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Human physiology > Vision > Flashcards

Vision Flashcards

1
Q

What is the iris?

A

The coloured visible part of the eye in front of the lens

Regulates amt of light that enters the eye through pupil

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2
Q

What is the iris?

A

The coloured visible part of the eye in front of the lens

Regulates amt of light that enters the eye through pupil

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3
Q

What is the pupil?

A

The circular opening in the cnetre of the iris which light passes into the lens of the eye

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4
Q

What is the lens?

A

Trnasparent structure situated behind the pupil

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5
Q

What is the cornea?

A

The transparent circular part of the front of the eyeball

Refracts light entering the eye into the lens which focusses it onto the retina

Cornea is extremely sensitive (containe nociceptors)

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6
Q

What does the sensory nerve supply of the cornea do?

A

Transduces thermal, mechanical & chemical stimuli

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7
Q

What are the proportions of the receptors in the cornea?

A
  • 20% of corneal nociceptors are mechanoreceptors
  • 70% are polymodal nociceptors associated w slow conducting C-fibres
  • 10% are Aδ and C fibre cold receptors
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8
Q

What do the mechanoreceptors in the cornea do?

A

Convey acute sharp pain in response to mechanical contact

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9
Q

What do the polymodal nociceptors associated w slow conducting C-fibres in the cornea do?

A

Sharp & sustained pain in response to chemical stimuli, heat & meachincal irritants

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10
Q

What do the corneal nerves do in general?

A

Induce tear production & stimulate the blinking reflex through crosstalk between the corneal surface & lacrimal glands

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11
Q

How can you tell if someone is prediabetic from their eyes?

A

Based on the conc of the receptors

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12
Q

How do you get corneal disease with diabetes?

A

1 - raised blood glucose reduces epithelial cell proliferation, inc apoptosis & inhibits epithelial wound healing in cornelial epithelium

2 - Prolonged hypogylcemia results in the accumulation of advanced glycation and products which promote inflammation & oxidative stress & samages nerves

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13
Q

What are NGF and sphingolipids important for and how does this relate to diabetes?

A

Are key to neuronal health & myelin formation –> their production is inhibited by hyperglycemic states

This leads to corneal disease with diabetes

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14
Q

Where is the foeva located?

A

In the centre of the macula lutea of the retina

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15
Q

What is the foeva responsible for?

A

For charp central vision & is specialised for daylight vision

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16
Q

What is the foeva made of?

A

It is densly packed w more than half of the human cone photoreceptors

17
Q

How thick is the retina?

A

~0.2mm thick & is considered as the CNS

18
Q

What does the retina do?

A

It acts as a light reciever & carries out image processing through 5 main classes of neurones

19
Q

What are the 5 main classes of neurone ussed in the retina that carry out image processing?

A
  • Photoreceptors
  • Bipolar cells
  • Amacrine cells
  • Horizontal cells
  • & retinal ganglion cells
20
Q

What is the role of the 5 main classes of neurones in the eye?

A

They collectively amplify, extract & compress light signals to preserve relevant info before it gets transmitted to the thalamus thru optic nerves

21
Q

What is the role of Muller glia in the eye?

A

Muller glia act as optc fibres for green/red light

They channel the light thru the layers of cells (optic fibres)

Before they were thought to only be structural

22
Q

Where are photoreceptors found in the retina & how does light enter them?

A

Outer part of the retina –> the region farthest from incoming light

Light passes thru transparent inner retinal layers before it can be captured by the photreceptor

23
Q

What does RPE stand for?

A

Retinal Pigmemnt Epithelial

24
Q

What do Retinal Pigmemnt Epithelial cells do?

A

They absorb scattered light or light unabsorbed by photorecetors

25
Q

What happens when light hits the photreceptors in the retina?

A

Photoexcited pigment initiates a signal transduction cascade that amplifies light signals

Leads to closure of cation channels in rods & cones

Cells become hyperpolaries

Hyperpolarized membran potential causes reduced NT (i.e. glutamate)

Infor relayed to bipolar cells & then retinal ganglion cells (RGCs) via foward pathway

26
Q

What are bipolar & RGC responses modified by?

A

Modified by laterally projecting interneurones

(i.e. amacrine cells & horizontal cells)

27
Q

What sort of vision are rods for?

A

Used for dim light (low-light) & usually respond to relatively slow changes

28
Q

What sort of vision are cones for?

A

For daylight & bright coloured vision

Can also detect rapid light fluctuations

29
Q

What colour vision are cones optimised for?

A

Red, green & blue colour vision (RGB)

30
Q

What wavelength are rods?

A

498nm

31
Q

What wavelengths are red, green and blue?

A

Red = 564nm

Green = 534nm

Blue = 420nm

32
Q

Describe the first half of the process of phototransduction?

A
  1. Rohodopsin in the disc membrane of the outer segment absorbs a photon
  2. Results in a series of unstable intermediates - last one activates TRANSDUCIN
  3. This is the first amplification step –> each photoactivated rhodopsin triggers activation of about 100 Transducins
  4. Each transducin activates the enzyme cGMP-specific phosphodiesterase (PDE)
  5. PDE then catalyses to 5’ GMP - second amplification step, single PDE hydrolyses about 1000 cGMP molecules
33
Q

Describe the second half of the process of phototransduction?

A
  1. The net conc of intracellular cGMP is reduced (due to its conversion to 5’ GMP via PDE) –> resulting in closure of cyclic nuclotide-gated Na+ ion channels located in photoreceptor outer segment membrane
  2. As a result, sodium ions cna no longer enter the cell & photoreceptors outer segment membrane becomes hyperpolarised, as charge inside memrbane is more -ive
  3. This change in cell’s membrane potential cuases voltage-gated clacium channels to close
  4. Leads to dec in the influx of calcium ions into the cell
  5. A dec in the intracellular Ca+ conc means less glutamate is released via calcium-induced exocytosis to the bipolar cell
34
Q

How is phototransduction energised?

A
  • ATP is provided by the innder segmenet powers the sodium-potassium pump
  • Pump is necessary to reset the intial state of the outer segment by taking the sodium ions that are entering the cell & pumping them back out
35
Q

What does the reduction in the release of glutamate from phototransduction mean?

A

It means that one population of bipolar cells will be depolarised & a seperate population of bipolar cells will be hyperpolarised

36
Q

Do rods and cones release more NT when it is light or dark?

A

Rod or cone ohotoreceptors actually release less NT when stimulated by light!!

When it is dark more glutamate is released

37
Q

If less NT is released when it is light what does this mean for the ON and OFF bipolar receptors?

A

Less NT in the synaptic cleft between a photoreceptor (presynaptic) and bipolar cell (postsynaptic) will:

  • Excite! (depolarise) ON bipolar cells
  • Inhibit (hyperpolarise) OFF (dark) bipolar cells
38
Q

What are the receptor pathways for photorecpetors split into?

A

ON = triggered by less glutamte when it is light

or

OFF = triggered by more glutamate when it is dark

39
Q

There are 2 slides at the end that need rewatching if I have time

A

Cool

Human physiology (43 decks)

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