lec #5 eyes

palpebral conjunctiva

membrane that lines underside of the eyelid

bulbar conjunctiva

membrane that covers the whites of the eye

fibrous layer

outer

cornea and sclera

vascular layer

choroid

cillary body/zonule

inner layer

back of eye

retina

iris

constrict pupil (parasympathetic)

dilate pupil (sympathetic)

hyperopia

farsightedness (cillary doesn’t relax enough)

pigment layer

stops light scattering

stores vitamin A

Neural layer

1. photoreceptors - rods (dark) cones (colour)

2. bipolar cells

3. ganglion cells

optic disk

blind spot where signal heads to the brain

photoreceptors segments

outer segment - receives light signal

inner segment - synapse with bipolar cells

phototransduction in visual pigment

1. rhodopsin absorbs light and turns 11-cis-retinal into all-trans-retinal

2. enzymes and ATP convert all-trans-retinal to 11-cis-retinal

3. 11-cis-retinal combines with opsin to make rhodopsin

phototrasduction out of the visulal pigment

1. visual pigment activates transducin

2. transducin activates phosphodiesterase (PDE)

3. PDE converts cGMP into GMP

4. lower cGMP levels = less cGMP-gated channels open

5. less channels = hyperpolarization

signal transmission in the retina

1. hyperpolarization causes calcium channels to close

2. stops neurotransmitters (IPSPs) from being released onto the bipolar cell

3. causes bipolar cell to depolarize

4. depolarization opens calcium channels and releases neurotransmitters (EPSPs) onto the ganglion cell

5. EPSPs causes action potential to carry along the optic nerve

visual pathways

right field of view - left side of the brain

left field of view - right side of the brain

dark adaptation

pupils dilate

rhodopsin accumulation increases sensitivity