12/9/2022 0 Comments Dendrite axon![]() ![]() In the case of the cones though, the outer segment discs remain attached to the outer segment membrane. #Dendrite axon free5 above) become detached as free floating discs inside the outer segment membrane in the case of the rods. ![]() These expanding membrane plates (b-c, Fig. Diagram of outer segment generationĬLICK HERE to see an animation of the outer segment generation Photoreceptor outer segments are generated at the cilium (red arrows)įig. 5 below) of the photoreceptor cell plasma membrane at this point (see below) (Steinberg et al., 1980).įig 4. Outer segments of both the rods and cones arises from outpouching (a, Fig. It is from the base of the cilium that membrane evaginations and invaginations occur to produce the outer segment (o.s.) or the important visual pigment-bearing portion of the photoreceptor. At the top of the inner segment a thin cilium joins the inner and outer segments of the rods and cones (Fig. Inner segment regions of both rods and cones are filled with long thin mitochondria. In the fovea, however, where there are only cone photoreceptors, the most central cones are even thinner than the average rod at about 1.5 microns diameter. For example, the rod inner segments are 2 microns and the cone’s about 6 microns in diameter in peripheral human retina. ![]() Outer and inner segments of rods (i.s.) are generally thinner than those of cones in mammalian retinas. ![]() #Dendrite axon movieMovie made by Carlos Rozas (CanalWeb, Chile). The photoreceptor consists of 1) an outer segment, filled with stacks of membranes (like a stack of poker chips) containing the visual pigment molecules such as rhodopsins, 2) an inner segment containing mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs, 3) a cell body containing the nucleus of the photoreceptor cell and 4) a synaptic terminal where neurotransmission to second order neurons occurs.ĬLICK HERE to see a photoreceptor with emphasis on the inner and outer segments and the disc structures within the outer segment. 2 and 3) show rods and cones from human and squirrel retinas (Anderson and Fisher, 1976). Ultrathin sections viewed in an electron microscope (Figs. High magnification EM images of cone and rod outer segments in the ground squirrel retina Low magnification EM image of monkey rods and conesįig. Apical processes from the pigment epithelium envelope the outer segments of both rods and cones (not always clear in histological sections). The higher magnification afforded by the electron microscope allows better resolution of rod and cone photoreceptors.įig 2. Rod cell bodies make up the remainder of the outer nuclear layer below the cone cell bodies. Rods, on the other hand, are slim rod-shaped structures with their inner and outer segments filling the area between the larger cones in the subretinal space and stretching to the pigment epithelium cells. In foveal retina, where only cones are concentrated, their cell bodies are layered in oblique columns below the outer limiting membrane. Scanning electron micrograph of the rods and cones of the primate retinaĬones are robust conical-shaped structures that have their cell bodies situated in a single row right below the outer limiting membrane (OLM) and their inner and outer segments protruding into the subretinal space towards the pigment epithelium (Figs. Semithin section of human outer retina to show the rods and conesįig1b. In vertical sections of retina prepared for light microscopy with the rods and cones nicely aligned, the rods and cones can be distinguished rather easily.įig. Light microscopy and ultrastructure of rods and cones. Some non-mammalian retinas have even more cone types (see later).ġ. Two or three types of cone photoreceptor and a single type of rod photoreceptor are present in the normal mammalian retina. ![]()
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