Sight/Vision

Conjunctiva

Thin layer of cells that lines the inside of your eyelids from the eye

Cornea

Transparent thick sheet of fibrous tissue, anterior 1/6th; starts to bend light, first part of eye that light hits

Anterior chamber

space filled with aqueous humor

• provides pressure to maintain shape of eyeball; allows nutrients and minerals to supply cells of cornea/iris

Pupil

The opening in the middle of the iris

• can get smaller/larger based on the iris relaxing/contracting respectively to modulate the amount of light able to enter the eyeball

Iris

Gives eye color

• is the muscle that constricts/relaxes to change the size of the pupil L

Lens

Bends the light so it goes to the back of the eyeball

• focuses light specifically on the fovea of the retina

• adjusts how much it bends the light by changing its shape using suspensory ligaments

Suspensory ligaments

Attached to the ciliary muscle

• ciliary muscle + suspensory ligaments = ciliary body which secretes aqueous humor

Posterior chamber

area behind iris to the back of the lens

• filled with aqueous humor

Vitreous chamber

Filled with vitreous humor (jelly like substance to provide pressure to eyeball and give nutrients to the inside of the eyeball

Retina

Inside, back area filled with photoreceptors, where the ray of light is converted from a physical waveform to an electrochemical; impulse the brain can interpret

Macula

Special part of a retina rich in cones

• also has some rods

Fovea

Special part of macula completely covered in cones, no rods

Cones

Detect color and discern high level of detail in what you are observing

• 6-7 million cones

• Types: red, green, blue

• detect color primarily but also some light

• fast recovery time: easy to detect changes in color

Rods

detect light

• 120 million rods for night vision

• Normally rods are turned on, but when light enters the pupil, it his the rod and light turns the rod off

• When the rod is off, it turns on a bipolar cell → on a national ganglion cell → optic nerve → enters the brain

• More rods than cones: more important to detect light than detail

• 1000x more sensitive to light than cones

• slow recovery time: longer time to detect changes in light

Choroid

pigmented black in humans

• network of blood vessels that helps nourish the retina

• all light is absorbed

  • some animals have a different color choroid which gives them better night vision

Sclera

The whites of the eyes, thick fibers tissue that covers 5/6th of eyeball

• attachment point for muscles

• extra layer of protection and structure of eyeball

• lines with conjunctivia

Anatomy of the eye

Transmission

The electrical activation of one neuron by another neuron

Perception

Conscious sensory experience of neural processing P

processing

The neural transformation of multiple neural signals into one perception T

transduction

Occurs when energy is transformed from one form to another

• Light energy is transformed to electrical energy by rods and cones

Sensation

Requires a physical stimulus to be converted into a neural impulse

• in the eye, light is being converted to a neural impulse by a photoreceptor

Light

An electromagnetic wave that is in the middle of the electromagnetic spectrum

Phototransduction cascade (PTC)

What happens when light hits rod/cone

1. Light hits rod → rod turns off → turns on bipolar cell → turns on retinal ganglion cells → optic nerve → brain

Makes the brain recognize there is light entering the eyeball

• takes light and converts to a neural impulse

More detailed PTC

1. Rods are made up of optic disk stacks

2. Proteins on disk stacks like rhodopsin which contains retinal (11-cis) that changes to 11-trans retinal when hit by light, changing the shape of rhodopsin

3. Transducin, which is attached to rhodopsin has 3 parts, alpha, beta, gamma

   1. When rhodopsin changes shape, transducin breaks off and the alpha subunit binds to phosphodiesterase (PDE)

   2. PDE takes cGMP → regular GMP

   3. cGMP concentration decreases, which closes Na+ channels (cGMP is bound to Na+ and keeps channels open) → hyper polarizes cell, turning rod “off”

4. Bipolar cells (ON center and OFF center)

   1. When light hits rod → ON center bipolar cells activate and OFF center bipolar cells inactivate → activates ON center retinal ganglion cell → sends signal to optic nerve → brain

What happens with rods when it is dark

Rod turns on

• ON center bipolar cells inactivate and off center bipolar cells active

• Off center bipolar cells turn on, activates off center retinal ganglion cell

• Signals optic nerve → brain

Photopic vison

Occurs at levels of high light

Mesopic vision

Occurs at dawn/dusk and involves both rods and cones

Scotopic vision

Occurs at levels of very low light

Photoreceptor distribution in retina

• Optic nerve connects to retina: blind spot ( no cones/rods)

• Rods are found mostly in periphery

• Cones are found primarily in fovea, few dispersed throughout the eye

Visual processing field

all right visual field goes to the left side of our brain, vice versa

Ray of light from left visual filed his nasal of left eye and temporal of of left eye

Feature detection

Broken down into color, form, and motion to identify what is being looked at

Color

• Cones

• Trichromatic theory: 3 cones

  • ex: red object reflects red → red hits red cone → fire axon potential → brain identifies red

Form

We need to figure out boundaries of the object and the shape of the object

• Parvocellular pathway: good at detecting boundaries, shapes, and color but not motion

• Cones are responsible

Motion

Magnocellular pathway: high temporal resolution (time and motion)

• no color and rods are responsible

Parallel processing

detects/focus all information (color, form, motion) at same time