Nanometer (nm)=1 billionth of a meter

(mm=.001, micrometer=.000 001, nm=.000 000 001)

meter=39.37inch so nm=.00000003937nm

• Wavelength=distance light travels per cycle (peak to peak)
• Purity=number of wavelengths present
• amplitude (intensity)=height of light wave

wavelength is the sensation

perception is the hue

color is an incorrect substitution for hue

violet=440

blue=470

green=540

yellow=570

orange=640

red=670

One wavelength=purity, adding waves decreases purity

if all wavelengths are the same it is a pure color and we perceive it as being saturated

Sensation:670nm, purity/ Perception:pure red, saturated

Saturated is incorrectly referred to as brightness

White light is incredibly unsaturated

(intensity) height of wave

Sensation:amplitude, Perception:brightness

Brightness is incorrectly called light or dark

High amplitude=brighter=light red

lower amplitude=less bright=dark red

Sclera: surrounds eye, joins w/ cornea, filled w/ fluids to keep spherical shape

cornea: transparent membrane in front of eye

-does 2/3 of light bending to focus on retina

Iris: pigmented set of muscles (2 sets-1 to constrict and 1 to dilate pupil)

-dilates when dark to get light on peripheral of fovea

Pupil: orpheus (hole) that gets light to the fovea

Lens: smart light bending, all the fine tuning to get light exactly on fovea

-behind cornea, pupils & iris

Extraocular muscles:lets us move our eyes, must be coordinated between two eyes

Ciliary muscles: connected to lens by zonules of zinn

contracts or relaxes to change shape of lens

• astigmatism: distortion of cornea, refracts light wrong
• acquired: big px, environmental cause (injury)
• congenital: born w/ it, pear shape, fixable
• conjunctivitis: inflamation of conjunctiva (pink eye)
• conjunctiva: pink mucus membrane (highly vasculized) connects lid to eye so stuff can't get behind eye
• cataract: cloudy lense
• lots of diff reasons, causes 50% of blindness
• surgical removal and replace w/ intraocular lens substitute
• Presbyopia: lens keeps growin, eventually old ppl can't thicken lens enough to see near objects and become hypermetropic
  

• between cornea and lense
• filled with aqueous humor which gets Oxy to eye bc you can't have blood bc light can't pass through it
• Aqueous humor also maintains eye's shape
• imp for light bending
• humor constantly replaced, drained out of canal
• glaucoma occurs when canal to drain humor is blocked (tx by lazor surgery & meds)
• tested using tonomoetry (test of eye pressure)

• Posterior chamber (larger back of eye) is filled with vitreous humor
• gelatin substance, keeps shape and gives some oxygen (some comes from blood)
• humor has floaters from erythrocytes/red blood cells (strains of material, black dots in vision)
• choroid: highly vasculized, gets most of oxy to retina
• between sclera and retina
• detached retina: seperation of choroid & retina doesn't get oxygen & nutrients

Transduction takes place in the retina by photoreceptors

Macula Lutea (2mm) in center of retina (mostly cones)

Fovea (.3mm) in center of macula lutea (only cones)

Macular Degeneration: leading cause of blindness

Dendrites: receive input from other neurons

ganglion: collection of cell bodies

nerve: collection of axons or fibers

Ganglion cells: collection of cell bodies from which the optic nerve extends

Optic Nerve: 2nd cranial nerve, collection of axons extending from ganglion cells

composed of one layer of protein between 2 lipid layers

called white mater (fat is white)

facilitate conduction

Ganglion cells are in posterior chamber

Axon of ganglion cells exit at the optic disc and become the optic nerve

Optic nerve is the bundle of neurons that carry information away from the retina

Optic disc-no photoreceptors, blind spot

direct relation b/ convergence & sensitivity

inverse relation b/ convergence & acuity

inverse relation b/ acuity & sensitivity

• convergence allows for high sensitivity bc multiple signals can summate to reach threshold
• convergence prevents acuity bc you can't actually tell where signal came from
• (cones w/ little convergence you know if it fires where it came from, but it might not fire all the time bc no summation)

• Rods, rhodopsin (not broken down, all the same) 
• 496 nm
• Cones (3 different opsin parts)
• long (L-cone), 560 nm
• Medium (M-cone), 530nm
• Short (S-cone), 420 nm
• each photopigment has a maximum absorption
• what they are most sensitive to in terms of wavelengths
• each one has a range around it (normal curve)

• Rhodopsin is the photopigment that tranduces light energy
• in dark Rhodopsin is stable
• in light it breaks down into 2 parts
• Opsin (larger part) has 4 different types
• Opsin makes diff photopigments in cones
• Retinal is the smaller part that is the same in all cells (vitamin A component)
• Break down effects G-proteins
• G-proteins inhibit Na+

Hyperpolarization

-35mV is resting

-70mv is hyperpolarization

M & Lcones-> on/off midget bipolar->midget ganglion

-Midget cells are small bc there isn't much convergence

-light on activates M&L, sends input to on midget bipolars

-light off activates off midget bipolar

-both on & off midgets go to midget ganglion

S cone ->on/off midget bipolar->small bistratified ganglion cells (bistratified means 2 layers)

-very few S cones exist (90-95% are M or L)

