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TSM > 1.44 Visual Pathways > Flashcards

1.44 Visual Pathways Flashcards

1
Q

What colours do cones pick up?

A

Red, blue and green

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2
Q

What colours do rods pick up?

A

Just black and white

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3
Q

Which cells modify the signal from the rods and cones before its passed onto the retinal ganglion cells?

A

Horizontal and and amacrine cells - modulate activity - turn it up or down or alter activity

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4
Q

Which receptor protein is found in rods?

A

Rhodopsin

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5
Q

Which receptor protein is found in cones?

A

Photopsin

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6
Q

What is contained in the outer and inner segments of cones and rods?

A

Outer compartment - photopigment

Inner compartment - nucleus and mitochondria

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7
Q

what do rods and cones synapse with?

A

Bipolar and horizontal cells

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8
Q

What is phototransduction in simple terms?

A

The process of a cell absorbing light which results in a change of transmitter that is released.

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9
Q

What is released when light hits rhodopsin?

A

Opsin is released - it is a transmembrane protein

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10
Q

What is retinal?

A

A protein found in the photopigments, the one type of rod and three types of cones all have a different amount of this protein, this allows for different wavelengths to be absorbed.

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11
Q

What happens to retinal once light hits?

A

It changes from “cis” form to “trans” form, this triggers changes in the opsin

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12
Q

What is transducin?

A

It gets activated by the changes in rhodopsin after light hits, when its activated it exchanges its GDP for a GTP

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13
Q

What activates phosphodiesterase in the disc membranes?

A

The alpha subunit of the transducin after it was activated

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14
Q

What does phosphodiesterase do?

A

Hydrolyses cGMP, thus lowering its concentration

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15
Q

What does a lower concentration of cGMP result in?

A

Less ion channels open, because theres less cGMP to keep them open

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16
Q

In the dark, what is the membrane potential status of the outer segment?

A

It is depolarised due to a positive influx of calcium and sodium ions, however there is an outward flow potassium, causing hyperporalisation, however the the net outcome is depolarisation

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17
Q

What effect does the demoralised state of the membrane in the dark have on neurotransmitter release?

A

Continuous release

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18
Q

What happens to the membrane when light hits?

A

Less cGMP, less open channels, more K out than Na and Ca in, so the membrane becomes hyperporalised (negative)

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19
Q

What effect does hyperpolarisation of the membrane on the neurotransmitter?

A

Decreases amount of neurotransmitter released

20
Q

What stops rhodopsin from continuing activating transducin?

A

Rhodopsin kinase phsophorylates then arresting binds to it

21
Q

What is protonopia, tritanopia and deutaronopia?

A

Protanopia - red missing - brownie
Deutaronopia - Green missing - yellowie
Tritanopia - blue missing

22
Q

Which gene is colour blindness carried in?

A

X chromosome

23
Q

What are the two main types of ganglion cells?

A

On-centre - fires when light hits centre receptive field

Off-centre - fires when light hits surround receptive field

24
Q

What happens when light hits the centre of the receptive field?

A

Hyperpolarisation - decreases neurotransmitter release

25
Q

What does decreased neurotransmitter release result in?

A

Decreased inhibition of the on-centre bipolar cell so increased activity on the on-centre ganglion
Decreased excitation of the off-centre bipolar cell so decreased activity of the off-centre ganglion

26
Q

Where do the axons from the retinal ganglion cells from both eyes meet?

A

Optic Chiasm

27
Q

How do axons cross over in the optic chiasm?

A

Axons from the right side of the visual field (from both eyes) project into the right optic tract and vice versa

28
Q

Where do the majority of axons within the optic tracts synapse?

A

In the lateral geniculate nuclei of the thalamus and superior colliculus

29
Q

How many layers of neuronal bodies are found in the LGN and what is their function?

A

6 layers - axons from there then project posteriorly through optic radiations to synapse in the occipital cortex

30
Q

What type of input do layers 1,4 and 6 transfer?

A

Contralateral

31
Q

What type of input do layers 2,3 and 5 transfer?

A

Ipsilateral

32
Q

Which layers are the magnocellular layers and what are they involved in?

A

1 and 2, they are involved in detecting “where” an object is, so movement and contrast

33
Q

Which layers are parvocellular and what are they involved in?

A

3,4,5 and 6, these are involved in deletion of colour and form

34
Q

How many layers is there in the primary visual cortex?

A

6

35
Q

Where is the calcarine sulcus?

A

Primary visual cortex

36
Q

How many visual cortex parts are there?

A

4 - V1, V2, V3 , V4

37
Q

Which parts of the visual cortex does the dorsal stream include and what is its function?

A

Magnocellular - V1, V2, V3 - Visuospatial - where things are

38
Q

Which parts of the visual cortex does the ventral stream include and what is its function?

A

Parvocellular - (lower) - V1, V2, V3, V4 - Features - colours - what things are

39
Q

If there is a lesion in the optic nerve in the right eye, what visual damage will that result in?

A

Loss of vision in the right eye

40
Q

If there is a lesion in the optic chasm, what visual damage would that result in?

A

Bitemporal (lateral) heteronomous hemianopia

41
Q

What causes right homonymous hemianopia?

A

A lesion in the left visual tract

42
Q

A patient present with loss of vision in the left temporal visual field and right nasal visual field, where is the lesion present?

A

A lesion in the right optic tract, producing a homonymous hemianopsia

43
Q

If a patient had a lesion in the right nucleus of Edinger Westphal, then a light shone in the right pupil would result in…

A

no direct effect on the pupil size, but a consensual effect on the left pupil size

44
Q

If a patient had a lesion in the left occipital cortex, they would present with…

A

Intact pupillary reflexes (loss of accommodation reflexes) in the right eye, but a loss of vision from the right visual field

45
Q

Glaucoma can be due to an increase in aqueous humour production from the ….

A

Ciliary body

46
Q

The signal from the retinal photoreceptors propagates through what to reach the ganglion cells?

A

Bipolar cells

TSM (67 decks)

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