Visual Systems

Question 2

What is the correct order of structures that light passes through in the eye?

Answer 2

Cornea → Pupil → Lens (suspended by fibers/ciliary muscles) → Vitreous humor → Retina.

Question 3

What is the macula?

Answer 3

Region of the retina responsible for central, high-acuity vision.

Question 4

What is the role of the cornea in vision?

Answer 4

The cornea provides most of the eye’s focusing power by refracting (bending) light toward the retina.

Question 5

What does a convex cornea do to light rays?

Answer 5

Converges (bends inward) light rays to focus them on the retina.

Question 6

What does a concave surface do to light rays?

Answer 6

Diverges (bends outward) light rays, moving the focal point backward.

Question 7

How does the lens focus far objects?

Answer 7

Ciliary muscles relax → zonule fibers tighten → lens flattens → less refraction.

Question 8

How does the lens focus near objects?

Answer 8

Ciliary muscles contract → zonule fibers slacken → lens becomes rounder → more refraction.

Question 9

What is myopia and how is it corrected?

Answer 9

Nearsightedness (long eyeball); corrected with concave lenses.

Question 10

What is hyperopia and how is it corrected?

Answer 10

Farsightedness (short eyeball); corrected with convex lenses.

Question 11

What does LASIK do?

Answer 11

Reshapes the cornea to correct refractive errors.

Question 12

What is the visual field?

Answer 12

The entire area seen by the eyes, with high-resolution vision in the center and blurrier vision in the periphery.

Question 13

How is the image projected onto the retina?

Answer 13

Upside-down and reversed left-to-right due to lens refraction.

Question 14

What is the retina?

Answer 14

A layered neural tissue (3 cell body layers + 2 synaptic layers) that develops from the CNS and contains photoreceptors.

Question 15

Why are photoreceptors located at the back of the retina?

Answer 15

To be close to the pigmented epithelium for metabolic support and light absorption; also possibly developmental constraint.

Question 16

What is eye shine and why do some animals have it?

Answer 16

A reflective layer (tapetum lucidum) gives light a second pass, improving night vision.

Question 17

What are the five main retinal cell types?

Answer 17

Photoreceptors (rods/cones), bipolar cells, retinal ganglion cells, horizontal cells, amacrine cells.

Question 18

Which retinal cells are light-sensitive?

Answer 18

Photoreceptors; a small subset of RGCs (intrinsically photosensitive) detect brightness for circadian rhythms.

Question 19

Which retinal cells fire action potentials?

Answer 19

Retinal ganglion cells (RGCs); most other retinal cells use graded potentials.

Question 20

Why do humans have a blind spot?

Answer 20

The optic disc lacks photoreceptors because axons and blood vessels exit the eye there.

Question 21

Why do octopuses not have a blind spot?

Answer 21

Their photoreceptors face forward and nerves enter from behind, avoiding interruption of the receptor layer.

Question 22

What are rods specialized for?

Answer 22

Low-light (scotopic) vision; high sensitivity; poor spatial resolution.

Question 23

What are cones specialized for?

Answer 23

Color and high-acuity (photopic) vision; low sensitivity; require bright light.

Question 24

What causes rods to bleach in daylight?

Answer 24

Rhodopsin becomes inactivated after absorbing too much light and must be regenerated.

Question 25

What determines cone color sensitivity?

Answer 25

Different cone opsins sensitive to short (blue), medium (green), or long (red) wavelengths.

Question 26

Where are rods and cones distributed in the retina?

Answer 26

Fovea: mostly cones. Peripheral retina: mostly rods.

Question 27

What gives the fovea high visual acuity?

Answer 27

Inner retinal layers are displaced allowing direct light access; high cone density; low convergence onto RGCs.

Question 28

What is macular degeneration?

Answer 28

Degeneration of photoreceptors in the macula causing central vision loss.

Question 29

What do photoreceptors encode about light?

Answer 29

Changes in light intensity via graded hyperpolarization.

Question 30

What do retinal ganglion cells encode?

Answer 30

Center-surround receptive fields representing contrast, edges, and spatial structure.

Question 31

What is the role of horizontal cells?

Answer 31

Lateral inhibition—enhancing contrast by inhibiting neighboring photoreceptors/bipolar cells.

Question 32

What is phototransduction?

Answer 32

Conversion of light energy into electrical signals by photoreceptors.

Question 33

What protein detects light in rods?

Answer 33

Rhodopsin, a GPCR activated when retinal absorbs a photon.

Question 34

What is retinal and how does it work?

Answer 34

The light-sensitive ligand in opsins; changes shape when absorbing light, activating rhodopsin.

Question 35

What is the membrane potential of a photoreceptor in the dark?

Answer 35

Depolarized (~ -30 mV) due to open cGMP-gated Na+ channels (dark current).

Question 36

What is cGMP’s role in photoreceptors?

Answer 36

Keeps Na+ channels open in the dark; levels drop in light causing channel closure.

Question 37

What happens to photoreceptors in light?

Answer 37

Light activates rhodopsin → transducin → phosphodiesterase (PDE) → cGMP decreases → Na+ channels close → cell hyperpolarizes.

Question 38

What is the 'dark current'?

Answer 38

Continuous Na+ influx in the dark through cGMP-gated channels, keeping photoreceptors depolarized.

Question 39

How does hyperpolarization encode light?

Answer 39

More light → more hyperpolarization → less neurotransmitter (glutamate) released.

Question 40

What is meant by photopigment bleaching?

Answer 40

Retinal dissociates from opsin after absorbing light and must be chemically regenerated before detecting light again.

Question 41

Why does vision recover slowly after moving from bright to dark?

Answer 41

Rhodopsin must be regenerated; cones recover faster, rods slower.

Question 42

What wavelengths do cones detect?

Answer 42

Short (blue), Medium (green), Long (red).

Question 43

Why is color blindness more common in males?

Answer 43

Red and green opsin genes are on the X chromosome; mutations lead to color vision deficits.

Question 44

What is dark adaptation?

Answer 44

Increased sensitivity in low light via pupil dilation + regeneration of unbleached photopigments.

Question 45

What is light adaptation?

Answer 45

Reduction in photoreceptor sensitivity in bright light by decreasing Ca2+, restoring cGMP, and reopening channels gradually.

Question 46

How does Ca2+ regulate adaptation?

Answer 46

In darkness Ca2+ enters photoreceptors and inhibits cGMP production; in light Ca2+ levels fall, disinhibiting cGMP synthesis and reopening channels slowly.

Question 47

What part of the visual spectrum can humans see?

Answer 47

Approximately 400–700 nm (visible light).

Question 48

What animals are tetrachromats and what does that mean?

Answer 48

Birds; they have four cone types including UV sensitivity.

Question 49

What is the function of center-surround receptive fields?

Answer 49

Detect edges and contrast, allowing the retina to emphasize meaningful visual information.

Question 50

What happens in ON vs OFF bipolar cells?

Answer 50

ON bipolar cells depolarize to light (less glutamate). OFF bipolar cells depolarize to dark (more glutamate).

Question 51

What do ganglion cells base their firing rate on?

Answer 51

Differences between center and surround illumination (contrast).