Flashcards in Chapter 50 Deck (21):
Give the layers of the cells from the anterior portion of the retina to the posterior portion
ganglion cells --> amacrine --> bipolar --> horizontal --> photoreceptors (rod/cones)
Where is rhodopsin found?
What is the fxn of rhodopsin?
When light energy gets to the rhodopsin, it causes its decomposition to scotopsin and
retinal. This breakdown causes the transmission of the action potential to the
optic nerve. There are a series of decomposition steps, but the important one to know is that metarhodopsin II is the activated rhodopsin and is when the action potential is sent down
Night blindness cna be caused by a deficiency in what vitamin?
What is the mechanism of rod excitation and phototransduction?
When a rod is exposed to light, it hyperpolarizes to be stimulated (this is the
opposite of almost every other sensory receptor). A hyperpolarization occursbecause when rhodopsin decomposes, it decreases the rod membrane
conductance for sodium ions in the outer segment of the rod, however the
sodium pump is still functioning, pushing all the sodium out of the cell. The
greater the amount of light energy, the more negative the rod becomes.
What are the 5 steps to phototransduction?
1. Light photon converts rhodopsin to metarhodopsin II (activated
2. Activated rhodopsin activates transducin
3. Transducin activates phophodiesterase
4. Phosphodiesterase hydrolyzes cGMP (the chemical that holds sodium
channels open in the dark) and causes a decrease in sodium conduction
5. Rhodopsin kinase inactivates rhodopsin and entire cascade reverses
What is light adaption?
If a person is in bright light for many hours, large portions of the photochemicals in both the rods and the cones will have been reduced.
Much of the retinal of both the rods and the cones will have been converted to vitamin A. The sensitivity of the eye to light is correspondingly reduced
What is dark adaptation?
If a person remains in darkness for many hours, the rods and cones have relatively high levels of light sensitive pigments. Furthermore,
vitamin A is converted back into retinal to give more light sensitive pigments.
The sensitivity of the eye to light is correspondingly increased. Cones adapt
much more quickly than rods, but do not achieve anywhere near the same
amount of sensitivity change as the rods do in darkness.
What are the 3 spectral sensitivites to each cone?
Different cones are sensitive to different colors of light (red, blue and green). The spectral sensitivities of the 3 types of cones in humans have proved to be
essentially the same as the light absorption curves for the 3 types of pigment
found in the cones.
What is color blindness?
Color blindness is when a singlegroup of color receptive cones is missing from the eye
What are the roles of the rods/cones?
transmit signals to the outer plexiform layer where theysynapse with bipolar cells and horizontal cells
What are the roles of the horizontal cells?
transmit signals horizontally in the outer plexiform layer fromthe rods and cones to the bipolar cells
What are the roles of bipolar cells?
transmit signals vertically from the rods, cones and horizontal
cells to the inner plexiform layer, where they synapse with ganglion cells andamacrine cells
What is the role of amacrine cells?
transmit signals in 2 directions, either directly from bipolar cells to ganglion cells or horizontally within the inner plexiform layer fromaxons of the bipolar cells to dendrites of the ganglion cells or to other
What are the roles of ganglion cells?
transmit output signals from the retina through the optic nerve into the brain
What are the roles of the interplexiform cells?
transmit signals in a retrograde direction from the innerplexiform layer to the outer plexiform layer, and are inhibitory to control
lateral spread of visual signals by the horizontal cells in the outer plexiform
Horizontal cells allow for what type of vision?
high visual accuracy in transmitting contrastborders in the visual image
Why can amacrine cells help tract predators?
Amacrine cells are interneurons that help analyze visual signals before they ever leave the retina. Directional Sensitive are a type of amacrine cell that respond to movement of a spot across the retina in a specific direction
What are "W" ganglion cells?
40% of all ganglion cells. Small and transmit signals in their optic nerve fibers at a slow velocity. Receive excitation from rods, transmitted by way of
small bipolar cells and amacrine cells. Broad fields in the peripheral retina
because the dendrites of the ganglion cells spread widely in the inner plexiform
layer, receiving signals from broad areas. Especially sensitive for detecting
directional movement in the field of vision, and important for crude rod vision
under dark conditions.
What are the roles of the "X" ganglion cells?
55% of ganglion cells. Medium diameter and transmit signals at a
moderate speed. Have small fields because their dendrites do not spread widely in the retina. Their signals represent discrete retinal locations. These cells
transmit fine details of the visual image. They are responsible for all color vision