W4 Physiology of Vision (part done) Flashcards
a particle of electromagnetic radiation is called what?
a photon
do shorter or longer wavelengths of photons contain more energy?
shorter
vision is the perception of light, what is the visible spectrum?
400-700nm (based on human vision)
the vertebrate eye has a lens system, what does this aid?
focus light from objects in the environment onto the retina (where the sensory cells are located) and transmits information to the brain where the image is interpreted
what is visual acuity?
a measure of the ability of the eye to distinguish shapes and details of an object at a given distance
what are the ciliary bodies?
thickened anterior parts of the choroid, contain circular and longitudinal muscle fibers that produce aqueous humour
what is the iris?
it is pigmented and opaque and contains constrictors of the pupil (circular) and dilators of the pupil (radial)
what is vitreous humour?
a gelatinous substance between the lens and retina
what is aqueous humour?
a clear liquid that nourishes the cornea and lens
what is the filtration angle (schlemm’s canal)?
at the junction between the iris and cornea, which drains aqueous humour
what is the sclera?
part of the globe wall - the outer layer of tough connective tissue which merges with the cornea
what is the cornea?
the transparaent layer of the globe wall at the fron t that is for physical protection, refraction of light and is highly sensitive
what is the choroid?
the vascularised middle layer of the globe wall
what is the retina?
the innermost layer of the globe wall containing sensory cells and neurones
light rays refract when passing from one medium to another due to what?
difference in density
parallel light rays striking a biconvex lens are refracted to a point behind the lens called what?
the principle focus
what is refractive index?
the ratio between the speed of light in a vacuum and in the material
what is principle focal distance?
the distance between the lens and principle focus
what lenses diverge light and what lenses converge light?
biconcave = diverge light
biconvex = converge light
what is the unit of refractive power of a lens measured in meters?
dioptres (a dioptre is the reciprocal of the principle focal distance)
when is the distance between the lens and focal point the smallest?
when the light source is so far away that the light rays are traveling parallel to the lens
the distance between the lens and the focal point decreases with increasing or decreasing curvature (convexity) of the lens?
increasing
what is accommodation?
the process by which the curvature of the lens is increased in order to focus on a near object
when looking at a near object are the ciliary muscles relaxed or contracted?
they contract (distance between the edges of the ciliary bodies decrease and the lens ligaments relax)
at rest objects objects closer than how many meters appear blurred?
6m
the elastic lens is attached to the circular ciliary muscles by what?
the zonulas which is made of inelastic fibres
when the ciliary muscles are relaxed what does the zonulas do?
zonulas pulls tight and keeps the lens flattened for distant vision
when the ciliary muscles contract what happens to the zonulas?
the tension of the zonulas releases and the elastic lens returns to a more rounded shape for near vision
what does the iris control?
the quantity of light entering the eye (smooth muscle in mammals and striated in birds and reptiles)
what fibers dilate the pupil?
radial fibers
what fibers constrict the pupil?
circular fibers
some carnivores have vertical slit pupils, what does this allow for?
greater light control and enhances distance judgement in brighter light
many herbivores have horizontal rectangular pupils, why is this?
shields eyes from high sunlight whilst maintaining panoramic vision to spot predators (eye rotates as head drops to keep pupil horizontal)
what are the two types of ocular humours?
aqueous and vitreous
where is aqueous humour produced and where does it drain into?
produced by the cells in ciliary body and drains into the venous plexus at the filtration angle (production and drainage must be balanced)
is vitreous humour continuously replaced?
no
vitreous humour is a gel-like mass of mostly water with a stroma of what?
transparent fibers
what humours function is to retain globe shape?
vitreous
the retina contains two sensory cell types, what are they?
rods - extremely sensitive (possible to see in low light (scotopic vison))
cones - convey colour vision
which of the three layers of the retina consist of the rods and cones?
the outermost, closest to the choroid
the innermost layer of the retina is nearest to the vitreous humour contains what cells (axons from these cells form the optic nerve)?
ganglion cells
the middle layer of the retina contains several what cell types?
interneuron:
- bipolar = connect sensory and ganglion cells
- horizontal = connects groups of sensory cells
- amacrine = forms connections between ganglion cells
the layers of the retina are backwards does light pass through layers of sensory cells or neurons first?
layers of neurons
what is the optic disc?
the point where the optic nerve leaves the eye and blood vessels enter, it is located 3mm medial to and slightly above the posterior pole of the globe
what causes a blind spot? why?
the optic disc, it doesn’t contain any visual receptors
what is the macula lutea?
a yellowish area near the posterior pole, it marks the location of the fovea centralis
what is the fovea centralis?
a thin, rod-free, cone-packed area, each cone synapses with a single bipolar cell, which in turn synapses with a single ganglion cell, no blood vessels, MAXIMUM VISUAL ACUITY
what vessels supply the bipolar and ganglion cells?
retinal vessels
what does the choroid plexus supply?
the rods and cones
where would you find the retinal pigmented epithelium?
cell layer outer to retina and attached to choroid overlying retinal vessels
