Lecture 21 - Vision 3 - Ganglion Cells & Parallel Paths FC

Visual System

The neural structures and pathways in the body that process visual information.

Ganglion Cells

Neurons in the retina that receive input from bipolar cells and relay visual information to the brain.

Contrast Detectors

Neurons in the visual system that respond to differences in light intensity.

Bipolar Cells

Retinal neurons that connect rods and cones with ganglion cells.

Luminance Contrast

The difference in the number of photons that fall on the center versus the surround of a receptive field.

Receptive Field

The specific area of the retina where a stimulus influences the firing rate of a neuron.

ON-center Cells

Ganglion cells that are excited by light in their center and inhibited by light in their surrounding.

OFF-center Cells

Ganglion cells that are inhibited by light in their center and excited by light in their surrounding.

Action Potentials

Rapid electrical signals that travel along neurons.

Photopigment

A light-sensitive molecule found in photoreceptors like rods and cones that undergoes a chemical change when exposed to light.

Rods

Photoreceptors responsible for vision in low-light conditions; highly sensitive to light.

Cones

Photoreceptors that facilitate color vision and are responsible for visual acuity in bright light.

Hyperpolarization

A change in a cell's membrane potential that makes it more negative compared to resting potential.

Depolarization

A change in a cell's membrane potential that makes it less negative compared to resting potential.

Midget Bipolar Cells

Bipolar cells that connect to a single cone and have small receptive fields.

Dark Noise

Random fluctuations in the membrane potential of photoreceptors in the absence of light.

GRK (G Protein-Coupled Receptor Kinases)

Enzymes that phosphorylate active opsins, regulating phototransduction.

Calcium Exchanger NCKX

A protein that helps regulate calcium ions in photoreceptors.

Scotopic Conditions

Lighting conditions that are low, where rods are primarily active.

Photopic Conditions

Lighting conditions that are bright, where cones are primarily active.

Mesopic Conditions

Lighting conditions that are intermediate, with significant input from both rods and cones.

Light Adaptation

The process by which photoreceptors adjust their sensitivity to the ambient light levels.

Duplex Retina

A retina with high rod density for low light vision and a fovea with high cone density for color vision.

Electromagnetic Spectrum

The range of all types of electromagnetic radiation, ranging from gamma rays to radio waves.

Visible Light

The portion of the electromagnetic spectrum that can be detected by the human eye, roughly between 400 nm and 700 nm.

Opsin

A protein that, combined with chromophore, forms photopigments in photoreceptors.

Chromophore

The light-absorbing part of a photopigment, such as retinal.

Absorption Spectrum

A graph that shows the ability of photoreceptors to capture light across various wavelengths.

S Cones

Short-wavelength photoreceptors, sensitive to blue light.

M Cones

Medium-wavelength photoreceptors, sensitive to green light.

L Cones

Long-wavelength photoreceptors, sensitive to red light.

Trichromacy

The condition of having three types of cones, each sensitive to different wavelengths of light.

Anomalous Trichromats

Individuals with abnormal color vision due to mutations affecting cone opsins.

Color Confusion

The inability to distinguish between certain colors due to similar absorption spectra of cone photopigments.

Chromatic Contrast

Color-based contrast produced by differences in the wavelengths of light detected by cone photoreceptors.

Spatial Contrast

Contrast based on differences in luminance across regions of visual stimuli.

Bistratified Ganglion Cells

Ganglion cells that receive signals from S (blue) cones and M/L (yellow) channels.

Parasol Ganglion Cells

Ganglion cells with large receptive fields that process luminance signals.

Amacrine Cells

Interneurons in the retina that mediate communication between bipolar cells and ganglion cells.

Horizontal Cells

Retinal neurons that integrate signals from multiple photoreceptors.

Sign-Preserving Synapse

A synapse at which excitation of a neuron leads to excitation in its target.

Sign-Reversing Synapse

A synapse at which excitation of a neuron leads to inhibition of its target.

Locus Control Region (LCR)

A regulatory region that determines which opsin genes are expressed.

Covalent Bond

A strong chemical bond that involves the sharing of electron pairs between atoms.

Phototransduction

The process by which photoreceptors convert light into electrical signals.

Retinal Circuits

The pathways and connections formed by various types of retinal neurons.

Peak Absorption Wavelength

The specific wavelength of light at which a photoreceptor is most sensitive.

Retinal Ganglion Cells

Neurons that carry visual information from the retina to the brain.

Outer Nuclear Layer

The layer of the retina containing the cell bodies of photoreceptors.

