move in opposite direction
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17
Q

pulse

A

burst of activity determining the velocity of eye movement and the position
- To overcome the inherent viscosity of orbital tissues

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18
Q

tonic firing

A

determines fixation in neurons ⇒ called the step which is the flat line
- To overcome inherent elasticity of the orbital tissues
- Without this then your eyes won’t fixate and your eyes drift back
- Constant firing but at a lower rate

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19
Q

internuclear neurons in the abducens excite what?

A

contralateral oculomotor neurons

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20
Q

where is the abducens and where is the oculomotor nerve?

A

abducens is in the pons and oculomotor is at the superior colliculus level

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21
Q

where does the abducens internuclear neuron cross the midline?

A

through the medial longitudinal fasciculus

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22
Q

what does the oculomotor nuclei coordinate?

A

the contraction of yoked extraocular muscles and the relaxation of antagonist extraocular muscles

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23
Q

paramedian pontine reticular formation (PPRF)

A

has excitatory burst neurons which send excitation to the abducens motor neurons which turn on motor neurons so the eyes move

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24
Q

What brain region controls the motor neurons in horizontal gaze shift?

A

excitatory burst neurons for horizontal gaze shifts are controlled by the cerebral cortex frontal eye fields

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25
Q

what initiates saccades and smooth pursuit?

A

the cortex

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26
Q

hypometric

A

when we make a saccade but we cannot quite get to the level we want so there is a second tiny saccade that occurs right after
- Could be basal ganglia or SC
- Can be manifestations of other issues

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27
Q

hypermetric

A

too far in the first saccade and then brings the eye back
- Almost always an injury to the cerebellum

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28
Q

how does the visual pathway influence gaze movement? (pathway)

A
  • the area of the cortex right above where the eyes are will send a signal to an excitatory burst neuron in the paramedian pontine reticular formation
  • the burst neuron synapses on the abducens nucleus neuron which will synapse on the contralateral oculomotor nucleus or go right to the lateral rectus of the ipsilateral eye
  • the oculomotor nucleus then synapses on the medial rectus
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29
Q

what type of eye movements happen during reading?

A
  • saccades
  • fixation => only can perceive here
  • also uses vergence
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30
Q

what movements does the superior oblique let you do?

A

out and down as a depressed

31
Q

what muscles are used for eye elevation?

A

the superior rectus and inferior oblique

32
Q

what movements do the superior rectus let you do?

A

eye looks up and in

33
Q

what does the inferior rectus let you do?

A

eye looks down and in

34
Q

what does the inferior oblique let you do?

A

eye looks up and out

35
Q

what is the VOR latency?

A

between 7-15 milliseconds because it is mediated by only 3 neurons

36
Q

what organs allow for your vestibular ocular reflex (VOR)?

A

the vestibular end organs
- semicircular cancels
- saccule
- utricle

37
Q

ampule

A

contain hair cells with fluids in the semicircular canals which moves the fluid to bend the hair cells
- The sensory activates information to your brain when you head moves

38
Q

what do the semicircular canals align with?

A

align with the main directions of pull of the extraocular muscles

39
Q

horizontal canals are in the place of what muscles?

A

horizontal muscles => medial and lateral rectus

40
Q

what do hair cells in the ampules head do?

A

send head acceleration information to the brain
- Each side sends either excitatory or inhibitory information via projections to the vestibular nuclei, which in turn project to the oculomotor nuclei

41
Q

what is the 3 neuron arc for VOR?

A
  • excited hair cells in horizontal semicircular canal send ipsilateral excitatory input into the vestibular and nuclear neurons
  • vestibular nuclear neurons send excitatory signals to ipsilateral oculomotor nucleus and the contralateral abducens nucleus and inhibitory signals to the contralateral oculomotor nucleus and ipsilateral abducens nucleus
  • these send excitatory signals to the ipsilateral medial rectus and contralateral lateral rectus muscles
42
Q

what happens when your head moves too fast for VOR?

A

You use the optokinetic reflex (OKR)
- transitions between slow phases (eye maintains gaze) and quick phases (when eye is resetting)

43
Q

does optokinetic reflex decrease or increase in the dark?

