07. Important Information Flashcards
What percentage of the human brain is devoted to the analysis of input from the eyes?
25- 40%
What are photoreceptors?
Specialized light-detecting cells connected to the nervous system in many multicellular animals. In humans and other vertebrates, the photoreceptors are rods and cones.
What is one theory of the early evolution of photoreceptors?
They initially enabled circadian rhythms
What is the retina?
A thin membrane of cells that lines the rear interior of the eyeball; it contains the receptor cells for vision (rods and cones).
What is the cornea?
he curved, transparent tissue at the front of the eyeball that helps to focus light rays as they first enter the eye.
What is the iris?
The coloured (usually brown or blue), doughnut-shaped, muscular structure in the eye, located behind the cornea and in front of the lens, that controls the size of the pupil and in that way controls the amount of light that can enter the eye’s interior.
What is the pupil?
The hole in the center of the iris of the eye through which light passes
What is the lens?
In the eye, the transparent structure behind the iris that helps focus light that passes through the pupil.
How is the brain wired to interpret images on the retina?
Input from lower on the retina is interpreted as up and input from higher is interpreted as down
Which cells are responsible for transduction in the eye?
photoreceptor cells
What are the two types of photoreceptor cells?
rods and cones
what are cones?
The class of receptor cells for vision that are located in and near the fovea of the retina, operate in moderate to bright light, and are most important for the perception of colour and fine detail
What are rods?
The class of receptor cells for vision that are located in the peripheral portions of the retina (away from the fovea) and are most important for seeing in very dim light.
What is the fovea?
The pinhead-size area of the retina of the eye in which the cones are concentrated and that is specialised for high visual acuity.
How many rods and cones does the human eye contain?
about 6 million cones and 120 million rods
What is the photochemical for rods called?
rhodopsin
What is rhodopsin?
The photochemical in rods that undergoes structural changes in response to light and thereby initiates the transduction process for rod vision
How many varieties of cones exhist?
3, each with their own photochemical
What is the optic nerve?
The cranial nerve that contains the sensory neurons for vision, which run from the eye’s retina into the brain.
What is the blind spot?
The place in the retina of the eye where the axons of visual sensory neurons come together to form the optic nerve. Because the blind spot lacks receptor cells, light that strikes it is not seen.
Define cone vision
The high-acuity color vision that occurs in moderate to bright light and is mediated by cones in the retina; also called photopic or bright-light vision.
Define rod vision
The low-acuity, high-sensitivity, noncolor vision that occurs in dim light and is mediated by rods in the retina of the eye. Also called scotopic vision
Why is it easier to see objects in dim light if you don’t look directly at them?
Because the fovea doesn’t contain any rods
Define dark adaptation
The increased visual sensitivity that occurs when the eyes are exposed for a period of time to dimmer light than was present before the adaptation period.
Define light adaptation
The decreased visual sensitivity that occurs when the eyes are exposed for a period of time to brighter light than was present before the adaptation period.
Describe rhodopsin’s role in dark adaptation
Rhodopsin is more sensitive to light than the cone photochemicals. Bright light causes it to break down thus making rods nonfunctional. It takes about 25 minutes for rhodopsin to regenerate and only 5 minutes to break down. Which is why it takes longer to adapt to darkness than brightness
What wavelengths of light are visible to humans?
400- 700 (nm) nanometers
Which shorter waves fall below human visible range?
ultraviolet rays, x-rays, and gamma rays