vision part 2

phototransduction

1. light

2. no light

no light

1. no light is hitting rhodopsin

2. sodium channels open

3. rod slightly depolarizes

4. generates graded potential

5. releases NT: glutamate

glutamate

releases an inhibitory effect which keeps bipolar cell hyper-polarized and stops neurotransmitter release towards ganglion cell

light

1. light reaches rhodopsin

2. rhodopsin becomes bleached

3. sodium channels close

4. rod becomes hyperpolarized

5. release of glutamate is reduced

6. inhibition of signal transmission ceases

7. bipolar cells depolarize

8. releases neurotransmitters towards ganglion cell

events at G protein coupled receptor

1. binding of nT activates G proteins

2. g protein activation stimulates various effector enzymes

3. enzymes alter the intracellular concentration of cytoplasmic second messengers

4. 2nd messengers either directly or indirectly alter membrane ion channels which alter membrane potential

dark current

movement of positive charge across the membrane

cGMP

produced continuously in phootoreceptors

optic nerve

axons of ganglion cells form the optic nerve

2 types of ganglion cells

1. m-type

2. p-type

m-type

large, activated by movement; activates layers 1, 2

p-type

small, activated by pigment (color); activates layers 3, 4, 5, 6

ipsilateral

same side

contralateral

opposite sides

decussate

crossing sides

assuming you cover an eye…

1. Left temporal hemifield is focused on left nasal retina

2. left nasal hemifield is focused on right temporal retina

3. right temporal hemifield is focused on right nasal retina

4. right nasal hemifield is focused on left temporal retina

pathway that connects retina to thalamus

1. optic nerve

2. optic tract

3. optic chasm

optic nerve

comes out of the back of the retina

optic tract

goes into thalamus

optic chiasm

allows some info to cross

optic radiation

connects thalamus to cortex

LGNucleus

• in thalamus

• receives info from retina

• has two sections

  • 1, 2

  • 3, 4, 5, 6

nasal retina

information goes to LGN layers: 1, 4, 6

temporal retina

information goes to LGN layers: 2, 3, 5

cortex IV (4)

1. recieves info from the thalamus

2. has 3 regions: a, b, c

c region

made up of alpha and beta (x/B)

alpha

activated by m-type ganglions

beta

activated by p-type ganglion