SWeek 7 ELM 14: Sensory Systems I - Vision

Flashcards covering the properties of light, the structure of the vertebrate eye, rods and cones, other cells in the retina, and brain circuitry related to vision.

Electromagnetic Wave

A way light can be described; its intensity is the amplitude (brightness) and its color is the wavelength.

Photons

A way light can be described; it represents the intensity of light.

Wavelength Range

The narrow range of electromagnetic radiation that humans can see, which can vary slightly between individuals.

Cornea

The part of the vertebrate eye with the greatest refracting power. Has a refractive power of approximately 42 diptometers (D)

Lens

The part of the vertebrate eye that accommodates by changing shape for more refractive power. Has a refractive power of 12 dipoters (D)

Myopia

Short-sightedness, often corrected with a concave lens.

Hyperopia

Far-sightedness, often corrected with a convex lens.

Astigmatism

A common vision problem caused by irregularities of the cornea and lens.

Retina

Part of the brain located at the back of the eye containing photoreceptors (rods and cones).

Rods

Photoreceptors responsible for night vision and peripheral vision; 1000 times more sensitive than cones.

Cones

Photoreceptors concentrated in the fovea, responsible for maximum visual acuity and color discrimination. That area is blind at night

Fovea

Area in the retina with the most cones, providing maximum visual acuity; blind at night.

Tapetum lucidum

Layer just behind the RPE (Retinal Pigment Epithelium) that causes eyeshine in some animals.

RPE (Retinal Pigment Epithelium)

Pigmented layer at the back of the retina essential for recycling retinaldehyde and helping rods and cones cope with oxidative stress. Make pupil look black

Opsin

GPCRs with 7 transmembrane domains found in different types of cones, rods, and melanopsin RGCs; combines with retinal to form photopigment.

Retinal

Vitamin A derivative that absorbs light and changes conformation, leading to bleaching; same for every opsin.

Phototransduction

Process in rods and cones where retinal absorbs light, causing a conformational change, leading to closure of sodium channels and hyperpolarization.

Trichromats

Humans with 3 types of cones, enabling color vision.

Dichromats

Animals with 2 types of cones, such as dogs, reptiles, mice, cats, and horses.

Monochromats

Animals with 1 type of cone, such as dolphins, wales and seals.

Horizontal Cells

Retinal cells involved in light intensity adaptation, spatial processing, and color processing (opponency). 2nd layer

Amacrine Cells

Retinal cells involved in directional motion detection, modulation of light adaptation and circadian rhythm, and sensitivity of night vision. 3rd level (looking top down cut)

Retinal Ganglion Cells (RGC)

The only output cells of the retina, firing action potentials, further processing color, motion, and shapes. ipRGC can detect light via melanospin

Melanopsin

Photopigment in intrinsically photosensitive retinal ganglion cells (ipRGC) that detects light and affects circadian rhythms, pupil size, and body temperature but doesn't contribute to image formation.

Lateral Geniculate Nucleus (LGN)

A part of the visual pathway where conscious visual information is processed.

V1 (Striate Cortex)

Cortical area located in the occipital lobe where conscious visual information is processed; exhibits orientation selectivity.

Relationship between amplitude and intensity of light

Direct, larger amplitude means brighter light

What is the color of light determined by

Wavelength

1st layer of retina is (looking top to down)

Mostly inhibitory neurons

Pathway of Glutamergic excitatory neurons

Rods, cones → Bipolar cells → retinal ganglion cells

What is the mechanism of photoreceptors

In the dark they are depolarised with sodium channels open. In the light, Na+ channels close leading membrane hyperpolarization (=presence of stimulus)