As was indicated earlier, the synapses occur in definite layers, the outer and inner plexiform layers. In the outer plexiform layer the bipolar cells make their contacts, by way of their dendrites, with the rods and cones, specifically the spherules of the rods and the pedicles of the cones. In this layer, too, the projections from horizontal cells make contacts with rods, cones, and bipolar cells, giving rise to a horizontal transmission and thereby allowing activity in one part of the retina to influence the behaviour of a neighbouring part. In the inner plexiform layer, the axons of the bipolar cells make connection with the dendrites of ganglion cells, once again at special synaptic regions. (The dendrites of a nerve cell carry impulses to the nerve cell; its axon, away from the cell.) Here, too, a horizontal interconnection between bipolar cells is brought about, in this case by way of the axons and dendrites of amacrine cells.
The bipolar cells are of two main types: namely, those that apparently make connection with only one receptor—a cone—and those that connect to several receptors. The type of bipolar cell that connects to a single cone is called the midget bipolar. The other type of bipolar cell is called diffuse; varieties of these include the rod bipolar, the dendritic projections of which spread over an area wide enough to allow contacts with as many as 50 rods; and the flat cone bipolar, which collects messages from up to seven cones.
Ganglion cells are of two main types: namely, the midget ganglion cell, which apparently makes a unique connection with a midget bipolar cell, which in turn is directly connected to a single cone; and a diffuse type, which collects messages from groups of bipolar cells.
A-horizontal-cross-section-of-the-human-eye-showing-theA horizontal cross section of the human eye, showing the major parts of the eye, including the …[Credits : Encyclopædia Britannica, Inc.]
Horizontal-section-of-the-eyeFigure 1: Horizontal section of the eye.[Credits : Encyclopædia Britannica, Inc.]
Structure-of-the-retinaStructure of the retina
Muscles-of-the-right-eyeMuscles of the right eye
Myopia-or-nearsightedness-can-be-corrected-with-glasses-that-haveMyopia, or nearsightedness, can be corrected with glasses that have concave lenses to allow near …[Credits : Encyclopædia Britannica, Inc.]
Hyperopia-or-farsightedness-can-be-corrected-with-glasses-that-containHyperopia, or farsightedness, can be corrected with glasses that contain convex lenses to reduce …[Credits : Encyclopædia Britannica, Inc.]
Visual-pathwaysVisual pathways
Perimeter-chart-showing-normal-visual-field-figures-on-the-perimeterFigure 2: Perimeter chart showing normal visual field; figures on the perimeter indicate degrees of …[Credits : Encyclopædia Britannica, Inc.]
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