NEU 201 - Quiz 2 Terms

Fraction of Cerebral Cortex used for vision

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Cornea

Frontmost part that light passes through; has a convex surface that allows for most of the eye’s focusing power so that light hits the retina

Pupil

Hole located at center of iris that light passes through after passing through the cornea

Iris

The colored part of the eye that is behind the cornea and contains the pupils

Lens

Part of the eye that light passes through 3rd; adds focusing power for close-up images through contractions of the cilliary muscles (important for closeup images)

Cilliary Muscles

Muscles connected to the lens that help adjust focus; relax for less refraction and tightens for more refraction

Myopia/nearsightedness

Caused by abnormalities in eye shape or stiffening of the cilliary muslces as people age; results in the light hitting the retina being offcenter to make farther objects harder to see

Hyperopia/farsightedness

Caused by abnormalities in eye shape or stiffening of the cilliary muscles as people age; results in the light hitting the retina being offcenter to make closer objects harder to see

Visual field

The area we can see with one or more of our eyes; approx. 130 degrees

Detail Sharp Vision Field

The small part of our visual field where we see the best

Retina

The layered back part of the eye where light hits after passing through viscous liquid; contains the blood vessels and has an invert of the visual field

Macula

Part of the retina that processes images directly in front - has no blood vessels

Optic Disk

Part of the eye where the axons go from the eye to the brain; corresponds to a small blind spot in each eye

Layering order of retina (front to back)

Retinal Ganglion cells (RGCs), bipolar cells, photoreceptors [Amacrine cells between first two; horizontal cells between last two]

Photoreceptors

Neurons that are light sensitive; found in the back of the retina

Photopigments

specific pigments that actually “recept” light

Pigmented Epithelium

Cell layer that helps support photoreceptor function and could also help provide nourishment/absorb excess light (not in all animals). Also helps in the unbleaching of rhodopsin

Retinal Ganglion Cells (RGCs)

Frontmost neurons in the retina that fire action potentials

Bipolar Cells

Intermediary cells that receive inputs from the photoreceptors/horizontal cells and sends information accordingly to the RGCs

Rods

A type of photoreceptor that’s longer and has more photopigment disks; primarily used for low light vision

Cones

A type of photoreceptor that’s shorter and has less photopigment disks; plays an important role in color vision

Distribution of Rods and Cones across the retina

Cones are more concentrated close to the centers with more rods as you start to move out

Fovea

Center pit with almost exclusively cones that helps increase resolution in the center retina

Ratio of RGCs to Photoreceptors

A lot more photoreceptors that RGCs, meaning that multiple photoreceptors line up into one RGC; usually more one to one the closer you get to the center of the eye

Macular Degeneration

Loss of photorecpetors in the fovea which leads to the blurring of central vision

Rhodopsin

The G-Protein coupled receptor (GPCR) and photopigment in photoreceptors that incurs response to the presence of light

Retinal

The ligand for Rhodopsin; it already sits inside the rhodopsin but only triggers activates upon light being present

Resting Potential of Photoreceptor Disk

approx. -30 mV

Dark Current

The passive influx of Na+ that flows into resting photoreceptors while it is dark and is kept open by cGMP; becomes closed once the rhodopsin GPCR is activated and cGMP gets reduced?

Transductin

The G-protein for the rhodopsin GPCR cascade

Bleaching

The process where retinal disassociates from rhodopsin under light and requires a set of chemical reactions to occur before their function can be regained; occurs often in rods 

Types of Cones

Blue, Green, and Red (increasing in size in that order)

Dark Adaptation

Involves pupils dialating and the unbleaching of rhodopsin to help ^ sensitivity

Light Adaptation

Involves the pupils constricting and the gradual increase of the membrane back to its resting potential via lack of calcium coming in through the non selective channel leading to the gradual reopening of the closed channel

Receptive Field

A specific spot within the visual field that a specific neurons (mainly bipolar/RGCs) will respond to

RGCs

Do RGCs or photoreceptors have larger receptive fields?

Center-Surround Receptive Fields

The type of receptive fields that RGCs and bipolar cells have that focuses on the contrast between the presence of light at the center of the receptive field in comparison to the surrounding area; enables the eyes to recognize contrast/edges more easily

ON Center Receptive Field (RGCs)

Receptive fields activated by light being in the center and the surround being surrounded by dark

OFF Center Receptive Field (RGCs)

Receptive fields activated by dark being in the center and the surround being surrounded by light

Glutamate

Neurotransmitter released by photoreceptors and taken up by bipolar signals; release more in the dark and less in the light

Phototransduction

The process of converting light energy to electrical signals

OFF Bipolar Cells

Follows the polarization of photoreceptors; becomes hyperpolarized by light and excited by dark via ionotropic receptors

ON Bipolar Cells

Does the opposite polarization of photoreceptors; becomes hyperpolarized by dark and excited by light via metabotropic receptors

Center Response

The response triggered onto the bipolar cell by the photoreceptors directly in line with it

Surround Response

The response triggered onto the bipolar cell by the photoreceptors surrounding it via lateral inhibition from the horizontal cells

Lateral Inhibition

The inhibitory response triggered by depolarized horizontal cells onto the center bipolar cell; response is based on the surround photoreceptors

Horizontal Cells

Neurons that have neurites extending laterally; follows the polarization of the surround photo receptors and inhibits the center bipolar cell if depolarized

When the surround and center have opposing stimuli that corresponds with their receptive field

Conditions under which bipolar cells get the most excited

Direct Pathway

The stimulus in the center that sets up the response of the central photoreceptors and their effect on the center bipolar cells

Indirect Pathway

The stimulus in the surround that involves the horizontal cells and their influence on the center bipolar cell

Luminence Opponents

Cells that detect in their visual field based on difference in light and dark

Color Opponents

Cells that detect in their visual field based on color contrast to enable color vision

Blue-Yellow Bipolars

Bipolar cells that receive a central input from blue cones and a surround input from red+green cones

Yellow-Yellow Bipolars

Just luminance opponent bipolars

Wavelengths that are absorbed by either the center or surround cones

What do color opponent cells exclusively distinguish between when determining their response instead of edges?

