Structure of the eye, process of transduction

Cones

retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to color sensations. Facts; Number: 6 million, Location in the retina: Center, Sensitivity in dim light: Low, Color Sensitivity: High, Detail Sensitivity: High.

Rods

retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond. They are about 20 times more common than cones. Facts; Number: 120 million, Location in the retina: Periphery, Sensitivity in dim light: High, Color Sensitivity: Low, Detail Sensitivity: Low.

Turning Neural Signals into Images

- Some ganglion cells in the eye send signals directly to the visual cortex in response to certain features such as visual patterns, certain edges, lines, or movements - In and around the visual cortex of the occipital lobe, supercells integrate these feature signals to recognize more complex forms such as faces

The retina process

1.) To the brain's visual cortex via the thalamus. 2.) A chemical reaction in turn activities bipolar cells. 3.) Bipolar cells then activate the ganglion cells, the axons of which converge to form the optic nerve. This nerve transmits information to the visual cortex (via the thalamus) in the brain.

Pathway of light through the eye

1.) light enter the eye through the cornea 2.) light then passes through the pupil and iris 3.) light is focused by the lens 4.) light strikes the eye's inner surface, the retina 5.) Rods and Cones convert light waves into neural impulses 6.) Neural impulses are processed by bipolar cells 7.) Neural impulses are processed by ganglion cells 8.) Neural information travels through the optic nerve to the thalamus and on to the visual cortex

Eye example

Light from the candle passes through the cornea and the pupil and gets focused and inverted by the lens. The light then lands on the retina, where it begins the process of transduction into neural impulses to be sent out through the optic nerve. The lens is not rigid; it can perform accommodation by changing shape to focus on near or far objects.

Visual Information Processing

The images we "see" are not made of light; they are made of neural signals which can be produced even by pressure on the eyeball. Once neural signals enter the optic nerve, they are sent through the thalamus to the visual cortex.

Cornea

When light enters the eye, it enters through the this, and this protects the eye and bends the light so that we can focus.

Iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

bipolar cells

eye neurons that receive information from the retinal cells and distribute information to the ganglion cells

pupil

the adjustable opening in the center of the eye through which light enters

Fovea

the central focal point in the retina, around which the eye's cones cluster

Retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

optic nerve

the nerve that carries neural impulses from the eye to the brain

blind spot

the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there

accommodation

the process by which the eye's lens changes shape to focus near or far objects on the retina.

lens

the transparent structure behind the pupil that changes shape to help focus images on the retina

ganglion cells

their axons form the optic nerve

The photorecptors (rods and cones)

when light reaches the back of the retina, it triggers chemical changes in the receptor cells, called rods and cones. The rods and cones in turn send messages to ganglion and bipolar cells and on to the optic nerve.