neuro 3000 lecture 19

light

Electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye (wavelength = 400-700nm) (for comparison, plasma membrane thickness = 5-10 nm; diameter of glutamate receptor channel pore is 0.5-1 nm)

Frequency

Waves per second

Wavelength

Distance between peaks (determines frequency, and thus energy)

Amplitude

Peak minus trough (how bright light is)

Optics

The study of light rays & their interactions

Light rays

travel in straight lines until they interact with the atoms and molecules of the atmosphere and objects on the ground

Reflection

Bouncing of light rays off a surface. Most of the light we see

Absorption

Transfer of light energy.

Compounds

absorb light of specific wavelengths and reflect others

Refraction

Bending of light rays when traveling from one transparent medium to another. This bending occurs because the speed of light differs in the two media. the property of most relevance to eye function.

Cornea

Transparent; no blood vessels; the main refractive component, and is continuous with the sclera

Pupil

Appears dark because of light-absorbing retinal pigments; entry for light!!

Iris

Gives eye its color. Contains two muscles that control pupil size (one contracts it, one expands it)

Sclera

Wall of eyeball; white of the eye; very tough; attached to 3 extraocular muscles

Conjunctiva

Mucous membrane that covers front of eye and attaches eyelids to sclera

Optic Nerve

Carries axons from retina to brain; exits back of eye; reaches base of brain near pituitary

Nasal

side of eye closest to nose

Temporal

side of eye closer to the temple

retina

Neural tissue at back of eye; the main sensory organ; it is part of the CNS!! gathers all the complex data we need to construct our perception of the world.

Optic disk

Area where blood vessels originate; area where optic nerve exits the retina; blind spot

Macula

Middle of each retina; for central vision as opposed to peripheral; important for fine vision (acuity) due to lack of blood vessels

Fovea

Dark spot, a thinning of the retina; at center of the macula; as part of the macula, it is important for high acuity vision; densely populated with cone photoreceptors which are important for seeing color

Lens

concentrates, and focuses the light at the retina (similar to magnifying glass). Forms crisp images of objects closer than 9 m from eye

Ciliary muscle

controls shape of lens enabling eyes to adjust their focus to different viewing distances

zonule fibers

connect the ciliary muscle to the lens, helping to stabilize the lens and facilitate changes in its shape for focusing.

Aqueous humor

water-like fluid between the cornea and the lens that maintains intraocular pressure and provides nutrients to the lens and cornea.

Vitreous humor

gel-like substance inside the eyeball filling the space between the lens and the retina, helping to maintain the eyeball's shape and providing support to the retina.

Accommodation

Contraction of ciliary muscles to change the shape (rounder, curved) of the lens

Hyperopia

Farsightedness due to eyeball being too short, and point of focus is beyond the retina; correct with convex lens (magnifier) to make image appear bigger and shortens the point of focus so it hits the retina

Myopia

Nearsightedness due to eyeball being too long (light focuses before retina), correct with concave lens that makes image appear smaller and lengthens the point of focus so it hits the retina

Pupillary light reflex

Connections between retina & midbrain that control the muscles in the iris that constrict the pupils

Visual field

Area seen by eye when looking forward. Each eye has a visual field of about 150 degrees; 90 degrees or more on temporal side and 60 degrees on nasal side. Image is inverted on the retina

Visual acuity

the ability to distinguish between nearby points due to refractive power and spacing of photoreceptors

visual angle

Distance across the retina is described in terms of degrees (~0.5 degrees)