Visual System

Question 1

what are the main challenges of the visual system?

Answer 1

1. detecting and coding the light signals (brightness, frequency)
2. use the light information for visual and non-visual behaviours
3. dynamically modulating this process in a context-specific manner

Question 2

light is detected by ____ in a thin layer of the eye called the _____

Answer 2

photoreceptors, retina

Question 3

photoreceptors project to _____, which project to the ______

Answer 3

bipolar cells, retinal ganglion cells (RGC)

Question 4

what make up the optic nerve?

Answer 4

retinal ganglion cells

Question 5

information dealing with the _________, crosses over at the ______ before terminating in the _______ of the ________.

Answer 5

contralateral visual field, optic chiasm, lateral geniculate nucleus, thalamus

Question 6

where is the light initially detected in the visual system?

Answer 6

photoreceptors in the retina

Question 7

at what point do RGC axons cross over in the visual pathway?

Answer 7

at the optic chiasm

Question 8

where do RGCs project after leaving the optic nerve?

Answer 8

to the lateral geniculate nucleus and other non-visual areas

Question 9

where does the info from the LGN ultimately project to?

Answer 9

the primary visual cortex in the occipital lobe

Question 10

Label this diagram:

Answer 10

A: optic nerve
B: optic chiasm
C: LGN
D: optic radiation
E: striate cortex
F: optic tract
G: hypothalamus
H: pretectum
I: superior colliculus

Question 11

circadian timekeeping: what is the typical activity pattern of nocturnal mice?

Answer 11

they are more active at night

Question 12

circadian timekeeping: how do mice respond to changes in the light/dark cycle?

Answer 12

they are sharply entrained to dark and light cycles; if you change the phase of the light/dark cycle, they can phase shift to be concurrent.

Question 13

what is the significance of IPRGCs in circadian timekeeping?

Answer 13

detecting light even without rods or cones

Question 14

if mice are kept in complete darkness, they still keep a ______ but their cycle shifts a bit every day.

Answer 14

12 hour endogenous rhythm

Question 15

what is lost if lesion in the retina?

Answer 15

endogenous rhythm

Question 16

_____ are maintained in the absence of _____

Answer 16

circadian cycles, rod and cone photoreceptors

Question 17

what are IPRGCs?

Answer 17

intrinsically photosensitive retinal ganglion cells

Question 18

what does maintained circadian cycle in the absence of rod and cone photoreceptors indicate?

Answer 18

that there must be some way of detecting light without rods or cones, and that there must be some other photopigment elsewhere in the retina.

Question 19

what did the study involving fluorescent dye injection into the hypothalamic suprachiasmatic nucleus aim to invesitgate?

Answer 19

examine the response of ganglion cells projecting to the SCN to light stimulation

Question 20

fluorescent dye injection into the hypothalamic suprachiasmatic nucleus: where did the dye travel to?

Answer 20

through the optic nerves back into the retina to label ganglion cells that project to the SCN

Question 21

fluorescent dye injection into the hypothalamic suprachiasmatic nucleus: what was the observed response in ganglion cells to light?

Answer 21

depolarization

Question 22

fluorescent dye injection into the hypothalamic suprachiasmatic nucleus: what happened to the ganglion cell response when cobalt (Cav) channel blocker) was applied?

Answer 22

depolarlization persisted even w the application, indicating an independent light response

Question 23

fluorescent dye injection into the hypothalamic suprachiasmatic nucleus: how did it provide evidence for the cells generating their own light response?

Answer 23

isolating retinal GCs from the retina and finding persistent responses confirmed the generation of an independent light response

Question 24

what was observed when measuring the response of ganglion cells to light?

Answer 24

depolarization in response to light, indicating light sensitivity