Ganglion Cells

There are many different varieties of ganglion cells which can be classified based on form, number of sublayers in the stratification levels in the inner plexiform layer, cell body and dendritic tree size. While small bushy ganglion cell types are concerned with processing small stationary, fine detail in tonically activated messages in all species. The optic nerve collects all the axons of the ganglion cells and this bundle of more than a million fibers (in humans) then passes information to the next relay station in the brain for sorting and integrating into further information processing channels. Each retinal ganglion cell has a receptive field that corresponds to input from part of a small region of the retina. This receptive field is made up of information from one to 1000s of photoreceptors arranged in a "centre-surround" fashion (seediagram). ]

The primary layers of the retina from outermost surface to innermost surface:

Pigment epithelium

Rod and cone layer/Bacillary layer,Layer of photoreceptor cells

Outer limiting membrane

Outer Nuclear Layer (ONL)

Outer Plexiform Layer (OPL)

Inner Nuclear Layer (INL)

Inner Plexiform Layer (IPL)

Layer of Ganglion cells (GCL)

Layer of optic nerve fibers

Optic disk/blind spot . [There are 130,000,000 photoreceptors per eye, but only 1,000,000 ganglion cells per eye. In the fovea (mainly cones) there is a 1:1 correspondence. Furthermore, the three main classes of ganglion cell types are: magno (Y) cells, parvo (X) cells and W cells (see below for description). ing the electrical signal to the retinal recipient areas of the brain many millimeters or centimeters distant from the retina. Sublamina a contained dendrites of cells with physiologically defined OFF-center receptive fields and sublamina b dendrites of cell with ON-center receptive fields.

Magno cells (Y-cells)

•large receptive fields

•large dendritic tree

•no magno cells in the fovea

•respond transiently to illumination

•fast conduction of neural impulse

•respond to large objects and to

movement of objects

•high contrast sensitivity

•found mainly in the peripheral retina

Parvo cells (X-cells)

•these are mainly connected to cones

•smaller and more numerous

•small receptive fields

•slow conducting therefore slow response•involved in colour vision

•used for high resolution analysis. In the peripheral retina there is a 1:1000 convergence of photoreceptors (mainly rods) onto retinal ganglion cells. For example the large ganglion cells, with open radiate branching patterns, process fast, transient impulse trains and in all vertebrate retinas are concerned with motion detection and alerting the animal to threatening, moving visual imagery.