BISC106 Vision

cones

___ (rods or cones) synapse with a *bipolar cell* in the *outer synaptic layer* at a ONE TO ONE RATIO

rods

___ are usually nonfunctional in daylight because *rhodopsin is split faster than it can be reformed*

melanin

___ in *choroid* absorbs stray light rays which prevents reflection and scattering of light within eyes, making the image cast on the *retina* by the *cornea* and *lens* sharp and clear

astigmatism

cornea or lens has an irregular curvature

zonular fibers

elastic protein fibers that construct the lens; attach the *lens* to the *ciliary muscle* and hold the lens in position

retina

ensures the correct amount of light makes proper "exposure"

emmetropic

normal eye

16

normal intraocular pressure ~___mmHg and is maintained by a balance between production and drainage of *aqueous humor*

photoreceptor

retinal neurons; specialized cells in the photo pigment layer that begin the process by which light rays are ultimately converted to nerve impulses; *rods* and *cones*

periphery of retina

rods are absent from the *fovea centralism* and *macula lutea* but increase in numbers towards the ___ ___ ___

pigmented

the ___ layer of the *retina* is a sheet of melanin-containing epithelial cells located between the *choroid* and the *neural* part of the retina

convergence

the ___ of many rods onto a single *bipolar* cell INCREASES light sensitivity of rod vision but slightly blurs image percieved

increases

the ability to refract ___ (increases or decreases) as curvature of the lens becomes greater (more convex)

cornea

transparent fibrous coat that covers the colored *iris*; curved, so it helps focus light rays onto the *retina*; in the *fibrous tunic* or outer coat of the eyeball

convergence

automatic movement of 2 eyes toward midline which is caused by coordinated action of extrinsic eye muscles; nearer objects= greater ___ needed to maintain *binocular vision*

fovea centralis

cones are most densely concentrated in the ___: a small depression in the center of the *macula lutea* or yellow spot in the exact center of *retina*; area of highest visual acuity or resolution bc of its high concentration of cones

aqueous humor

helps maintain the shape of the eye and nourishes the *lens* and *cornea*-- neither of which has blood vessels

constriction

3rd process of image formation; ___ or narrowing of the *pupil*

sclera

"white" of the eye; coat of dose connective tissue that covers all of the entire eyeball except the *cornea*; gives shape to the eyeball, makes it more rigid and protects its inner parts; in the *fibrous tunic* or outer coat of the eyeball

refraction

1st process of image formation; bending of light by the *lens* and *cornea*

lens

2nd process of image formation; after *refraction* is the change in shape of the ___

anterior cavity

a portion of the interior of the eye; lies ANTERIOR to the *lens* and is filled with *aqueous humor* which is secreted into this by the blood capillaries of the *ciliary processes*

cornea

about 75% of *refraction* occurs at the ___ then the *lens* further refracts the light rays so they come into exact focus on the *retina*

conjunctiva

an epithelial layer covers the *sclera* but not *cornea* and lines the inner surface of eyelids

ciliary body

at the front of the eye; consists of *ciliary processes* and the *ciliary muscle*; found in the *vascular tunic* or middle layer of the eye

vitreous chamber

behind the *lens*; the second and larger cavity of the interior of the eye; contains a clear jellylike substance called the *vitreous body* which forms during embryonic life and is not replaced thereafter; helps prevent the eyeball from collapsing and holds the *retina* flush against the *choroid*

rods

between 6 and 600 ___ (rods or cones) synapse with a single *bipolar cell* in the *outer synaptic layer*

scleral venous sinus

blood capillaries of the *ciliary processes* secrete *aqueous humor* into the *anterior cavity* of the interior of the eyeball; it then drains into the ___ ___ ___ : an opening where the *SCLERA* and the *CORNEA* meet; and then it re-enters the blood

binocular (vision)

both eyes focus only on one set of objects; allows perception of depth

constriction

bright light causes a *parasympathetic* ANS response; contract CIRCULAR smooth muscles of the *iris* and DECREASE the size of the *pupil*

iris

colored circle/colored part of the eyeball; included both CIRCULAR and RADIAL smooth muscle fibers; the hole in the center of this is the *pupil*

circular

constriction or decrease in the size of the *pupil* is accomplished by contraction of ___ smooth muscles of the *iris*

ciliary muscle

contained in the *ciliary body*; a smooth muscle that alters the shape of the *lens* for viewing objects up close or at a distance

ciliary processes

contained in the *ciliary body*; folds on the inner surface of ciliary body whose capillaries secrete a fluid called aqueous humor