Midget Bipolar Cells

Cells that have central inputs from either red or green cones, and the surround being yellow (but in practice being the opposite - red or green)

Parallel Processing

The idea that the brain has to process multiple forms of input from various different places at the same time to properly interpret things (i.e. in the case of vision)

Optic nerve 

Part where the axons of RGCs leave the retina

Optic Chiasm

Part where the outcoming axons from each eyes cross over

Optic Tract

The part at the base of the optic chaism where the optic nerves end up

Nasal retina

The part of the retina that is closer to the side of the nose; crosses over to the other side at the optic chiasm

Temporal retina

The outer part of the retina; stays on the same side even after the optic chiasm

hemifields

Part of the visual field that combines the nasal side of the opposite eye and the temporal side of the eye on that side

Binocular Visual Field

The part where the visual fields overlap allowing for clearer vision in the centerP

Pretectum

The part that controls light reflexes - dilation and constriction; target of RGCs

Superior Colliculus

Guides eye movements aka saccades; target of RGCs

Suprachiasmatic Nucleus

Part of hypothalamus that controls circadian rhythms; target of RGCs

LGN (Lateral Geniculate Nucleus)

Part of the thalamus where 80-90% of RGCs project and has 6 layers; allows for visual perceptions; draped over the optic tract

Primary Visual Cortex (V1)

9 layered part of the brain that receives signals from the LGN and is responsible for much of visual processing

Pyrimidal Cells

Neurons across V1 that have axons that go outside the region

Spiny Stellate Cells

Neurons found in layer IVC of the primary visual cortex and mostly synapse locally; its around here where most LGN signals come in and then move radially (horizontally in layer III) to send signals out depending on the layer

Retinotropic Map of V1

Reflects how neighboring cells have similar receptive fields and how much of V1 is dedicated to the central visual field

Cortical Magnification

The magnification of the central visual field on the retinatropic map

Ocular Dominance Columns

Stripes/grooves in V1 that show where most inputs come in from one specific eye; left eye = dark stripes, right eye= light stripes

Layer III, which is where the ocular dominance columns start to blend together

Binocularity begins in what layer?

Hebbian Synapses

Synchronous inputs that fire together to sync up inputs coming from both eyes in ocular dominance columns

Strabismus and Congenial Cateracts

Conditions where the signal inputs from both eyes are not synced up

Cortical Receptive Fields

Are generally not super sensitive to light, but rather respond to bars of light

Simple Cells

Cortical neurons that fire when they detect bars of light in a specific orientation and can also be selective for direction of movement; theorized to act they way due to lines of ON Center RGCs being surrounded by OFF centers in a specific orientation

Complex Cells

Cells that respond to bars of light in a specific orientation regardless of location in the visual field; composed of clusters of simple cells that detect for bars of light in the same orientation

Ventral Stream

Projects into the temporal lobe from V1; allows for the perception/recognition of things seen - also helps attunes us to things like faces and shadows

Dorsal Stream

Projects into the parietal lobe from V1; allows for the detection of motion/action

Chemical Senses

Involves the pathways for taste and smell; broadly speaking refers to the ability to detect chemicals

Gustation/taste

Primarily detected by the tongue; helps to detect nutritious quality in food, avoid toxins, and do other things in other species

Sweet

Appetitive taste that is used to detect sugars; detected by GPCRs using T1R2 and T1R3 proteins

Umami

Appetitive taste that is used to detect protein; detected by GPCRs using T1R1 and T1R3 proteins

Bitter

Aversive taste that is used to detect toxins (strong reaction/high affinity); detected by GPCRs that use approx. 30 T2R compounds

ATP

The neurotransmitter used by GPCR taste receptors

Seratonin

The neurotransmitter used by ionotropic taste receptors

Sour

Aversive taste that is used to detect low pH/acids; detected by ionotropic receptors that are theorized to function as proton channels

Salt

Neutral taste that is used to detect sodium and response changes based on sodium concentrations; detected by ionotropic Na+ channels

Bitter + Sour

The combination of modalities used to generate an averse response to high concentrations of salt

Papillae

The visible bumps on the tongue that contain approx 1-500 taste buds each

Taste Buds

Small grooves on papillae that contain 50-150 taste receptor cells bunched together

Taste Receptors

The specific touch/epithelial cells that detect specific tastes based on their proteins, and have cilia that extends up into the taste pore to detect taste modalities

Generally scattered with some areas having higher concentrations to detect certain tastes

How are taste receptors scattered across the tongue based on taste?

Gustatory “Axons”/Afferents

Unipolar neurons that connect from taste receptors to the brain to send taste signals and project to the medulla

Labelled-Line Coding

The idea that single cells are attuned to a single stimulus and in turn produce a specific corresponding behavior (characteristic of taste)

Supertasters

People who have more papillae and are able to taste better

Nontasters

People who have less papillae and are unable to taste as well