L07: Vision Flashcards
What is the order of structures that light passes through in the eye
Cornea Iris Lens Retina Fovea
What is the fovea
Specialised part of the retina
What role does the fovea have in the eye
Focus the image in detail
What is the space behind the lens filled with
Vitreous humor
What is the space in form of the lends filled with
Aqueous humus
How is the lens attached to the outer edges of the eyeball
Via zonule fibres
What is the zonule fibres attached to
Ciliary muscle
What happens to the shape of the lens when the ciliary muscles contract
Flattens
Where is the aqueous humor located
In front of the lens
What is the role of the aqueous humor
Provide nutrients for the cells of the cornea
Why does the cornea need nutrients from the aqueous humor
It doesn’t not have a blood supply hence the reason it is transparent
What is the chamber behind the iris known as
Posterior chamber
What is the chamber called that is in front of the iris but behind cornea
Anterior chamber
When aqueous humor is produced which chamber does it get secreted into
Posterior chamber
How is the aqueous humor flow into the anterior chamber
It gets reabsorbed from the posterior chamber cells
Therefore overall where is aqueous humor located
Posterior and anterior chamber that are part fo a compartment
What happens when the pressure inside the compartment that contains aqueous humour increases
Glaucoma
What can happen if glaucoma is left untreated
Increased pressure can block the eye and cut off blood flow to the retina
What are the 2 causes of glaucoma
Angel closure
Open angle
What is angle closure
When the iris adheres to the cornea so you block the sire where aqueous humor is reabsorbed into the anterior chamber
What is open angle
Where angle of reabsorption is not blocked and it is caused by sclerosis of the veins in the angle which slows the reabsorption
What is the treatment of glaucoma
Surgery
Beta blockers
Prostaglandins blockers
What is the role of beta blockers for treatment
Reduces the production of aqueous humor
What is the role of prostaglandin analogues
Increase blood drainage by vasodilation the vessels
What are the cell types found in the retina
Photoreceptors Bipolar Horizontal Amacrine Ganglion cells
Do photoreceptors or bipolar cell generate AP
No
Which cells in the retina generate AP
Ganglion cells
What is the role of horizontal and amacrine cells
Modulate transmission of info and enable lateral transmission for indirect pathway
Where does the ganglion cell axons join
At the optic disc to form optic nerve
What does the optic nerve do
Leave the eye and go to the brain
What is the main role of photo receptors
Detect light
What are the 2 types of photoreceptors
Rods
Cones
How many segments to photoreceptors have in their structure
Outer segment
Inner segment
Synaptic terminals
What does the outer segment of photoreceptors contain
Photopigments
What does the inner segment of the photoreceptors contain
Nucleus
What does the synaptic terminals of photoreceptors synapse with
Bipolar cells
In terms of the photoreceptors structure which segment differs between rods and cones
Outer segment with photopigments
How many photopigments does rods have
1 type of photopigments
What is the one type of photopigments in rods known as
Rhodopsin
Where are rhodopsin located
In the intracellular disk of outer segments
What is the density of rhodopsin like in the outer segment of rods
High
If there are high density of rhodopsin what is the sensitivity to light like
High sensitivity
How many photopigment types does cones haves
3 types
What are the types of photpigments in cones based on
Colours of light that they respond to
What are the 3 colours of light that photopigments of cones detect
Red light
Green light
Blue light
Where in the outer segment are photopigments of cones found
In folding surface membrane
What is the density of photopigments in cones like
Low density
If there are low density of photopigments in cones what does it mean to generate an electrical signal
We need a higher light level due to lower sensitivity to light
What time of the day of photopigments in cones involved
Seeing colour during day time and not at night
What is the blind sport
The point where the optic nerve leaved the eye at the optic disc
Where are the the most proportion of cones located
The closer you get to the fovea
Why does the peripheral retina have high sensitivity to light
Has lots of rods
Many Rods are connect via bipolar cells to 1 ganglion cells
