Histology Of The Visual, Vestibular, And Auditory Systems Flashcards
What is the zone of transition of the epithelium of the conjunctiva with that of the cornea? It is also the boundary of transparent cornea with opaque sclera.
Limbus
What are the layers of the cornea from anterior surface to aqueous humor?
Corneal epithelium Bowman's layer Stroma Descemet's membrane Corneal endothelium
What anchors the basal cells of the corneal epithelium to Bowman’s layer?
Hemidesmosomes
What participates in active transport of materials from aqueous humor into Descemet’s membrane and part of the corneal stroma?
Corneal endothelium
Where are myelinated nerves and unmyelinated nerves in the cornea?
Myelinated nerves are in the stroma.
After crossing Bowman’s layer, nerves become unmyelinated and extend toward the surface in intercellular spaces of corneal epithelium.
What is the anterior part of the corneal stroma?
Bowman’s layer
What is formed by collagen lamellae oriented at an angle to each other, has fibroblasts between the lamellae, and does not have blood vessels?
Stroma
What is permeable to air oxygen used for various oxidative reactions like glutathione reduction and oxidation?
Corneal endothelium
What is the most common form of tissue allotransplantation with a success rate of over 90%?
Cornea transplant (penetrating keratoplasty)
What is the vascular layer called in the posterior 2/3 of the eye?
Choroid
In the anterior part of the eye, the vascular layer thickens to become what?
Ciliary body
What extend inward from the ciliary body?
Ciliary processes
The vascular layer from the ciliary body continues as what?
Iris, whose free edge outlines the pupil
Describe properties of the vascular layer of the uvea
Pigmented, which light-proofs the inner surface of the eye and reduces reflection of the light
Blood vessels travel through this layer
Its anterior portion contains smooth muscle: muscle of ciliary body and dilator & constrictor of the iris.
What does the muscle of the ciliary body do?
Regulates tension of zonule or suspensory ligament of the lens
It is an important element in accommodation (relaxes tension of zonule)
Describe the anterior surface vs posterior surface of the iris
Anterior surface lacks epithelial lining
Posterior surface is lined by a dual layer of pigmented epithelium cells (direct continuation of the pigmented layer of the retina)
The stroma contains melanocytes and myoepithelial cells forming the ___?
Dilator pupillae
Describe innervation and function of dilator pupillae
Contains alpha-adrenergic receptors and is innervated by sympathethic nerve fibers
Contraction of the dilator causes pupil dilation (mydriasis)
Describe innervation and function of sphincter pupillae
Consists of smooth muscle
Has acetylcholine receptors and is innervated by parasympathetic fibers
Sphincter contraction reduces diameter of pupil (miosis)
Describe the layers of the retina
Outer pigmented layer
Inner retinal layer
Describe the light zones of the retina
Posterior 2/3 light-sensitive zone
Anterior 1/3 light-nonsensitive zone
Scalloped border between these two zones is called ora serrata
What neurons does the retina contain?
Photoreceptor neurons (cones and rods) Conducting neurons (bipolar and ganglion cells) Association neurons (horizontal and amacrine cells) Supporting neuroglia cells (Muller cell)
What photoreceptor neurons are only present in the fovea?
Cones
This is where detail vision is the best
Where do axons from retinal ganglion cells converge?
Pass across surface of retina
Converge on papilla or optic disk
Leave eye through many openings in sclera (lamina cribrosa) to form optic nerve
Describe the layers of the retina from inner region to outer region
Inner limiting membrane Nerve fiber layer (axons of ganglion cells) Ganglion cell lyaer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer Outer limiting membrane Inner and outer segments of rods and cones Pigmented epithelium
What does the inner limiting membrane represent?
Basal lamina of Muller cells
What happens in the inner plexiform layer?
Axons of the bipolar cells synapse with dendrites of ganglion cells
What makes up the inner nuclear layer?
Nuclei of bipolar cells and nuclie of Muller cells
What makes up the outer plexiform layer?
Axons of cones and rods that synapse with dendrites of bipolar cells
What are in the outer nuclear layer?
Nuclei of rods and cones
What does the outer limiting membrane correspond with?
