7: Physiology II Flashcards Preview

Ophthalmology Week 1 2017/18 > 7: Physiology II > Flashcards

Flashcards in 7: Physiology II Deck (24)
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1
Q

What are the two types of photoreceptor found in the retina?

A

Rods (low-light vision)

Cones (acute colour vision)

2
Q

What happens to the membrane potential of a photoreceptor when light strikes it?

A

Hyperpolarises

3
Q

Which type of channel is open in the dark and closed in the light?

A

cGMP-gated Na+ channel

“dark current”

4
Q

Why do cells tend to have a negative resting potential?

A

Action of NaKATPase: Na+ actively transported out so resting membrane potential is closer to conductance of K+ (-90mV)

5
Q

What causes the photoreceptors to hyperpolarise when struck by light?

A

Closure of cGMP-Na+ channel

i.e “dark current” is turned off

Cell’s rmp was previously between sodium and potassium

Now potassium only > more negative

6
Q

Which protein is the pigment in photoreceptors?

A

Rhodopsin

7
Q

What are the rho and opsin parts of rhodopsin?

A

Rho = retinal (Vitamin A)

dopsin = opsin (G protein coupled receptor)

8
Q

What happens when rhodopsin is struck by light?

A

Opsin activates cGMP

cGMP activates Na+ channel, causing it to CLOSE

Hyperpolarisation due to reduced Na+

Nerve impulse

9
Q

What happens to glutamate release when photoreceptors are:

a) depolarised
b) hyperpolarised?

A

a) Higher glutamate secretion

b) Lower glutamate secretion

10
Q

What is visual acuity?

A

Ability to distinguish two nearby points

i.e how blurry your vision is

11
Q

What determines your visual acuity?

A

Photoreceptor spacing

12
Q

Which type of photoreceptor is concerned with

a) acute, colour vision
b) low light vision?

A

a) Cones

b) Rods

13
Q

Why is low-light vision less acute than colour vision?

A

Rods are more WIDELY spaced at the peripheries of the retina

Cones are more DENSELY packed at the fovea

14
Q

Why is low-light vision more sensitive than colour vision?

A

Ganglia pick up impulses from a GREATER number of rods than they do cones

Multiple rods to a ganglia, few cones to a ganglia

So all the information is added together - your vision is more sensitive but less acute

15
Q

Acute, colour vision depends on the ___ of cones.

Low light vision depends on the ___ of rods connected to each retinal ganglion cell.

A

density

convergence

16
Q

Why can we see more than one colour?

A

Different CONES for different wavelengths of light

17
Q

Nerve fibres from the (nasal / temporal) side of the each retina cross over where?

A

nasal retina

optic chiasm

18
Q

Optic ___ travel to the optic ___ and then continue on as optic ___.

A

Optic nerves

Optic chiasm

Optic tracts

19
Q

Because the (nasal / temporal) optic nerves cross over at the optic chiasm, the brain processes light from the left and right at the opposite visual cortex.

A

nasal crossover

LEFT VISUAL FIELD > RIGHT VISUAL CORTEX

and vice versa

20
Q

Information from the superior visual field is processed by the ___ visual cortex.

A

inferior visual cortex

and vice versa

21
Q

Which layer of the visual cortex receives all the information from the left and right visual fields?

A

4C

22
Q

In layer 4C of the visual cortex, light from each eye is processed (individually / collectively).

A

individually

23
Q

Past layer 4C of the visual cortex, information from each eye is processed (individually / collectively).

A

collectively

no distinction anymore

24
Q

What is Hebb’s postulate?

A

Cells that fire together, wire together

i.e input from right and left visual fields is required for optic pathway to develop properly, otherwise you get stunted development and vision problems