NBL356 Final Exam

Visual system

a complex part of the central nervous system responsible for visual perception. It involves receiving, processing, and interpreting information from the visual world. This system builds a coherent representation of the external environment by converting light into electrical signals, integrating these signals, and interpreting them to form visual images.

Detection of light

• the initial step in visual processing where photoreceptor cells in the retina absorb photons and convert this light information into electrical signals in the form of action potentials.

• Involves phototransduction, where photopigments in rods and cones change configuration upon light absorption, leading to a cascade of intracellular events that generate electrical signals.

Monocular vs binocular vision

involve visual information processed from one eye, which is then integrated with information from the other eye to build binocular perceptions, vs allows for depth perception and three-dimensional understanding of the environment by combining slightly different views from each eye.

Object identification and categorization

• complex processes where the visual system recognizes and differentiates visual objects based on features such as shape, color, texture, and spatial orientation.

• involves higher-order visual processing in areas like the inferotemporal cortex, where neurons respond to specific object categories and identities.

Distance Calculation

• visual system's ability to determine distances to and between objects.

• This information is crucial for coordinating motor actions and guiding body movements.

• It relies on depth cues such as binocular disparity, motion parallax, and perspective, which are processed in cortical areas like the parietal lobe to aid in spatial awareness and navigation.

Pupillary Light Reflex (PLR)

• non-representational function of the visual system.

• involves the reflexive constriction of the pupil in response to bright light, mediated by a neural pathway that includes the retina, pretectal area, Edinger-Westphal nucleus, and the oculomotor nerve.

• helps regulate the amount of light entering the eye to protect retinal photoreceptors and optimize vision.

Circadian rhythm regulation

• non-visual function of the visual system where information about light and dark cycles is transmitted from the retina to the suprachiasmatic nucleus (SCN) in the hypothalamus.

• This input helps synchronize the body's internal clock with the external environment, regulating sleep-wake cycles, hormone release, and other physiological processes.

Visual field

• divided into left and right hemifields, with each hemifield's information being processed by the opposite hemisphere of the brain.

• This information is sent to different parts of the primary visual cortex (PVC) via the optic chiasm, where nerve fibers partially cross, ensuring that visual data from each eye contributes to binocular vision and depth perception.

Retina

• multi-layered structure at the back of the eye, crucial for detecting light and converting it into electrical signals.

• comprises several types of neurons, including photoreceptors (rods and cones), bipolar cells, horizontal cells, amacrine cells, and retinal ganglion cells.

• These cells work together to process visual information before it is transmitted to the brain via the optic nerve.

Optic nerves

• composed of the axons of retinal ganglion cells and transmits visual information from the retina to the brain.

• After leaving the eye, the ______________ from each eye meet at the optic chiasm, where fibers partially cross, ensuring that visual information from both eyes is integrated and processed in the appropriate hemispheres of the brain.

LGN (Lateral geniculate nucleus)

• a specific thalamic nucleus that acts as a relay center for visual information.

• receives input from the optic tract and sends projections to the primary visual cortex.

• organized into layers, each receiving input from either the ipsilateral or contralateral eye, facilitating the processing of visual information for perception and reflexive responses.

Photoreceptor cells

• including rods and cones

• specialized neurons in the retina responsible for detecting light.

• Rods are sensitive to low light levels and are crucial for night vision, while cones detect bright light and enable color vision.

• These cells contain photopigments that change configuration upon light absorption, initiating the phototransduction cascade.

Rods

• a type of photoreceptor cell in the retina, characterized by their long, slender shape and high sensitivity to low light levels.

• primarily located in the peripheral regions of the retina and are essential for scotopic (low-light) vision. contain the photopigment rhodopsin, which undergoes a conformational change when exposed to light, triggering the phototransduction process.

Cones

• photoreceptor cells in the retina, concentrated in the macula and fovea, responsible for photopic (bright light) vision and color discrimination.

• There are three types of cones, each sensitive to different wavelengths of light (red, green, and blue).

• contain photopigments called conopsins, which absorb light and initiate the phototransduction cascade, enabling high visual acuity and color perception.

Fovea

• the central part of the retina, located within the macula, with a high density of cone photoreceptors.

