88. Visual receptors. Light transduction mechanisms. Organization of the retinal neural network.
Covers the photoreceptors of the retina, rods and cones, and how they differ in threshold, sensitivity, acuity, colour vision and distribution, with the fovea singled out. It then walks through the phototransduction cascade from rhodopsin and transducin to cGMP, the closing of sodium channels and hyperpolarization, and how glutamate release changes. It ends with the retinal neural network, including center-surround receptive fields, lateral inhibition, and a set of recap questions.
Topic 87 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 5 sections, about 910 words (6 min of reading), with 14 flashcards.
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Visual receptors. Light transduction mechanisms. Organization of the retinal neural network.
Visual Receptors
Light Transduction Mechanisms
Organization of the Retinal Neural Network
Organization of the retinal neural network
Visual Receptors
The retina contains photoreceptors, interneurons (bipolar cells, horizontal cells, and amacrine cells), and ganglion cells. Visual receptors, rods and cones, are located in the innermost part of the retina, specifically the photoreceptor layer. They differ in shape, pigment, distribution, and organization, leading to functional differences.
Rods have low thresholds, are sensitive to low-intensity light, and function well in darkness. They do not participate in color vision and have low acuity. Cones have a higher threshold for light and operate best in daylight. They provide higher visual acuity and participate in color vision.
The human eye contains approximately 120 million rods and 6-7 million cones, with 1 million ganglion cells.
Rods are distributed throughout the retina except for the fovea, while cones are concentrated in the fovea, the central point of the retina responsible for sharp central vision.
Because the distribution of cones is central, our visual field for color is narrower.
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