Difference between revisions of "Orientation Selective Ganglion Cell"
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Revision as of 19:21, 23 March 2012
Orientation Selective Ganglion Cell
Introduction
Orientation selective ganglion cells (OSGC) are ganglion cells that respond The majority of these ganglion cells are located in the visual streak region of the retina (Levick 1967). In a study by Levick and Thibos in 1982 it was found that 70% of ganglion cells in the cat retina are orientation selective ganglion cells. Orientation selective ganglion cells are categorized into ON-center and OFF-center cells. The responses recorded from both ON-center and OFF-center orientation selective ganglion cells have shown that there is an initial hyperpolarization at light onset regardless of the orientation of the stimulus(Bloomfield 1994). The receptive fields of these cells consist of a center, excitatory region surrounded by inhibitory sections (Bloomfield 1994). The initial hyperpolarizations recorded are thought to have been caused by the field peripheral to the center (Bloomfield 1994).
ON-center orientation selective ganglion cells have a preferred orientation that results in an initial hyperpolarization followed by a large depolarization and increased spiking when a slit of light is introduced to the receptive field of the cell (Bloomfield 1994). As the orientation of the slit was moved away from the preferred orientation, the initial hyperpolarization remained the same, while the depolarization decreased (Bloomfield 1994). At 90 degrees from the preferred orientation there was an initial hyperpolarization followed by sustained hyperpolarization (Bloomfield 1994). OFF-center orientation selective ganglion cells respond with an initial hyperpolarization followed by sustained hyperpolarization and then depolarization when the light is removed from the center (Bloomfield 1994). When the slit of light was placed at the null angle (90 degrees from the preferred orientation) there was no longer a depolarization when the light was removed, but rather a declining hyperpolarization was found (Bloomfield 1994).
ON-center orientation selective ganglion cells have asymmetric dendritic arbors and have a wavy appearance (Bloomfield 1994). OFF-center orientation selective ganglion cells have cell-bodies that are shaped like elipsoids and have two main dendrites extending from either side of the cell body (Bloomfield 1994). The dendrites of OFF-center orientation selective ganglion cells are wavy in appearance, as well, and are longer than the ON-center cell dendrites.
