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Stratum Opticum
The retinal nerve fiber layer (RNFL) or nerve fiber layer, stratum opticum, is formed by the expansion of the fibers of the optic nerve; it is thickest near the optic disc, gradually diminishing toward the ora serrata. As the nerve fibers pass through the lamina cribrosa sclerae they lose their medullary sheaths and are continued onward through the choroid and retina as simple axis-cylinders. When they reach the internal surface of the retina they radiate from their point of entrance over this surface grouped in bundles, and in many places arranged in plexuses. Most of the fibers are centripetal, and are the direct continuations of the axis-cylinder processes of the cells of the ganglionic layer, but a few of them are centrifugal and ramify in the inner plexiform and inner nuclear layers, where they end in enlarged extremities. Patients with retinitis pigmentosa have abnormal thinning of the RNFL which correlates with the severity of the disease. However the thickness of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera. The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins, as well as high-acuity vision used for task ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optic Nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, Pretectal area, pretectal nuclei, and superior colliculus. Structure The optic nerve has been classified as the second of twelve paired cranial nerves, but it is technically part of the central nervous system, rather than the peripheral nervous system because it is derived from an out-pouching of the diencephalon (optic stalks) during embryonic development. As a consequence, the fibers of the optic nerve are covered with myelin produced by oligodendrocytes, rather than Schwann cells of the per ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optic Disc
The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye. The ganglion cell axons form the optic nerve after they leave the eye. The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. The optic disc is also the entry point for the major blood vessels that supply the retina. The optic disc in a normal human eye carries 1–1.2 million afferent nerve fibers from the eye towards the brain. Structure The optic disc is placed 3 to 4 mm to the nasal side of the fovea. It is a vertical oval, with average dimensions of 1.76mm horizontally by 1.92mm vertically. There is a central depression, of variable size, called the optic cup. This depression can be a variety of shapes from a shallow indentation to a bean pot—this shape can be significant for diagn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ora Serrata
The ora serrata is the serrated junction between the choroid and the ciliary body. This junction marks the transition from the simple, non-photosensitive area of the ciliary body to the complex, multi-layered, photosensitive region of the retina. The pigmented layer is continuous over choroid, ciliary body and iris while the nervous layer terminates just before the ciliary body. This point is the ora serrata. In this region the pigmented epithelium of the retina transitions into the outer pigmented epithelium of the ciliary body and the inner portion of the retina transitions into the non-pigmented epithelium of the cilia. In animals in which the region does not have a serrated appearance, it is called the ''ora ciliaris retinae''. Additional images File:Gray875.png, Interior of anterior half of bulb of eye. File:Gray876.png, Vessels of the choroid, ciliary processes, and iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lamina Cribrosa Sclerae
The nerve fibers forming the optic nerve exit the eye posteriorly through a hole in the sclera that is occupied by a mesh-like structure called the lamina cribrosa. It is formed by a multilayered network of collagen fibers that insert into the scleral canal wall. The nerve fibers that comprise the optic nerve run through pores formed by these collagen beams. In humans, a central retinal artery is located slightly off-center in nasal direction. The lamina cribrosa is thought to help support the retinal ganglion cell axons as they traverse the scleral canal. Being structurally weaker than the much thicker and denser sclera, the lamina cribrosa is more sensitive to changes in the intraocular pressure and tends to react to increased pressure through posterior displacement. This is thought to be one of the causes of nerve damage in glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Medullary Sheath
Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be likened to an electrical wire (the axon) with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Rather, myelin sheaths the nerve in segments: in general, each axon is encased with multiple long myelinated sections with short gaps in between called nodes of Ranvier. Myelin is formed in the central nervous system (CNS; brain, spinal cord and optic nerve) by glial cells called oligodendrocytes and in the peripheral nervous system (PNS) by glial cells called Schwann cells. In the CNS, axons carry electrical signals from one nerve cell body to another. In the PNS, axons carry signals to muscles and glands or from sens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Choroid
