The Visual System Flashcards
cornea
the transparent covering of the eye that lets light in. Not only does it protect the eye but also focus the light on the retina at the back of the eye
pupil
black area, controlled by circular sphincter muscles (iris)
When the environment is dark, the pupil enlarges to let more light in; when the environment is bright, the pupil becomes smaller to let less light in
iris
circular, colored area of the eye. It controls the amount of light that enters the eye by making the pupil large or small
Contains 2 sets of smooth muscles:
- Pupillary dilator muscle
- Pupillary constrictor muscle
Responsible for dilating or constricting the pupil
sclera
the white portion of the eye. Tougher layer of the eye
conjunctiva
Thin, clear layer of mucous membrane that covers the front of the eye (except cornea) and lines the inside of the eyelids
Secretes mucus to lubricate the eye keeping bacteria and foreign material from getting behind the eye
lacrimal glands
produce watery portions of tear. Located at the top outer edge of each eye
lacrimal glands
produce watery portions of tear. Located at the top outer edge of each eye
what cells does the retina contain?
photoreceptors
photoreceptors are…
Each photoreceptor is attached to a nerve fiber. All nerve fibers are bundled together to form the optic nerve
Convert image into electrical impulses, which are carried to the brain by the optic nerve
what is the most sensitive area in the retina?
“the area centralis”
layers of the posterior eyeball
- Outer: sclera
- Middle: choroid
- Inner: retina
Macula lutea
a dark area, situated at the posterior pole of the eye, also called as a “yellow spot” or “area centralis”
*Primary function: photopic vision
Fovea centrali
a central depression in the macula thickness. MOST sensitive part of the retina
what are the 2 main photoreceptors within the retina?
- rods: dim light, peripheral vision
- cones: bright light, high acuity color vision
Visual of retina
highest concentration of cones is in the fovea or fovea centralis
cones
- responsible for fine detailed and color vision
- Clustered near the center of the retina, called the fovea
- There are 5 million cones in the average retina
rods
- Responsible for low light and peripheral vision
- They are present everywhere in the retina EXCEPT the fovea
- There are 125 million rods in the average retina
Do animals see one or more color (s)?
Dogs, cats, and most mammals only have 2 color receptors. They’re missing the one that detects the one that detects red. So, it’s true dogs don’t see many colors, but they are not colorblind! They only see shades of blue and yellow
*Birds have 4 kinds of cones
3 types of cones
- red
- blue
- green
Color Blindness
- based upon or defects in the red and green cone pigments
- Inheritance in males
- A genetic disorder
Trichromats
normal color vision
Dichromats
have 2 types of cones
*most animals are dichromats
Monochromats
have 1 type of cone system
why do females rarely get colorblindness?
colorblind chromosome is mostly “X” females are carriers of the color-blind gene. Male have “XY”, hence the likelihood for males to only get the color-blind gene
what are 5 major retinal cell types
- Photoreceptor cells (rod or cone)
- Bipolar cells (neuron)
- Horizontal cells
- Amacrine cells (interneuron), and
- Ganglion cells
Sequence of events involved in the phototransduction
- Activation by the affects Na+ channels, through transducing, a G protein that controls formation of cyclic GMP
- In the dark, there is a constant release of the neurotransmitter (glutamate). In the light, hyperpolarization causes a reduction in the release of glutamate
what molecule is extremely sensitive?
rhodopsin
Range of light sensitivity of rods and cones
- As long as the light is of low intensity, rods quickly regenerate rhodopsin, and the retina continues to respond to light stimuli
- High light intensity, rhodopsin is bleached quickly as rhodopsin can be produced = rods nonfunctional
- If this happens, cones take over
what cranial nerves control extrinsic eye muscles?
(III) oculomotor: medial rectus, superior rectus, inferior rectus, inferior oblique
(IV) trochlear: superior oblique
(VI) abducens: lateral rectus
Strabismus
“cross-eyed” is a condition where the eye rotates medially or laterally. Usually due to congenital weakness of eye muscles
is it the rectus or obliques that permit the eye to move up and down?
obliques
Accommodation
Curvature of the lens to bring other objects into focus
ciliary muscle
- Changing the shape of the lens is done
- is relaxed when the light rays from an emmetropic eye (normal vision) are brought into focus on the retina
what happens when ciliary muscles deteriorates?
with age, it results in presbyopia-loss of accommodation
Presbyopia
a farsightedness caused by loss of elasticity of the lens of the eyes
normal vision
the lens focuses the visual image on the retina
myopia
or near-sighted, short sighted. The lens focuses the distant images in front of the retina. Myopia corrected by a diverging lens
hyperopia
or far-sighted. Closer images are focused “behind” the retina. Hyperopia corrected by a converging lens
The aperture controlling the amount of light entering the eye is called:
Cornea
Lens
Pupil
Ciliary muscle
pupil
Changing the shape of the lens is done by the_____
Ciliary muscle
Iris muscle
Eyeball
Ciliary muscle
