the visual system - introduction and spatial location

Question 1

what is the environmental stimulus that allows us to see?

Answer 1

light

Question 2

what is a photon?

Answer 2

one unit/packet of energy

Question 3

wavelength and frequency are the 2 properties of waves. what do each represent?

Answer 3

wavelength (nanometres) - the length of each wave from each point at the bottom.
frequency (Hz) - the number of times an event repeats within a given amount of time.

Question 4

what does it mean by saying that wave properties are inversely proportioned?

Answer 4

high frequency means low wave length. low wave length means high frequency.

Question 5

what is the first stage of visual information processing?

Answer 5

the retina

Question 6

how is the retina mapped?

Answer 6

3 vertical layers of cells

1. photoreceptors (rods/cones)
2. bipolar
3. ganglion

Question 7

what are photoreceptors and what do they do?

Answer 7

they are the input cells. they release neurotransmitters which control the activity of the bipolar cells that synapse with them,

Question 8

how does the ganglion cell pass on information?

Answer 8

the axons of ganglion cells form the optic nerve, which carries information from the eye to the brain.

Question 9

what can be said about rods?

Answer 9

• about 120 million of them
• primarily black and white receptors
• used for night vision
• gives information about brightness

Question 10

what can be said about cones?

Answer 10

• about 4 million
• colour receptors
• less sensitive, used for day vision
• densely packed in the fovea

Question 11

the amount of neurotransmitter released from the axon terminal depends on…

Answer 11

the level of light produced.

Question 12

name some characteristics of the photopic system?

Answer 12

• cones
• 4 million per eye
• rapid temporal responses
• concentrated in the fovea
• the basis of colour vision
• low sensitivity

Question 13

name some characteristics of the scotopic system?

Answer 13

• rods
• 120 million in each eye
• slow temporal responses
• larger, less acuity field
• located outside the fovea
• used for night vision - high sensitivity

Question 14

what is transduction?

Answer 14

the process of rods and cones detecting electromagnetic energy - evironmental stimuli are transformed into a neural impulse

Question 15

what do photopigments (found in photoreceptors) do?

Answer 15

they capture the photon of light that strike the cell.

Question 16

what is meant by the term that photoreceptors use a secondary message system?

Answer 16

the neurotransmitter binds to the gprotein receptors which break off and bind to a channel.

Question 17

light ………. the photoreceptor

Answer 17

hyperpolarises (further from 0, more negative). this reduces neurotransmitter release.

Question 18

when do photoreceptors release neurotransmitters?

Answer 18

in resting state.

Question 19

which cells in the retina produce action potentials?

Answer 19

ganglion cells.

Question 20

which are the 2 classes of ganglion cells?

Answer 20

magnocellular (M)

parvocellular (P)

Question 21

what are the characteristics of magnocellular cells

Answer 21

• think RODS
• have large receptive fields
• respond to large objects
• the analysis of MOVEMENT
• think M for movement

Question 22

what are the characteristics of parvocellular cells?

Answer 22

• think CONES
• have small receptive fields
• involved in colour vision
• the analysis of fine detail

Question 23

what is the optic disc?

Answer 23

the area where ganglion cells and blood vessels exit the eyeball. located on the nasal side of the fovea.

Question 24

what are saccades?

Answer 24

fast movements of the eyes that present various parts of the visual system in the fovea.

Question 25

what is the optic chaism?

Answer 25

the point at which the two optic nerves meet.

Question 26

where do temporal retinal cells send their exons? (which side of head)

Answer 26

to the same side of the brain - eg do not pass through the optic chaism

Question 27

where do nasal retinal cells send their axons? (which side of head)

Answer 27

to the opposite side - across the optic chaism.

Question 28

where does information go once it has travelled along the optic nerve?

Answer 28

the Lateral Geniculate Nucleus (LGN) - located in the thalamus

Question 29

what function does the LGN serve?

Answer 29

• it receives information via optic tract and sends it to visual areas in the occipital lobe
• information is kept segregated - Marvocellular and parvocellular

Question 30

how is the LGN mapped and which cells are in which layers?

Answer 30

retinotopic mapping - 6 layers.
layers 1,4 + 6 receive input from the eye on the opposite side
layer 2, 3 + 5 receive input from the eye on the same side.
spatial location is therefore mapped onto the LGN

Question 31

what do we know about area V1?

Answer 31

information is passed here via optic radiations from the LGN.
spatial location is mapped onto the visual cortex.