L11- vision

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Questions and Answers

What type of input does the B/Y bistratified ganglion cell receive?

Only excitatory input from L+M cone bipolars

Excitatory input from S cone bipolars and inhibitory input from L+M cone bipolars (correct)

Inhibitory input from S cone bipolars and excitatory from L+M cone bipolars

Only inhibitory input from S cone bipolars

What is the main function of phototransduction in the retina?

To convert light into electrical signals (correct)

To amplify sound waves

To regulate blood flow in retinal vessels

To inhibit neuronal action potentials

In the visual processing pathway, where do neighboring parts of the retina project?

To neighboring regions in central targets (correct)

To only the lateral geniculate nucleus

To distant regions in central targets

Randomly across the visual cortex

What role does the retinotectal tract play in visual processing?

It coordinates eye movements Signup and view all the answers

Which pathway is primarily responsible for pupillary reflexes?

Pretectal nuclei pathway Signup and view all the answers

What is the primary role of the lateral geniculate nucleus (LGN)?

To relay visual information from the retina to the visual cortex Signup and view all the answers

What aspect of color processing is impacted by opponent processing in the retina?

It distinguishes between red-green and blue-yellow Signup and view all the answers

What is the primary function of receptive fields in retinal ganglion cells?

To encode specific patterns of light and dark Signup and view all the answers

What is the primary role of simple cells in the primary visual cortex?

Detect edges and orientations Signup and view all the answers

Which type of visual cell receives input primarily from simple cells and responds best to moving edges?

Complex cells Signup and view all the answers

What distinguishes hypercomplex cells from complex cells in terms of their receptive fields?

Hypercomplex cells respond to edges with inhibitory flanks. Signup and view all the answers

In the visual processing hierarchy, what is the primary function of the ventral stream?

Facilitating conscious perception and object recognition Signup and view all the answers

What is indicated by the term 'ocular dominance columns' in the primary visual cortex?

Columns that alternate in their input from the left and right eyes Signup and view all the answers

How do receptive field sizes change with retinal eccentricity?

They increase in size towards the periphery. Signup and view all the answers

Which of the following best describes the overall architecture of the primary visual cortex with respect to its layers?

There are six layers, with layer IV receiving the main input from the LGN. Signup and view all the answers

Which type of retinal ganglion cells (RGCs) is primarily responsible for the 'what' pathway related to form and color?

Midget cells Signup and view all the answers

How do complex and hypercomplex cells contribute to visual perception?

They work together to analyze moving objects and their outlines. Signup and view all the answers

What biological mechanism primarily allows the conversion of light into neural signals in phototransduction?

Chemical changes in retinal photopigments Signup and view all the answers

What is the primary function of parasol cells in the retinal processing pathway?

Motion detection Signup and view all the answers

What characterizes the opponent chromatic organization in primate midget RGC receptive fields?

Red on, green off represents a chromatic opponent response. Signup and view all the answers

Which retinal cells are involved in connecting S cones and establishing blue-yellow opponent pathways?

S-cone bipolar cells Signup and view all the answers

What percentage of retinal ganglion cells are midget cells in primates?

80-90% Signup and view all the answers

In the lateral geniculate nucleus (LGN), how are the three pathways of RGCs anatomically distinguished?

By the location of their synaptic inputs. Signup and view all the answers

What role do horizontal cells play in retinal processing?

They mediate contrast and help establish chromatic pathways. Signup and view all the answers

What is the primary function of the lateral geniculate nucleus (LGN)?

To bring retinotopic maps from both eyes into register Signup and view all the answers

Which type of retinal ganglion cells (RGCs) are involved in the koniocellular layers of the LGN?

Small bistratified B/Y RGCs Signup and view all the answers

In terms of visual processing, what is meant by 'centre-surround' in LGN receptive fields?

They have an excitatory center and inhibitory surround Signup and view all the answers

Which layer of the LGN is associated with ipsilateral eye inputs?

Alternating layers Signup and view all the answers

What is a consequence of the central visual field being magnified in visual processing?

Enhanced visual acuity in the foveal area Signup and view all the answers

Why is only about 10% of inputs to the LGN from the retina considered significant?

It suggests that the LGN relies heavily on modulatory signals from other regions Signup and view all the answers

Which statement about trichromacy is accurate in the context of visual information processing?

It is the basis of color vision resulting from three types of cones Signup and view all the answers

What is the significance of maintaining topographic order in visual mapping?

It facilitates spatial organization and processing of visual information Signup and view all the answers

What type of neurotransmission occurs between photoreceptors and second order neurones in the retina?

Glutamatergic transmission Signup and view all the answers

Which best describes the response of ganglion cells to light?

