. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 435 optic nerve discharge^' or optic ganglion response^'^^" in time; it has also been shown that a nerve impulse mav appear on illumination (usually low levels) in the absence of detectable retinal action potential. In response to high intensity flashes of light the train of nerve impulses may last for several seconds, whereas the retinal action potential is over in a fraction of a second (Wulff, unpublished). These observations do not permit an answer; future observations will undoubtedly se
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 435 optic nerve discharge^' or optic ganglion response^'^^" in time; it has also been shown that a nerve impulse mav appear on illumination (usually low levels) in the absence of detectable retinal action potential. In response to high intensity flashes of light the train of nerve impulses may last for several seconds, whereas the retinal action potential is over in a fraction of a second (Wulff, unpublished). These observations do not permit an answer; future observations will undoubtedly serve to clarify this problem. LIGHT ADAPTATION t= 10 SEC. !â 10 20 10. 5MIN. lOMIN. TIME IN DARK IS MIN. 20MIN. Fig. 139. Dark adaptation of single visual elements of Limulus after exposure to lights of different intensities (indicated on the curves in relative units). The response of the eye is measured by recording spike potentials of single visual elements in response to a constant intensity, constant duration test flash. Note the of the recovery curve after adaptation to more intense illumination. From Hartline and ; The Central Visual Mechanism Central Visual Pathways. A vertical line drawn through the center of the fovea of the human retina demarcates the two hemiretinas, the fibers of which follow different pathwavs to the brain. Fibers from the temporal hemiretina of the left eye pass through the optic chiasma and without crossing pass to the lateral geniculate body of the left side of the brain; those of the temporal side of the right eye enter the right optic tract. Fibers from the nasal half of each retina cross in the optic chiasma, enter the optic tract of the opposite side of the brain, where they join the uncrossed fibers from the temporal half of the other eye, and end in the contralateral genicu- late body. In the geniculate bodies the visual fibers enter into synaptic rela- tions with the fourth order neurones which continue on to the
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