Junctional complexes (zonula adherens) between rods, cones, and Muller cells
What do horizontal cells and amacrine cells synapse with?
Horizontal cells synapse with several rods and cones
Amacrine cells synapse with axons of bipolar cells and dendrites of ganglion cells
Describe the fovea centralis
Tightly packed cones are arranged at an angle to the pigmented layer
Thus, the outer nuclear layer and other layers of sensory retina do not obstruct the light pathway
The outer segment of the photoreceptor cells receives light that has not passed first through other layers of retina
What part lacks photoreceptors and corresponds to the blind spot of the retina?
Optic disk
What is pale in comparison to surrounding nerve fibers in the optic disk? Clinical relevance?
Optic disk
A loss of nerve fibers in glaucoma results in an increase in optic cup area
What happens to the optic disk when intraocular pressure increases? If intracranial pressure increases?
The disk of the optic nerve appears concave
The disk becomes swollen (papilledema), and the veins are dilated
What is the macula lutea?
Yellow spot produced by xanthophyll pigments within retinal cells
Provides for central vision
Describe detachment of retina
Separation of two layers of retina
Caused by trauma, vascular disease, metabolic disorders, and aging
Describe color blindness
When a single group of color-receptive cones is missing, the individual cannot distinguish some colors from others
Missing green and red-sensitive visual pigments in cones determines red-green color blindness (X-chromosome-linked gene)
What produces aqueous humor?
Epithelial lining of ciliary processes
Describe the flow of aqueous humor
Flows from posterior chamber through pupil into anterior chamber
Fluid percolates through a thin endothelial lining and loose connective tissue (trabecular meshwork)
Then in Canal of Schlemm
Aqueous veins drain canal of Schlemm into episcleral veins
Describe glaucoma
Obstruction of aqueous humor that causes an increase in intraocular pressure
Produces pain and nausea
Either by blockage of canal of Schlemm (most common) or inflammation preventing aqueous humor from reaching trabecular meshwork
How do cataracts develop?
Proteins filensin and crystallins become insoluble due to aging or diabetes. This causes opacity When glucose (the main metabolite of the lens) concentration is high, the byproduct sorbitol accumulates. Excess sorbitol reduces the solubility of the crystallins
What secrete a lipid-containing product that retards evaporation of the tear film?
Tarsal glands
Describe the conjunctiva
Stratified-to-columnar epithelium with mucus-secreting goblet cells, supported by a thin lamina propria
It lines anterior surface of eyeball up to limbus (bulbar conjunctiva) and inner surface of eyelid (palpebral conjunctiva)
What is opaque and lined by middle or vascular pigmented layer that absorbs light?
Sclera
What do the sensory receptors in the crista ampullaris respond to?
Position of the head, generating nerve impulses necessary for correcting the position of the body
Describe the maculae
Sensory receptor areas located in the wall of the saccule and utricle
They are concerned with the detection of directional movement of the head
Position of the macula in the utricle is horizontal
Position of the macula in the saccule is verticle
Describe the otolithic membrane
Composed of the same gelatinous glycoprotein-rich material as the cupula of the crista ampullaris
There are otoliths in macula
Base of the membrane is supported by filamentous base with small pores in the areas overlying each hair bundle
What happens when the stereocilia move toward the kinocilium?
Depolarization
What happens when stereocilia are displaced away from the kinocilium?
Hyperpolarization
Describe location of type 1 hair cells vs type 2
Type 1 cells predominate at ridge of crista
Type 2 cells are more numerous at the base
what is the cupula?
Glycoprotein-containing gelatinous structure surrounded by endolymp
Describe the conduction of sound
- Sound waves traveling across the perilymphatic channels produce oscillatory movements of the cochlear partition, including the basilar membrane
- Oscillatory movements against the oval window result in equal but opposite movements of the round window.
- An inward movement of the stapes against the oval window - caused by airborne sound - is transmitted to the cochlear partition by the noncompressible perilymph fluid
What is the helicotrema?
At the apex or cupula of the cochlea
Links the perilymph-filled scala vestibuli and scala tympani
Which hair cells in the cochlea are in direct contact with the tectorial membrane?
Outer hair cells
