A. Cornea, retina, iris, and ciliary body (Figure 28-2)
B. Rod outer segment (Figure 28-3)
Connecting T cilium I_
Connecting T cilium I_
Mitochondria Basal body Centriole Cilium
Sodium ion channels Membrane disks
Figure 28-3. (A) Various portions of a rod. The outer segment has sodium ion channels on the cell membrane and contains membrane disks. The connecting cilium, inner segment, cell body, and synaptic body are also shown. (B) Electron micrograph of the outer segment (OS) and connecting cilium (CC). Note the cilium, basal body, and centriole. (B Reprinted with permission from Fawcett DW: A Textbook of Histology, 12th ed. New York, Chapman Hall, 1994, p 902. Courtesy of T. Kuwabara.)
Figure 28-2. (A) Light micrograph of cornea. The five layers of the cornea are indicated, cpi = corncal epithelium; bm - Bowman's membrane; str = stroma; dm = Descemet's membrane; endo = corneal endothelium. (B) Light micrograph of retina. The 10 layers of the retina are indicated. The asterisk indicates the site of retinal detachment; the double asterisk indicates the presence of sodium ion channels; the triple asterisk indicates the site of action potential generation. (C) Light micrograph of iris. The posterior surface of the iris is lined by two layers of simple columnar epithelium, which are derived embryologically from the outer pigment layer (out) and inner (in) neural layer of the optic cup. Both of these layers are so highly pigmented that the two cell layers cannot be distinguished (see dotted line for boundary). The iris contains the dilator pupillae muscle and sphincter pupillae muscle, which are formed from the epirhelium of the outer pigment layer (out) by a transformation of these epithelial cells into contractile cells. The stroma (str) of the iris contains connective tissue, blood vessels, nerves, and melanocytes. The number of melanocytes in the stroma determines eye color. (D) Light micrograph of ciliary body. The ciliary body is lined by two layers of simple columnar epithelium, which arc derived embryologically from the outer pigment layer (out) and inner neural layer (in) of the optic cup. The outer pigment layer is pigmented, but the inner neural layer is nonpigmented. The ciliary body is thrown into folds called ciliary processes (cp). Both layers of epithelium are involved in the production of aqueous humor and suspensory fibers of the lens. The stroma (str) of the ciliary body contains connective tissue and the ciliary muscle.
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