PURVES NEUROSCIENCE CHAPTER 11: VISION: THE EYE
In the retina photoreceptors do not exhibit action potentials; light activation causes a graded change in
membrane potential and a corresponding change in the rate of transmitter release onto postsynaptic
neurons.
Shining a light onto a photoreceptor leads to a membrane hyperpolarization.
Each transducin molecule activates only one PDE molecule, each PDE is capable of catalyzing the
breakdown of 6 cGMP molecules.
Photoreceptors are most sensitive to light at lower levels of illumination. As illumination increases,
sensitivity decreases.
Scotopic vision = rod-mediated vision, at the lowest levels of illumination when only the rods are
activated.
Mesopic vision = both rods and cones are activated.
Photopic vision = only cones are activated.
Rod system is more convergent, making it a better detector of light. This convergency at the same time
reduces the spatial resolution of the rod system.
Foveola = central 300 micrometer of the fovea, totally rod-free.
In the retina photoreceptors do not exhibit action potentials; light activation causes a graded change in
membrane potential and a corresponding change in the rate of transmitter release onto postsynaptic
neurons.
Shining a light onto a photoreceptor leads to a membrane hyperpolarization.
Each transducin molecule activates only one PDE molecule, each PDE is capable of catalyzing the
breakdown of 6 cGMP molecules.
Photoreceptors are most sensitive to light at lower levels of illumination. As illumination increases,
sensitivity decreases.
Scotopic vision = rod-mediated vision, at the lowest levels of illumination when only the rods are
activated.
Mesopic vision = both rods and cones are activated.
Photopic vision = only cones are activated.
Rod system is more convergent, making it a better detector of light. This convergency at the same time
reduces the spatial resolution of the rod system.
Foveola = central 300 micrometer of the fovea, totally rod-free.
