Eye Nervous System

Sensory Receptors

• activated by specific stimuli

• once activated, it converts to an electrical impulse which goes to the brain

• FORM FITS FUNCTION

Electrical Pathway

sensory receptors – neurons – electrochemical impulses – brain

Chemoreceptors

sense specific chemicals

• taste buds

• lining of the nasal cavity

Photoreceptors

sense visible light

• retina of the eye

Thermoreceptors

sense temperature

• skin

Proprioceptors

sense stretching in muscle fibers, ligaments, and tendons

• tension and stretching

Mechanoreceptors

sense changes in pressure

• fingertips. hearing SENSORY ADAPTATION occurs when the sensory neurons become accustomed to the stimulus. Neurons cease to fire even though the stimulus is present.

• Examples: cold pool, bad smell in the locker room.

Orbital Cavities

where the eyes located in two depressions at front of the skull

Structures found in the Orbital Structure

• muscles to move the eye

• tear producing (lacrimal) gland

• nerves

• blood vessels fat deposits

Protective Structure found in the Orbital Structure

• eyebrows

• eyelashes

• eyelids

• conjunctiva (mucous membrane that covers the front of the eye and lines the inside of the eyelids)

Structure of the Eye

a hollow ball, bulging at the front, with an extension out the back.

Coverings of the Eye Ball

• sclera—protection, help maintain shape

• choroid—vessels that helps blood supply

• retina—tissue responsible for vision, where the rods and cones are, with the photoreceptors

Sclera

A white fibrous material that protects the inner layers of the eye. Corne

Cornea

Transparent part of the sclera. It refracts (bends) light toward the pupil.

• no blood supply

• gets oxygen directly from the air

• only tissue that a donor could get without rejection because there is no blood supply.

Aqueous Humor

A chamber of transparent fluid behind the cornea. It helps to refract light and supplies nutrients to the cornea.

• what the hollow part fills in the eye (one of the fluids that fill the eye)

• right behind the cornea

• it actually provides nutrients (not oxygen–no blood supply)

Choroid Layer

Middle layer of the eye

• highly vascularized (blood vessels) to provide gases and nutrients to the retina

Pupil

• opening within the iris

• hole into the eyeball—not a tissue

• less light = pupil dilates to let all the light in

• more light = pupil constricts

Iris

regulates the amount of light entering the eye

• pigmentation

• has sphincter muscles that controls the pupil around the iris

Lens

A transparent convex structure that can change shape. It helps focus the image on the retina.

Ciliary Body

changes the shape of the lens to allow for focusing on near and distant objects—ACCOMODATION.

Accommodation

Contract: lens goes spherical (near objects)

Relax: lens flattens (far objects)

Vitreous Humor

A cloudy jelly-like fluid that maintains the shape of your eye.

Retina

contains four different layers of cells (from external to internal)—WHERE VISION BEGINS

• pigmented epithelium

• light-sensitive cells (rods and cones)

• bipolar cells

• cells of the optic nerve

Blind Spot

an area where the optic nerve attaches to the retina.

• no photoreceptors cells in this area.

Pigmented Epithelium

prevents light that has entered the eye from scattering

Bipolar Cells

once excited, the message from the rods and cones passes through here and to the optic nerve.

• the cells in the retina that are responsible for converting light to an action potential

Cells of the Optic Nerve

carries impulse to the CNS

Rods

being able to see in dim light setting

• more rods than cones

• allows for black and white vision and are located on the periphery of the retina

• “night vision”

Cones

to perceive colors—high light intensity

cones that respond to colors:

• red light

• green light

• blue light

Fovea Centralis

small depression in the retina of the eye where visual acuity is highest—highest concentration of photoreceptors

• lots of rods and cones packed in this area Lig

Vision Pathway

• light comes in to the eye

• the first point of refraction is the cornea–light will bend at the cornea first.

• It will pass through the pupil and from the pupil, it hits the lens–second point of refraction where the light bends.

• The aqueous humor does refract too but not as much–only cornea through the pupil and the lens. 

• Converges in the back of the eye in the back of the retina where all the photoreceptors are located and what ends up happening, 

When the rods and cones are stimulated. Energy passed to the bipolar cell that converts to an action potential. Travels from the optic nerve to occipital lobe. Myopi

Myopia

• nearsightedness

• trouble seeing distant objects

• images focuses on the FRONT of the retina

• lens cannot flatten enough

• corrected with a concave lens

Hyperopia

• farsightedness

• trouble seeing near objects

• images focuses behind the retina

• lens cannot become oval enough

• corrected with a convex lens ASti

Astigmatism

A vision defect due to an abnormal curvature of the cornea or lens

• having “chipped” lens

• parts of the image are out of focus

• needs special shaped lens