Chapter 5: Vison Flashcards
What some one sees depends on what?
How far one sees is dependent on how far
light travels before it strikes one’s eyes
where does the perception of what we see happen
it happens in our brain in fact the perception of all our sensory organs happens in our brain, not in our sensory organs
Law of specific nerve energies
this law states that activity by a particular nerve always
conveys the same type of information to
the brain
How light or visual stimuli go throughout the eye and to the brain
The light enters the eye through an opening called the pupil and goes to the retina which contains nerve cells: bipolar and ganglion and photoreceptors
bipolar cells are in the middle and connect between the photoreceptors and the ganglion cells so when the light comes in it goes through the ganglion cells and travels through the bipolar cells to the photoreceptors and that’s where transduction happens and info comes back to the ganglion cells and it sends it to the thalamus through the optic nerve which then will be sent to the occipital lobe which has to the primary visual cortex or V1
Bipolar Cells
Bipolar cells are one of the main retinal interneurons and provide the main pathways from photoreceptors to ganglion cells
ganglion cells
– The axons of ganglion cells join one another to form the optic nerve that travels to the brain
Amacrine Cells
Additional cells that receive information from bipolar cells and send it to other bipolar, ganglion, or amacrine cells
Control the ability of the ganglion cells to respond to shapes, movements, or other specific aspects of visual stimuli
The Optic Nerve
Consists of the axons of ganglion cells that band together and exit through the back of the eye and travel to the brain
blind spot
the point at which the optic nerve leaves the s back of the eye contains no receptors that are why its called a blind spot
this does not contain rodes or cones
Fovea
area in the center of the retina at which the vision is the best highly dense with cones and rods are absent
Each receptor in the fovea attaches to a single bipolar cell and a single ganglion cell is known as a midget ganglion cell
Each cone in the fovea has a direct line to the brain which allows the registering of the exact location of the input
- Our vision is dominated by what we see in
the fovea
the adaptability of Visual Receptors
Highly adaptive: Example: predatory birds have a greater
the density of receptors on the top of the eye; rats
have a greater density on the bottom of the
eye
foveal vision
cones are the receptors responsible for it, Each ganglion cell excited by a single cone sensitive to bright light responds poorly to dim light Good detail vision because each cones own ganglion cell sends a message to the brain and there aremany cones in there
Peripheral vision
have many rodes, Each ganglion cell is excited by many
receptors Responds well to dim light, and dominates in darkness Poor detail vision because many receptors converge their input onto a given ganglion cell that has few cones.
this vision helps you sense motion, and view objects, and sceneries. It also helps you walk around without running into things.
types receptors in the retina
the retina consists of two kinds of receptors which are cones and rods
Visual Receptors: Rods
mostly serve in the periphery vision and respond to faint light (120 million per retina) they are very dominant in the darkness
Visual Receptors: Cones
Cones: most abundant in and around the fovea (6 million per retina) Essential for color vision and more useful in bright light mostly serves foveal vision and dominates in brightness thought there fewer cones compared to rods but they provide about 90% of the brain’s input
Rods and Cons ratio in other species that are more active in darkness
The ratio of rods to cones is higher in species that are more active in dim light
Photopigments
Chemicals contained by both rods and cones that release energy when struck by light