• It is responsible for sharp central vision (visual acuity), allowing us to see fine details. The foveal pit is free of blood vessels and other cells, providing a direct path for light to reach the cones, optimizing visual clarity and resolution.

Optic disk

• the region in the retina where axons from retinal ganglion cells converge to form the optic nerve.

• This area lacks photoreceptors, resulting in a blind spot in the visual field. Despite this, the brain compensates for the missing information through visual processing mechanisms, effectively "filling in" the gap in our vision.

Phototransduction cascade

• biochemical process triggered by the absorption of light by photopigments in photoreceptor cells.

• This cascade involves changes in the configuration of opsins, activation of transducin, and a series of intracellular events that ultimately lead to the hyperpolarization of the photoreceptor cell membrane, generating an electrical signal.

Opsins

• light-sensitive transmembrane proteins in photoreceptor cells that initiate the phototransduction cascade.

• In rods- rhodopsin, while cones have different (conopsins) for red, green, and blue light.

• contain a chromophore (11-cis retinal) that changes shape upon light absorption, activating the phototransduction pathway.

Accommodation of the lens

• refers to the ability of the lens to change its shape to focus light on the retina, allowing for clear vision of objects at various distances.

• This process involves the ciliary muscles adjusting the curvature of the lens, enabling it to become more convex for near objects and flatter for distant objects, thus maintaining a sharp image on the retina.

Photopigment disks

• structures within the outer segments of photoreceptor cells, densely packed with membranes containing photopigments (opsins).

• These disks increase the surface area for light absorption, enhancing the efficiency of phototransduction.

• The photopigments within these disks capture photons, triggering a cascade of biochemical events that convert light into electrical signals.

Rhodopsin

Photopigment in rod cells composed of opsin protein and 11-cis retinal, which changes conformation when absorbing light, triggering the phototransduction cascade.

Dark current

Baseline electrical activity in photoreceptor cells with open cGMP-gated channels, maintaining a depolarized membrane potential and continuous neurotransmitter release in darkness.

Transducin

G-protein activated by rhodopsin that stimulates phosphodiesterase, critical for initiating the light-triggered signaling cascade in photoreceptor cells.

cGMP gated channels

Ion channels in photoreceptors regulated by cyclic GMP, allowing cation flow and playing a crucial role in light-induced membrane potential changes.

Photoreceptor adaptation

Mechanism reducing cellular sensitivity to continuous light stimulation through rhodopsin phosphorylation and G-protein inactivation.

Phosphodiesterase

Enzyme activated during phototransduction that hydrolyzes cGMP, causing cGMP-gated channel closure and membrane hyperpolarization.

Disk membranes

Specialized intracellular membranes in rod outer segments containing high concentrations of rhodopsin and essential for phototransduction machinery.

Rods vs Cones

Two types of photoreceptors with distinct characteristics: ____ for low-light (scotopic) vision and black-and-white perception, ____ for color and bright-light (photopic) vision.

GPCR

Large receptor family that includes rhodopsin, characterized by seven transmembrane domains and ability to activate intracellular signaling cascades.

Light Sensitivity Range

Visual system's ability to detect light across 10 orders of magnitude, from 10^-6 to 10^8 luminance units.

Guanylyl Cyclase

Enzyme synthesizing cGMP in photoreceptors, maintaining high cGMP levels in darkness that keep cGMP-gated channels open.

Retinal Pigmented Epithelium

Specialized cell layer absorbing stray photons, preventing light scattering, and recycling photoreceptor outer segment components.

Signal amplification

Phototransduction's ability to generate massive cellular response from single photon absorption, with one rhodopsin potentially activating 500-800 transducin molecules.

Chromophore

Light-sensitive molecule (11-cis retinal) that undergoes structural changes when absorbing photons, initiating conformational shifts in photopigments.

Voltage gated Calcium Channels

Ion channels in photoreceptors controlling neurotransmitter release, activated at specific membrane potentials.

Arrestin

Protein binding phosphorylated rhodopsin, preventing further G-protein activation and contributing to light adaptation.

Scotopic vision

Low-light vision primarily mediated by rod photoreceptors, effective in starlight and moonlight conditions.

Photopic vision

Bright-light vision primarily mediated by cone photoreceptors, enabling color perception and high visual acuity.

