Anatomy and Physiology Flashcards
Orbit
Bony structures in the skull that houses the eyeball (globe).
7 Bones of the orbit
Ethmoid Frontal Lacrimal Maxillary Palatine Sphenoid Zygomatic
Cranial Nerves: III IV VI VII
Oculomotor-opens eye, elevation, depression, adduction, extortion/elevation, accommodation (parasympathetic).
Trochlear-intortion/depression
Abducens-abduction
Facial Nerve-Closes eye
Cranial Nerves and muscles: III IV VI VII
Occulomotor-Levator Palpebrae, Superior rectus, inferior rectus, medial rectus, inferior oblique, ciliary muscle
Trochlear- Superior oblique
Abducens-lateral rectus
Facila nerve-Orbicularis oculi
OCC III parasympathetic
OCC III sympathetic
Iris sphincter muscle-constricts pupil
Iris Dilator Muscle-dilates pupil
Eyeball (globe)
Structures that focus and transmit light to the brain for the sense of sight
average length-24 mm
average keratometry (measurement of the curvature of the anterior surface of the cornea)-42.50 d
Cornea
clear, dome shaped, avascular (no blood vessels), comprised of 5 layers, provides 2/3 of the refracting power of the eye (bends light rays into retina), average central thickness (500 microns) 0.5mm
Anterior Chamber
Space between corneal endothelium and iris surface
Contains aqueous humor to maintain intraocular pressure
Iris
Colored portion of eye
Regulates amount of light entering globe
Contains sphincter and dilator muscles that control pupil size.
Crystalline Lens
Clear, disc shape
Helps bring rays of light into focus on the retina. When the ciliary muscle in relaxed during distance vision, the crystalline lens counts for up to 1/3 of the eye’s refracting power. The process of accommodation occurs when the ciliary muscle contracts, releasing tension on the zomular fibers and allowing the crystalline lens to expand, resulting in increased plus power of the eye that allows for near vision. The process of accommodation decreases after the age of 40.
3 parts of crystalline lens:
Capsule, cortex, nucleus
Angular structure
Aqueous humor is produced by ciliary body.
Flow of aqueous humor
Behind the iris into posterior chamber
Through the pupil and into anterior chamber
Out through the trabecular meshwork
Into the Canal of Schlemn
Exiting eye through episcleral veins
Vitreous body
Clear, gel-like substance
Occupies 2/3 of the volume of the eye
Provides for some retinal nutrition
Retina
Receives light impulses and transmit them to the brain via the optic nerve.
10 layers
Two photoreceptor types
Rods-120 M
Cones-6MLayers of the retina
Bruch's membrane Pigment epithelium Rods and cones External limiting membrane Outer nuclear layer Outer Plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Capillary Nerve fiber layer Internal limiting membrane
Choroid
Intraocular blood supply for the retina
Schlera
protective outer layer of the eye (covered by the conjunctiva)
Limbus
Junction between the corneal epithelium and conjunctiva
Lacrimal Gland
responsible for tear production
Medial rectus
Lateral rectus
Superior rectus
Rotates eye inward
Rotates eye outward
Turns eye upward
Inferior rectus
Superior oblique
Inferior oblique
Turns eye downward
Rotates eye down and inward
Rotates eye up and outward
Eyelids
Upper and lower moveable folds that acts as shutters
Protect the eye
Keep out light
Spread tear film evenly over cornea
Puncta
Tiny openings on upper and lower eyelid margins near nose that drains excess tears (puncture is the singular form)
Eyelashes (cilia)
Sweep away airborne dust particles and other foreign matter when eyelids blink
Levator Palpebrae superioris muscle
Elevates eyelid
Orbicularis oculi muscle
Circular muscle that closes eyelid
Conjunctiva
Translucent membrane from limbus to inner portion of the lid margin
Three areas of the conjunctiva:
Bulbar-covers eyeball
Palpebral-lines inner surface of upper and lower eyelid
Fornix-where bulbar and palpebral conjunctiva meet
Tear film: Three layers
Outer: lipid (oily)- secreted by meibomian gland (prevents evaporation of tears)
Middle: aqueous-secreted by lacrimal gland (supplies cornea with moisture, nutrients and oxygen)
Inner: Mucous-secreted by goblet cells (promotes even spread of tear film over cornea)
Tear production
Main volume of tear production arises from the lacrimal gland
Tear outflow
Punctum—>Canaliculi—>Lacrimal Sac—>Nasolacrimal Duct
Tears leave the eye in the following manner:
The tear film is spread over the ocular surface by the closure of the lids with each blink.
The blink mechanism (tear pump) directs the tears toward the puncture; into the canaliculi; to the lacrimal sac; and then the nasolacrimal duct
Uveal tract
Composed of iris choroid and ciliary body
Pigment layers of the eye
Contains most of the intraocular blood vessels
Rods
120 millions rods (ration 20:1-rods:cones)
Concentrated in peripheral retina
Function best in dim light
Allows detection of movement peripherally
Cones
6 million cones
Concentrated in macula
Function best in lighted conditions
Allows fine resolution and detection of colors
Optic Disc
Area in retina where retinal nerve fibers leave the eye (resulting in a physiological blind spot)
