Vision III: Beyond Retina

Vocabulary flashcards covering visual pathways beyond the retina, subcortical targets, LGN structure, primary visual cortex organization, and extrastriate visual processing streams.

Optic Chiasm

The anatomical site where visual information from the nasal retina crosses to the opposite hemisphere, while temporal retina information remains uncrossed.

Suprachiasmatic Nucleus (SCN)

A hypothalamic structure with endogenous cycling neuronal activity that uses input from the eyes to synchronize circadian and seasonal rhythms.

Accessory Optic System

A visual pathway projecting from retina to midbrain, pons, and cerebellum that mediates reflexive eye movements such as optokinetic nystagmus and the vestibulo-ocular reflex.

Optokinetic Nystagmus

A reflexive eye movement controlled by the accessory optic system that maintains a stationary visual world despite a moving visual field.

Vestibulo-ocular Reflex

A reflex mediated by the accessory optic system that keeps the eyes fixed on a target while the head or body is in motion.

Pretectum

A midbrain region receiving retinal inputs that regulates pupil size in response to ambient light and controls the looming reflex.

Superior Colliculus

A visual structure containing a topographic representation of the retinal surface that controls head and eye orienting reflexes.

Lateral Geniculate Nucleus (LGN)

The principal thalamic target of retina projections in primates, organized into six main layers plus six koniocellular layers that segregate eye-specific inputs.

Magnocellular Layers

LGN layers that receive input from M-type ganglion cells and project to cortical simple cells to analyze object motion.

Parvocellular Layers

LGN layers that receive input from P-type ganglion cells and project to cortical complex cells to analyze object shape.

Koniocellular Layers

LGN layers receiving input from nonM-nonP ganglion cells that project to cytochrome oxidase blobs in primary visual cortex.

Cortical Magnification

The anatomical overrepresentation of the central retina in visual processing centers, where 5% of the central retina occupies roughly 50% of LGN and cortical area.

Optic Radiation

Axonal projections extending from LGN neurons that terminate primarily in layer IV of the primary visual cortex.

Primary Visual Cortex (V1)

The primary cortical area for visual processing, also termed striate cortex or Brodmann's area 17, located in the occipital lobe.

Simple Cells

Cortical neurons whose receptive fields sum inputs from multiple LGN neurons to extract stimulus shape, width, orientation, and motion direction.

Complex Cells

Cortical neurons in the parvocellular pathway that respond to light ON and OFF with orientation specificity regardless of absolute position within their receptive field.

Orientation Columns

Vertical functional groupings of visual cortical neurons where cells in a given column respond preferentially to the same stimulus orientation.

Ocular Dominance Columns

Vertical columns in layer IV of primary visual cortex where neurons respond preferentially to inputs originating from one eye over the other.

Cytochrome Oxidase Blobs

Cylindrical structures in layers II and III of V1 that receive direct koniocellular LGN projections and participate in color vision analysis.

Cortical Module

A functional unit of primary visual cortex containing orientation columns, ocular dominance columns, and blobs that fully analyzes a specific area of the visual field.

Extrastriate Cortex

The collection of more than 20 visual cortical regions outside V1 involved in higher-level visual processing divided into dorsal and ventral streams.

Dorsal Stream

An extrastriate visual processing pathway directed towards the parietal cortex that analyzes object motion and guides motor action.

Ventral Stream

An extrastriate visual processing pathway directed towards the temporal cortex dedicated to object recognition and form analysis.