Brainscape's Knowledge GenomeTM

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


See full index

1B Neurology & Neuroscience > VIsual system- pathways > Flashcards

VIsual system- pathways Flashcards

1
Q

what is the visual pathway?

A

neurological pathway whereby vision is converted to neurological impulses to be transmitted from eye to visual cortex in posterior part of brain

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

how is the eye connected to the brain?

A

optic nerve (second cranial nerve)

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

what is the optic nerve made up of?

A
  • Optic nerve made up of myelinated ganglion nerve fibres w. cell bodies originating within retina
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how to signals travel from the eye?

A

from eye to optic nerve

  • Optic nerves from both eyes converge at optic chiasm
    • Above + in front brain stem
    • Half ganglion nerve fibres cross at optic chiasm and exit along contra-lateral optic tract
    • Remaining ganglion nerve fibres exit along optic tract on same side
  • via optic tract to lateral geniculate nucleus
  • via optic radiation to primary visual cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

where do ganglion fibres originate?

A

within retina

  • Synapse upton next order neruons
  • At lateral geniculate nucleus
  • Relay centre situated within thalamus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what forms the 4th order neuron?

A

optic radiation

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

what does the optic radiation do?

A
  • Relaying signsals from lateral geniculate ganglion to primary visual cortex within occipital lobe for lower visual processing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what does the primary visual cortex do?

A
  • Relays visual information to the extra-striate cortex
    • Region adjacent to primary visual cortex for further higher visual processing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is the visual pathway within retina?

A
  1. 1st order neurons= photoreceptors detect light
  2. 2nd order neurons= synapse upon bipolar cells
  3. 3rd order nerons= retinal gangion nerve cells
  4. half retinal ganglion nerve cells cross to opposite side at optic chiasm= partial decussaion
  5. retinal ganglion fibres terminate at lateral geniculate nucleus in thalamus and synapse on 4th order neurons
  6. 4th order neurons= optic ratiation
  7. optic radiation relays visual information to visual cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what do retinal ganglion nerve fibres do?

A
  • Relay visual information out of eye to brain along optic nerve (CNII)
  • To improve signal transmission-retinal ganglion nerve fibres become myelinated after entering optic nerve
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is the effect of lesions anterior to optic chiasm?

A

affect visual field in one eye only

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the effect of lesions posterior to optic chiasm?

A

affect visual field in both eyes

due to ganglion fibre crossing in chiasm to exit along contralateral optic tract (53%)

contralateral homonymous hemianopia in both eyes

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

where do crossed fibres predominantly originate?

A

nasal retina- responsible for temporal half of visual field in each eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

where do uncrossed fibres originate?

A

temporal retina- responsible for nasal half of visual field in each eye

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

what happens in lesions at optic chiasm?

A
  • Damages crossed ganglion fibres from nasal retina in both eyes but spares uncrossed ones originating from temporal retina
    • Temporal field loss in both eyes simultaneously
    • Bitemporal hemianopia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what happens in a right sided lesion posterior to optic chiasm?

A

left-sided homonymous hemianopia in both eyes and vice versa

17
Q

overall what are the effects of lesions posterior and anterior to opic chiasm?

A
18
Q

what are the effects of each of these disorder locations?

A
19
Q

what is a bitemporal hemianopia usually caused by?

A

enlargement pituitary gland tumour (tumour sits under optic chiasm)

20
Q

what is a homonymous hemianopia usually caused by?

A

stroke of CVA in brain

21
Q

how does homonymous hemianopia with macular sparing occur?

A
  • Damage primary visual cortex
    • Often due to stroke
  • Area within primary visual cortex representing macular is well protected as received dual blood supply from both right and left posterior cerebral arteries
22
Q

what happens to the pupil in light?

A
  • Pupil constriction
  • Iris circular muscle contracts and constricts pupillary aperture
  • Decreases spherical aberrations and glare
  • Increases field of depth
  • Reduces bleaching of photo-pigments
  • Pupillary constriction mediated by parasympathetic nerve (within CN III)
23
Q

what happens to pupil in light?

A
  • Pupil dilation
  • Increases light sensitivity in dark by allowing more light in to eye
  • Pupillary dilation mediated by sympathetic nerve activating iris radial muscle
  • radial muscles contract
24
Q

what is the afferent pathway of signals from eye?

A
  • Rod and cone photoreceptors synapsing on bipolar cells synapsing on retinal ganglion cells
  • Pupil-specific ganglion cells exit at posterior 3rd of optic tract before entering the lateral geniculate nucleus
  • Afferent pathways from each eye synapses on Edinger-Westphal nuclei on both sides in brain stem
25
Q

what is the efferent pathway of signals from the eye?

A
  • Provided by parasympathetic nerve arising from brainstem synapsing at ciliary ganglion upon short posterior ciliary nerve
  • Short posterior ciliary nerve innervates directly on iris pupillary sphincter
  • Edinger Westphal nucleus -> ocular motor nerve efferent -> synapse ciliary ganglion -> short posterior ciliary nerve -> pupillary sphincter
  • Note: afferent pathway from either eye stimulates efferent pathway on both eyes
    • Only 1 eye needs to be stimulated with light to elicit pupillary constriction response in both eyes
26
Q

what is the direct light reflex?

A
  • constriction of pupil of the light stimulated eye
27
Q

what is the consensual light reflex?

A
  • constriction pupil of other eye
28
Q

what is the neurological basis of direct and consensual reflex?

A
  • Afferent pathway on either side alone with stimulate efferent pathway on both sides
29
Q

what happens on a right afferent defect?

A
  • E.g damage optic nerve
  • No pupil constriction in both eyes when right eye is stimulated with light
  • Normal pupil constriction in both eyes when left eye is stimulated with light
30
Q

what happens on a right efferent defect?

A
  • E.g damage right 3rd nerve
  • No right pupil constriction whether right of left eye stimulated with light
  • Left pupil constricts normally whether right or left eye is stimulated with light
31
Q

what is the swinging torch test?

A

Relative efferent pupillary defect:

  • Partial pupillary response still present when damaged eye stimulated
  • Elicited by swinging torch test- alternating stimulation right and left eye with light
  • Both pupils constrict when light swings to left undamaged side
  • Both pupils dilate when light swings to right damaged side (reduced drive for pupillary constriction in both eyes)

1B Neurology & Neuroscience (14 decks)

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