Chapter 15: special senses vision

sclera

- white of eye

- F: muscle attachment, maintains shape of eyeball

cornea

- transparent layer, bulges avascular

-F: refracts light

Iris

- pigmented

-F: contains muscle that control amount of light enter eye by changing pupil diameter

Ciliary body

- contains ciliary muscle and process

-F: change shape of lens

Choroid

- dark membrane with blood vessels

- F: nourishes eye, absorbs excess light

pupil

- opening of iris

- F: allows light to enter eye

superficial layer of retina

- pigmented

-F: absorbs light (reduces scattering)

deep layer of retina

- contains photoreceptors

-F: detects light

lens

-F: refracts light rays to focus them onto retina

vitreous body( Humor)

- gelatinous material fills posterior cavity

- F: maintains shape of eye, does some refracting of light

pupillary constriction

- less light in

- pupillary sphincter muscle contracts

- occurs in parasympathetic system

pupillary dilation

- more light in

- pupillary dilator muscle contracts

- occurs in sympathetic system

rods

F: respond to low light, night vision, peripheral vision

cones

f: function best in bright light, perceive color

macula lutea

area if high photoreceptor density

fovea centrails

- center of macula lutea, has many cones

- F: produces highest visual acuity

optic disc

region with no photoreceptors because the optic nerve exits the eye here

blind spot

no image seen when light enters your eye and lands on optic disc

phototrandsduction

changing light into electrical signal (AP)

photopigment

- chemical that absorbs light

rods- one type

cones- 3 type: blue, green, red

what is the structure of the retinal layers

1. rods/cones

2. bipolar cells- synapse with rods/cones and ganglion cells

3. retinal ganglion cells- axons gather to for optic nerve

Step 1: sensation of light

1: light breaks down photopigment in rods/cones

Step 2: sensation of light

2. alters membrane potential ( rod or cone) and NT released/decreased

step 3: sensation of light

3. alters membrane potential of bipolar cell and NT released/decreased

step 4: sensation of light

4. bipolar cell influence ganglion cell, may generate AP

step 5: sensation of light

5. ganglion cell Ap tranmits to brain via optic nerve ( axons of ganglions)

step 6: sensation of light

AP to brain and cortex

refraction

bending of light rays

focal point

point where rays converge

focal length

distance from lens or surface to focal point

convex surface

light rays converge and focus on the focal point

concave surface

light rays diverge and do not focus

accommodation

- adjust lens thickness

- changes refraction

Hyperopia

- farsightedness

- focal point behind retina

-eyeball to short or cornea to flat

-correction: add convex lens

Myopia

-nearsightedness

- eyeball to long or cornea curves to much

-focal point in front of retina

- correction : add concave lens

emmetropia

-20/20 vision

-lights rays converge right on retina

Presbyopia

- lens stiffens, doesn't bulge poor accommodation

- near object focal point behind retina

Astigmatism

-irregular curvature of the cornea or lens

- light rays unevenly refracted, blurry vision