The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye, and contains connective tissues, and lies between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The structure of the choroid is generally divided into four layers (classified in order of furthest away from the retina to closest): *Haller's layer - outermost layer of the choroid consisting of larger diameter blood vessels; *Sattler's layer - layer of medium diameter blood vessels; * Choriocapillaris - layer of capillaries; and *Bruch's membrane (synonyms: Lamina basalis, Complexus basalis, Lamina vitra) - innermost layer of the choroid. Blood supply There are two circulations of the eye: the retin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plexuses
In neuroanatomy, a plexus (from the Latin term for "braid") is a branching network of vessels or nerves. The vessels may be blood vessels (veins, capillaries) or lymphatic vessels. The nerves are typically axons outside the central nervous system. The standard plural form in English is plexuses. Alternatively, the Latin plural plexūs may be used. Types Nerve plexuses The four primary nerve plexuses are the cervical plexus, brachial plexus, lumbar plexus, and the sacral plexus. Cardiac plexus Celiac plexus Renal plexus Venous plexus Choroid plexus The choroid plexus is a part of the central nervous system in the brain and consists of capillaries, brain ventricles, and ependymal cells. Invertebrates The plexus is the characteristic form of nervous system in the coelenterates and persists with modifications in the flatworms. The nerves of the radially symmetric echinoderms also take this form, where a plexus underlies the ectoderm The ectoderm is one of the three pri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ganglionic Layer
The ganglion cell layer (ganglionic layer) is a layer of the retina that consists of retinal ganglion cells and displaced amacrine cells. The cells are somewhat flask-shaped; the rounded internal surface of each resting on the stratum opticum, and sending off an axon which is prolonged into it. From the opposite end numerous dendrites extend into the inner plexiform layer, where they branch and form flattened arborizations at different levels. The ganglion cells vary much in size, and the dendrites of the smaller ones as a rule arborize in the inner plexiform layer as soon as they enter it; while those of the larger cells ramify close to the inner nuclear layer The inner nuclear layer or layer of inner granules, of the retina, is made up of a number of closely packed cells, of which there are three varieties, viz.: bipolar cells, horizontal cells, and amacrine cells. Bipolar cells The bipolar cells, by .... References External links * Human eye anatomy {{eye-st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centrifugal Force
In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is parallel to the axis of rotation and passing through the coordinate system's origin. If the axis of rotation passes through the coordinate system's origin, the centrifugal force is directed radially outwards from that axis. The magnitude of centrifugal force ''F'' on an object of mass ''m'' at the distance ''r'' from the origin of a frame of reference rotating with angular velocity is: F = m\omega^2 r The concept of centrifugal force can be applied in rotating devices, such as centrifuges, centrifugal pumps, centrifugal governors, and centrifugal clutches, and in centrifugal railways, planetary orbits and banked curves, when they are analyzed in a rotating coordinate system. Confusingly, the term has sometimes also been used for the reactiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inner Plexiform
The inner plexiform layer is an area of the retina that is made up of a dense reticulum of fibrils formed by interlaced dendrites of retinal ganglion cells and cells of the inner nuclear layer The inner nuclear layer or layer of inner granules, of the retina, is made up of a number of closely packed cells, of which there are three varieties, viz.: bipolar cells, horizontal cells, and amacrine cells. Bipolar cells The bipolar cells, by .... Within this reticulum a few branched spongioblasts are sometimes embedded. References External links Overviewat utah.edu * Human eye anatomy {{eye-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inner Nuclear Layer
The inner nuclear layer or layer of inner granules, of the retina, is made up of a number of closely packed cells, of which there are three varieties, viz.: bipolar cells, horizontal cells, and amacrine cells. Bipolar cells The bipolar cells, by far the most numerous, are round or oval in shape, and each is prolonged into an inner and an outer process. They are divisible into rod bipolars and cone bipolars. * The inner processes of the rod bipolars run through the inner plexiform layer and arborize around the bodies of the cells of the ganglionic layer; their outer processes end in the outer plexiform layer in tufts of fibrils around the button-like ends of the inner processes of the rod granules. * The inner processes of the cone bipolars ramify in the inner plexiform layer in contact with the dendrites of the ganglionic cells. Connection types Midget bipolars are linked to one cone while diffuse bipolars take groups of receptors. Diffuse bipolars can take signals from up to 5 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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