How we see 2 - transduction Flashcards Preview

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Flashcards in How we see 2 - transduction Deck (13)
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1
Q

What is phototransduction?

A

The conversion of light energy to an electrochemical response by the photoreceptors of the retina (rods and cones)

2
Q

What is the role of photoreceptors (rods and cones) once activated?

A

The phototransduced rods and cones need to activate optic nerve cells (generate an action potential)

3
Q

Identify the labels on this lovely diagram of a rod and cone.

A

JP domestically abuses women

4
Q

Describe the structure of the lamellae found in rods and cones

A

Each lamella is made of cell membrane with some extra stuff integrated into it:

Cones:

  • Cone opsins
    • S (short) - Blue 437 nm
    • M (med) - Green 533 nm
    • L (long) - Red 564 nm

Rods:

  • Rhodopsin (a visual pigment)
    • Low Green 498 nm
5
Q

Describe the structure of Rhodopsin

A

2 bits:

  • Opsin - Helical protein that is integrated into the membrane
  • 11-cis Retinal - Vitamin A compound
    • Nestled inside the Opsin
    • This is the part that ‘reacts’ to light hitting the rod
6
Q

How does Rhodopsin react when light hits? Shown below is the resting version of 11-cis retinal

What is the effect of this?

A

When light falls on 11-cis retinal, it isomerises to form ‘all-trans-retinal’

All-trans-retinal can not fit inside Rhodopsin so rhodopsin splits

The effect of this is Bleaching of the visual purple

7
Q

What links the bleaching of purple by rhodopsin to phototransduction?

A

The Phototransduction cascade

“highly amplified cascade of light-triggered changes in protein conformation, and changes in interactions of proteins with one another and with guanine nucleotides”

8
Q

Photoreceptor cells are kinda different from other cells in terms of their state (polarity) when they are at rest

How is this?

A

Unlike other cells in the body, the photoreceptor cells are, at rest (in the dark), kept in a depolarised state by open Na+/Ca+ channels

9
Q

Complete the diagram of the phototransduction cascade

(its a bit aids but cba typing it all)

A

General idea:

  • Photon of light = bunch of reactions
  • Reactions = Na+ channel closes = hyperpolarisation
  • Transmission through Ca2+ flux to bipolar cell synapse
10
Q

Why is Vitamin A so important in the visual pigments?

A

Used in visual pigment regeneration

11
Q

Complete the diagram showing how pigment regeneration works

A
12
Q

What are the effects of vitamin A deficiency?

A

Night blindness (ie struggle to see in low levels of light)

Vitamin A is also essential for healthy epithelium. So conjunctiva and corneal epithelium are also abnormal.

Causes by malnutrition as well as coeliacs, sprue etc

13
Q

What are the signs of vitamin A deficiency?

A

Bitot’s spot

Corneal ulceration

Corneal melting - (Which leads to future opacification of the cornea)