Bipolar cells

• Neurons in the retina that relay information from light-sensitive cells to more complex processing cells within the visual pathway.

• integral in transforming raw visual information from the sensory cells into signals that can be interpreted by the brain.

• characterized by a receptive field that consists of a center and a surrounding area, where light input from the central region produces one type of response, and light from the surrounding area leads to an opposing response.

• This dual processing helps to enhance contrast detection and the overall visual clarity.

Horizontal cells

• specialized cells in the retina

• involved in lateral processing and play a key role in regulating the interaction between adjacent light-sensitive cells.

• receive input from these cells and transmit feedback signals, which can either amplify or dampen the responses of neighboring cells, creating a feedback loop that sharpens the contrast between illuminated and dark areas.

• function is essential for maintaining the sensitivity of the visual system, especially in environments with varying light levels, by contributing to the spatial organization of receptive fields.

Receptive field

• A defined region of visual space in which a specific sensory cell can detect light and produce a response.

• For light-sensitive cells, this area can be as small as a single point in the visual field for each individual cell, but for cells higher up in the processing pathway, these fields become more complex, encompassing both a central area that directly receives light input and a surrounding area that processes light through lateral pathways.

• The structure and organization of these fields are crucial for distinguishing fine details and contrasts in the visual scene.

Center-surround organization

• A structural and functional characteristic of many retinal cells, where the region of the receptive field at the center responds to light through a direct neural pathway, while the surrounding area is processed through lateral connections that modulate the central response.

• This arrangement enhances the ability to detect differences in light intensity across space, aiding in the identification of edges, boundaries, and contrasts in the visual environment. This form of spatial contrast detection is essential for distinguishing objects from their backgrounds.

On-center bipolar cells

• These specialized retinal neurons are excited when light is present in the central region of their receptive field, leading to depolarization.

• They use a specific class of glutamate receptors that, in the absence of light, maintain a hyperpolarized state but allow for depolarization when light reduces the glutamate release from light-sensitive cells.

• The depolarization of these cells activates downstream pathways, increasing the likelihood of visual signals being transmitted to higher brain centers.

• This functionality is essential for detecting regions of the visual field with high light intensity.

Off-center bipolar cells

• These retinal neurons exhibit an inverse response compared to on-center cells, where light in the central region of their receptive field causes hyperpolarization, leading to decreased activity.

• These cells express a different class of glutamate receptors that respond to the presence of glutamate with a depolarizing effect in the dark, and light-induced reduction in glutamate release results in further hyperpolarization.

• Their role is to detect areas of the visual field that are darker relative to their surroundings, and their activity patterns help in contrast enhancement.

Retinal Ganglion Cells

• These are the final output neurons in the retina that convey visual information from the eye to the brain.

• They receive input from bipolar cells and generate action potentials that travel through the optic nerve to the brain's visual processing areas.

• Their response is contingent on the combined input from both the center and surround regions of receptive fields, allowing for sophisticated processing of contrast and edge detection.

• These cells can exhibit baseline activity and adapt to changes in visual stimuli, contributing to the overall clarity and detail of vision.

Sign-conserving response

• A response characteristic of certain retinal cells where the activation of photoreceptors by light results in a decrease in glutamate release, leading to a consistent reduction in the depolarization of downstream cells.

• This effect occurs in cells that hyperpolarize in response to light, maintaining the same sign of the signal through each successive synapse, which modulates the overall output in the visual pathway.

Sign-inverting response

• This refers to a mechanism in which light-induced changes in photoreceptor activity lead to a reversal in the response polarity of downstream cells.

• In this case, the hyperpolarization of light-sensitive cells results in the depolarization of bipolar cells, which then increases the firing of action potentials in retinal ganglion cells.

• This inversion of signal direction is crucial for processing information such as contrast and boundaries within the visual field.

Metabotropic Glutamate Receptor (mGluR6)

• A specific class of receptors present on certain retinal neurons that mediate responses to the neurotransmitter glutamate.

• These receptors function by inhibiting certain ion channels when glutamate binds to them, leading to a hyperpolarizing effect in the absence of light.

• The reduction in glutamate release upon exposure to light diminishes the inhibition of these receptors, allowing for the depolarization of the affected retinal cells, which is key for processing visual information in regions of high light intensity.

