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- Glossary
Photoreceptors
Photoreceptors are the light-sensitive cells of the retina; they convert light into electrical potentials. There are approximately 127 million photoreceptors in the retina, including seven million cones and 120 million rods.
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Glossar
15.03.2017
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- Glossary
Retina
The retina is the inner layer of the eye covered with pigment epithelium. The retina is characterized by an inverse (reversed) arrangement: light must first pass through several layers before it hits the photoreceptors (cones and rods). The signals from the photoreceptors are transmitted via the optic nerve to the processing areas of the brain. The reason for the inverse arrangement is the evolutionary development of the retina, which is a protrusion of the brain.The retina is approximately 0.2 to 0.5 mm thick.
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Adaptation
Adaptation refers to the process by which the sensory organs, the perceptual system, or the entire organism adjusts to the intensity and quality of stimuli and to changes in environmental conditions. In visual adaptation, for example, the pupil and the sensitivity of the photoreceptors regulate themselves according to the prevailing light conditions.
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Amacrine cells
Amacrine cells are interneurons of the retina. They are located between photoreceptors and bipolar cells on the one hand and ganglion cells on the other. The name was coined by Ramón y Cajal and means "without axon."
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Bipolar cells
The bipolar cell is a bipolar neuron, i.e., a neuron with one axon and one dendrite located in the middle layer of the retina. It transmits sensory information from the photoreceptors to the ganglion cells.
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Blind spot
A blind spot in visual perception caused by the anatomy of the eye: since the optic nerve leaves the eye at the optic disc, there are no photoreceptors there – and no perception can occur. This blind spot is not consciously perceived.
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Ganglion cell
The ganglion cell bundles the signals from the photoreceptors in the retina and transmits them via its axons (long, fiber-like extensions of a nerve cell. All of these axons together form the optic nerve.
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Macula
The area of the retina with the highest density of photoreceptors. Due to this high "resolution," we see very sharply here. The diameter of the macula in humans is approximately 5 mm. The fovea centralis is located in the center of the macula.
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Horizontal cell
Horizontal cells are nerve cells in the retina. They form a lateral connection between photoreceptors and bipolar cells. In this way, they increase the contrast of what is seen.