-there is some convergence but there are few S cones

-have diffuse dendrites on bipolar

≤50 rods ->rod bipolar->amacrine cells (act laterally)-> parasol ganglion cells

in a few rare cases ≤10 cones go to diffuse conce bipolars then to parasol ganglion cells

But we should associate parasol ganglions with rods for this class

Resting membrane potential is -70mV (based on distribution of ions across cell membrane)

Types of ions (electrically charged particles: anions=negative,  cations=positive

Depolarization: more positive due to

-ions flow down concentrationg gradient

-ions more attracked to unlike charges

(action pot for depolarization to +40mV)

• A- are too big to move out bc of semi-permeable membrane
• NA+ voltage channels keep them out at resting
• NA+ and CL- stay because concentration gradient balances out charges

• Depolarizes to +40mV
• voltage-gated Na+ channels open and Na+ enters cell
• action potential happens
• refractory period: ions are re-establishing resting pot

Single cell recording of ganglion cells

-put a microelectrode (1mm) into a single cell

basal firing rate: is the chronic/spontaneous act pot (50/sec) in the absence of any stimulation

-compare basal to firing in presence of stimulation

Antagonistic center-surround receptive fields

on center/off surround: light in center of receptive field excites cells light in surround inhibits it

-center is more powerful then surround

photoreceptors that the ganglion responds to

(find receptive field by putting line in diff places and measuring ganglion activity)

Midget cells maintaing firing the whole time light is on, parasol get a burst that doesn't last

ipsilateral: same side

contralateral: opposite side

mesial/medial: middle

lateral: at the side

chiasm: decussation/crossover

Nucleus: collection of cell bodies in  (PNS-Ganglion)

Tract: collection of axons/fibers (PNS-nerve)

Geniculate: bent like a knee (what LGN looks like)

fibers of ganglion cells cross over

-really impr for binocular vision

-coordinates inform from 2 eyes diff visual fields

No synapses at the optic chiasm

Optic nerve changes to optic tract at this point just because it goes from PNS -> CNS

lack of coordination between muscles in the 2 eyes

-messes up binocular vision

12 layers (6 main, 6 sub)

• 1 & 2 (ventral) are from M pathways/parasol/rods
• 3,4,5,6 (dorsal) are from P pathway/Midget/M&L
• below each is a layer from K/small bistratified/S
• 1,4,6 & Ks beneath get input from contralateral eye
• 2,3,5, & Ks beneath get input from ipsilateral eye

retinotopic: cells near each other on LGN get info from photoreceptors close to each other

LGN cells have center-surround receptive field but surround is more powerful than in ganglion cells (all lit would have less activation)

only 10% of LGN input is from retina (other info comes in for integration)

• Left eye
• left visual field hits right part of eye and goes contralateral to right hemisphere
• right visual field hits left part of eye and goes ipsilateral to left hemisphere
• Right eye
• left visual field hits right part of eye and goes ipsilateral to right hemisphere
• right visual field hits left part of eye and goes contralateral to left hemisphere
• reason optic disc is in the left visual field for R eye and right visual field for L eye

primary visual cortex=area 17=striate (striped) cortex=V1

secondary visual cortex=area 18 & 19=nonstriate cortex=extrastriate cortex=V2-V5

layer IVc of the primary visual cortex

-other layers of primary visual cortex don't have center-surround receptive field (only IVc, where LGN is)

primary visual cortex sends info it gets from LGN on to secondary visual cortex

ove-representation of info originating in fovea

-occurs mainly im primary visual cortex

-fovea is small but 1/2 of visual cortex gets info from fovea

Most ganglion go to LGN but 10% go to superior colliculus

-receives input from visual, auditory,and sensory systems

-plays a role in control of eye movements

-ganglion here have large dendritic fields (might be from K or rods)

Hubel and Wiesel

-put electrode into each subsequent layer (deeper) and assessed response to diff stimuli

-then moved electrode over .05 mm and repeated

cells respond the most to a certain orientation, as you get closer to that orientation firing increases

column:vertical set of cells that have best response to the same line (break at IVc bc of cent/surr structure)

-cells in subsequent columns make best response to a line rotated 10^o from previous column's best line

hypercolumn-sequence of 18-20 adjacent columns that make up a full cycle of line orientations

• simple cells: response best to lines and edges
• complex cells: respond best to moving stimuli
• larger receptive fields bc they have to be big enough that the stimuli can move around in it 
• end-stopped cells: best if stimulus is all in receptive field
• can be either simple or complex cells
• important in detecting boundaries
• blobs: convey color info (cone info, P/K system)
• not sensitive to line orientation
• interspersed w/in hypercolumns
• interblobs: occupy space between blobs
• sensitive to line orientation
• not sensitive to wavelength, no color
• get info that starts from cones (P system)

1/3 of brain is comitted to visual system

-vision is primary sensory system for cognition and intelligence bc of large amount of integration

Gross: studied response of inferior temportal cortex to a lot of stimuli

-barely responded to anying, til he waved goodbye and it fired

inferior temporal cortex is related to perception

Agnosia: loss of ability to recognize a sensory stimulus

-can happen in any sense

-detect stimuli but don't know what it is

-can still describe the parts

visual agnosia: inability to recognize familiar objects by sight

Prosopagnosia: inability to recognize other people or one's own face