NB22 Eye

Question 1

What are retinal ganglionic cells?

Answer 1

Sensory neurons from the retina to the brain

Question 2

They are involved in reflexes related to motor aspects , which are:

Answer 2

• The pupillary light reflex (not working sign of brainstem damadge- thats why )
• Accomodation reflex

Question 3

The Retina

1) What is the function of Pigmented epithelium ?
2) What is the function of Horizontal cells and amacrine cells?
3) Rod/cone to bipolar cells to ___a___ to CNS

Answer 3

1) absorbs all uncaptured light to prevent it reflect and leading to detection of a repetitive image.
2) modify and look after those areas. They aren’t important as the other cells.
3) a) retinal ganglionic cells

Question 4

Rod cells communicate with__

Answer 4

bipolar cells

Question 5

Describe transduction in rods and cones:

Answer 5

1) Membranous disks contain light-sensitive photopigment that detect the light, photopsin in cones and rhodospin in rod cells.
Rhodopsin contains retinal made from vitamin A derivatives. When rohodopsin is hit by light it activates a cascade in the cell activating a trimeric G protiein called transducin.GTP Is converted to GMP. This results in closing of ion channels leading to an alteration in membrane potential.

Question 6

What is contained with light-sensitive photopigment of:

a) rods
b) cones

Answer 6

a) Rhodopsin ( contains retinal made form vitamin A derivatives)
b) photopsin

Question 7

Deescribe how rhodopsin works?

Answer 7

1) is hit by light it activates a cascade in the cell activating a trimeric G protiein called transducin.
2) GTP Is converted to GMP.
3) This results in closing of ion channels leading to an alteration in membrane potential.

Question 8

describe the ion channels in the retina in the dark?

Answer 8

1) no light hits rhodopsin
2) ion channels open
3) resting membrane potential maintained , K+ flows out and Na+& Ca++ flows in,

Question 9

describe the ion channels in the retina in the light?

Answer 9

1) inward channels close
2) K+ channels still open
3) hyperpolarisation occurs as K+ flowing out
4) sensory cell inhibits bipolar neuron
5) retinal ganglion cells recieve more stimulation
6) thus retinal ganglion cells receive more stimulation
7) they send signals to primmary visual cortex via optic nn. pathway.

Question 10

What are the 2 main reflexes of the eye?

Answer 10

1. Pupillary light reflex: light shone in eye and both pupils contract
2. Accomodation reflex: focus on near / incoming objects

Question 11

1) Name the light reflex for each eye when light is shone onto the eye:
2) What happens when light is shone onto the eye?

Answer 11

both pupils contract
Constriction pupil same eye – direct light reflex
Constriction pupil opposite eye – consensual light reflex
2) Optic nerve activated – synapsiong through branches in pre-tectal area
Bilateral activation of Edinger-Westphal

Question 12

What is bitemporal heminopia?

Answer 12

when the optic chiasm is cut

Question 13

What causes right optimous heminopia?

Answer 13

left optic tract cut