eye section from notes

what adjusts the size of the pupil

the Iris

Circular muscles (sphinctor)

close the pupil with parasympathetic stimuli, turning and cutting on themselves

Radial Muscles

open the pupil with sympathetic stimuli, dialate pupil

what muscles work together in the iris to change the size of the pupil

circular muscles and radial muscles

how is the lens inside the eye

convex

convex lens

bends light inward to middle, helps focus

looks like an oval

______ objects need less bending of light

distant

how does eyes adjust focus

does not adjust pupil, instead changes curvature (retina) in lens, a little bit of the cornea

how much can the cornea move

can barely move, does the first bending for adjusting pupil but thats it

how much can the human eye move its lens

not very forward or backward, mainly changes curvature

visual accommodation

contracting muscles to see near objects

emmetropia

normal focal ability (20/20 vision)

myopia

near sighted, retina behind focal point

hyperopia

far sighted, shallow, lens trying to focus behind retina

can see distance but not up close

astigmatism

irregular lens surface or corneal surface

elasticity work well but not smooth

presbyopia

age related loss of accommodation

inability to accommodate, as get older have to move stuff farther away to focus and read

elastic lens

changes shape (curvature)

becomes rounder/thicker for near vision

becomes flatter for distance vision

ciliary muscle

controls the tension on the suspensory ligaments

contracts for near vision

relaxes for distance vision

controls shape of lens

suspensory ligaments

connect the lens to the ciliary body

hold the lens in place

change tension to help the lens change shape

how near vision works

ciliary muscle contracts

suspensory ligaments loosen

lens becomes rounder/thicker

eye focuses on nearby objects

how distance vision works

ciliary muscle relaxes

suspensory ligaments tighten

lens becomes flatter/thinner

eye focuses on distant objects

parasympathetic nervous system

stimulates ciliary muscle contraction= near vision

sympathetic nervous system

ciliary muscle relaxation= distance vision

how is the lens in ciliary body

elastic not plastic

can light hit anywhere in the eye

no, need to hit a certain point in order to be focussed

fixed part of the eye

the outer origin is the fixed point

origin insertion

insertion sits precisely at the outside margin of iris

what does the origin come into contact with

with the sclera, anchoring the muscular framework of the iris

insertion point

traces the distinct path of the insertion line extending down toward the inner pupillary boundary

which side of the lens is more flat

the front side is more flat, inside is more curved

how lens, siliary body, and suspensory ligaments are connected

the lens is in the middle, gets pulled by cable like suspensory ligaments attached to ciliary body

what is the ciliary body made of

smooth muscle

how does ciliary body work

smooth muscle contracts, relaxing the lens and leting the lens curve for near.

when relaxing muscle, it dialates to original size and flattens lens

when eye is relaxed

the suspensory ligaments gets pulled and tugs on the elastic lens, make a flatter lens and better for longer distances

eye when focused

has more curved lens from smooth muscles, causing the lens to be pulled less, curved for near sight because it can bend light more

fovea mainly made of

almost all cones

what if the light does not hit the retina

you will not see that light

what is mainly in the peripheral retina

almost all rods

structure of photoreceptors

possess an outer segment of folded membranes (stacks) embedded with photosensitive photopigment molecules

2 parts of photopigments

chromophore (retinal) and (opsin)

chromophore (retinal)

made from vitamin A (from beta-carotene)

protein in photopigments

opsin

is retinal the same for all rods/cones

retinal is the same but the light sensitivity is different.

RODS ARE LESS SENSITIVE

differences rest in different opsins in each of the different cones and the rods

what are rods sensitive to

dim light

what are cones sensitive to

colors

blue, green, red

choroid

a blood-vessel-rich layer that supplies nutrients and oxygen and absorbs excess light

pigmented epithelium

supports photoreceptors, absorbs stray light and helps maintain visual pigments

photoreceptors

rods and cones, detect light

bipolar cells

transfer signals from photoreceptors

ganglion cells

send visual information toward the brain

why is there arteries and veins in the retina

bc it is an oxygen demanding organ

how light goes through retina

rods and cones—→ bipolar cells——> ganglion cells——> optic nerve——>brain

do rods or cones more likely to be a 1:1 ratio of connections

individual cones can connect through individual bipolar cells , many rods converge onto same bipolar cell

first part of retina

pigmented epithelium

does retina push in or out

pushes in

what color fades away first and is most sensitive to light

red

what protein does rods use

phodosin

what do photoreceptors synapse with

with horizontal cells and bipolar cells

typically _________ will synapse onto one bipolar cell, but ______— can synapse with a single bipolar cell

1 to a few cones, up to 100 rods

whats more common in periphery of retina

rods

where are cones concentrated

in fovea

resting rods and cones exist in a state of what

partial depolarization

secretes the neurotransmitter glutamate onto bipolar cells

when reading a book what helps distinguish individual letters and what helps you notic object in peripheral

cones helps see letters and rods help see peripheral vision

when light reacts with photopigments

decompose photopigments

cause a cascading chemical reaction to occur, leading to graded potentials in photoreceptor cell

receptor cell hyper polarizes, glutamate secretion slows or stops

two types of bipolar cells

on-pathway and off-pathway bipolar cells

what happens to on bipolar cells in the light

they depolarize because glutamate release decreases

what happens to off bipolar cells in the dark

they depolarize in response to glutamate

what happens to off bipolar cells in the light

they hyperpolarize because glutamate decreases

what happens to on bipolar cells in the dark

they hyperpolarize because glutamate inhibits them

what do bipolar cells stimulate

ganglion cells through neurotransmitter release

what happens when light hits the center of an on center ganglion cells receptive field

its cation potential firing increases

what happens when light hits the center of an off center ganglion cells receptive field

its action potential firing increases

what type of electrical signals do ganglion cells produce

action potentials

what type of electrical signals do photoreceptors and bipolar cells use

graded potential

how many rods are in bipolar cells

has up to 100 rods

bipolar cells on pathway

depolarized by rod

bipolar cells off pathway

hyper polarized by rods, turns active ones off

in total darkness, photo receptors in a state of what

partial depolarization

what happens when light hits photoreceptors

chemical reaction with chromophors and photoreceptive pigments causing them to breakdown

what is the miracle of vision

how rapidly photoreceptive pigments regenerate

flashblindness

sudden bright light hits eye, destroys photopigments, need time to regenerate

______ never fire action potentials

bipolar cells

______ fire when excited

ganglion cells

secrete more neuro transmitters

depolarizes on pathway

secretes less neurotransmitters

repolarizes-off pathway

concept of nerve cells communicating with each other

bipolar cells release neurotransmitters which bind to receptors on ganglion cells, ganglion cells can then generate action potentials

why can bipolar cells not fire action potentials

because they use graded potentials not action potentials

which cells convert retinal information into electrical signals that can travel long distances

ganglion cells

pathway for vision

retina——>optical nerve—→ optical chiasma—→ optical tract (white matter)——> superior colliculi and lateral geniculate nucleus of thalamus—→ visual cortex and suprachiasmatic nucleus