Locations and functions of structures of th eye

Choroid

-Separates the fibrous and sensory tunics

-Contains a dense capillary bed that provides oxygen and nourishment to the eye

-Contains many melanocytes which give the choroid its dark appearance

iris

-Lies just beneath the cornea and layer with eye color

-Composed of two papillary muscles that control diameter of pupil/ amount of light entering the eye

Pupil

Round central opening to the center of the eye

Ciliary body

-Thick ring of tissue attached to and lies beneath the iris

-Holds lens in place beneath iris and centered on pupil

-Contains ciliary muscle that changes lens shape to focus light onto the retina

Lens

-Located beneath the iris and held in the center of the pupil by suspending ligaments extending from the ciliary body

-Focuses an image on the retina by changing shape under the influence of the ciliary muscles

Optic nerve

Transmits visual information from the eye to the brain

Fovea centralis

-Portion of the retina that is responsible for sharp central vision

-Humans use this region for any activity that requires detailed vision, such as driving

Optic disc

-Area of the retina where optic nerve leaves the eye

-Not covered by retina and is literally a blind spot in the eye

Ganglion cells

-Forms a synapse with axons of bipolar neurons

-Axons combine to form the optic nerve, sending nerve impulses to the brain

Bipolar neurons

-These cells form a synapse with the dendrites of the rods and cones

-They transmit nerve impulses to the ganglion cells

Cones

-Photoreceptor cells responsible for high acuity color vision

-They only operate in bright light

-Three types of cones: sensitive to red, green, or blue light

Rods

-Photoreceptor cells that are very sensitive to light

-They enable us to see shades of gray in dim light

Retina

-The delicate, two innermost layers of the eye

-The neural layer contains photoreceptors and neurons that react to light and transmit and integrate visual signals

-Beneath the neural layer lies the pigmented layer

-It absorbs light that has passed through the neural layer to prevent the light from bouncing back and causing “visual echoes”