radial

dilation or increase in size of the *pupil* is accomplished through contraction of ___ smooth muscles of the *iris*

dilation

dim light causes a *sympathetic* ANS response; contract RADIAL smooth muscles of the *iris* and INCREASE the size of the *pupil*

hyperopia

farsightedness

divergent

light rays from objects closer than 6 meters are ___ (parallel or divergent)

parallel

light rays reflected from objects that are far away are ___ (parallel or divergent)

vascular (tunic)

middle layer of eyeball; composed of *choroid*, *ciliary body* and *iris*

mypoia

nearsightedness

fibrous (tunic)

outer coat of the eyeball; consists of the *cornea* (anterior) and *sclera* (posterior)

rhodopsin

photopigment in *rods*; composed of protein called *opsin* and a derivative of vitamin A: *retinal*; any amount of light in a darkened room causes some ___ molecules to split into opsin and retinal and initiate series of chemical changes in rods

intraocular (pressure)

produced mainly by the *aqueous humor* with smaller contribution from the *vitreous body*; this pressure helps maintain the shape of the eyeball and keeps the *retina* smoothly pressed against the *choroid* so the retina is well nourished and forms clear images

neural

the _-- layer of the *retina* is a multi-layered outgrowth of brain; three distinct layers of retinal neurons: *photoreceptor cell layer*, *bipolar cell layer*, and *ganglion cell layer* which are separated by 2 zones--> the outer and inner *synaptic* layers where synaptic contacts are made

pupil

the hole in the center of the *iris* through which light enters the eyeball

accommodation

the increase in curvature of *lens* for near vision

lens

the interior of the eyeball is divided by the ___ into two cavities: *anterior cavity* and the *vitreous chamber*

lens

the smooth muscle of the *iris* regulates the amount of light that passes through the ___

choroid

thin membrane that lines most of the internal surface of the *sclera*; contains many blood vessels that help nourish the *retina*; contains melanocytes which produce pigment *melanin* which cause this layer to appear dark brown; found in the *vascular tunic* or middle layer of eyeball

retina

third and inner coat of eyeball; lines the posterior three quarters of eyeball; beginning of visual pathway; has two layers: *neural layer* and *pigmented layer*

lens

transparent structure focuses light rays on the retina; constructed of many layers of elastic protein fibers: *zonular fibers* which attach this to the *ciliary muscle* and hold this in position

rods

type of photoreceptor; allow us to see shades of gray in dim light; ~120 mil

cones

type of photoreceptor; stimulated by brighter light; give rise to highly acute color vision; three types: blue, green, red; color vision results from the stimulation of various combos of these 3 types

photopigment

visual pigment; substance that absorbs light and undergoes a change in structure

rods

what is absent from the *fovea centralis* and the *macula lutea* but increase in number towards the *periphery of the retina*

aqueous humor

what is the fluid secreted by the capillaries of the ciliary processes

rhodopsin

when light is dim, *opsin* and *retinal* recombine into ___

lens

when light rays are *divergent* (when objects are up close) the rays must be refracted more if they are to be focused on the *retina*-- this additional refraction is accomplished by changes in the shape of the ___ [accomodation]

refraction

when light rays traveling through a transparent substance (air) pass into a second transparent substance with a different density (water) they *bend* at the junction of the 2 substances

increases

when viewing close objects and the *ciliary muscle* CONTRACTS which pulls the *ciliary process* and *choroid* forward to the *lens* releasing tension and allowing to be more round, there is an ___ (increase or decrease) in power and convergence

contracts

when viewing close objects, the *ciliary muscle* ___ (contracts or relaxes) which pulls the *ciliary process* and *choroid* forward to the *lens* releasing tension and allowing rounder

zonular fibers

when viewing distant objects the *ciliary muscle* is RELAXED and the *lens* is fairly flat because it is stretched in all directions by taut ___

relaxed

when viewing distant objects, the *ciliary muscle* of the eye is ____ (contracted or relaxed)

vitreous body

which of the two liquids in the two cavities of the interior of the eye is formed during embryonic life and not replaced thereafter (*aqueous humor* [anterior cavity] or *vitreous body* [vitreous chamber])

aqueous humor

which of the two liquids in the two cavities of the interior of the eye is replaced approx. every 90 minutes (*aqueous humor* [anterior cavity] or *vitreous body* [vitreous chamber])

cone

whose photopigments reform more quickly: rods or cones

macula lutea

yellow spot int he exact center of the *retina*; *fovea centralis* is a small depression in the center of this-> the area of highest visual acuity or resolution bc of the high concentration of cones