Task 2 - The Retina

Question 1

What is the electromagnetic spectrum (EMS)?

Answer 1

A continuum of electromagnetic energy produced by electric changes and radiated as waves.

Question 2

What range of wavelengths does visible light have?

Answer 2

About 400 to 700 nanometers.

Question 3

What is the retina?

Answer 3

A network of neurons at the back of the eye that contains photoreceptors.

Question 4

What are the two types of photoreceptors in the eye?

Answer 4

Rods and cones.

Question 5

What is the function of visual pigments?

Answer 5

They react to light and trigger electrical signals.

Question 6

Where are visual pigments made and stored?

Answer 6

Made in the inner segment and stored in the outer segment of photoreceptors.

Question 7

What is the fovea?

Answer 7

A part of the retina that contains only cones and provides sharp central vision.

Question 8

What is the peripheral retina?

Answer 8

The area outside the fovea containing both rods and cones but more rods.

Question 9

What is the blind spot?

Answer 9

The area where the optic nerve leaves the eye, containing no photoreceptors.

Question 10

What is macular degeneration?

Answer 10

A disease that destroys the cone-rich fovea, leading to central vision loss.

Question 11

What is retinitis pigmentosa?

Answer 11

A genetic disease causing degeneration of rods, leading to peripheral vision loss and eventually blindness.

Question 12

What is the function of the cornea?

Answer 12

It is a transparent covering that focuses light but cannot adjust focus.

Question 13

What is accommodation?

Answer 13

The change in the lens shape to focus on objects at different distances.

Question 14

How does the eye accommodate for near objects?

Answer 14

The ciliary muscles tighten, increasing the curvature of the lens.

Question 15

What is myopia?

Answer 15

Nearsightedness; light is focused in front of the retina, causing blurry distance vision.

Question 16

What causes hyperopia?

Answer 16

A short eyeball, causing light to focus behind the retina, leading to difficulty seeing nearby objects.

Question 17

What is presbyopia?

Answer 17

Age-related loss of accommodation due to lens hardening and weakened ciliary muscles.

Question 18

What is visual transduction?

Answer 18

The process of converting light into electrical signals in the photoreceptors.

Question 19

What is isomerization?

Answer 19

A process where retinal changes shape upon absorbing light, triggering a chemical reaction.

Question 20

What is dark adaptation?

Answer 20

The process of increasing sensitivity to light when moving from a bright to a dark environment.

Question 21

Which photoreceptor regenerates its pigment faster?

Answer 21

Cones (~6 minutes), while rods take more than 30 minutes.

Question 22

What is the rod-cone break?

Answer 22

The point in dark adaptation when rods become more sensitive than cones.

Question 23

What type of cells connect photoreceptors across the retina?

Answer 23

Horizontal cells and amacrine cells.

Question 24

What is neural convergence?

Answer 24

When multiple photoreceptors send signals to a single neuron.

Question 25

Which photoreceptor has more convergence, rods or cones?

Answer 25

Rods, making them more sensitive but less precise than cones.

Question 26

What is a receptive field?

Answer 26

The area of the retina that must be illuminated to activate a neuron.

Question 27

What is center-surround organization?

Answer 27

A pattern where the center of a receptive field responds opposite to its surrounding area.

Question 28

What is lateral inhibition?

Answer 28

A process where neighboring neurons inhibit each other to enhance contrast.

Question 29

What is the difference between diffuse and midget bipolar cells?

Answer 29

Diffuse bipolar cells receive input from many photoreceptors, while midget bipolar cells receive input from a single cone.

Question 30

What are the three types of ganglion cells?

Answer 30

P ganglion cells – Small receptive fields, high resolution. M ganglion cells – Large receptive fields, high sensitivity. Koniocellular cells – Receive input from S-cones, less researched.

Question 31

What happens to visual pigments after absorbing light?

Answer 31

Retinal separates from opsin, causing visual pigment bleaching.

Question 32

What is visual pigment regeneration?

Answer 32

The process where retinal reattaches to opsin, restoring light sensitivity.

Question 33

How long does it take for cone and rod pigments to regenerate?

Answer 33

Cones take ~6 minutes; Rods take over 30 minutes.

Question 34

What condition prevents visual pigment regeneration?

Answer 34

Detached retina – the retina separates from the pigment epithelium, leading to blindness.

Question 35

What is spectral sensitivity?

Answer 35

The eye’s sensitivity to light at different wavelengths

Question 36

What is the Purkinje shift?

Answer 36

The enhanced perception of short wavelengths (blues) in dim light due to rod sensitivity.

Question 37

Which wavelengths do rod and cone pigments absorb best?

Answer 37

Rod pigment (rhodopsin): ~500 nm. S-cones (short): ~419 nm. M-cones (medium): ~531 nm. L-cones (long): ~558 nm.

Question 38

What is the function of ganglion cells?

Answer 38

They receive signals from bipolar cells and transmit them to the brain via the optic nerve.

Question 39

How do bipolar and ganglion cells respond differently?

Answer 39

Bipolar cells respond with graded potentials, while ganglion cells fire action potentials.

Question 40

What are the two types of cells that connect neurons across the retina?

Answer 40

Horizontal cells – connect photoreceptors laterally. Amacrine cells – receive and send signals between bipolar and ganglion cells.

Question 41

What is an ON-center receptive field?

Answer 41

A ganglion cell that is excited by light in the center and inhibited by light in the surround.

Question 42

What is an OFF-center receptive field?

Answer 42

A ganglion cell that is inhibited by light in the center and excited by light in the surround.

Question 43

How does lateral inhibition enhance perception?

Answer 43

It increases contrast at edges, making boundaries between light and dark clearer.

Question 44

What is the Chevreul illusion?

Answer 44

A visual effect where edges between light and dark bands appear exaggerated due to lateral inhibition.

Question 45

How do horizontal cells contribute to center-surround receptive fields?

Answer 45

They release GABA to inhibit neighboring photoreceptors, enhancing edge contrast.