W4: Physiology Of The Eye Flashcards
Functions of the eye
Produce clean crisp images
Self cleaning through tears and blinking
Retina converts light into electrical signal
What is contained in the anterior segment of the eye?
Outer cornea, portion of white sclera, the iris, pupil, lens, ciliary bodies, zonule fibres.
What is the fluid in the anterior chamber?
Aqueous humour, AqH
Describe aqueous humour
Nourishes the cornea. Produced in the ciliary body and flows through from posterior to anterior chamber. Removes waste and debris.
What is in the posterior segment of the eye?
Vitreous body - gel-like substance
Retina
Choroid - heavily innervated by blood vessels
Outer tough collagenous sclera
What is the route of light through the retina?
Light passes all the way through the retina until it hits the photoreceptors at the back of the eye. Signal is transduced down to the retinal ganglion cells. This causes a hyperpolarisation of bipolar cells so we get signals in from photoreceptors to bipolar cells. They then converge on retinal ganglion cells (RGCs). Axons from these cells make up the optic nerve.
How do retinal cells connect?
Via chemical synapses
What cells generate action potentials in the retina?
Ganglion cells - direct pathway
What do horizontal and amacrine cells do?
They modulate transmission of information and enable lateral transmission. Information flowing through this region is the indirect pathway.
Where do signals go from the direct and indirect pathways?
Signals go through the optic disc = a portion of the back of the retina where all of the axons go through into the brain
What are photoreceptors?
Light sensitive cells in the retina. Rods or cones.
What are rods and cones?
Membranous disks which contain light sensitive photopigments - leads to the alteration in the membrane potential in the photoreceptor,
Which has more membranous disks?
Rods have more membranous disks than cones.
Structure of rods
Inside another membrane
Structure of cones
Made up of folds
What are the photopigment(s) in rods?
One photopigment = rhodopsin
What are the photopigment(s) in cones?
3 photopigments (opsins) - red, green and blue. Gives colour vision.
What are rods responsible for and how?
Since there are more discs which contain rhodopsin which is activated by light they are more sensitive to light than cones, so responsible for night vision.
What are cones responsible for and how?
Needs higher light levels in order to function because of the less discs. Hard to see colour in the dark. Gives night vision.
What is the blind spot?
Where the optic nerve leaves the eye. Has no rods or cones.
Where are the most cones found?
There are an increasing proportion of cones closer to the fovea (all cones)
Describe the peripheral retina
Has a high sensitivity to light
Has mostly rods so lots of photopigment
Many rods connect (via bipolar cells) to 1 ganglion cell, meaning there is a high sensitivity but low visual acuity (peripheral vision is more blurry)
Describe the macula
Central retina
Has more cones
Contains the fovea
What is the fovea?
A pit inside the macula with only and all cone cells.