L3 - Visual System Flashcards
Outline the balloon model of eye growth
Tested in rabbits it was found that the retinal area increases long after cell proliferation has stopped.
With tissue expansion there was a decrease in cell density.
This indicates the sclera is passively stretched from the inner pressure of the eye.
This is still a controlled process. For example if a goggle is placed over the developing eye –> axial myopia
Outline basic signalling in the rod discs
Light hits opsin activating Gt. This activates PDE leading to a reduction in cGMP and an increase in GMP. This means that the cGMP activating Na channels close leading to hyperpolarisation.
Do photoreceptors fire APs?
No they have graded analogue signals
Why do photoreceptors have graded analogue signals?
More information can be conveyed in a short time range across a short distance
What is the function of oil droplets in photoreceptors?
In birds and lower vertebrates this has been developed in cones to act as additional colour filters
What is cone mediated vision for?
Colour and contrast
Why did the modern day retina develop a higher rod to cone ratio than the prototypic vertebrate retina?
In nocturnal species seeing at night is vital therefore their rod/cone ratio increased to 20:1. They also developed the tapteum lucidum
In diurnal species seeing at night was also important for safety. There were two possible solutions for this:
Expand by integrating interneurons and ganglion cells - this path was followed by reptiles and birds
Fovea centralis development
What is the tapetum lucidum?
A highly reflective layer which gives a second chance to catch a photon
Describe the fovea centralis in non-primate species
An extremely packed retina with a steep pit
Describe the fovea centralis in primates
A shallow pit comprised of cones
Outline the experiment in which an optical light trap was used to study isolated Müller cells.
Müller cell is trapped and orientates itself along the axis of 2 IR beams,
A secondary green laser beam is included into the trap.
The intensity of the light passing through the gap with and without Müller cells was measured.
If an isolated Müller cell was trapped in the light path than the transferred light energy was 3x higher than when there is only physiological salt there.
What is the function of a Müller cell?
It acts as a light cable which illuminates the photoreceptors of it’s columns
