Vision in Vertebrates

?
How does light affect receptor membranes?
It causes graded hyperpolarisation.
1 of 46
What are some features of rod cells (3)?
Specialised for sensitivity, many receptors on each cell allows absorption of large proportions of light, G-protein cascade produces high amplification.
2 of 46
What are some features of cone cells (4)?
Specialised for acuity, small and possibly directionally selective, not saturated at high light levels, photoreceptor recovers rapidly from change.
3 of 46
What two components are light receptors composed of?
Opsin- similar to transmembrane proteins in olfactory receptors. Retinal- absorption of light causes a conformational change in retinal molecule to the activated form.
4 of 46
What does a change in retinal cause?
A conformational change in rhodopsin, which activates a transducin.
5 of 46
How does the membrane become more polarised?
Activated rhodopsin activates transducin ---> Breakdown of cGMP ---> Na/ Ca channels close, only K channels remain open.
6 of 46
What happens to cGMP in a "normal" state (light falling on receptors)?
cGMP is constantly produced, but high levels of activated transducin cause cGMP to be constantly broken down again, so Na/ Ca channels remain closed.
7 of 46
What does levels of activated rhodopsin depend on?
The balance between the relative levels of light activation and of retinal recycling.
8 of 46
What happens to activated retinal in the epithelium?
It is constantly transformed back into unactivated retinal.
9 of 46
What happens to retinal in the absence of light?
Retinal recycling decreases amount of activated rhodopsin, reducing levels of transducin. cGMP levels increase and allow Na/ Ca channels to open, causing influx of ions and depolarisation.
10 of 46
How do we adapt to ambient light levels?
By ensuring that photo receptors are tuned so that small changes will open or close Na/ Ca channels.
11 of 46
How does adaptation work in light conditions?
It keeps more channels open.
12 of 46
How does adaptation work in dark conditions?
Makes it easier for channels to close.
13 of 46
Which cells are specialised for day vision and night vision?
Cone cells and rod cells respectively.
14 of 46
What is the purpose of the lens?
Focuses image.
15 of 46
What is the purpose of the cornea?
Filter to protect lens.
16 of 46
What is the purpose of the iris?
Aperture to control light entering.
17 of 46
What is the purpose of the eyelid?
Lens cover for when not in use.
18 of 46
What is the purpose of photoreceptors?
Pixels to register image.
19 of 46
What is the purpose of tears?
Cleaning mechanism.
20 of 46
Which parts of the eye refract light to form an image?
Lens and cornea.
21 of 46
What is accomodation?
Changing the strength of the lens to form a focussed image.
22 of 46
What type of cells have a graded response (5)?
Rod, cone, horizontal, bipolar and amacrine.
23 of 46
What do ganglion cells do?
Produce action potentials and provide afferent pathways from the retina.
24 of 46
How can processing in the retina be investigated?
By recording spike patterns in ganglion cells.
25 of 46
What is lateral inhibition?
Producing the surround in the centre-surround patterns.
26 of 46
What do rod and cone cells do when light levels decrease?
They become depolarised and release more glutamate. This have an excitatory effect on horizontal cells.
27 of 46
What are horizontal cells?
They receive input from many receptor cells and form a net connected by electrical synapses.
28 of 46
When is a receptor cell depolarised less?
When all its neighbours are also depolarised, as the cell is inhibited through lateral connections with its neighbours.
29 of 46
What does glutamate do in off-centre bipolar cells?
Activates AMPA receptors, which opens Na channels.
30 of 46
What does glutamate do in on-centre bipolar cells?
Activates metabotropic receptors. G-protein cascade closes Na channels.
31 of 46
When is an on-centre cell depolarised and how does this affect ganglion cells?
If a receptor cell is hyperpolarised. Ganglion cells fire if bipolar cells is sufficiently depolarised. The retinal ganglion cells are specialists for picking out bright or dark spots.
32 of 46
What mechanisms have developed to help stabilise an image (3)?
The inner ear- sense organs for detecting rotations and accelerations, the cerebellum- processing area to compute the stabilising movement, muscles to move the eye.
33 of 46
What in the inner ear senses rotational acceleration?
Semicircular canals.
34 of 46
How is an image kept horizontal?
Sensing linear acceleration using gravity.
35 of 46
How is directional sensitivity determined?
By alignment of hair bundles.
36 of 46
What is the purpose of the laternal geniculate nucleus (LGN)?
To make sense of the visual input. 90% of axons from the retina go here.
37 of 46
What is the purpose of the superior colliculus (SC)?
To orientate the eyes in directions of interest.
38 of 46
Where does concious control come from?
The frontal eye fields (FEF).
39 of 46
Where does automatic control come from?
The SC. Also has sensory inputs direct from retinal ganglion cells, auditory and somatosensory systems.
40 of 46
Where are sensory and motor maps located?
Both in the SC.
41 of 46
Where does the left half of both visual fields go?
To the right LGN.
42 of 46
What are P-ganglion cells?
Small, dendritic field, sustained response, slow axons. Respond best to details of stationary objects.
43 of 46
What are M-ganglion cells?
Large, dendritic field, phasic response, fast axons. Respond best to large, fast-moving objects.
44 of 46
What are K-ganglion cells?
Function unknown, possibly for colour.
45 of 46
Where do processing streams from LGN travel to?
Primary visual areas in the cortex.
46 of 46

Other cards in this set

Card 2

Front

What are some features of rod cells (3)?

Back

Specialised for sensitivity, many receptors on each cell allows absorption of large proportions of light, G-protein cascade produces high amplification.

Card 3

Front

What are some features of cone cells (4)?

Back

Preview of the front of card 3

Card 4

Front

What two components are light receptors composed of?

Back

Preview of the front of card 4

Card 5

Front

What does a change in retinal cause?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Psychology resources:

See all Psychology resources »See all PSY1202 resources »