Vision Sense organs: eye Receptor cell: photoreceptor Receptor signal transduction mechanism: activated opsin membrane receptor (transducin G-protein) activates cGMP path to hyperpolarization in light Pathway of conduction: photoreceptor  bipolar cell ganglion cell (as optic nerve)  thalamus  visual cortex  visual assoc. area

Information passes from retinal photoreceptor cells to bipolar neurons to ganglion neurons. (There is some convergence.) photoreceptors

http://www.blackwellscience.com/matthews/rhodopsin.html

http://www.blackwellscience.com/matthews/rhodopsin.html http://www.webvision.med.utah.edu/movies/trasduc.mov

What effect would a decrease in phosphodiesterase activity in photoreceptor cells have on vision? A decrease in phosphodiesterase activity would lead to a higher level of intracellular cGMP. This rise would, in turn, keep the gated cation channels open and keep the photoreceptors depolarized. This would decrease the ability of receptor neurons to respond to photons. And reduce the receipt of visual sensory information.

Vision Pathway of conduction: photoreceptor  bipolar cell ganglion cell (as optic nerve)  thalamus  visual cortex  visual assoc. area

‘Shortsighted’ or ‘Near-sighted’ ‘Farsighted’ http://www.clinicareinoso.com/conditns/refract.htm

Eye Muscles Superior Oblique (IV) Lateral Rectus (VI) Inferior Rectus All others (CN III) Inferior Rectus Medial Rectus, Superior rectus Inferior Oblique Eye Lid: Levator Palpebrae