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the constricted proximal portion of the optic vesicle in the embryo; it contributes to the formation of the optic nerve.
one of a pair of slender embryonic structures that becomes the optic nerve. In the embryo the optic stalk develops during the second week and attaches the optic vesicle to the wall of the brain. The stalk becomes complete during the seventh week of pregnancy when the choroidal fissure closes and is later converted into the optic nerve when retinal nerve fibers fill the cavity of the stalk. A few fibers grow into the stalk from the brain. About the tenth week after birth, the fibers of the optic nerve receive their myelin sheaths. Compare optic cup.
1. A double layered cup-shaped structure attached to the forebrain of the embryo by means of a hollow stalk. It develops into the retina and inner layers of the ciliary body and iris. It is formed by the invagination of the outer wall of the optic vesicle. Subsequently, nerve cells develop in its invaginated layer and some of these send their axons back along the hollow stalk (optic stalk or lens stalk) to form the optic nerve. Syn. ocular cup; ophthalmic cup; secondary optic vesicle.
of or pertaining to the eye.
see optic chiasm.
see visual cortex.
optic cup activity
see intraretinal space.
the disk in the fundus of the eye marking the point at which the optic nerve enters; it is accompanied by blood vessels, is oval, light in color and the blind spot of the retina.
the second cranial nerve; it is purely sensory and is concerned with carrying impulses for the sense of sight. The rods and cones of the retina are connected with the optic nerve which leaves the eye slightly to the nasal side of the center of the retina. The point at which the optic nerve leaves the eye is called the blind spot because there are no rods and cones in this area. The optic nerve passes through the optic foramen of the skull and into the cranial cavity. It then passes backward and undergoes a division; those nerve fibers leading from the nasal side of the retina cross to the opposite side in the optic chiasma while those from the temporal side continue to the thalamus uncrossed. The nerve tracts proceeding backward from the optic chiasm, pass around the cerebral peduncle, and dividing into a lateral and medial root, which end in the superior colliculus and lateral geniculate body, respectively. After synapsing in the thalamus the neurons convey visual impulses to the occipital lobe of the brain.
Injury to the nerve leads to partial or complete loss of sight on the opposite side. Commonly bilateral.
optic nerve aplasia
an uncommon congenital anomaly, most frequently seen in Collie dogs; affected animals are blind from birth. Hypovitaminosis A and prenatal infection with bovine virus diarrhea are possible causes.
optic nerve inflammation
the eyes begin in the embryo as a pair of shallow optic grooves on each side of the developing forebrain. The grooves form optic vesicles which invaginate to form a double-walled optic cup.
fibers from the lateral geniculate body entering the occipital cortex.
the evagination from the neural tube of the developing embryo which develops the optic cup at its extremity; the stalk persists as the optic nerve.
see optic groove.
the initial evagination from the neural tube which gives rise to the optic cup and the optic stalk.