Chapter 56: Sensation And Visual System Flashcards
What is the visual info components we receive
Wavelength: distance between peaks of waves. Determines colour that people see
Amplitude: height of waves. Determines brightness. The greater the amplitude the brighter light experienced.
Purity: mix of light waves that reaches eye. Is associated with saturation or clarity of colour. Pure wavelength or single kind of wavelength are experience as a pure or clear colour while mixed wavelength are experience as less clear colour.
Name and discuss parts of the eye
Visual receptors found in eye where light enters through cornea which is transparent and passes through fluid into the anterior chamber of eye.
Front part divided from rest of eye by iris with its opening the pupil. The iris gives eye colour and white part is the sclera that maintain shake of eye.
6 ocular muscle attached to sclera to move eye. Muscle in iris change pupil size to accommodate light.
Ciliary muscle change shape of lens to keep focus on objects through accommodations.
Blind spot found in optic disc which is place in retina where axons grouped to form optic nerve which has no receptors.
What are the visual receptors
Cones which are responsible for Vision in daylight as well as colour vision. Most found in fovea and allow us to obtain sharp image of what’s seen ( visual acuity). Have higher sensitivity threshold and are less sensitive to light and require more intense light stimulation to be activated.
Rods are important for vision at night and in poor light. Distributed more periphery and more sensitive to light and can function when level of light is poor.
State the chemicals within cones and rods
Rods contain rhodopsin and when receive light it’s absorbed by rhodopsin which is broken down into retinene and rod opsin. When light stimulation stops rhodopsin is resynthesised. Contain only one kind of opsin
Cones contain iodopsin when light falls on cones iodopsin is broken down into retinene and cone opsin. When it’s dark again iodopsin resynthesised. Has 3 kinds of opsin which absorb red blue and green wavelength.
What is bleaching
A chemical process that allows us to adapt to abrupt changes from light to dark. In bright light rhodopsin in rods remains in bleached state and resynthesised in dark.
Dark adaptation occurs when rhodopsin is resynthesised and receptors are more sensitive to be able to see in poor light.
What is the trichromatic theory
According to theory Colour vision is result of 3 retinal systems one for red blue and green. When all 3 are stimulated at same time and intensity we see white.
Different combinations of red blue and green seen according to system stimulated most.
Describe the opponent process theory
According to this theory colour vision is result of 3 opposing processes a green- red process a yellow- blue process and white- black process. The particular colour is experienced according to wavelength of the light stimulating it. Black or White depends on brightness of light.
What is the retinex theory
We perceive colour through cerebral cortex comparison of various retinal patterns. The visual cortex compares pattern of light coming from different areas of retina and forms a colour perception for each one.
What is cause of colour blindness according to opponent process theory
People with normal vision have 3 kinds of iodopsin ( red blue and green) but colour blind people have . Common form of colour blindness is inability to distinguish red and green where the cones with of red and green have same iodopsin so see 2 as same colour.
Explain the visual pathway
Area eye can see is visual field. Light coming from visual field projects onto retina and area or retina review lights is retinal field.
The axons of neurons linking receptors to brain are grouped in bundle optic nerve where it and optc tract carry info from visual receptors to visual area of brain in occipital lobe.
Optic nerve come together at base of midbrain where some axons cross optic chiasm. Some extend in superior colliculus for control of head and eye movements but most end in thalamus where info is related to occipital cortex.
