Can humans or non-human animals see in the dark?

NO……You need light!

Light?

Waves of electromagnetic energy Photons: = discrete particles of energy

Travel in space at high speeds (186,000/second!)Measure in length nanometers (billionth of a meter)

So, we call these wavelenths

Visable to humans 380 – 760 nm

Visible Spectrum of Wavelength - Humans

*snakes see infrared (too long for humans)

Anatomy of the Eye

4. Iris: muscle, control of light intake, color (melanin)

5. Pupil: hole in iris --dilates/contract based on available light

10. Optic Nerve

6. Lens: adjusts the eye’sfocus (20%) accomdation

2. Cornea: covers iris & pupil focusing begins (80%)

3. Anterior Chamber (aqueous): clear fluid nutrients/shape

7. Vitreous Humor: gives eyeball shape

1. Sclera: covering of eye

1.

8.

2.

3.

4.5.

6.

7.

9.

10.

8. retina: transduction rods & cones

9. Fovea: acuity, cones

Anatomy of the Eye Light entering the eye

Lens of the eye inverts the visual image – Upper half of visual field projects onto the ventral portion of the retina …Lower half of visual field projects to the dorsal portion of the retina

Thank God (or whomever) that the visual cortex inverts it back to its original orientation!

The visual system is like a Camera

Normal Vision

Problem in lens Cataracts protein clumping together

Problem in the macula (fovea)Macular Degeneration: loss of acuity and center vision

Anatomy of the Eye - Retina

Retina: PhotoreceptorsTransduction of light

Into electrical chemical Message

Instead of NT Binding to receptor…

Light cause cascade of Intercellular messages

Cell Layers in the Retina

…notice anything funky about the set up?

Ganglion Cell Axons form optic nerve

Rods (scotopic)-responsible for night vision-very sensitive to light (low levels)-found in the periphery of retina- more than cones- Provide monochromatic info (Achromatic)- Provides poor acuity- Night blindness

Cones (photopic): -responsible for day vision (sensitive to mod-hi light) - found in fovea - provides greater acuity - trichromatic – color vision - legally blind (day blindness)

All sensory info must under go a series of 3 steps (sight, sound, touch):

1. RECEPTION: Absorption of physical energy by a receptorlight PHOTORECEPTORS

2. TRANSDUCTION: Conversion of one form of energy to another

light electrical chemical message

3. CODING: The one-to-one correspondence with a stimuli and the nervous system activity AP send message to visual cortex

Conversion of light to neural signal: visual transduction

Anatomy of the Eye – Blind Spot

blind spot

The blind Spot

1 million nerve fibers

* Exercise in book (pg 139)

Glaucoma: problem in the Anterior Chamber fluid there doesn’t drain correctly which puts pressure on the back of the eye especially the optic nerve

Damage to the optic nerve = Glaucoma

Optic Tract1/2 axons go to right side of the brain1/2 go to left side of brain

Not the same in all animals – depending on location of eyes

Ex: Rabbits & Guinea Pigs

IPSI & CONTRALATERAL PATHWAYS

How does the signal get to the Visual Cortex?

VIA the Retinal Ganglion Cell Axons

OPTIC TRACT

OPTIC TRACT