Key Concepts in Visual Processing and Movement Control

Retina

Multicellular epithelium converting light to membrane potential.

Inner Retina

Layer towards the middle of the eye.

Outer Retina

Layer towards the outside of the eye.

Outer Nuclear Layer

First layer of the retina.

Outer Plexiform Layer

Layer where synaptic connections occur.

Inner Nuclear Layer

Layer containing nuclei of bipolar cells.

Inner Plexiform Layer

Layer where bipolar cells synapse with ganglion cells.

Ganglion Cell Layer

Contains retinal ganglion cells.

Optic Disc

Blind spot where optic nerve exits retina.

Photoreceptors

Cells converting light into membrane potential changes.

Rods

Photoreceptors sensitive to low light levels.

Cones

Photoreceptors responsible for color vision.

Cone Photopigment

Coneopsin is the photopigment in cones.

Rod Photopigment

Rhodopsin is the photopigment in rods.

Fovea

Area of highest visual acuity in the retina.

Convergence

Multiple photoreceptors connect to single ganglion cell.

Color Sensitivity of Rods

Rods have no color sensitivity.

Color Sensitivity of Cones

Cones have three types for color vision.

Dark Current

Depolarization in rods due to cGMP.

Response to Light

Light causes hyperpolarization of photoreceptors.

G-Protein-Coupled-Receptor Pathway

Pathway involving rhodopsin or coneopsin.

Retinal Conversion

Light converts retinal from cis to trans.

Transducin

G protein activated during phototransduction.

Phosphodiesterase (PDE)

Enzyme breaking down cyclic GMP.

Receptive Fields

Area where a stimulus affects neuron response.

Photoreceptor Receptive Fields

Determined by lens direction; simple structure.

Retinal Ganglion Cell Receptive Fields

Circular fields responding to light spots.

Photoreceptor

Cells in the retina that detect light.

Retinal Ganglion Cell (RGC)

Neurons that transmit visual information from the retina.

Convergence

Multiple photoreceptors connect to one RGC.

M-type RGCs

Large receptive fields, sensitive to light.

P-type RGCs

Small receptive fields, specialized for color detection.

On-Center RGCs

Increase firing rate with light in the center.

Off-Center RGCs

Increase firing rate in absence of light.

Antagonistic Surround

Surround light decreases firing of center RGCs.

Graded Responses

Firing rate varies with light intensity.

Suprachiasmatic Nucleus (SCN)

Regulates circadian rhythms based on light exposure.

Superior Colliculus

Involved in reflexive orientation to visual stimuli.

Lateral Geniculate Nucleus (LGN)

Thalamic relay center for visual information.

Center-Surround Organization

RGCs respond differently to light in center vs. surround.

Fovea

Central region of the retina, high acuity vision.

Periphery of Retina

Area with larger receptive fields, more rods.

Light Sensitivity

Ability to detect low levels of light.

Divergence

Photoreceptors send outputs to various RGC types.

Bipolar Cells

Connect photoreceptors to RGCs, influence firing.

Horizontal Cells

Modulate signals between photoreceptors and RGCs.

Contrast Detection

System designed to perceive edges and borders.

Jet Lag

Disruption of circadian rhythm due to light exposure.

Reflexive Orientation

Automatic response to visual stimuli.

Visual Pathways

Parallel processing pathways established in the retina.

Light Perception

Focus on light location rather than darkness.

RGC Axons Targets

SCN, Superior Colliculus, LGN are primary targets.

Maximum Firing Rate

Occurs when light fully fills the receptive field.

Spontaneous Activity

RGCs fire at baseline rates without light.

Circadian Rhythm

Biological clock regulated by light exposure.

Thalamus

Acts as a gate for sensory information.

Primary Visual Cortex (V1)

First cortical area for visual processing.

Visuotopic Maps

Visual world representation mapped onto each eye.

Retinotopic Organization

Arrangement of visual information based on retina.

Visual Field

Total area that can be seen at once.

Hemiretina

Half of the retina, either nasal or temporal.

Axon Behavior

Pathways of axons in visual processing.

Projection Target

Destination of visual information in the brain.

Right Eye

Sees B, C; does not cross midline.

Left Eye

Sees B, C; crosses at optic chiasm.

Left Visual Hemifield

Projects to right brain structures.

Point-to-Point Representation

Adjacent neurons activate corresponding adjacent neurons.

Visual Cortices

Includes V1, V2, V3, V4, V5 for processing.

Superior Colliculus

Integrates visual and auditory information for reflexes.

Foveal Part

Represents center of visual field in SC.

Peripheral Part

Represents outer visual field in SC.

Superior Colliculus Layers

Includes visual, auditory, sensory, and motor layers.

Visual Layer

Receives visual input in superior colliculus.

Deep Layer

Initiates movement based on visual stimuli.

Visual Acuity

Sharpness of vision assessed by stimuli.

Cranial Nerves

Nerves controlling eye and neck movement.

Ocular Motor Nerve

Cranial nerve responsible for eye movement.

Response Time

Time taken for neural response to stimuli.

Temporal Summation

Combining signals over time for stronger response.

Spatial Summation

Combining signals from different locations for response.

Optic Nerve Lesion

Loss of peripheral vision on lesion side.

Optic Tract Lesion

Inability to see contralateral visual hemifield.

Optic Chiasm Lesion

Results in tunnel vision; peripheral vision loss.

Lateral Geniculate Nucleus (LGN)

Thalamic structure relaying visual information.

LGN Structure

Layered structure, six layers from deep to superficial.

Magnocellular Layers

Two layers with large, dark-staining cells.

Parvocellular Layers

Four layers with smaller cells, color-sensitive.

M-type Cells

Retinal ganglion cells projecting to magnocellular layers.

P-type Cells

Retinal ganglion cells projecting to parvocellular layers.

Contralateral Input

Input from the opposite eye.

Ipsilateral Input

Input from the same eye.

Koniocellular Layers

Receive cone inputs, specialize in color processing.

Parallel Processing Streams

Three streams: Magno, Parvo, and Konio.

Rod-driven

Magno layers respond primarily to low light.

Cone-driven

Parvo and Konio layers respond to color and detail.

Topographic Organization

Adjacent visual field points activate adjacent neurons.

Visuotopic Map

Visual space mapping in the brain.

Retinotopic Map

Visual space mapping onto the retina.

Cortical Columns

Vertical arrangements of neurons in V1.

Ocular Dominance Columns

Columns receiving input from one eye.