Vision Flashcards
What does the outer fibrous layer of they eye have?
Has a non-sketchy sclera around the outside
What happens to the sclera at the front of the eye?
Becomes the non-transparent cornea the front of they eye
What is the cornea at the front of the eye inflated by?
Inflated by fluid
What humor is nicely hydrated and where is it located?
vitreous humor is nicely hydrated and is located at the back
What allows cornea to bend light rays?
Cornea is highly curved so bends light rays
What does the lens do?
Lens inside bends light further
What is the lens suspended on the ends of?
Suspended on the ends of suspensory ligaments from the cillary body
What does the cillary body include and what can this do?
Cillary body includes a muscle which can contract and relax making the lens fatter or flatter
What does a fatter lens do to light?
Fatter lens refracts light more
What does the iris control?
Iris controls central size of pupil and amount of light entering eye
What is the cornea primarily responsible for?
Primarily responsible for focusing light rays
What does a lens additionally provide?
lens provide additional variable fine focus
What is the job of the pupil?
Pupils job is to stay as small as possible to improve focus
Why is the retinal pigment epithelium an important structure?
Important structure as it keeps the neural retinal alive
What is the neural retina?
Neural retina is an outpost of the brain and generated from the neural tube
What does the neural retina contain and what does this link?
Neural retina contains a neural circuit which links the photo receptors to the retinal ganglion cells
What is the primary visual pathway?
- Axons from the retinal ganglion cells project back via the optic nerve
- The 2 optic nerves meet at the optic chiasm
- The optic nerves run along the optic tract which dives up the brain
- Many of the axons have branches that extend to the brain stem
- Main branch goes to the lateral geniculate nucleus in the thalamus
- Relay cells are activated in the LGN that carry signals to the primary visual cortex
What are rod receptors for?
For night vision
What are cone receptors for?
For day vision
What is the structure of cone photoreceptors?
- Outer segment involves membrane discs
- Inner segment involves nucleus
What is the membrane potential of cone photoreceptors?
-45mV
Why are cone photoreceptors polarised?
- They’re polarised because they have K+ channels that are leaking out
- Also have channels in there outer-segments that leak Na+ in and these are open by default
What happens if light over outersegment gets brighter?
If light over outer-segment gets brighter, the cell hyperpolarises reducing release of glutamate
What happens if light over outersegment gets darker?
If light over outersefment goes darker, the cells depolarise and more Na+ channels open and more release of glutamate
Where is opsin present?
Opsin present on membrane discs in outer segment
What is the protein component of photopigment?
Opsin
What is the non protein component of photo pigment?
Retinal
What are the 2 components that photopigment is made up of?
- Opsin
- retinal
Steps involved in the initiation of light response in transduction
11-cis C bind is fairly unstable in retinal
- When light strikes the retinal, it ruptures that bond and when the bond reforms it forms in the trans configuration
- All trans retinal acts an agonist on a GPCR
- Leads to the activation of G proteins which activate enzymes that breakdown cGMP
- This allows Na+ to close
Steps involved in the termination of response in transduction
- The opsin gets capped off by enzymes which causes trans retinal to go away
- Opsin stops activating protein and stops activating enzymes
- Enzymes form cGMP
- 11 cis retinal then binds to opsin again
What does loss of peripheral vision occur due to?
Occurs due to glaucoma, retinitis pigmentosa
What happens if you lose your fovia?
You are registered blind
What do photoreceptors communicate via to the ganglion cells?
Photoreceptors communicate via bipolar cells to the ganglion cells
How do bipolar cells gather information and why is this done so?
Bipolar cells gather information through a whole pool of photoreceptors before passing it on to the ganglion cells so there is convergence in the pathway
What does convergence increase and what does this mean?
Convergence increases pixel size therefore that’s why peripheral vision is more blind
Why don’t blood vessels cross the fovea?
Blood vessels don’t cross fovea because that’s where the foveal pit is
What types of images do you get at the foveal pit and why?
You get high detailed images at the pit because you can get good focus on the image
What cones are in the foveal pit?
Only red and green cones in this area
What is the image inverted by and so what does this mean?
Image in inverted by the optics
-So left side of the image found on the right side of both retinae
What do axons from nasal retina do?
Axons from nasal retina swap sides therefore right side of both retinae go to the right side of the brain
What is the image mapped on to?
Image is mapped on to the LGN and cortex with expanded central regions of the image
What do the axons form in the LGN and cortex?
Axons form a retinotopic map in the LGN and cortex with the map for the 2 eyes in register
What does the retinal ganglion cells report?
Report changes in illumination form one location to another
What happens if theirs a change in brightness causing the excitation of a ganglion cell?
If there’s a change in brightness causing the excitation of a ganglion cell, then information from excited cones will be fed through an inhibitory interneuron and they’ll inhibit that ganglion cell
-This means its not responding to absolute illumination, its the difference between brightness of the center vs the surroundings
