Vision+JO


 * SENSE OF VISION**



Vision requires the work of the eyes and brain.
 * researchers estimate that **at least** a third of the cerebral cortes takes part in processing visual information.

Anatomy: The eye is approximately 2.5 cm in diameter.

It has three layers: **the Outer:** sclera and cornea **the Middle:** choroid, iris, and the ciliary body **the Inner:** retina

The **sclera** is white and fibrous but it attaches/ turns into the cornea and at that point it is clear (so we can see out). The **cornea** is made of transparent collagen fibers. The **choroid** is thin, darkly pigmented layer, absorbs stray light rays that photoreceptors have not absorbed. Toward the front it becomes the Iris. the **iris** is the dough-nut shaped color pigment of the eye. The iris also regulates the size of the pupil. the **pupil** is the the hole in the center that light travels through. Behind the iris the choroid thickens to form the **ciliary body.** This body contains the ciliary muscles which controls the shape of the lens for near and far vision. Rods: are light (in a darkroom; only see shades of gray) Cones: are color the special region of the retina is called the **fovea centralis.** this is where cells are densely packed. light is focused here when we are looking directly at the object.
 * Retina** is located in the posterior of the eye and is filled with the **vitreous humor**; a clear gelatinous material. this is where the **photorecptors** are located. the photoreceptors are then composed of **rod** and **cone** cells.
 * sensory fibers** from retina form **optic nerve** which relays nerve impulses to visual cortex.

the anterior; is filled with a clear and watery liquid called **aqueous humor** -normally the aqueous humor is produced and released periodically throughout the day. if it is not released then the person has a build up or **glaucoma** if not treated then the arteries that serve the nerve fibers are compressed and the nerve fibers begin to die. the person becomes partially blind.
 * The Lens**: divides the eye into two compartments; the anterior and the posterior.
 * eventual total blindness**


 * Visual Accommodation**



when viewing and object that is **Far** away the ciliary muscle is relaxed. Which means the suspensory ligaments are taut and the lens is relatively flat. When the object is **Near** the muscle contracts; this releases tension on the ligaments and the lens rounds (natural elasticity) working too close can cause eyestrain or ciliary muscle fatigue. Around the age of 40 the lens loses some elasticity and is unable to accommodate (bifocals and contacts)

--> when rod cells absorbs light, rhodopsin splits into the two molecules which then leads to a cascade of reactions and the closure of an ion channels in the rod's cells plasma membrane. the signal then travels to the other neurons in the retina. (**carrots can improve your night vision, due to vitamin A)
 * Visual pathway to the Brain**
 * function of the photoreceptors**: there are outer and inner segments that are connected by (many disk of outer to membrane) and by (synaptic vesicles for the inner to outer)
 * rhodopsin**: is a complex molecule made up of protein opsin and light-absorbing molecule called retinal. **retinal** is a derivative of vitamin A.