Sensory Systems Pt 2 – Vision (Chapter 7)

What part of the eye bends incoming light and is responsible for most of the eye’s refraction?

The cornea.

Which eye structure changes shape to focus light on the retina?

The lens, via contraction or relaxation of the ciliary muscles.

What is refraction in the context of vision?

The bending of light rays as they pass through mediums of different densities, causing the visual field to appear inverted on the retina.

List the correct order in which light passes through the eye to reach the photoreceptors.

Cornea → pupil → lens → retina.

Which retinal region provides the highest visual acuity and why?

The fovea, because it has a high density of small, tightly packed cones and receives light with minimal distortion from overlying cells.

What is the optic disc and how is it related to the blind spot?

The optic disc is where blood vessels and ganglion-cell axons exit the eye; it lacks photoreceptors, creating the blind spot.

Name the two types of photoreceptors and specify which lighting conditions they specialize in.

Rods – scotopic (dim-light) vision; Cones – photopic (bright-light and color) vision.

Describe two key characteristics of rods.

High sensitivity to dim light and low acuity; they are color-insensitive.

Describe two key characteristics of cones.

Require more light, provide high acuity, and are wavelength-specific for color vision.

Which retinal cells generate action potentials?

Ganglion cells.

Which retinal cells relay graded (non-spiking) potentials only?

Photoreceptors, bipolar cells, horizontal cells, and amacrine cells.

In darkness, do photoreceptors release more or less glutamate?

More; they are depolarized and continuously release glutamate in the dark.

What happens to a photoreceptor’s membrane potential and neurotransmitter release when light hits it?

It hyperpolarizes and releases less glutamate; the reduction is proportional to light intensity.

Define ‘visual acuity’.

The ability to see fine detail; it is highest at the center of the visual field (fovea).

State the six-step ‘quick version’ of the central visual pathway from retina to cortex.

1) Ganglion cells → 2) Optic chiasm → 3) Optic tract → 4) LGN (thalamus) → 5) Optic radiations → 6) Primary visual cortex (V1).

Which retinal fibers cross at the optic chiasm—nasal (medial) or temporal (lateral)?

Nasal (medial) retinal fibers cross; temporal (lateral) fibers remain ipsilateral.

If an object is in your left visual field, to which thalamic LGN does its information project?

To the right LGN.

What is meant by a ‘topographic projection’ in the visual system?

A point-to-point mapping of the visual field onto successive neural structures (retina, LGN, V1), preserving spatial relationships.

Which LGN layers receive input from the contralateral eye?

Layers 1, 4, and 6.

Which cortical layer of V1 is the primary recipient of LGN inputs?

Layer 4 (specifically 4C in primates).

Define ‘optic radiations’.

Axonal projections from LGN neurons that fan out through the temporal and parietal lobes to reach the primary visual cortex.

What physical property of light primarily determines color (hue)?

Wavelength of the photons reflected to the eye.

List the three perceptual dimensions of color.

Brightness, hue, and saturation.

Summarize the trichromatic hypothesis of color vision.

Color is encoded by three types of cones, each maximally sensitive to different wavelength ranges; color perception arises from the pattern of activation across these cones.

What form of color blindness results from the absence of medium-wavelength (M) cones?

Deuteranopia (a red-green