Ch. 11 Vision

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sclera: a tough conn. tissue
makes up the "white" of the eye
cornea: front of eye
a transparent structure that allow light to enter the eye.
choroid: middle layer of the eye
a highly pigmented layer of tissue beneath the sclera.

absorbs light that reaches the back of the eye so that it is not reflected, which cause distortion of the visual image.
ciliary body: contain ciliary muscles attached to the lens by strands of conn. tissue called zonular fibers.
zonular fibers: attached to the lens by strands of conn. tissue called ________ ______.
lens: focuses the light on the retina where the visual info is transduced.
ciliary muscles: change the shape of the lens to focus light waves.
pupil: a hole in the center of the iris that allows light to enter the post. part of the eye
it is NOT a structure
iris: regulates the diameter of the pupil, thereby regulating the amount of light that reaches the back of the eye.
middle layer: The ________ _______ of the eye consists of the choroid, ciliary body, and iris.
retina: 1. an inner layer containing neurons called ganglion cells
2. a middle layer containing neurons called bipolar cells
3. an outer layer containing rods and cones.

amacrine cells & horizontal cells(communication btwn cells in the retina)
Photoreceptors: cells that detect light waves
two types, rods and cones
Phototransduction: the conversion of light energy to electrical energy.
fovea: The ______ contains cones only; the ratio of rods to cones increases w/ distance from the ______, until at the periphery of the retina only rods are present.
Optic disk: the portion of the retina where the optic nerve and blood vessels supplying the eye pass through the retina.
blind spot: there are no photoreceptors in the optic disk
a reion where light striking the retina cannot be transduced into neural impulses and cannot be perceived.
ant. cavity aqueous humor: In front of the lens and ciliary body is the called the ________ _______ containing a clear, watery fluid called __________ ______, which supplies nutrients to the cornea and lens.
vitreous chamber vitreous humor: Behind the lens and ciliary body is the __________ ________ containing a firmer, jellylike material called _________ ______, which maintains the spherical structure of the eye.
electromagnetic waves: Light is a form of energy. Light exists as ________________ ______.
reflection: a phenomenon in which light waves strike and bounce off a surface.

important in vision because much of the light we perceive has reflected off the objects we are observing.
refraction: the bending of light waves as they pass through transparent materials of different densities.

its path from objects to the photoreceptors in the retina, light must pass through several different materials, including air, cornea, the lens, and the vitreous and aqueous humor.
focal point: the convex lens causes the light waves to converge at a single point called the ______ ______.
focal length: The distance from the long axis of the convex lens to the focal point is called the _______ _______.
Concave: surfaces cause a divergance of light waves
Convex: surfaces cause convergence of light waves to a focal point.
visual field: what we are looking at
must converge at a single point on the retina.
rounder: When viewing close objects, the lens becomes ________, increasing its refractive power to focus the image on the retina.
parallel: When viewing something far away, the light waves enter the eye almost ________ to each other, so little refractive power of a rounder lens is needed to focus the light on the retina.
Accomodation: reflex adjustments of the eye to view near objects

including rounding of the lens, constriction of the pupil, and post. movement of the lens.
accommadation: under control of the parasympathetic nervous system, which triggers contraction of the ciliary muscle for near vision.
myopia: _________ can be corrected by using a concave lens to produce divergence of light waves before they enter the eye.
hyperopia: _________ can be corrected by using a convex lens to produce convergence of light waves that supplements the convergence produced in the eye.
emmetropia: normal vision
a person can see both distant and close up objects clearly becuase the eye can focus light from far sources without accommadation, and from near sources w/ accomadation.
astigmatism: irregularities on the surface of the cornea or lens cause erratic bending of light waves.
presbyopia: a hardening of the lens that occurs w/ aging; as the lens hardens, its loss of elasticity decreases its ability to become spherical, making accommadation for near vision more difficult.
cataract: an age-related discoloration of the lens that decreases its transparency.
glaucoma: increase in the volume of aqueous humor raises pressure in the ant. carity of the eyeball, which can distort the shape of the cornea and shift the position of the lens.
circular muscle (constrictor muscle): form concentric rings around the pupil
when they contract, the diameter of the pupil decreases.
pupillary contriction: The contraction of the circular muscles cause __________ __________.
radial muscles: dialator muscle
are arranged like spokes in a wheel
When they contract, the diameter of the pupil increases
leads to pupillary dialation.
parasympathetic neurons: ___________ _______ innervate the circular muscles, which leads to pupillary constriction.
sympathetic neurons: ____________ ________ innervate the radial muscles, which leads to pupillary dialation.
Rods: provide the ability to see in black and white during relatively low light conditions, such as the light provided by the moon at night.
Cones: provide us with color vision, but they are active only relatively bright light, such as the sunlight during the day.
Macula lutea: a depression in the center of the retina that surrounds the fovea.
outer and inner segments: The two types of photoreceptors is the same; each consists of 2 major portions referred to as _______ and ________ _________.
outer segment: contains invaginations w/membranous disks that contain the molecules that absorb light waves, giving the photoreceptors the ability to respond to light.
inner segment: contains the cell nucleus and various organelles and ends at the receptor's synaptic terminal, which is anaglogus to an ordinary neuron's axon terminal and is where a chemical messenger is stored in synaptic vesicles.
photopigment: absorption of light is the first step in phototransduction, and the molecule in the photoreceptors that absorbs light
retinal opsin: The _______ portion is the same in all photopigments, but the kind of ______ present determines which light wavelengths are absorbed by a given photopigment by altering the electromagnetic energies to which the retinal is sensitive.
high: Do rods have a high sensitivity or a low sensitivity to light?
low: Do cones have a high sensitivity or a low sensitivity to light?
at the periphery of retina: Where is the site of greatest concentration in the rods?
in the fovea: Where is the site of greatest concentration in the cones?
rods rhodopsin: When exposed to bright light, the ____ become "bleached"; that is, most of the ___________ has absorbed light, and the opsin in in its active form. No more light can be absorbed until the ___________ has been returned to original (bleached) state.
unbleached: ____________ rods are extremely sensitive to light.

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