What does it mean if rods are connected via bipolar cell to 1 ganglion cells
It the light is low and a signal is small in the RODS because it is connected to 1 ganglion cells the sum total of signal from the rods will be enough to produce a signal
What is the macula
Central part of the retina
What is the fovea
Where you have cones
What are the cones connected to in the Forvea
1 cone is connected to 1 ganglion cell
What does it mean if 1 cone connects to 1 ganglion cell
There is high detail because 1 ganglion is relieve info from 1 cone
What time of the day is the activity of rods more
In the dark
What is the activity in the dark for rods like
1) rhodopsin is inactive in the dark because there is no light
2) on the rod cell membrane there are cyclic GMP- gated cation channels
3) in the dark when there is a lot of cyclic GMP, it binds to cyclic GMP gates cation channels that open
4) this causes sodium influx when the cyclic GMP gated cation channel open
5) sodium influx causes depolarisation = dark current
6) membrane potential becomes -30mv
7) at -30mv the photoreceptors that have the synaptic terminal connecting with bipolar cells causes the release of glutamate at the synapse
8) bipolar cells receive a synaptic signal in the absence of a signal in the dark
What happens to the rods when there is light
1) retinal (component of rhodopsin) absorbs light and undergoes changes in structure
2) this activates the opsin (GCPRs -component of rhodopsin)
3) opsin acitvates G protein when GTP binds to it
4) G protein acitvates PDE
5) PDE breaks cyclic CGMP
6) breakage of cyclic CGMP causes a closure of cyclic CGMP channels
7) this stops sodium influx
8) resting hyperpolarisation
9) hyperpolaristion causes a decrease in release of glutamate at the synapse with bipolar cells
What are the 2 pathway a signal is sent form the photoreceptors to the ganglion cell
Direct pathway
Indirect pathway
What cells the direct pathway involve
Photoreceptors
Bipolar cells
Ganglions cells
What happens to the photoreceptors in the direct pathway in light
Hyperpolarise (rods and cones)
What does electrical response that you get depend on
On bipolar cells and ganglion cells
Off bipolar cells and ganglion cells
What happens to on bipolar and ganglion cells in repsonse to light
Depolarise
What happens to the off bipolar cells and ganglion cells in repsonse to light
Hyperpolarise
For on bipolar cells and ganglion cells what happens to the glutamate released by photoreceptors in the light
Decrease to cause depolarisation in on cells
What happens to the glutamate from photoreceptors to off bipolar and ganglions cells in the light
Glutamate decreases to cause hyperpolarization
Why do we get a decrease of glutamate from photoreceptors in light
Remember opsin and retinal are activated that causes PDE to break cyclic GMP so sodium influx decreases and hyperpolarization occurs to cause decrease in glumate in light
What causes glutamate to cause depolarisation of hyperpolarization in on/off cells
Differnt glumate receptors on off/on cells
What are the 2 parts of receptive filed
Central part
Surround part
What cell connections does the central part involve
Direct connection with photoreceptors
What connection does the surround part involve
Indirect connections with horizontal or amacrine cells
What pathway is the central part involved in
Direct pathway
What pathway is the surround part involved in
Indirect pathway
When light hits the surround part how does signals reach the bipolar or ganglion cells
Via the indirect pathway that involves horizontal or amacrine cells
What is the impact of the indirect pathway
To produce the opposite electrical response in bipolar and ganglion cells
In the indirect pathway if the bipolar cells is on what is the overall response
Hyperpolarization of on bipolar cells becuase the indirect pathway causes the opposite response
Which part of the receptive filed dominates
The central part i.e the direct pathway
Where does the optic nerve join at to becomes the optic tract
Optic chiasm
What side of the hemifield does the right optic tract take info from
Left hemifield
What side of the hemifield does the left optic tract take the infor from
Right hemifield
If there is a transaction fo the left optic tract what side of the hemifield is lost completely
Right hemifield
If there is a transection of the optic chiasm which side of the hemifield is lost completely
Left and right sides of hemifield
