Unit 1.3 and 1.4 Retinal Info Processing and Diseases

Question 1

What are photoreceptors?

Answer 1

cells in the retina that initially transduce light energy into neural energy

Question 2

What are the two main pathways of information processing in the retina?

Answer 2

The vertical pathway (photoreceptors → bipolar cells → ganglion cells) and the horizontal pathway (horizontal cells and amacrine cells).

Question 3

What are the two types of photoreceptors in the retina?

Answer 3

Rods (for night vision) and cones (for daylight vision, color, and fine visual acuity).

Question 4

Where are rods and cones located in the retina?

Answer 4

Rods are more concentrated in the peripheral regions of the retina, while cones are densely packed in the fovea, the central part of the retina responsible for sharp vision.

Question 5

How do rods and cones differ in terms of sensitivity to light?

Answer 5

Rods are more sensitive to light than cones, allowing them to function in low-light conditions, while cones require brighter light to operate effectively.

Question 6

How does a chromophore function in photoreceptors?

Answer 6

In photoreceptors, chromophores undergo a biochemical cascade when they absorb light. This process leads to changes in the electrical state of the photoreceptor cells, ultimately resulting in the transduction of light energy into neural signals.

Question 7

What are the steps involved in the biochemical cascade initiated by a chromophore?

Answer 7

1. Closing of ion channels in the outer segment of the photoreceptor.
2. Hyperpolarization of the cell body.
3. Reduction of neurotransmitter release (specifically glutamate) at the synaptic level.

Question 8

What role do chromophores play in the function of rods and cones?

Answer 8

Chromophores in rods and cones are essential for detecting light. Rods are sensitive to low light levels (night vision), while cones are responsible for color vision and function best in bright light.

Question 9

Why is the structure of a chromophore important?

Answer 9

The structure of a chromophore determines its ability to absorb specific wavelengths of light, which is crucial for the phototransduction process in vision.

Question 10

What happens to photoreceptors when chromophores absorb light?

Answer 10

When chromophores absorb light, they trigger a series of reactions that lead to the hyperpolarization of photoreceptor cells, which reduces the release of neurotransmitters and signals the presence of light to the bipolar cells.

Question 11

How does the chromophore relate to visual acuity?

Answer 11

The efficiency of chromophores in absorbing light and initiating phototransduction is directly related to visual acuity. The better the chromophore functions, the clearer the image perceived by the brain.

Question 13

What is the standard way to measure the size of visual stimuli on the retina?

Answer 13

In terms of “degrees of visual angle.” For example, a thumbnail held at arm’s length is about 2 degrees of visual angle.

Question 14

What is the “degrees of visual angle”?

Answer 14

the visual angle of an object is a function of both its actual size and distance from the observer

Question 15

What is lateral inhibition?

Answer 15

Lateral inhibition is a process in the retina where interconnected neurons inhibit their neighbors, enhancing contrast and edge detection in visual stimuli.

Question 16

Why is lateral inhibition important in visual processing?

Answer 16

It helps to sharpen the perception of edges and contrasts, allowing the visual system to detect boundaries and shapes more effectively.

Question 17

Which cells are primarily involved in lateral inhibition?

Answer 17

Horizontal cells and amacrine cells play key roles in lateral inhibition by connecting between photoreceptors and ganglion cells.

Question 18

What is the vertical pathway in the retina?

Answer 18

The vertical pathway describes the flow of visual information from photoreceptors to bipolar cells and then to retinal ganglion cells.

Question 19

What is the function of the vertical pathway?

Answer 19

It transmits the initial visual signals from the photoreceptors to the brain, forming the basis for further processing in the visual system.

Question 20

What is the horizontal pathway in the retina?

Answer 20

The horizontal pathway refers to the connections between horizontal cells and photoreceptors, allowing for lateral inhibition and integration of visual information across the retina.

Question 21

How do horizontal and vertical pathways interact in visual processing?

Answer 21

Horizontal pathways enhance contrast through lateral inhibition, while vertical pathways carry the processed signals to the brain, contributing to a more refined visual perception.

Question 22

What are bipolar cells?

Answer 22

Bipolar cells are neurons in the retina that transmit signals from photoreceptors (rods and cones) to ganglion cells.

Question 23

How do bipolar cells function in the visual pathway?

Answer 23

Bipolar cells receive input from photoreceptors and relay this information to ganglion cells, which then send visual information to the brain.

Question 24

What are the two main types of bipolar cells?

Answer 24

1. Diffuse bipolar cells - receive input from multiple rods (up to 50).
2. Midget bipolar cells - receive input from a single cone.

Question 25

How do bipolar cells respond to changes in light?

Answer 25

Bipolar cells can be classified as “On” cells, which respond to increases in light, and “Off” cells, which respond to decreases in light. (midget bipolar cells)

Question 26

What is the role of ganglion cells in the retina?

Answer 26

Ganglion cells are the last stage of retinal processing before visual information leaves the eye and travels to the brain.

Question 27

What are the two main types of ganglion cells?

Answer 27

The two main types are P ganglion cells (small cells connected to the parvocellular pathway) and M ganglion cells (large cells connected to the magnocellular pathway).

Question 28

What is the function of P ganglion cells?

Answer 28

involved in fine visual acuity, color, and shape processing, with good spatial resolution but poor temporal resolution.

Question 29

What is the function of M ganglion cells?

Answer 29

involved in motion processing, with excellent temporal resolution but poor spatial resolution.

Question 30

What is a receptive field in the context of ganglion cells?

Answer 30

A receptive field is the specific region in space where stimuli will activate a neuron, with all ganglion cells having center-surround receptive fields.

Question 31

How do ganglion cells respond to light in their receptive fields?

Answer 31

Ganglion cells respond positively when light is present in the center of their receptive field and negatively when light is present in the surrounding area.

Question 32

What are Off Center Ganglion Cells?

Answer 32

Off Center Ganglion Cells are retinal ganglion cells that respond to decreases in light intensity in the center of their receptive field while responding positively to light in the surrounding area.

Question 33

What are On Center Ganglion Cells?

Answer 33

On Center Ganglion Cells are a type of retinal ganglion cell that responds to increases in light intensity in the center of their receptive field while inhibiting responses to light in the surrounding area.

Question 34

How do On and Off Center Ganglion Cells work together?

Answer 34

They work in opposition to enhance contrast detection in visual scenes. When one type is activated (e.g., On Center), the other is inhibited (e.g., Off Center), allowing for a clearer perception of edges and transitions in light.

Question 35

What are the mechanisms for dark and light adaptation?

Answer 35

• pupil dilation
• photoreceptors and their replacement
• computation of center-surround contrasts

Question 36

What is Retinitis Pigmentosa?

Answer 36

A family of hereditary diseases that involve the progressive death of photoreceptors and degeneration of the pigment epithelium.

Question 37

What are the visual field changes associated with Retinitis Pigmentosa?

Answer 37

It typically starts with peripheral vision loss (tunnel vision) and can lead to complete blindness.

Question 38

What is Macular Degeneration?

Answer 38

A degeneration of the macula, leading to loss of central vision and sharp details. It can result in legal blindness by age 40.

Question 39

What causes Macular Degeneration?

Answer 39

It is caused by the formation of new blood vessels or thinning of tissue, leading to the death of rods and cones.

Question 40

How does Macular Degeneration affect vision?

Answer 40

Patients may experience distorted vision and have difficulty seeing details, although peripheral vision may remain intact.