Sensory systems Flashcards
What are the layers of the wall of the eye?
3 layers - coats/tunics
- Outer (fibrous) coat = cornea and sclera
- Middle (vascular, uveal) coat = iris, ciliary body, choroid
- Inner (retinal) coat = retinal pigmented epithelium (RPE) and neural retina
What are the chambers of the eye?
- Anterior - between cornea and iris
- Posterior - between back of iris and lens with attached fibers
- Vitreous cavity - between lens and retina
What is the conjuctiva?
Thin membrane that covers a portion of the exposed surface of the eye and continues onto the inner surface of the eyelid. Stratified columnar epithelium with mucus cells.
Describe the cornea.
- Transparent, with a convex shape that aids in focusing light and images on retina
- Avascular, with no blood or lymph in the central portion
- 5 different layers
- Can be transplanted without rejection
How does the cornea get nutrients?
- Central part gets nutrients by diffusion from the aqueous humor
- Peripheral part supplied by blood from limbus vessels
What are the corneal layers?
Epithelium, Bowman’s layer, stroma, Decemet’s membrane, corneal endothelium
Describe the corneal epithelium
Anterior layer, non-keritanized stratified squamous epithelium with small microvilli. Has pain receptors (trigeminal and oculomotor nerves) and can regenerate.
Describe the corneal Bowman’s layer/”membrane”
Layer of Type 1 collagen, cannot regenerate. Part of stroma.
Describe the corneal stroma
Lattice of Type 1 and Type 5 collagen fibers with an ECM rich in chondroitin and keratan sulfate.
Describe the corneal Decemet’s membrane
Thick (5-10 micrometer) basement membrane (contains Type 7 collagen) produced by corneal endothelium.
Describe the corneal endothelium
Surface faces anterior eye chamber. Impermeable intercellular spaces prevent leakage of fluid into corneal stroma.
Describe the structure and function of the sclera.
- Dense irregular connective tissue - opaque
- Provides protection, structural support, and is an insertion point for the extraocular muscles
What is the limbus?
The limbus is the corneoscleral junction. It is adjacent to the trabecular meshwork and canal of Schlemm.
What is aqueous humor?
It is fluid which resembles plasma, but with less protein.
What is the pathway aqueous humor follows?
Produced by ciliary body epithelium –> flows into anterior chamber through pupil –> drains through a trabecular meshwork at the limbus –> enters canal of Schlemm –> aqueous veins –> episcleral veins
What is glaucoma?
-Obstruction of aqueous humor flow leading to increased pressure in the eye
Describe the choroid
Highly vascular nutrient supplier to all eye layers. Contains melanin. 3 layers - Bruch’s membrane, choriocapillaris, chroidal stroma.
Describe the ciliary body. How many (named) parts does the ciliary body have?
Wedge-shaped expansion of the choroid peripheral to the lens. Smooth muscle (primarily)
2 parts - uveal and neuroepithelial portions
Describe the uveal portion of the ciliary body.
Outer layer of choroid (supraciliaris), ciliary muscle attached to suspensory ligament, and layer of fenestrated capillaries
Describe the neuroepithelial portion of the ciliary body.
2 layers of ciliary epithelium consisting of an outer pigmented layer continuous with retinal pigmented epithelium, and inner nonpigmented layer
Describe the anterior portion of the ciliary body epithelium.
The anterior portion of the CB epithelium is folded to form ciliary processes. Epithelium in this region produce the aqueous humor.
What is the iris?
Continuation of the ciliary body. Anterior part of middle coat (uvea). Has smooth muscle which controls size of pupil.
What are the smooth muscle layers of the iris?
2 smooth muscle layers - circular and radial.
Smaller size pupil - constrictor muscle (circular) - parasympathetic.
Dilated pupil - dilator muscle (radial) - sympathetic.
Describe the lens.
Avascular, transparent, elastic, and biconvex in shape.
What is the lens capsule?
Thick basement membrane-like material enclosing the lens
When does the lens change shape?
When tension on suspensory ligament fibers (zonular fibers) changes
Describe the vitreous humor.
Gel-like, transparent, water and hyaluronic acid, fills vitreous chamber/cavity, keeps lens and retina in place
What is a cataract?
Opacity of the lens associated with aging
What is the retinal pigmented epithelium (RPE) - retinal layer #1?
- Absorbs scattered light rays
- Phagocytosis of worn out discs shed from rods
- Stores and releases vitamin A to photoreceptors
- RPE closely adhered to choroid. There can be a space between the RPE and the rest of the retina (embryonic development). Trauma can dislodge retina at this site.
What is retinal layer #2?
Layer of rods and cones (photoreceptors)
Tall cylindrical cells. Function in low light and peripheral vision. Outer segments - modified cilia. Have discs derived from plasma membrane containing rhodopsin pigment (transducer of light energy)
Shorter cone-shaped cells. Color vision and bright light. Outer segments - modified cilia. Have discs and pigments sensitive to red, green, and blue light. Located more centrally.
What kind of cells can be found in the fovea?
Describe the renewal process of photoreceptors.
Outer discs of old rods are shed into the space between outer segments and the RPE, which phagocytoses them. New discs made from below and move upward, replacing the old. Cones’ discs shed and replaced more slowly.
What are the macula lutea and the optic disc?
Posterior retina landmarks, can be viewed through the pupil by a scope.
Describe the optic disc.
The optic disc is made of papilla where optic nerve fibers exit the retina, but no photoreceptors.