AMPA receptor

• Ionotropic glutamate receptors found on certain retinal cells, such as off-center bipolar cells, that mediate depolarization in response to glutamate.

• These receptors are nonselective cation channels, meaning they allow the influx of various ions, including sodium, in response to glutamate release.

• The activity of these receptors leads to depolarization in the dark and is reversed in the presence of light, which reduces glutamate release and causes hyperpolarization of these retinal cells.

Contrast Detection

• The process by which the visual system distinguishes differences in light intensity across different regions of the visual field.

• This ability is crucial for detecting edges, textures, and variations in the environment.

• The retina achieves this by comparing the light levels in the center and surround of receptive fields, and this comparison is central to the formation of high-contrast images in the brain.

• Such detection is vital for recognizing objects against varying backgrounds.

Horizontal cell feedback

• Horizontal cells play a regulatory role in the retina by modulating the output of neighboring photoreceptors and bipolar cells through feedback mechanisms.

• These cells are depolarized in the dark by glutamate release from photoreceptors and provide feedback that can either enhance or suppress the activity of adjacent cells, refining the processing of visual signals.

• This lateral interaction is crucial for sharpening the contrast between light and dark areas in the visual field.

Volume Transmission

• A process in which neurotransmitters are released from one cell and affect multiple target cells within a certain area.

• This type of transmission allows for widespread modulation of cell activity in the surrounding region.

• In the retina, this process occurs at cone pedicles, where neurotransmitter release affects multiple neighboring photoreceptors, ensuring coordinated responses to visual stimuli across a broad area of the visual field.

Retinal adaptation

• A dynamic process through which the retina adjusts its sensitivity to changing light conditions.

• This process enables the visual system to remain effective across a wide range of light intensities, from bright daylight to dim moonlight.

• Adaptation mechanisms adjust the responsiveness of retinal cells, including those that process contrast, ensuring that visual perception remains stable and clear under different lighting conditions.

Center-surround contrast mechanism

• A critical feature of the visual system where the retina processes differences in light intensity between the central and surrounding regions of receptive fields.

• This mechanism relies on the interactions between center and surround, which are mediated by both direct and indirect pathways.

• By detecting changes in light intensity, this system enhances the ability to perceive contrasts, which is essential for detecting edges, objects, and features in the visual field.

Divergence of bipolar cells

• A characteristic of certain retinal neurons where a single bipolar cell forms connections with multiple downstream cells, such as ganglion cells.

• This allows for the broad dissemination of visual signals to different regions of the visual system, helping to integrate and process complex visual information across different areas of the retina.

• The spreading of signals contributes to the brain’s ability to interpret complex visual scenes and detect patterns across the field of view.

Vertical pathway in retina

• refers to the direct flow of visual information from photoreceptor cells to bipolar cells and then to retinal ganglion cells (RGCs).

• Can exhibit different wiring configurations, such as one-to-one, divergent, or convergent connections between photoreceptors and bipolar cells, and typically involves one-to-one or convergent wiring between bipolar cells and RGCs.

• Crucial for transmitting initial visual signals to the brain, but there are fewer RGCs than photoreceptor or bipolar cells, indicating significant signal processing at earlier stages of retinal processing.

Lateral pathways in retina

• involves horizontal and amacrine cells, which mediate feedback and lateral communication between retinal cells.

• Horizontal cells receive input from photoreceptors and send inhibitory signals to bipolar cells, refining the contrast of visual information. Amacrine cells receive input from bipolar cells, send output to RGCs, and provide feedback to the bipolar cells.

• Enable the center-surround receptive field organization in RGCs, enhancing the contrast sensitivity of the visual system.

Types of RGCs

• M-type, P-type, and K-type.

• M-type cells have larger receptive fields and respond to low contrast with transient, high temporal frequency responses, and are involved in motion detection.

• P-type cells, smaller with high spatial resolution, have sustained responses and are sensitive to color, playing a key role in high-acuity vision and color discrimination.

• K-type cells, with mixed responses to space and time, are involved in chromatic processing, particularly related to S-cones, and provide input to the koniocellular layers of the LGN.

Cones and Photopic Vision

• specialized photoreceptor cells responsible for photopic (daylight) vision, high visual acuity, and color perception.

