Vision Flashcards
Where does the optic nerve relay back to?
• The optic nerves relay back to the optic chiasm
Describe the vision of the eye
and the inversion of the eye
- There is a temporal half and a nasal half for the temporal bone and the nose
- Each eye has a temporal and nasal visual field – the temporal focuses on the nasal side of the eye and vice versa
- Eyes invert the image (top to bottom) – so the bottom part of the world is on the top part of the retina
What is the sclera of the eye?
The sclera is a non-stretchy part of the eye, it runs all the way round the eye to the back. It creates an anchoring point for the ocular eye muscles, they move the eye around.
What forms the outer layer of the cornea?
The collagen fibres and cells at the front that make up the outer layer form the cornea
What is the purpose of the intraocular pressure?
What is the pressure generated by?
Intra ocular pressure is generated to ensure the sclera is firm – hold it rigid. The pressure is generated by the production of aqueous humour, a fluid that fills the eye produced by the ciliary body and flows outwards and reabsorbed through the angle of the eye.
What is the function of the lens?
What is it suspended by?
The lens changes the focus of the eye. The lens is suspended by suspensory ligaments from the cillary body (which can change the shape of the lens, as it contains a ring of muscle, when it contracts its diameter becomes smaller which causes the lens to become fatter. When he ring relaxes the diameter increases making the lens flatter for distance vision.)
What is the purpose of the retina?
Retina adjusts your eye for different levels of brightness
What is the purpose of the pupil?
The pupil maintains the smallest aperture for the illumination conditions. The smaller the aperature the greater the focus.
How does photons enter the eye?
Rays of photons pass through the cornea. That are brought to focus by the cornea and the lens to a single point.
Some are stopped by the iris
Identify the retinal pigment epithelium
What is its function?
- The black line is the retinal pigment epithelium that provides a lot of biochemical support for the photoreceptors and also holds the retina in place
- The neural retina contains the photoreceptors and has afferent which are retinal ganglian cells, that have axons that run across the surface of he retina and then form the optic nerve
Describe the pathway of the optic nerve
- They pass the optic chiasm
- They project to the LGN that sevres the visual system and then pass through white matter to the cortex which is the primary visual area. This is conscious vision
- Some axons make branches that head down to the brainstem that innovate different nuclei such a control of eye movements or pupils
Describe the photoreceptors
What are rods and cones?
Do they interact?
Do they have the same neuroal pathway
- Rods are used for nigh vision and cones are used for day vision.
- They are mostly separate systems that only interact at around twilight
- They mainly use the same neural circulatory from the retina to the brain. However at the level of the retina you have either the rod and there circulation or the cone and there circulation (nerves).
- Cones are used most of the time, whereas rods are used in the dark
Describe the structure of a single photoreceptor
- The inner segment is where the nucleus is kept, protein machinery
- The axon does not fire axon potential
- The synaptic terminal does released glutamate that is an excitatory neurotransmitter depending on the level of depolarisation which is determine by the transductor apparatus.
- The transductor apparatus is found in the outer segment, which contains layers of phospholipid membrane. They hold the chromofor in neat layers, perpendicular to the light path, to ensure efficient trapping of the light rays
Describe the membrane potentials of a cone cell?
- Here we are measuring the membrane potential of this cell.
- There is leaking potassium that causes a negative internal potential. It creates a negative internal potential.
- The resting membrane potential in these cells if -45mv to -40mv. They are therefore depolarised even at rest, as there are sodium channels that are open by defult.
- If light hits the outer segment, the sodium channels close which cause the cells to become more negative inside (hyperpolarises) which stops releasing to much glutamate.
- If it gets darker more sodium channels open, depolarising the cell and causing it to release more glutamate
What keeps the sodium ion channels open?
What is the photopigment made from?
What configuration is it in?
What happens when light hits this part?
- Here is a membrane disk.
- The intraceullar sodium channels are held open by cyclic GMP, which depolarises the cell
- The photopigment is made of opsin which is a protein. It also contains a molecule of retinal (the light sensitive region.) It has a carbon ring and tail. It is in the cis configuration so it is more stable.
- When light hits the photopigment a bond in the retinal will rupture and form the more stable trans configuration. It will activate a G-protein which activate enzymes that destroy cyclic GMP, so levels fall, so the sodium channels close.
- The G-proteins are only active briefly, so the retinal is activated in order to stop this process, so you can see fast moving events.