A

in darkness the vestibular nystagmus response decays as the hair cells in the semicircular canals (SCC) habituate to a constant rotation (zero acceleration)
- in light with constant rotation the optokinetic reflex will not decay due to the continued visual input to the ocular motor system

44
Q

strabismus

A

leads to loss of visual acuity in the turned eye (amblyopia = lazy eye) if untreated
- There is a critical period during development of binocular vision where binocular vision must be restored prior to this time (8-10 years) for normal visual acuity

45
Q

Duanes syndrome

A

strabismus can be caused by a mutation in the alpha2-chimaerin gene that has been implicated in axon pathfinding
- No abducens nerve on one side and no lateral rectus muscle
- Have binocular input but they cannot see as well due to restricted movements

46
Q

infantile nystagmus syndrome

A

involuntary eye oscillations that prevent stable images from forming on the retina
- A number of genes are associated with this ⇒ no known cure

47
Q

limbic system

A

interconnected set of brain structures important for emotion, motivation, memory, and automatic control
- Collectively the limbic system integrates these processes to control behavior

48
Q

telencephalon limbic structures

A
  • Cingulate cortex/gyrus
  • Insular cortex
  • Nucleus accumbens
  • Septal nuclei ⇒ thin next to LV
  • Hippocampus
  • Amygdala
  • Olfactory system
49
Q

diencephalon limbic structures

A
  • Mammillary bodies in the hypothalamus
  • Anterior nucleus of the thalamus
  • Mammillothalamic tract
  • Fornix tract (out of the hippocampus)
50
Q

prefrontal cortex

A

roles in executive function such as complex cognition, abstraction, planning, decision making, social awareness ⇒ governing area

51
Q

what lobe contains core memory and emotional expression systems?

A

medial temporal
- Amygdala and hippocampus with associated connections

52
Q

hippocampus

A

has to do with memory and sends axons out through the fornix
- the fornix is outside of the hippocampus

53
Q

fornix

A

fibers wrap around the diencephalon and terminate the mammillary bodies to make a “C” shape ⇒ comes out of hippocampus

54
Q

mammillary bodies project to ___ which project to the ______

A

Mammillary bodies project to the anterior thalamus which projects to the cingulate gyrus
- Can see it in dorsal and ventral locations

55
Q

mammillary bodies

A

dangle off the bottom of the diencephalon in a bean shape which the fornix communicates to so they can project to the anterior nucleus of the thalamus via the mammillothalamic tract (white)

56
Q

functional roles of the limbic system (5)

A
  • Motivation and emotion ⇒ fear, anger, etc.
  • Self control
  • Learning and memory
  • Dysfunction contributes to psychiatric disease ⇒ addiction, mood disorders, schizophrenia
  • Much more of these functions in upcoming lectures on learning, memory, and addiction
57
Q

what process motivation and reward

A

septal nuclei and nucleus accumbens
- Stimulation of these structures is rewarding or reinforcing

58
Q

septal rage

A

septal lesions enhance aggression

59
Q

selective prefrontal cortex damage can do what?

A

decrease aggression

60
Q

Phineas gage

A

an explosion blasted a rod through his left cheek and out of the top of his head
- extensive damage to prefrontal cortex and anterior cingulate gyrus (mostly unilaterally)
- Prior to the accident Gage was described as responsible, hard working, and generally agreeable
- After he became short tempered, impulsive, and socially awkward

61
Q

what brain regions involve learning and memory

A
  • Amygdala
  • Hippocampus
62
Q

Patient H.M

A

treated for temporal lobe epilepsy with a bilateral lesion of part of his medial temporal lobes
- removal/disconnection of his hippocampi and amygdala
- After he was unable to form new declarative memories but his procedural memory was intact
- His presurgical memories and general intellectual abilities were intact

63
Q

Declarative memories

A

memories of facts, events, people ⇒ encyclopedia information

64
Q

Procedural memories

A

motor memories

65
Q

Korsakoff syndrome

A

damage to the mammillary bodies and thalamus from malnutrition, usually from severe alcoholism
- Disruption in the ability to form new declarative memories

66
Q

confabulation

A

inventing memories ⇒ makes new declarative fake memories
- People will black out and then try to piece together their events

67
Q

papez circuit

A

is critical for declarative memory formation ⇒ broadly the limbic system

68
Q

Amygdala

A

stimulation of the amygdala can evoke fear responses in animals and humans
- Elevated amygdala activity is associated with fear and anxiety and disgust
- Damage or lesion to the amygdala reduces fear/threat responses, reduces ability to recognize fear in other people

69
Q

Kluver-bucy syndrome

A

temporal lobe lesions
- Docility, low fear, irresponsible to threats
- Other symptoms are hypersexuality, compulsive eating

70
Q

Urbach Wiethe disease

A

bilateral loss of amygdala ⇒ low/no fear

71
Q

what suggests fear is not fully localized to the amgydala?

A

fear can be induced in people with these disorders under the right conditions

72
Q

rewarding stimuli

A

things that feel good and stimulate dopamine release in the nucleus accumbens
- Eating, sex, exercise, social activities, etc.
- The signal is needed for learning and motivational drive

73
Q

drugs

A

exploit the endogenous reward system, producing exaggerated dopamine release in the nucleus accumbens
- All drugs do this ⇒ nicotine, cocaine, heroin, marijuana, ethanol

74
Q
A

Neuroscience (18 decks)

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