• contain one of three photopigments (photopsins) sensitive to different wavelengths of light: red (L-cones), green (M-cones), and blue (S-cones).

• Color vision arises from the brain's ability to compare the responses of different cone types to light.

• Activation of at least two types of cones is necessary to distinguish colors, with each wavelength of light exciting a combination of these cones to create color perception

Photosensitive ganglion cells

• including giant retinal ganglion cells, contain the photopigment melanopsin, enabling them to respond directly to light without the involvement of rods or cones.

• These cells project to the suprachiasmatic nucleus (SCN) in the hypothalamus, which controls circadian rhythms, as well as to the pretectum and superior colliculus, which are involved in pupil constriction and eye movement control.

• These cells contribute to non-image-forming visual functions such as regulating the sleep-wake cycle.

Superior Colliculus and eye movements

• a structure in the midbrain that is crucial for controlling various types of eye movements, including saccades (rapid eye movements), smooth pursuit (tracking moving objects), fixation (maintaining gaze on stationary objects), and vergence (coordination of both eyes to maintain binocular vision).

• receives visual input from the retina and helps integrate visual information with motor commands, enabling accurate and coordinated eye movements in response to visual stimuli.

Suprachiasmatic Nucleus

• located in the hypothalamus, is the body's central circadian pacemaker, controlling daily cycles of behavior and physiological processes such as sleep, alertness, hormone secretion, and body temperature.

• receives direct input from photosensitive ganglion cells in the retina, allowing it to synchronize the body's internal clock with the external day-night cycle, a process essential for maintaining rhythmicity and proper bodily functions.

Optic nerve vs Optic Tract

• formed by the axons of retinal ganglion cells (RGCs), transmitting visual information from the retina to the brain.

• After partial decussation (crossing) at the optic chiasm, the optic nerve becomes the optic tract, which carries visual signals to various brain regions, including the lateral geniculate nucleus (LGN) in the thalamus, the pretectum (for pupil control), and the superior colliculus (for eye movement).

• The optic tract also sends projections to the suprachiasmatic nucleus (SCN), helping regulate circadian rhythms.

Dorsal stream; ventral stream

• The visual system processes information through two main pathways:

• _______________ which is involved in spatial awareness, motion perception, and guiding actions (the "where/how" pathway, projecting to the parietal lobe), and

• ___________ which handles object recognition, form perception, and color discrimination (the "what" pathway, projecting to the temporal lobe).

• These pathways work in parallel, processing different aspects of the visual scene, such as motion and identity, to construct a coherent representation of the environment.

Fusiform Face Area

• a region in the inferior temporal cortex, specifically in the fusiform gyrus, that is specialized for recognizing faces. It is part of the ventral stream and plays a crucial role in processing facial features and distinguishing individuals.

• shows lateralization, typically being larger in the right hemisphere, and is more responsive to faces than to other objects.

• However, there is ongoing debate about whether it is exclusively dedicated to face processing or whether it is involved in the recognition of other familiar objects that require expertise.

Prosopagnosia

• a cognitive disorder that impairs the ability to recognize familiar faces, including one's own, despite intact visual processing for other objects.

• typically associated with damage to the fusiform gyrus, particularly in the right hemisphere. People with prosopagnosia may rely on other cues, such as voice or context, to recognize individuals.

• The disorder can be acquired (due to brain injury) or developmental (present from birth), with a prevalence rate of approximately 2.5%.

Optical dominance columns

• alternating regions in the primary visual cortex (V1) that receive input from the ipsilateral or contralateral eye.

• crucial for binocular vision and depth perception, as they integrate visual information from both eyes to create a single, cohesive visual representation of the environment.

• The LGN and V1 maintain a retinotopic map, where the visual information from both eyes is processed within these alternating columns, aiding in the perception of depth and spatial relationships.

Retinotopy

• refers to the spatial arrangement of visual information from the retina that is preserved throughout higher visual processing areas, such as the lateral geniculate nucleus (LGN) and primary visual cortex (V1).

• This topographical mapping allows visual areas to maintain a direct correspondence between the retina's representation of the visual field and the brain's processing areas, ensuring that objects in the environment are represented in a precise and organized manner. Retinotopy is essential for accurate visual perception.

