Lecture 20: Vision 2 Flashcards
What two parts of the eye are crucial for focusing light onto the plane of the retina?
The cornea and the lens
The retina is part of the ________
brain
What type of cells are furthest from incoming light located at the back of the retina?
light sensitive cells (photoreceptors)
What does light travel through before reaching the photoreceptors in the retina?
ganglion cells and interneurons
What are the three types of interneurons in the retina?
bipolar cells
horizontal cells
amacrine cells
Describe bipolar cells
these have two connections connecting photoreceptors and retinal ganglion cells
Describe horizontal cells
their dendrites run horizontally across the top of the photoreceptor
these are needed to mediate the input between the photoreceptor and the bipolar cells
Describe amacrine cells
their dendrites are touching the bipolar cells and the retinal ganglion cells and they help to mediate input and modulate the input between bipolar cells and the retinal ganglion cells
Do interneurons fire action potentials?
no, they communicate by graded changes in the membrane potential (local change in excitability) and then there is a local release of neurotransmitter into the synapse to influence the excitability of neighbouring cells
Do retinal ganglion cells fire action potentials?
yes, they fire action potentials to the brain
What are the two types of photoreceptors called?
rods and cones
Which of the photoreceptors functions in low light?
Rods
Which of the photoreceptors is responsible for day and twilight vision?
cones
Which of the photoreceptors is not colour sensitive?
rods
Which of the photoreceptors is responsible for night vision?
rods
Which of the photoreceptors requires relatively high light levels?
cones
Are there more cones or rods per retina?
rods
Which photoreceptor has three types and what are these three types?
cones
these are ones that are sensitive to red light, ones that are sensitive to green light and ones that are sensitive to blue light
Why are photoreceptors sensitive to light?
because they have photopigment
Where is the photopigment located on a rod?
it sits on the outer segment of the rod formed into discs of membrane to increase the surface area hugely
Why are rods sensitive to low light?
because due to the discs of membrane, the surface area of the photopigment is very large
Where is the photopigment located on a cone?
it sits on the outer segment of the cone formed into small invaginations of the membrane
Why are cones sensitive to bright light?
because the invaginations of the membrane mean that there is only a small surface area of photopigment
The presence of photopigments makes photoreceptors what?
light sensitive
What are the two components of photopigment?
- a membrane spanning protein called an “opsin”
2. a chromophore called retinal
Retinal is a derivative of what?
vitamin A
What does a deficiency in retinal mean?
night blindness
Rods and cones differ in what opsin they have. What opsin do rods have?
rhodopsin
Rods and cones differ in what opsin they have. What opsin do cones have?
they have either an S (blue), M (green) or L (red) photopsin
Cones that are sensitive to blue light have what photopsin?
short wave length photopsin