Vision

Question 1

Electromagnetic radiation

Answer 1

Exists in waves which are long radio waves and short X rays

Question 2

Light

Answer 2

• An electromagnetic radiation with a wavelength between 400-700 nanometers
• Different wavelengths = different colours

Question 3

Wavelengths of light

Answer 3

Refraction- the bending of light as it passes through a transparent object ie a prism splitting white light into different wavelengths (reflections)

Question 4

Tetrachromats

Answer 4

Ancestral creatures that have four kinds of cone cells to see different colours; red, green, blue and ultraviolet

Question 5

Dichromats

Answer 5

Modern creatures that lost two cone cells and have difficulty seeing red and green at night

Question 6

Trichromats

Answer 6

Species that have re-developed the ability to see red and orange

Question 7

Phototransduction

Answer 7

The process by which light energy produces graded receptor potentials

Question 8

Photoreceptors

Answer 8

• Modified neurons that have their ends inserted into the pigmented layer of the retina
• Vulnerable to damage as they can be destroyed by intense light

Question 9

Photopigment

Answer 9

• Visual pigment molecules that change shape when they absorb energy from photons of light
• Embedded in stacked discs of rod and cone cells
• Vision is repaired every 24 hrs as the tip of the rod/cone cells are phagocytized
• Made by a combination of retinal and 4 other opsin proteins to determine what colours of light are being absorbed

Question 10

Rods

Answer 10

• Contain one type of pigment (rhodopsin) to perceive vision in one colour
• More sensitive to light than cones
• 92 million rods in the retina

Question 11

Cones

Answer 11

• Each cone has one of three pigments to detect different colours
• Require brighter light to activate
• Direct connection to the optic nerve making visual image sharper

Question 12

Optic Nerve

Answer 12

• Formed by ganglion cell axons
  Visual signal direction:
• Rods/cones -> bipolar neurons
• Bipolar neurons -> ganglion cells

Question 13

Threshold depolarization

Answer 13

The amount of depolarization required to activate voltage-gated ion channels to allow Na+ arrival

Question 14

What potential is an all-or-none phenomena

Answer 14

Action potentials as they either happen completely (threshold stimulus) or not at all (sub-threshold stimulus)

Question 15

What can produce graded potentials

Answer 15

Changes in membrane potential from sensory to neurotransmitter receptors

Question 16

Graded Potentials

Answer 16

Brief changes in polarization near the dendrite of the neuron
- Depolarization through the action potential threshold can cause voltage-gated ion channels to open = Action potentials travelling along the neuronal axon. Can be found throughout the sensory system (rods and cones are an exception)

Question 17

Resting membrane potential changes

Answer 17

• Depolarization: the inside of the membrane is more positive. Increases the probability of producing nerve impulses
• Hyperpolarization: the inside of the membrane becomes more negatively charged. Decreases the probability of producing nerve impulse

Question 18

What happens in the dark?

Answer 18

Photoreceptor cells are slightly depolarized, releasing an inhibitory neurotransmitter to the bipolar cell stopping it from stimulating the ganglion cell to fire

Question 19

What happens in the light?

Answer 19

• Light bleaches the pigment which hyperpolarizes the photoreceptor and it stops releasing inhibitory neurotransmitters to the bipolar cell
• The bipolar cell can now depolarize/release an excitatory neurotransmitter to the ganglion cell, sending an action potential along the optic nerve

Question 20

Light adaptation

Answer 20

• Occurs when we move from darkness to bright light
• First, both rods and cones are strongly stimulated
• Then, glare is produced by large amounts of pigments broken down instantaneously
• Pupils become narrower to reduce the amount of light reaching the retina
• After 5-10 minutes, visual sharpness improves as the rod system turns off and retinal sensitivity decreases

Question 21

Dark adaptation

Answer 21

• Occurs when we go from a bright area to a dark one
• Bright light has bleached rod pigments, has shut off and requires time to reactivate
• The pupils dilate to maximize the amount of light reaching the retina
• Rhodopsin accumulates in the dark, which allows retinal sensitivity to increase
• At about 20-30 minutes, peak sensitivity is reached

Question 22

Visual perception

Answer 22

• Ganglion cells merge in the back of the eyeball = the optic nerve which crosses at the optic chiasma = the optic tracts which are connected to the thalamus
• Optic radiations project to the primary visual cortex in the occipital lobes

Question 23

Visual processing

Answer 23

Retinal ganglia: Simplify and condense information. Look for particular things like sharp changes in colour and brightness

Lateral geniculate nucleus: Integrates visual information to emphasize cone vision and begin processing depth perception

Question 24

Primary visual cortex

Answer 24

• Maps retinal information onto the occipital lobe for further processing for contrast, colour, shape and movement
• Ventral “what” stream goes to the temporal lobes for memory, and the limbic system for emotions
• Dorsal “where/how” stream goes tot he occipital and parietal lobes to let you recognize what you’re looking at and how you can interact with it

Question 25

Depth perception

Answer 25

• Created when the visual fields of each eye overlap
• Visual cortex fuses these slight images into a 3D perception
• Your brain relies on many other cues in order to perceive depth