Light

Question 1

visible light

Answer 1

1) photoreceptors in the eye are sensitive to wavelengths 400-700 nm (visible light)
2) light energy varies in intensity (amplitude of the wave)

Question 2

focal point and visual field

Answer 2

1) visual field
- field of view observes without moving our head or eyes
2) light waves diverge in all directions
- forward movement in a direction = light ray
- light reaching the eye mut be focused to one focal point on the retina

Question 3

accomodation

Answer 3

1) to adjust the strength of the lens
- dependent on the shape
2) lens shape regulated by ciliary smooth muscles
- part of ciliary body (anterior specialization of the choroid layer)
- attached to lens by suspensory ligaments
3) ciliary muscle relaxed
- weaker flattened lens
- further away items

*it is controlled by autonomic nervous system

Question 4

focal point

Answer 4

1) sharp image
- has to come into focus on the retina
2) blurred image
- comes into focus ahead or behind the retina

Question 5

visual acuity

Answer 5

1) snellen eye chart
2) 20/20 is normal vision
- most clear items are at 20 feet
3) legally blind is 20/200
- you can read at 20 feet what people can read at 200 feet

Question 6

myopia

Answer 6

1) eyeball is too long or lens is too strong
- lens cant relax
- the focal point is focused in front of the retina (unclear image of something far)
2) close images does not need accommodation

Question 7

hyperopia

Answer 7

1) same concept
2) too short eyeball or too weak lens

Question 8

visual pathways

Answer 8

1) each optic nerve carries info from both halves of the retina it serves
2) info is separated as the optic nerves meet at optic chiasm

Question 9

optic chiasm

Answer 9

1) fibers from the medial half of each retina cross to the opposite side, but those from the lateral half remain

Question 10

optic tracts

Answer 10

1) bundle of fibers leaving the optic chiasm
2) each carries info from the lateral half of one retina and medial half of the other
3) partial crossover brings information from the same half of visual field
4) each optic tract delivers to the half of the brain on its same side information about the opposite half of the visual field

Question 11

depth perception

Answer 11

1) ability to distinguish the relative distance of objects
2) information from the visual field is delivered to each half of the cortex simultaneously
- binocular field of vision: each eye views an object from a slightly different vantage point => the image from each eye is not identical (disparate images)

Question 12

phototransduction

Answer 12

1) converting light stimuli into electrical signals

Question 13

neural portion of retinal consist of three layers of excitable cells

Answer 13

1) photoreceptor cells
2) bipolar cells
3) ganglion cells

Question 14

horizontal and amacrine cells

Answer 14

1) provide pathways for interactions between photoreceptors = feedback signals (lateral inhibition)
2) horizontal cell synapse: rods, cones, bipolar cells
3) amacrine cells synapse
- bipolar cells and ganglion cells

Question 15

convergence

Answer 15

1) receptor cells
- rods 120 million
- cones 6 million
2) optic nerve
- ganglion cells 1 million
3) convergence >100 million receptor cell to 1 million neurons
4) receptor cell may not have its own label line to the brain

Question 16

receptive field

Answer 16

1) ratio of receptors to ganglion
2) smallest in the fovea
- increases moving towards the periphery

Question 17

signal transmission

Answer 17

1) light activates photopigments
2) receptor potential
3) action potential generated in ganglion cells
4) information is transmitted to the brain for visual processing

Question 18

photoreceptors (rods and cones)

Answer 18

1) outer segment
- discs that contain light absorbing photopigments
2)inner segment
- metabolic machinery
3) synaptic terminal
- stores and release NT

*rods are more sensitive to light than cones

Question 19

properties of rods and cones

Answer 19

1) rods
- 120 million
- high sensitivity to light
- low acuity
- vision in shades of gray
2) cones
- 6 million
- low sensitivity
- high acuity
- color vision

Question 20

rhodopsin

Answer 20

1) in disk membrane of rods
2) opsin
- protein in disc portion of plasma membrane
3) retinal
- vitamin A derivative
- light absorbing part of photopigment

Question 21

receptive field response pattern

Answer 21

1) useful for enhancing the difference in light level between adjacent objects
2) emphasizes differences in relative brightness
- advantage: help define contours of images
- consequences: information about absolute brightness is sacrificed (because we need to see clarity)

Question 22

photopigments

Answer 22

1) red
- L type
2) green
- M type
3) blue
-S stype
4) each photopigment has the same retinal but a different opsin

Question 23

cones and colors

Answer 23

1) light wavelength absorbed by each photopigment varies
- peak absorbance plus range of wavelengths shorter and longer than peak absorption
2) absorption curves for the three cone types overlap
- two or three cones may respond to a given wavelength

Question 24

trichomatic theory

Answer 24

1) color vision
- absorption of light by three classes of cones
2) depends on: ratios of stimulation in response to different wavelengths by three cone types
- white is mixture of all wavelengths of light
- black is absence of light

Question 25

opponent process theory

Answer 25

1) we saturated the receptors that respond to that particular color
2) under white light, you will see the opposite color because they are already saturated

Question 26

color blindness

Answer 26

lack of sensitivity to certain wavelengths
1) four types of red-green color blindness
- protanopia - red cannot be seen
2) two types of blue-yellow blindness
- tritanopia - cannot distinguish blue and green, purple and red, and yellow and pink

Question 27

smooth muscle of the iris

Answer 27

1) sphincter pupillae
- decrease pupil size
2) iris
- pupillary sphincter (circular)
- pupillary dilator (radial)
3) dilator pupillae
- increase pupil size

Question 28

light sensitivity

Answer 28

1) the eyes sensitivity to light depends on the amount of light responsive photopigment present in rods and cones
2) intense light (sunlight) breaks down photopigments
- decreases photoreceptor sensitivity
3) absence of light (dark) allows photopigments to regenerate
- increases photoreceptor activity

Question 29

dark adaptation

Answer 29

1) bright sun to darkened surroundings
- sensitivity gradually increases
- amount of photopigments increase

Question 30

light adaptation

Answer 30

1) dark to bright light
- little contrast between lighter and darker parks
- entire image appears bleached
- some photopigments are rapidly broken down by the intense light
- sensitivity of the eyes decrease
- normal contrast returns