Monitoring visual function Flashcards
what is the main structure responsible for reflecting light rays onto the retina
cornea
what is the blind spot
point where optic nerve leaves the eyeball so contains no photoreceptors
what is accommodation
the change in the shape of the lens to focus objects from a particular distance
how does the lens focus on a nearby object
Ciliary muscles contract
Suspensory ligaments slacken
lens becomes more spherical
refracts light more
how does the lens focus on a distant object
ciliary muscles relax
suspensory ligaments pulled taut
lens becomes less spherical
refracts light less
myopia. Possible causes? lens?
lens too thick. Use concave lens
hyperopia. possible causes? lens?
lens too thin. Use convex lens
why are rod and cone cells in contact with pigmented epithelium
it will absorb any light that passes through rod and cone cells so that it is not reflected back into the eye
similarities between rod and cone cells
-both photoreceptors
-both detect and respond to stimulus (receptors)
-Transducers
-both contains opsins
-Outer segment (stacks of membranes), inner segment (mitochondria), connecting cilium, synaptic bulb
info about rod cells
Night vision
High sensitivity
Rhodopsin (opsin + retinal)
Low visual acuity (many rod cels converge into one bipolar cell)
Not in fovea
info about cone cells
Colour vision
Low sensitivity
3 types of cell: each sensitive to a different wavelength
3 different types of opsin called iodopsin
High visual acuity (1 cone cells only goes to 1/2 bipolar cell)
In fovea
where is the highest concentration of cone cells
centre of fovea
what happens in the retina when no light is present
Na/K pump transports Na out and K in
open Na channels allow Na in
open K channels allow K out
This prevents potential difference from becoming greater than -40
rod cells release small amounts of glutamate
it is an inhibitory neurotransmitter
prevents bipolar cells from getting depolarised
so no action potential cases to ganglion cell. no electrical impulse sent along optic nerve
what happens when light hits the retina
Rhodopsin absorbs light
Causes kinked 11-cis-retinal to be converted to straight all-trans-retinal
Retinal no longer fits opsin binding site
Causes Na channels to close
Rod cell become hyperpolarised
No Glutamate is released
Bipolar cell becomes depolarised
so action potential is generated in ganglion cell
impulse sent along optic nerve
dark adaptation
unstable rhodopsin broken down into all-trans-retinal and opsin
all-trans-retinal is converted back to 11-cis-retinal
combined with opsin and rhodopsin is reformed
how cone cells respond to light
at high light intensity, iodopsin breaks
causes cone cell to become hyper polarised
what is visual acuity
the resolution of an image that is perceived by the brain
outline the role of the autonomic NS on pupil action
sympathetic: radial –> open pupil
parasympathetic: circular –> closed pupil
light intensity detected by retina –> optic nerve –> brain
too much light –> reflex action –> impulses sent to iris
circular muscles contract/radial muscles relax –> pupil constricts
too little light –> reflex action –> impulses sent to iris
radial muscles contract/circular relaxes –> pupil dilates
What parts of the eye refract light?
-cornea
-aqueous humour
-lens
-vitreous humour
Sclera
-Outer layer (very tough with collagen fibres)
-Protects+maintains shape of eyeball
Conjunctiva
Thin layer of protective cells which covers cornea
Lachrymal gland
Secretes tears (contain lysosomes) to lubricate conjunctiva + kill pathogens
Cornea
-Continuous with sclera
-Main refractor
Vitreous humour
-Maintains shape of eye by exerting outward pressure on sclera
-Supplies oxygen to cornea + lens
-INSIDE