Cortical magnification

• phenomenon where areas of the visual field that require higher acuity, such as the fovea, are represented by disproportionately larger regions of the primary visual cortex (V1).

• Results in a higher density of neurons in cortical areas devoted to processing high-resolution stimuli, particularly in the central visual field.

• The foveal region of the retina, due to its high concentration of cones, is thus represented by a larger area of cortical space compared to the peripheral visual field.

Contrast

The human visual system is especially good at detecting _______ whether it be chromatic, luminance or timing, allowing the brain to perceive color, edges, shadows, depth and motion.

Ultraviolet radiation

Contrast

Plasma

Polarized light

Light scattering

All of these answers

The visual system ____.

Builds a representation of the visual environment

Includes the visual field, eye, thalamus and visual cortex

All of these answers

Is required for visual perception

Is involved in receiving, processing and interpreting visual information

Cornea and lens

The main function of the _______ is/are to refract light.

Vitreous humor

Sclera

Pupil and iris

Cornea and lens

Retina

All of the neurons in the eye are located in the retina

Which of the following BEST DESCRIBES the visual system?

The right eye transmits information to only the left thalamus

About 95% of optic nerve axons decussate at the optic chiasm

The optic radiation transmits visual information from the optic tract to the thalamus

All of the neurons in the eye are located in the retina

The retina is considered part of the peripheral nervous system

All of these answers

What is/are the function(s) of the human visual system?

Perception of movement and moving objects

All of these answers

Identification and categorization of visual objects

Pupillary light reflex (PLR) and circadian photoentrainment

Buildup of a nuclear binocular perception from monocular representations

Cellular and synaptic layers

The retina contains ______.

Cellular and synaptic layers

Photoreceptor cells

Bipolar and retinal ganglion cells

All of these answers

Pigmented epithelial cells

All of these answers

Retinal ganglion cell axons form the ______.

Optic tract

Output from the retina

Optic chiasm

All of these answers

Optic nerve

True

An object in the left visual field is detected by the left nasal retina and the right temporal retina.

True

False

True

Humans can detect electromagnetic radiation in the range of ~380 to 740 nm.

True

False

Rods and cones have different luminence sensitivities

Which of the following BEST DESCRIBES photoreceptor cells (rods and cones)?

Rods and cones have three regions called proximal segments, middle segments and distal segments

Rods and cones are located in two separate layers of the retina

Rods and cones produce action potentials

Light passes first through the rods and cones before reaching the other layers of the retina

Rods and cones have different luminence sensitivities

It involves opening of voltage gated Ca2+ channels at the presynaptic region

Which of the following BEST DESCRIBES the “dark current” components in photoreceptors in the dark?

It includes an outward Na+ leak current in the inner segment

It involves opening of voltage gated Ca2+ channels at the presynaptic region

It includes the cGMP dependent inward K+ current in the outer segment

It produces membrane depolarization to about -67 mV

It inhibits the release of neurotransmitter

All of these answers

Which of the following BEST DESCRIBES rhodopsin and cone opsins (photopsin)?

They are transmembrane proteins that bind retinal

All of these answers

They are synthesized in the RER in the inner segment

They are G protein coupled receptors

They are located on the disc membrane or plasma membrane in the outer segment

11-cis retinal absorbs a photon and isomerizes to all-trans retinal

The first step in the phototransduction cascade occurs when ___.

Light is absorbed by and closes the cation channels

Rhodopsin binds glutamate

11-cis retinal absorbs a photon and isomerizes to all-trans retinal

Light is absorbed by and activates transducin

Rhodopsin binds to and opens the cation channels

Activates phosphodiesterase (PDE)

Transducin is a G protein that ______.

Regulates retinal isomerase

Activates phosphodiesterase (PDE)

Inhibits an ion channel

Controls rhodopsin

Increases cGMP levels

cGMP gated channels close, leading to hyperpolarization of the photoreceptor

In response to light, the ________.

TRP channels open leading to the receptor potential

Nonselective cation channels open, leading to depolarization of the photoreceptor

Rhodopsin channels close, leading to hyperpolarization of the photoreceptor

cGMP gated channels close, leading to hyperpolarization of the photoreceptor

Hyperpolarize and release less glutamate

In response to light, all photoreceptor cells (rods and cones) ______.

