Exam #6: Vision Flashcards Preview

Medical Physiology > Exam #6: Vision > Flashcards

Flashcards in Exam #6: Vision Deck (34):
1

What is accommodation? What are the physiologic events that give rise to accommodation?

1) Contraction of ciliary muscle
2) DECREASE in tension on suspensory ligaments
3) Lens RELAXES and become more spherical

*****This is used for NEAR vision

2

What is presbyopia?

Age related decline in near-vision due to an inability to accommodate

3

What is the blind spot?

Region of the optic disc WITHOUT photoreceptors

****Note that the optic disc is the head of the optic nerve in the retina

4

What is the fovea?

- Depression in the macula, which is the area of maximal focus of the light i.e. best vision
- Avascular zone

5

What is binocular disparity?

Difference in image location of an object seen by the left and right eyes, resulting from the eyes' horizontal separation (parallax). The brain uses binocular disparity to extract depth information from the two-dimensional retinal images in stereopsis.

6

What is prosopagnosia?

Patients with problems visually identifying faces

7

What is object agnosia?

Patients with problems visually identifying objects

8

What is scotoma?

Visual field defect

9

Outline the position of the visual fields to the retina.

- Temporal visual field (monocular segment) projects nasally
- Nasal/ binocular segment projects to the temporal retina

10

Where does the retina project?

- Optic chiasm
- Right ends up in left hemisphere
- Left ends up in the right hemisphere

****Only the nasal crosses

11

What is the difference between the locations of rods and cones?

- Center of the fovea contains only cones that decrease laterally
- Lateral to the fovea, rods appear & increase in number

12

What are the functional differences between rod and cone vision?

Rods= black & white
- Peripheral vision
- Nighttime vision

Cones= color

13

Which receptor mediates scotopic vision? Photopic vision?

Scotopic= rods
- No color
- Poor acuity

Phototopic= cones
- High color
- High acuity

14

What are the electrophysiological changes that occur when a photoreceptor is stimulated by light?

Dark= entry of Na+ & Ca++ via channels held open by cGMP
- DEPOLARIZED in DARK

Light=
- Decrease cGMP & Na+ & Ca++ DECREASE
- K+ leaves
- Cell hyperpolarized

****Dependent on glutamate release

15

Define the term receptive field for visual neurons.

Area of the retina from which the neuron can be influenced

16

Which retinal cell type can produce action potential?

Ganglion cells

17

Which retinal cells are output cells?

Ganglion cells

18

Which retinal cells capture photons?

Photoreceptors--rods & cones

19

What is the function of retinal projections to the suprachiasmatic nuclei?

Hypothalamus: regulation of the circadian rhythms

20

What is the function of retinal projections to the pretectal nuclei?

Reflex control of pupil and lens

21

What is the function of retinal projections to the LGN?

This how we "actually see things"

22

What is the function of retinal projections to the superior colliculi?

Orienting movements of the head & eyes toward visual stimuli

23

What is the function of the dorsal visual stream to higher visual areas?

Motion and relative position of objects

24

What is the function of the ventral visual stream to higher visual areas?

High level form vision & object recognition

25

What is the clinical significance of having different pathways for different aspects of vision?

When the system breaks down, patients will have complex visual defects

26

What are the pigments associated with rods, cones, and ganglion cells?
Where are the genes located that code for cone pigments related to color blindness?

- Three cone pigments:
Red= x-chromosome
Green= x-chromosome
Blue= #7

- Rods= rhadopsin= #3

- Ganglion cells= melanopsin

27

Outline the mechanisms for depth perception. Which are monocular and which require vision in both eyes?

Depth perception requires only MONOCULAR ques
- Size of the object
- Motion parallax

For really good depth perception, need binocular vision for stereopsis

28

What is strabismus? Describe how strabismus can result in suppression of the visual image from one eye.

Strabismus refers to "squint" or cross-eyedness
- Causes one-eyed fixation
- Brain suppresses input from the other eye

29

Which type of vitamin deficiency can cause night blindness?

Vitamin A

30

Outline the pupillary light reflex. What is the different in function between the SNS & PNS?

PNS= contriction
SNS= dilation

31

What is the result of a lesion to the optic nerve?

Ipsilateral monocular blindness

32

What is the result of a lesion to the optic chiasm?

Bitemporal hemianopsia

33

What is the result of a lesion to the optic tract?

Homonymous hemianopsia

34

What is the result of a lesion to Meyer's Loop?

Superior quadrant anopsia

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