They primarily respond to contrast. Signup and view all the answers

What defines the receptive field of a retinal ganglion cell (RGC)?

The specific location in the visual field that influences the cell's response. Signup and view all the answers

In the context of ganglion cells, what does the term 'antagonistic center-surround receptive field' refer to?

The center must be light while the surround must be dark, or vice versa. Signup and view all the answers

What is the primary role of retinal ganglion cells (RGCs) in vision?

To serve as the output cells of the retina. Signup and view all the answers

Why do ganglion cells not respond significantly to diffuse light?

Because they require specific contrast to activate. Signup and view all the answers

Which of the following is NOT a characteristic of how RGCs process visual information?

They integrate visual information across large areas. Signup and view all the answers

How does the reconstruction of visual scenes benefit from the organization of RGCs?

It enables detailed analysis through multiple detectors dedicated to small portions. Signup and view all the answers

Study Notes

Bistratified Ganglion Cells

Receive excitatory input from S cone bipolars and inhibitory input from L+M cone bipolars.
Involvement in color opponency mechanisms.

Retinal Code and Phototransduction

Phototransduction occurs in rod/cone outer segments, converting light signals into electrical signals.
Spike trains represent coded electrical processing in retinal ganglion cells (RGCs).
Information is relayed to higher brain visual areas.

Visual and Non-visual Pathways from the Retina

Retinal signals are processed through various pathways:
- Dorsal Pathway: Retina → LGN (lateral geniculate nucleus) → Primary visual cortex → Extrastriate visual areas.
- Non-Visual Pathways:
  - Retinotectal tract to superior colliculus for eye movements.
  - Pretectum for pupillary reflexes.
  - Retinohypothalamic tract influences circadian rhythms via SCN.

Retinal to Central Target Projections

Topographically organized projections: neighbouring retinal areas connect to neighbouring central target areas.
Receptive field sizes vary with retinal eccentricity, larger in periphery and smaller in the fovea for detailed vision.

Types of RGCs in Primates

Midget Cells (P): Predominantly responsive to form and color (80-90% RGCs).
Parasol Cells (M): Responsive to motion and distance (10-20% RGCs).
K Cells: Small bistratified cells involved in specific color processing.
Over 30 recognized RGC types perform different functional roles.

Chromatic Organization in RGC Receptive Fields

Midget RGCs exhibit opponent chromatic organization, such as:
- S+(L+M), S-(L+M)
- Specific responses for yellow-blue and red-green color pairs.
Established through synaptic connections among cones, horizontal, and bipolar cells.

Primary Visual Cortex (V1)

Receives input from the LGN and features a stria of Gennari with parallel myelinated axons along the calcarine fissure.
Organized into six layers, with main input from LGN concentrated in layer IV.
Ocular dominance columns represent left and right eye input, with monocular and binocular cells.

Functional Organization in V1

Organized into:
- Color processing areas (color blobs) receiving koniocellular input.
- Orientation preference columns for detecting lines and edges.

V1 Receptive Fields

Simple Cells: Orientation selective with defined ON and OFF subregions, responsive to elongated bars.
Complex Cells: Large receptive fields without ON/OFF subregions, respond to moving edges and maintain orientation selectivity.
Hypercomplex Cells: Similar to complex cells but include inhibitory flanks, respond to oriented edges with end-stopping.

Ventral and Dorsal Streams

Ventral Stream (WHAT):
- Pathway from V1 to inferotemporal cortex.
- Responsible for color, shape, scene understanding, and object recognition.
Dorsal Stream (WHERE):
- Pathway from V1 to posterior parietal cortex.
- Involved in motion, depth perception, and visual control of motor actions.

Topographic Organization and Magnification

Foveal area is magnified in visual processing areas while maintaining retinotopic order.
The arrangement supports detailed processing of central visual fields.

Lateral Geniculate Nucleus (LGN)

Features koniocellular layers responding to input from small bistratified B/Y RGCs.
Contains alternating layers related to inputs from ipsilateral and contralateral eyes.
Plays crucial roles in refining retinotopic maps and processing additional inputs from brain regions.

Ganglion Cell Receptive Fields

Function as multiple detectors within the visual scene, with each cell's receptive field collecting information from a specific area.
RGCs favor contrast detection through antagonistic center-surround field organization, enhancing sensitivity to edges and patterns.

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Description

This quiz explores the functions and mechanisms of B/Y bistratified ganglion cells, focusing on their excitatory and inhibitory inputs from cone bipolars. Participants will also delve into concepts such as color opponency and the retinal code, and how phototransduction contributes to visual processing.