Lecture 16

Question 1

Describe the anatomy of the eye

Answer 1

pupil, iris, cornea, aqueous humor, lens, vitreous chamber, zonules, ciliary muscles, retina, macula, fovea, sclera (connective tissue), optic disk (blind spot where optic nerve leaves eyeball)

Question 2

Describe accommodation and vision problems

Answer 2

Accommodation = change in lens shape to focus light on retina. Ciliary muscles + zonules (ligaments) is like a trampoline, when ciliary muscles contract, ligaments go slack, lens becomes rounder = focus on close objects.

Presbyopia = loss of elasticity of lens
Hyperopia = far sighted, therefore near objects not refracted enough, so fix with convex lens
Myopia = short sighted, therefore far objects refracted too much, fix with concave lens
Astigmatism = uneven cornea shape

Question 3

Describe the structure of the retina

Answer 3

Has pigment epithelium then rods/cones then horizontal cells then bipolar cells then amacrine cells then ganglion cells

Question 4

Describe the pigment epithelium and rods/cones structure

Answer 4

Pigment epithelium has melanin to absorb light
Rods have disks with rhodopsin in the membrane, cones use similar photopigment in the three types of cones
rhodopsin (photopigment) = opsin (GPCR) + retinal (visual pigment)

Question 5

Describe differences between rods/cones

Answer 5

photopigment used
cones for colour, central vision
rods for b/w, periphery

Question 6

Describe signal transduction in the light

Answer 6

Light causes change in retinal from cis to trans conformation, this means retinal doesn’t bind to opsin therefore Gprotein (transducin) is activated. Activates phosphodiesterase to break down cGMP, closes cyclic nucleotide gated channels (cationic), hyperpolarization, Cav channels close so decreased glutamate release

Question 7

Describe signal transduction in the dark

Answer 7

Retinal in cis form, binds to rhodopsin, so transducin is inactive, cGMP is high, so CNG is open therefore cell depolarizes, Cav channels open and glutamate is released

Question 8

What does glutamate do?

Answer 8

activates “off” bipolar cells (turns off in light)

inhibits “on” bipolar cells (turns on in light)

Question 9

Describe the neural pathway of vision

Answer 9

goes through optic nerve, nasal hemisphere crosses over at the optic chiasm and goes to laternal geniculate body to the occipital lobe