Neural Basis of Vision: The Retina

Vocabulary terms covering retinal development, blood supply, cellular organization, and visual transduction processes based on the lecture transcript.

Diencephalon

The part of the brain from which the neural retina is derived.

Optic Stalk

The structure connecting the optic vesicle to the neural tube; its lumen is obliterated during development.

Subretinal Space

The residue of the optic vesicle cavity in the adult vertebrate, located between the retina and the pigment epithelium.

4th Week of Development

The time during which the lateral aspects of primary optic vesicles invaginate to form double-walled optic cups.

7 Months Gestation

The point at which the developing eye becomes sensitive to light.

Central Retinal Artery

A branch derived from the ophthalmic artery that supplies the inner retinal layers, providing $20\text{--}30$% of the retinal blood supply.

Choroidal Blood Vessels

The primary source of blood flow ($65\text{--}85$%) which maintains the outer retina, especially the photoreceptors.

Retinal Pigment Epithelium (RPE)

A layer responsible for light absorption, heat removal, nutrient/$\text{O}_2$ transport, vitamin A storage, and the phagocytic breakdown of photoreceptor discs.

Photoreceptors (PRs)

The primary light-sensing cells of the retina, consisting of approximately $120 \times 10^6$ rods and $6 \times 10^6$ cones.

Rhodopsin

The visual photopigment found in rod cells, composed of an opsin (amino acid) and retinal (vitamin A derivative).

Spherule

The small, round terminal ending of a rod cell containing one invagination.

Pedicle

The large, flat terminal ending of a cone cell containing $20\text{--}25$ invaginations.

Ribbon Synapse

A specialized synapse found only in the retina that uses a double-layered membrane (ribbon) to direct neurotransmitter vesicles.

Triad Ribbon Synapse

A specific cone synapse arrangement consisting of two horizontal cells and one bipolar dendrite at each invagination.

Transducin

A protein (G protein) activated by light that subsequently activates Phosphodiesterase (PDE) during visual transduction.

Visual Transduction Bleaching

The process where light exposure converts $11\text{-cis}$ retinal into $11\text{-trans}$ retinal.

Outer Limiting Membrane (OLM)

A non-true membrane that provides mechanical stability and acts as a blood-brain barrier, separating the PR outer/inner segments from their nuclei.

Outer Plexiform Layer (OPL)

The site of the first synapse where visual messages are integrated between photoreceptors, horizontal cells, and bipolar cells.

Horizontal Cells

Inner nuclear layer cells that provide negative feedback to receptors and perform lateral inhibition to recognize contrast and borders.

Midget Bipolar Cells

A type of cone bipolar cell (80% of total) responsible for color and fine spatial information, synapsing on X ganglion cells.

Conventional Bipolar Cells

A type of cone bipolar cell (20% of total) that handles coarse spatial information and movement detection, synapsing on Y ganglion cells.

AII Cell

A specific amacrine cell that links the rod and cone pathways by communicating with ON and OFF cone bipolar cells.

Interplexiform Cell

A neuromodulator cell that releases dopamine into the OPL to disconnect gap junctions, enhancing acuity at the cost of sensitivity.

Diad Synapse

A synapse in the inner plexiform layer involving a bipolar cell and two post-synaptic elements (amacrine or ganglion cells).

X Type Ganglion Cells (P cells)

Sustained-response cells that transmit information about pattern and color to the parvocellular layers of the LGN.

Y Type Ganglion Cells (M cells)

Transient-response cells (alpha cells) sensitive to moving objects, projecting to the magnocellular layers of the LGN and superior colliculus.

W Type Ganglion Cells (Gamma cells)

Sluggish cells sensitive to luminance changes and coarse textures, involved in pupil reflexes and OKN responses.