12 - The Visual System

Question 1

What is the fibrous tunic?

Answer 1

cornea- anterior, transparent, focuses light, avascular

sclera- posterior, collagen fibres, rigid for protection

Question 2

What is the vascular tunic?

Answer 2

Choroid- highly vascular
ciliary body- makes aqueous humor
iris-regulating light entry

Question 3

What are the cavities of the eye?

Answer 3

Anterior- between cornea and iris, contains aqueous humour

Vitreous chamber between the lens and retina contain vitreous body/ humour that is jelly like and clear.

Question 4

what is the aqeous humor?

Answer 4

composes the anterior chamber, provides support, in front of pupil, made in ciliary process and pressurised.

Question 5

What does the lens do?

Answer 5

• Crystallins arranged like layers of an onion
Transparent and no blood vessels.
-Alters suspensory ligaments by making them more round for focusing on close objects and flatter for distant objects.
• light refracted – image focussed on fovea

Question 6

Accommodation -distance

Answer 6

Ciliary muscle relaxes, suspensory ligaments taut, pulls lens flatter

Question 7

Accommodation - close

Answer 7

ciliary muscle contracts, suspensory ligaments’ tension released, lens more curved because it is ELASTIC, greater convergence of light.

Question 8

The Retina

Answer 8

Ganglion cells transmit signals from bipolar cells to the brain
Horizontal and amacrine cells help integrate visual information before it is sent to the brain
Rods 6 to 600:1 with single bipolar cell = CONVERGENCE

Question 9

What are the differences between rods and cones?

Answer 9

Rods- sensitive in dark, containing rhodopsin pigment, none in fovea, more in retina periphery, black and white
Cones- red 625, blue 455, green 530, colourful image

Question 10

What is rhodopsin?

Answer 10

A photoreceptor pigment in membrane disks, from retinal vitamin A derivative, opsin protein.

Question 11

What are the two retinal isomers?

Answer 11

cis and trans.
Retinal isomerase turns trans to cis in the dark.
Cis to trans in the light so it cannot bind to opsin, causing pigment bleaching.

Question 12

How is rhodopsin bleached and regenerated?

Answer 12

Trans activates rhodopsin to activate the transduction for phosphodiesterase to hydrolase cGMP to GMP.
Na channels close so the rod is hyperpolarised.