Special Senses: Sight A PowerPoint presentation by Nick Wester, Maxwell Fabella, and Sung Kim.

Sensory Organs Associated With Sight  The eyeball is the main organ involved in sight.  The key parts of the eyeball are: pupil, iris, retina, optic nerve, lens, cornea, aqueous humor, and the vitreous humor.  Each of these parts have specific functions that produce sight within the eyeball.

Specific Functions  Pupil- Round opening which light passes through.  Iris- Muscle that regulates the amount of light entering the eye so that one can see as clearly as possible in the available light.  Retina- Contains millions of receptor cells, the rods and cones, which are called photoreceptors, because they respond to light. Retina absorbs light and prevents light from scattering inside the eye.  Optic Nerve- Interprets impulses sent by retina and sends interpretation to brain, which results in vision.  Lens- Focuses light entering retina.  Cornea- The “white of the eye”. This is where the light first enters the eye.

Specific Functions Continued  Aqueous Humor- Helps maintain pressure inside the eye. Provides nutrients for the lens and cornea.  Vitreous Humor- Helps prevent the eyeball from collapsing inward by reinforcing it internally.

Parts of the Eye

Exploring Rods and Cones  The names of these photoreceptors reflect the shape of the cells.  Rods are slender, elongated neurons, whereas the fatter cones taper to pointed tips.  The outer segment corresponds to a light-trapping dendrite, in which the discs containing visual pigments are stacked like a row of pennies.  The behavior of the visual pigments is dramatic. When light strikes them, they lose their color, or are “bleached”; shortly afterward, they regenerated their pigment. Absorption of light and pigment bleaching cause electrical changes in the photoreceptor cells that ultimately cause nerve impulses to be transmitted to the brain for visual interpretation.

Pathway of Light Through the Eye

Explanation of the Pathway  The basic explanation of the pathway goes as such: light travels through the cornea to the aqueous humor, from the aqueous humor to the pupil, from the pupil to the lens, from the lens to the vitreous humor, and finally the rods and cones of the retina.  From the retina, the message is carried via the optic nerve, then the optic chiasma, and finally the optic tract. The optic tract delivers the message to the primary visual cortex of the occipital lobe.

Disorders Associated With Sight  Glaucoma- If drainage of the aqueous humor is blocked, fluid backs up like a clogged sink. Pressure within the eye may increase to dangerous levels and compress the delicate retina and optic nerve. This condition eventually causes pain and possibly blindness unless detected early.  Color Blindness- Lack of all three cone types results in total color blindness, whereas lack of one cone type leads to partial colorblindness. Most common is the lack of the red or green receptors, which leads to two varieties of red- green color blindness. Red and green are seen as the same color- either red or green, depending on the cone type present.