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Fundamentals of Neuroscience > Sensory Systems - Vision > Flashcards

Sensory Systems - Vision Flashcards

1
Q

What are the compartments of the eye?

A

Vitreous Humour
Aqueous Humour
Cornea

Iris divides the eye into two compartments (in front and behind)

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2
Q

What is the vitreous humour?

A

Fills compartment behind the iris and lens

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3
Q

What is the aqueous humour?

A

Fills the compartment in front of the iris and lens

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4
Q

What does the aqueous humour do?

A

Nourishes the cornea since this section does not have a blood supply (provides glucose)

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5
Q

What is Glaucoma?

A

Increased pressure due to decreased removal of the aqueous humour which can lead to blindness

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6
Q

What are the 2 types of glaucoma?

A

Angle closure - where iris adheres to cornea and blocks reabsorption of aqueous humour

Open angle - Sclerosis of veins

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7
Q

What is the treatment for glaucoma?

A

Surgery
Beta blockers - decrease aqueous humour production
Prostaglandin analogues to increase blood drainage.

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8
Q

What are some cells found in the retina?

A

Cells connect via chemical synapses
Ganglion cells
Horizontal and amacrine cells

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9
Q

What do the ganglion cells in the retina do?

A

generate action potentials (not photoreceptors)

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10
Q

What do the horizontal and amacrine cells in the retina do?

A

Modulate transmission of information and enable lateral transmission

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11
Q

What is the structure of the retina?

A

Peripheral retina
Macula (central retina)
Fovea (specialised part with only cones)
Blind spot (optic nerve leaves the eye)

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12
Q

What is the relationship between cone cells and the fovea?

A

Increasing proportion of cone cells closer to the fovea

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13
Q

What are the photoreceptors of the eye?

A

Rods and Cones

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14
Q

What are rod cells?

A 
1 type of rod cell
Rhodopsin (photosynthetic pigment)
Intracellular disks
Very sensitive to light 
Responsible for viewing in black and white.
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15
Q

Why are rod cells so light sensitive?

A

1 photon is able to generate a signal

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16
Q

What is the purpose of the intracellular disks in rod cells?

A

Increase surface area to increase the density of rhodopsin

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17
Q

What are cone cells?

A

3 types of cone (green, red, blue)
Iodopsin (photosynthetic pigment)
Need high light intensity to help see in colour
Responsible for coloured vision

18
Q

Why is a high light intensity required for cone cells to be activated and help us see in colour?

A

Infoldings of the membrane mean that there is a decreased surface area leading to a lower density of iodopsin so more light is required to activate cells.

19
Q

What are the properties of the peripheral retina?

A

Highly sensitive to light
Mostly rod cells
Many rod cells connect to 1 ganglion cell
Low visual acuity

20
Q

What is retinal convergence?

A

Where multiple photoreceptor cells converge onto one ganglion cell.
This reduces visual acuity

21
Q

What are the properties of the fovea?

A

Low sensitivity to light
All cones - less photopigment
1 cone per ganglion cell
high visual acuity

22
Q

How does phototransduction occur in rod cells whilst in the dark?

A

Rhodopsin is inactive
Cyclic GMP binds intracellularly to gated cation channels opening them.
Channels open leading to Na influx and depolarisation
Em = -30mV
Depolarisation causes glutamate release at synapse with bipolar cell
Bipolar cell receives signal in absence of a stimulus.

23
Q

What is the structure of Rhodopsin?

A

Retinal (chromophore responding to light)

Opsin (GPCR)

24
Q

How does phototransduction occur in rod cells when exposed to light?

A

Exposure to light causes hyperpolarisation of rod cell:

  1. Retinal absorbes light and activates opsin (GPCR)
  2. opsin activates phosphodiesterase (PDE)
  3. PDE breaks down cGMP
  4. less cGMP binds so gated channels closed and therefore no ion influx
  5. Causes hyper polarisation.
25
Q

What is the direct pathway of signal transmission through the retina?

A

Photoreceptor => bipolar cell => ganglion cell => visual cortex

26
Q

What do photoreceptors do when exposed to light?

A

ALWAYS hyperpolarise

27
Q

What are ON or OFF cells?

A

Subtypes of bipolar and ganglion cells that either depolarise or hyperpolarise in light.

28
Q

How do ON bipolar cells respond to light?

A

ON cells are depolarised by light:

Light - Rod cell is hyperpolarised - so less glutamate is released causing the cell the depolarise

Dark - Rod cell is depolarised - Increase glutamate causes cell to hyperpolarise

29
Q

How do OFF bipolar cells respond to light?

A

OFF cells are hyperpolarised by light:

Lights - Rod cell hyperpolarised - Less glutamate release causes hyperpolarisation

Dark - Rod cell depolarised - Increased glutamate release causes cell to depolarise

30
Q

What is responsible for the different and opposite electrical responses to light?

A

Different glutamate receptors in ON and OFF cells.

ON cells - Inhibitory glutamate receptors causing hyperpolarisation in ON cells

OFF cells - Excitatory Glutamate receptors causing depolarisation in OFF cells.

31
Q

What is the indirect pathway of signal transmission through the retina?

A

Each bipolar/ganglion cell has a receptive field

Central part - direct connections from photoreceptor
Surround part - Indirect connections via amcrine and horizontal cells.

32
Q

What is the receptive field of a bipolar/ganglion cell?

A

Region of retina that influencesthe cell.

33
Q

What response does the indirect pathway have on bipolar/ganglion cells?

A

Opposite response to the direct pathway.

34
Q

What is the purpose of the receptive field in bipolar/ganglion cells?

A

Important for contrast at image borders.

35
Q

What is the optic chiasm?

A

Where the optic tracts cross over

36
Q

What is the right optic tract?

A

Visualises the temporal side of the right optic nerve and nasal side of the left optic nerve.

37
Q

What is the left optic tract?

A

Visualises the temporal side of the left optic nerve and nasal side of the right optic nerve.

38
Q

What happens after transection of the left optic nerve?

A

Loss of sight in the left eye periphery.

39
Q

What happens after transection of the left optic tract?

A

Loss of sight in the right visual hemisfield

40
Q

What happens after transection of the optic chiasm?

A

Lose of sight in the periphery.

Fundamentals of Neuroscience (16 decks)

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