Hyperpolarize and release less glutamate

Depolarize and release more glutamate

Hyperpolarize and release less GABA

Depolarize and release more GABA

Adaptation

The process of ______ in the phototransduction cascade involves mechanisms that lead to a decrease in response to the same intensity of light.

Regeneration

Transduction

Photon detection

Adaptation

Transmission

Amplification

The process of ______ in the phototransduction cascade means that the retina is highly sensitive to light and can produce a response to even a single photon of light.

Amplification

Regeneration

Adaptation

Sensation

Desensitization

All of these answers

What is a reasonable explanation for why the visual system may have evolved G protein signaling for phototransduction?

All of these answers

It provides significant amplification, which increases sensitivity

The disc membrane provide a large membrane area that can accommodate many components of the G protein signaling cascade

It provides multiple points for adaptation, which helps increase the dynamic range of the stimulus

The visual system may have evolved from evolutionary ancient G protein signaling cascades

Retinal pigment epithelial

The ______ cells absorb light, and phagocytose rod and cone outer segments to help repair and recycle photodamaged components.

Photoreceptor cells

Glial

Retinal pigment epithelial

Horizontal

T cells

Cones are concentrated in the fovea and rods are absent from the fovea

Only cone photoreceptor cells are involved in high acuity vision because ____.

There are more cones than rods

Cones are concentrated in the fovea and rods are absent from the fovea

There are three types of cones called S, M and L cones but only one type of rod

Cones produce larger responses to light than rods do

Cones are more sensitive to light than rods are

Rod

Cone

Cone

Rod

Cone

Rod

Rod

Cone

Rod

Cone

Cone

Rod

Rod

Cone

Cone

Rod

Match the type of photoreceptor cell with its characteristic.

One photopigment (rhodopsin)

Three photopigments (photopsins)

Concentrated in the fovea but also present in the periphery

Located only in the periphery

Lower sensitivity to light

Higher sensitivity to light

Slower temporal response

Faster temporal response

Saturates in bright light

Does not saturate in bright light

Photopic vision

Scotopic vision

Higher total number

Lower total number

Fewer discs and disc is part of plasma membrane in outer segment

More discs and separate discs in outer segment

Depolarization

In On-center bipolar neurons, light in the center leads to a decrease in glutamate binding to mGluR6 receptors, which leads to _____ in response to light in the center.

An increase in Ca2+ levels

Depolarization

Hyperpolarization

A decrease in glutamate release

Decrease in cGMP levels

Inverting

In the question above, this is a type of sign ______ response.

An increase in the frequency of action potential firing

Increased light in the center of the receptive field of an On-center bipolar cells leads to ______ in retinal ganglion cells.

An increase in the frequency of action potential firing

A decrease in the rate of action potential frequency

The stimulation of mGluR6Rs and AMPARs

The release of photons

Adaptation

Hyperpolarization

In an Off-center bipolar neuron, light in the center leads to a decrease in glutamate binding to AMPA receptors, which leads to ________ in response to light in the center.

An increase in action potentials

Hyperpolarization

Depolarization

A decrease in action potentials

A depolarization followed by a hyperpolarization

Conserving

In the question above, this is a type of sign _____ response.

Decreased action potential frequency

Increased light in the center of the receptive field of an Off-center bipolar cell leads to ______ in the retinal ganglion cells.

Increased action potential frequency

No change in the action potential frequency

The release of photons from

Adaptation of

Decreased action potential frequency

Horizontal

_____ cells are GABAergic inhibitory interneurons that mediate and control the surround response to light.

Bipolar

Photoreceptor

Retinal pigmented epithelial

Retinal ganglion

Horizontal

All of these answers

The human visual system can detect light over a luminance range of 9-10 orders of magnitude. What is the mechanism involved in this?

Pupil dilation

All of these answers

Rods and cones have different luminance sensitivities

Adaptation in the phototransduction cascade response to light

Lateral processing by horizontal and amacrine cells

All of these answers

The mammalian retina can respond to both increases in light and decreases in light through changes in action potential output. Retinal Ganglion Cells (RGCs)

Off center bipolar cells synapse onto Off center RGCs

RGCs have a significant baseline firing rate

On center bipolar cells synapse onto On center RGCs

On and off center cells express different types of glutamate receptors

All of these answers