Vision Sense organs: eye Receptor cell: photoreceptorReceptor 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.webvision.med.utah.edu/movies/trasduc.mov

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

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

http://www.clinicareinoso.com/conditns/refract.htm

‘Shortsighted’ or ‘Near-sighted’

‘Farsighted’

Eye MusclesSuperior Oblique (IV)Lateral Rectus (VI)

All others (CN III)

Inferior RectusMedial Rectus, Superior rectus Inferior Oblique• Eye Lid: Levator Palpebrae