Inner Plexiform Layer (IPL)

The retinal layer where synapses between bipolar cells and ganglion cells occur.

Vitreous Humor

The clear gel that fills the space between the lens and the retina of the eyeball.

Fovea

The central region of the retina that contains a high density of cones for sharp central vision.

Photoadaptation

The process by which photoreceptors lower their sensitivity following exposure to bright light.

Threshold Stimulus

The minimum level of stimulus intensity that will elicit a response.

Excitatory Postsynaptic Potential (EPSP)

A temporary increase in postsynaptic membrane potential that makes a neuron more likely to fire.

Inhibitory Postsynaptic Potential (IPSP)

A temporary decrease in postsynaptic membrane potential that makes a neuron less likely to fire.

Electrophysiology

The study of electrical properties of biological cells and tissues.

Neurotransmitter Release

The process of neurotransmitters being released from a neuron to communicate with another neuron.

Signal Transduction Pathway

A series of molecular events and reactions that lead to a cellular response.

AII Amacrine Cells

A specific type of amacrine cell that plays a crucial role in relay signals from rods to ganglion cells.

Retinal Pigment Epithelium

A layer of cells that nourishes retinal visual cells and is essential for visual function.

Light Capture

The process by which photoreceptors absorb photons and initiate phototransduction.

Calcium Ions (Ca2+)

Ions that play critical roles in cellular signaling, including in phototransduction.

Visual Acuity

The ability to discern fine details in visual images.

Luminance Channel

The neural pathway that processes differences in brightness of visual stimuli.

Chromatic Channel

The neural pathway that processes differences in color of visual stimuli.

Dynamic Range

The range of light intensities over which a photoreceptor can respond.

Inner Segment

The part of photoreceptors that contains the cell organelles and connects to the axon.

Outer Segment

The part of photoreceptors that contains the photopigment discs.

Retinal Layers

Different levels or strata within the retina, each containing specific types of cells.

Anatomical Specialization

Structural adaptations of the retina for specific visual functions.

Neuronal Plasticity

The ability of neural networks in the brain to change through growth and reorganization.

Color Spectrum

The range of colors that can be perceived by the human eye.

Absorptive Capacity

The ability of photoreceptors to absorb light across different wavelengths.

Pupil Dilation

The process by which the pupil enlarges, allowing more light to enter the eye.

Neural Integration

The combination of synaptic inputs to produce a single output signal.

Pathway of Visual Signals

The route visual information takes from the photoreceptors to the optic nerve and brain.

Convergence

The process by which multiple photoreceptors send signals to a single ganglion cell.

Center-Surround Organization

The arrangement of receptive fields in which light in the center affects the ganglion cell response differently than light in the surround.

Neurogenesis

The process of generating new neurons from neural stem cells.

Electrophysiological Properties

Characteristics of neurons that define their electrical behaviors.

Gene Duplication

A process whereby a segment of genetic material is copied, leading to new functions or traits.

Light Penetration Depth

The distance that light can travel through different mediums before being absorbed.

Synaptic Plasticity

The ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity.

Wavelength Tuning

The ability of photopigments to selectively absorb photons of specific wavelengths.

Neurotransmitter Receptor Types

Different proteins that are activated by neurotransmitters to initiate a response in the postsynaptic neuron.

Cone Types and Sensitivity

The classification of cones based on their sensitivity to different wavelengths of light.

Neural Conduits

The pathways through which neural signals travel.

Retinal Signal Processing

The mechanisms by which visual signals are modified and transmitted in the retina.

Neurotransmitter Release Mechanisms

The processes involved in the discharge of neurotransmitters from neurons.

Transgenic Models

Genetically modified organisms used to study gene function and expression.

Retinal Deconstruction

The breaking down of retinal signals into their constituent parts for analysis.

Neuromodulation

The process whereby a given neuron uses neurotransmitters to regulate diverse populations of neurons.

Spatial Frequency

The level of detail in an image, defined by the frequency of light and dark patterns.

Quantum Capture

The process of absorbing individual quanta (or photons) of light.

Cellular Response to Stimuli

How cells react to external stimuli, which can involve changes in membrane potential.

Gene Expression Profiling

The measurement of the activity (expression) of thousands of genes at once to create a global picture of cellular function.

Bipolar Cell Types

Different subtypes of bipolar cells that have distinct pathways and functions in signal transmission.

Action Potential Generation

The process through which neurons generate action potentials in response to stimuli.

Calcium Dynamics

The study of how calcium ions move within cells and affect cell signaling.