tailieunhanh - Ebook Human neuroanatomy (2nd edition): Part 2

Part 1 book “Human neuroanatomy” has contents: The visual system, ocular movements and visual reflexes, the thalamus, lower motor neurons and the pyramidal system, the extrapyramidal system and cerebellum, the olfactory and gustatory systems, the limbic system, the hypothalamus, the autonomic nervous system, and other contents. | CHAPter 12 The Visual System RETINA VISUAL PATH INJURIES TO THE VISUAL SYSTEM FURTHER READING Vision, including the appreciation of the color, form (size, shape, and orientation), and motion of objects as well as their depth, is somatic afferent sensation served by the visual apparatus including the retinae, optic nerves, optic chiasm, lateral geniculate nuclei, optic tracts, optic radiations, and visual areas in the cerebral cortex.  RETINA The photoreceptive part of the visual system, the retina, is part of the inner tunic of the eye. The retina has 10 layers, that can be divided into an outermost, single layer of pigmented cells (layer 1), the pigmented layer, and a neural part, the neural layer (layers 2–9).   Pigmented layer1 The pigmented layer1 [Note that in this chapter, the layers of the retina are indicated as superscripts in the text] is formed by the retinal pigmented epithelium (RPE), a simple cuboidal epithelium with cytoplasmic granules of melanin. Age‐related decrease and regional variations in melanin concentration in the pigmented layer1 occur in humans. The pigmented layer1 (Fig. ) adjoins a basement membrane adjoining choroidal connective tissue. The free surfaces of these pigmented cells are adjacent to the tips of the outer segments of specialized neurons modified to serve as photoreceptors. One pigmented epithelial cell may contact about 30 photoreceptors in the primate retina. Outer segments of one type of photoreceptor, the rods, are cylindrical whereas the outer segments of the other type, the cones, are tapering. By absorbing light and heat energy, pigmented cells protect photoreceptors from excess light. They also carry out resynthesis and isomerization of visual pigments that reach the outer segments of retinal photoreceptors. Pigmented cells demonstrate phagocytic activity, engulfing the apical tips of outer segments of retinal rods detached in the process of renewal. Age‐related accumulation of .