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Exam 4: Vision

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Question 1

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What is the 'blind spot'? Select all that are correct.

A) The place in the retina in which all axons exit the retina to go to the brain.
B) The place the lens focuses light on the retina.
C) The location in the retina where light has a direct path to the photoreceptors.
D) The location in the retina with the highest density of capillaries.

E) B) and C)
F) None of the above

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Question 2

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Match the receptive field to the appropriate location(s) in the visual system. There is more than one answer to each.

Premises

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V1

LGN

Retina

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V1

LGN

Retina

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Question 3

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In the photoreceptor, stimulation of light results in an increase or decrease in glutamate release? Explain your answer. refer to Figure Q4-25. You record from an on-center ganglion cell in complete darkness, present a light stimulus (horizontal bar), and elicit an increase in the number of action potentials in the RGC as in Figure Q4-25. Figure Q4-25

You are out in the middle of the desert star-gazing trying to see the North Star. What is the best way to look at the star? Why?

Why are most laser pointers colored green or red, but not blue?

What is the smallest number of photons of light that are able to elicit a change in membrane potential in a photoreceptor?

Which of the following is not a feature of certain V1 neurons?

Rhodopsin is what kind of protein?

Fill in the missing words in the following paragraph. Light is absorbed by the protein ______, which changes from _____ to a _____ configuration. This causes a structural change in the ____ protein. This conformational change allows the G protein called __________ to bind, and results in the exchange of _____ for GDP. The _______subunit of the G protein then activates the protein ______, which breaks down cGMP. The reduction in cGMP causes CNG channels to ______ and the cell to ______.

In photoreceptors, in the presence of light, injection of cGMP would:

Why are men more likely to be red/green color blind?

Hubel and Wiesel identified simple cells and complex cells in the visual cortex. Simple cells respond to bars of light in a particular orientation. For example, stimulation by a bar of light in the center of the visual field could excite the V1 neuron but moving the bar of light to either side of the center will inhibit the neuron. What anatomical structure did Hubel and Wiesel propose that would confer this response on the V1 neuron?

What would happen if you blocked phosphodiesterase (PDE) and then stimulated the photoreceptor with light?

What is the receptive field of a visual neuron?

Our visual system has a remarkable dynamic range. When you go to a matinee movie (during the daytime) and walk out of the theater it is difficult to see. After a few minutes your eyes adapt to the new light levels. Some of the molecular mechanisms of light adaptation are known and most involve changes in Ca²⁺ concentration. (A) (B) Figure Q4-13 A. Based on the data from the experiments shown in Figure Q4-13, what is one mechanism of adaptation? Figure Q4-13A shows the dark-adapted response to a flash of light in wild type and GCAP knockout mice. Figure Q4-13B shows the rod response to a flash of light relative to the same flash after dark adaptation. B. What is the probable molecular mechanism of reduced light adaptation involving GCAP?

Where does binocular input first occur in the visual system and why does it emerge at this location?

When people get older the lens becomes stiffer and is not able to change shape as readily as when people are younger. Why would the inability of changing the angle of light through the lens cause objects (particularly those that are close) to become out of focus?

What type of visual information is coded in the retina? Choose all correct?.

The visual system is organized into two pathways: the ventral stream and the dorsal stream. Indicate whether the following is associated with either the ventral stream or the dorsal stream. $\begin{array}{llcc} \text { Motion } &\underline{\quad\quad} \\ \text { Color} &\underline{\quad\quad}\\ \text { Temporal cortex } &\underline{\quad\quad}\\ \text { Parietal cortex } &\underline{\quad\quad}\\ \text { Form } &\underline{\quad\quad}\\ \text { Depth } &\underline{\quad\quad}\\\end{array}$

An object of interest is to your right. The light from this object excites the temporal left eye and the nasal right eye as in Figure 4-32. Figure 4-32 A. What happens to the organization of that image from the retina to the LGN and then to primary visual cortex? That is, what is the anatomical organization of the visual circuitry? Include the organization of the terminal projections in the LGN and cortex. B. What would the projection pattern look like if you traced the path from two neighboring RGC from the left eye to the LGN and cortex?