Special Senses: Eye Anatomy and Physiology
Ciliary Body (location and function)
- anterior portion of the choroid layer - muscles attached to the lens pulls on the edge of the lens to change the shape of the lens so it can focus incoming light onto the retina
Pupil (location and function)
- anterior portion of the choroid layer - opening in the center of the iris allows light rays to enter the eyeball
Cornea (location and function)
- anterior portion of the sclera - clear, transparent area that allows light to enter the interior of the eyeball - bends, or refracts, light rays
Canal of Schlemm (location and function)
- around the outer angle of the anterior chamber anatomical structure of the eye which allows for the outflow of aqueous humor from the anterior chamber
Nasolacrimal Duct (location and function)
- connected to lacrimal ducts drains tears from lacrimal ducts into the nasal cavity
Zonule of Zinn (location and function)
- located between the lens and ciliary body anatomical structure that connects the horizon of the lens to the ciliary body allowing for the deformation of the lends during accommodation
Sebaceous Glands (location and function)
- located in the eyelids secrete lubricating oil onto the eyelid
Lacrimal Ducts (location and function)
- located in the inner corner of the eye socket collect tears and drain them into the nasolacrimal duct
Oblique (function)
- on an angle produce diagonal eye movement
Conjunctiva (function)
forms a continuous covering on the underside of each eyelid and across the anterior surface of each eyeball also serves as protection for the eyeball sealing off the eyeball in a socket - mucous membrane lining
Lacrimal Apparatus (function)
produces and drains tears - lacrimal glands - lacrimal ducts - nasolacrimal duct
Sclera (function)
provides a tough protective coating for the inner structures of the eye - outermost layer -contains the cornea - aka the white of the eye
Inferior Oblique (function)
pulls the eye to produce upward and outward movement
Two General Names of the Extraocular Muscles
rectus and obliques
Tears (function and where they are produced)
serves important function of washing and lubricating the anterior surface of the eyeball - produced in the lacrimal gland
Aqueous Humor (location and function)
watery fluid found in the spaces between the cornea and lens that maintains intraocular pressure
Diagram of the Extraocular Muscles (EOM)
Diagram of the Right Eye Muscles: A. Medial Rectus B. Superior Rectus C. Superior Oblique D. Lateral Rectus E. Inferior Rectus F. Inferior Oblique
How We See
*light rays strike the eye* - first pass through the cornea, pupil, aqueous humor, lens, and vitreous humor - then strike the retina and stimulate the rods and cones - when light rays hit the retina, an upside-down image is sent along the nerve impulses to the optic nerve - optic nerve transmits these impulses to the brain, when the upside-down image is translated into the right-side up image we are looking at
Fovea Centralis (location and function)
- a depression in the center of the macula lutea - means "central pit" contains high concentrations of sensory receptors which make it the point of clearest vision
Iris (location and function)
- anterior portion of the choroid layer - colored portion of the eye - contains smooth muscle muscle that contracts and relaxes to change the size of the pupil and controls how much light enters the interior of the eye
Lens (location and function)
- behind the iris - attached to the muscular ciliary body by zonule fibers the shape of the lens focuses incoming light onto the retina
Lacrimal Gland (location and function)
- located under the outer upper corner of each eyelid produces tears
Rectus (function)
- means "straight" these muscles pull the eye up, down, left or right in a straight line
Optic Disk (location and function)
- point were the retinal blood vessels enter and exit the eyeball - where the optic nerve leaves the eyeball - contains no sensory receptors which causes a blind spot in each eye's field of vision
Cones (location and function)
- sensory receptor cells in the retina that respond to light rays active only in bright light and are responsible for color vision
Rods (location and function)
- sensory receptors in the retina that respond to light rays active in dim light and help us see in gray tones
Retina (location and function)
- third and innermost layer of the eyeball contains sensory receptor cells(rods and cones) that respond to light rays
Eyelashes (location and function)
- upper and lower edges of the eyelid protect the eye from foreign particles - aka cilia
Eyelid (function)
- upper and lower edges of the eyelid contain eyelashes(cilia) provides protection from foreign particles, injury from the sun and intense light, and trauma - eyelids contain sebaceous glands
Macula Lutea (location and function)
- yellow spot on the retina where an image falls when you look directly at an object- contains the fovea centralis
The Required Proper Functioning of Four Mechanism so that We Can See
1. coordination of the external eye muscles so that both eyes move together 2. correct amount of light admitted by pupil 3. correct focus of light on the retina by the lens 4. optic nerve transmitting sensory images to the brain
Layers of the Retina (innermost to most superficial)
1. internal limiting membrane 2. nerve fiber layer 3. ganglion cell layer 4. inner plexiform layer 5. inner nuclear layer 6. outer plexiform layer 7. outer nuclear layer 8. external limiting membrane 9. layer of rods and cones 10. pigmented part
3 Layers of the Eyeball (outermost to innermost)
1. sclera 2. choroid 3. retina
Medial Rectus (location and function)
extraocular muscle closest to the midline of the body pulls the eye to create inward movement
Inferior Rectus (location and function)
extraocular muscle on the bottom of each eye pulls the eye to produce downward movement
Lateral Rectus (location and function)
extraocular muscle on the lateral side of each eye pulls the eye to produce outward movement
Superior Rectus (location and function)
extraocular muscle on the top of each eye that pulls the eye to produce upward movement
Choroid (function)
provides the blood supply for the eye - middle, opaque layer - consists of the iris, pupil, and ciliary body
Superior Oblique (function)
pulls the eye to produce downward and outward movement - controlled by the trochlea
Vitreous Humor (location and function)
semisolid gel found in the large open area between the lens and the retina
Two Parts of the Lacrimal Gland
superior lacrimal gland inferior lacrimal gland
Oblique Muscles (names)
superior oblique inferior oblique
Rectus Muscles (names)
medial rectus lateral rectus inferior rectus superior rectus
