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OFS3 > visual systems > Flashcards

visual systems Flashcards

1
Q

how many fibers are there in the optic nerve?

A

over 1 million

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2
Q

what is visual perception?

A

the flow of visual information from the retina to the primary visual cortex

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3
Q

Which structures are responsible for the absorption of light + transduction into electrical signals?

A

rods and cones in the retina

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4
Q

The retina has 3 major functional classes of neurons, what are they?

A
  1. photoreceptors (rods and cones) i
  2. interneurons (bipolar, horizontal, amacrine cells)
  3. ganglion cells
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5
Q

What are photoreceptors?

A

(rods and cones) in outer nuclear layer. Transmit visual information to interneurons.

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6
Q

What are interneurons?

A

(bipolar, horizontal, amacrine cells) in inner nuclear layer

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7
Q

What are ganglion cells?

A

cells in ganglion cell layer (axons form optic nerve), 1st level of visual analysis

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8
Q

What are the 2 groups of ganglion cells?

A
  • -> specialized for detection of contrast and rapid changes in visual image, have circular receptive fields centrally and around
  • ->Able to analyze color, form and movement
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9
Q

What are the 2 groups of cells specialized for detection of contrast and rapid changes in visual image, have circular receptive fields centrally and around?

A
  • on-center cells exited when light falls in center of receptive field, inhibited when stimulated in surroundings
  • off- center cells exited when light falls in surroundings of receptive field, inhibited when stimulated in center
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10
Q

What are the 2 groups of cells specialized in colour vision?

A
  1. M-cells: large receptive fields (large dendrites), respond to large objects, able to follow rapid changes –> analysis of gross features of a stimulus and its movement.
  2. P-cells: smaller, more numerous, small receptive fields, specific wavelength response–> perception of form and color, analysis of fine detail (some M-cells aswell)
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11
Q

What is the visual field?

A

the view seen by the two eyes without movement of the head

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12
Q

What is the retinal image?

A

an inversion of the visual field: projected on the retina smaller, inverted and laterally reversed due to refraction of light through convex lens.

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13
Q

What happens to a single point in the binocular portion of one visual hemifield ?

A

it projects onto different regions of the two retinas

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14
Q

the retina shows a retinotopic organization of the visual field, what is it?

A

fibres of the upper retina contain information on lower visual field
fibres of the lower retina contain information on upper visual field.
Inverted + laterally reversed all the way of the pathway to the cortex.

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15
Q

What is the Binocular portion of visual field?

A

seen by 2 eyes

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16
Q

What is the monocular portion of visual field?

A

seen by 1 eye

17
Q

The retina is subdivided into regions, there correspondence between regions of the visual field and the retinal image, how is it divided?

A

surface of retina is divided in midline: nasal hemiretina lies medial to fovea//
the temporal hemiretina lateral to fovea.
Each half of the retina further divided into dorsal (or superior) and ventral (or inferior) quadrants.

18
Q

What does the optic nerve carry?

A

carries all visual information from one eye, from both nasal and temporal hemiretina.

19
Q

The optic nerve (CNS) through optic canal in orbit, how does the cranial nerve form and leave?

A

unmyelinated axons of ganglion cells collect the optic disc (the region where ganglion cell axons leave the retina, free of photoreceptors –> blind spot in visual field of each eye)

20
Q

in normal vision we are unaware of blind spots, we experience blind spot only by using one eye, why is that?

A

Since disc is nasal to fovea in each eye, light coming from single point in binocular zone never falls on both blind spots simultaneously

21
Q

Explain the Meningeal covering of the optic nerve

A

sclera continues as its dural sheath, lined in turn by arachnoid and pia. Subarachnoid space around optic nerve dead-ends at back of eye but communicates with subarachnoid spaces around other parts of brain.

22
Q

Why are increases in intercranial pressure full of risks?

A

thy are transmitted to optic nerve, compress it, and choke off both venous flow and axoplasmic transport

23
Q

What are central visual pathways?

A

o Fibres from nasal hemiretina of each eye cross the midline and move to the contralateral side at the optic chiasm.
o Fibers from the temporal hemiretina do not cross.
o Each optic tract carries complete representation of one half of the binocular zone in the visual field

24
Q

What is the lateral geniculate nucleus?

A

layered, dome-shaped, main terminus for input to the Visual Cortex.

25
Q

What are the 6 layers of the lateral geniculate nucleus?

A

Layers 1 and 2 = magnocellular layers
layers 3 to 6 = parvocellular layers.
The parvocellular and magnocellular layers project to separate layers of the primary visual cortex.
All project to area 17, the primary visual cortex.

26
Q

What do the parvocellular and magnocellular layers do?

A

they project to separate layers of the primary visual cortex.

27
Q

What does the optic tract do?

A

curves posteriorly around cerebral peduncle and most of its fibres terminate in the LGN.

28
Q

What does each lateral geniculate nucleus have?

A

has a retinotopic representation of the contralateral half of the visual field.

29
Q
  • Projections from the CONTROLATERAL NASAL HEMIRETINA reach layers _______
A

1
4
6

30
Q
  • Projections from the HOMOLATERAL TEMPORAL HEMIRETINA reach layers ________
A

2
3
5

31
Q

What is the course of visual information starting in the LGN?

A
  • Visual information from LGN –> through Optical radiation –> passes through the retro-lenticular part of internal capsule –> primary visual cortex.
32
Q
  • Lesions in the retino-Geniculate-Cortical pathway are associated with __________________
A

specific and predictable gaps in the visual field

33
Q

lesions in optic nerve of one eye leads to

A

complete blindness of ipsilateral eye

34
Q

Lesions at optic chiasm leads to ___________

A

bitemporal hemianopsia

35
Q

Lesions in the optic tract (carries information from the contralateral portion of the visual field) leads to __________

A

controlateral homonymous hemianopsia. (loss of visual field on contralateral side)

36
Q

Lesions of large tract which may be represented by genicular calcanean radiation leads to ____________

A

Contralateral homonymous quadrantopsia

37
Q

What are visual reflexes?

A 
The Retina (besides projections to cerebral cortex) to subcortical Regions in the Brain, some nuclei of the brainstem
 eg.Superior colliculus: this projection contributes to visually-guided eye movements. alternating gray cellular and white (axonal) layers on roof of the midbrain. 
Retinal ganglion cells project directly to the superficial layers and form a map of contralateral visual field.
38
Q

What does the Pretectum of the Midbrain do?

A

controls Pupillary Reflexes (Light shining in one eye causes constriction of pupil in that eye (the direct response) as well as in the other eye (the consensual response))

39
Q

How does the pupil contrict or dilate? Whate are the 5 steps?

A
  1. A set of fibers leave the optic tract and terminate in the pretectal nuclei, located just rostral to the superior colliculus on each side.
  2. The cells in the pretectal area project bilaterally to preganglionic parasympathetic neurons in the Edinger-Westphal (or accessory oculomotor) nucleus, which lies immediately adjacent to the neurons of the oculomotor (cranial nerve III) nucleus. The contralateral nucleus is reached though the POSTERIOR COMMISSURE.
  3. Preganglionic neurons in the Edinger-Westphal nucleus send axons out of the brain stem in the oculomotor nerve to innervate the ciliary ganglion.
  4. This ganglion contains the postganglionic neurons (the short CILIARY NERVE) that innervate the smooth muscle of the pupillary sphincter that constricts the pupil.
  5. A sympathetic pathway innervates the pupillary radial iris muscles that dilate the pupils.

OFS3 (15 decks)

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