lecture 16 - the eye Flashcards
What are the three tunics of the eye?
- Fibrous tunic
- sclera (tunica fibrosa)
- Cornea
- Vascular tunic
- choroid
- Ciliary body
- Inner tunic
- Retina
What are the layers of the sclera?
-
Episcleral Layer
- Outer layer
- loosely arranged collagen and elastic fibers
- highly vascular
- attaches the lining of the eyelid (conjunctiva) to the sclera
-
Sclera Proper
- made up of interlacing collagen fibers
- attachement site for tendons of extrinsic eye muscles
- collagen bundles are always parallel to outer surgace of scelera
- Lamina Cribrosa
- Perforated disc of sclera
- pass through for optic nerve fibers
- Anteriorly the sclera is continuous with the cornea
- the junction between the two is the limbus; it is highly vascularized
- posteriorly the sclera is continuous with the dural covering of the optic nerve
what are the layers of the cornea ?
-
Cornea epithelium
- stratified non keratinized squamous epithelum
- high mitotic activity in the basal layer
- turnover = 1 week
-
Bowmans membrane
- Acellular layer separates epithelium from stroma
- randomly arranged collagen fibers
-
Corneal Stroma
- Thin layers of ordered arrays collagen fibers
-
Descemets membrane
- Acellular layer of collagen bundels separates stroma from endothelium
-
Corneal endothelium
- single layer of large squamous cells
What is the choroid ?
- Part of the Vascular Tunic (uvea)
- Extends anterior to ora serrat of retina
- highly vascularized with loose connective tissue
- forms choriocapillary network that supplys retina cells and outelayers
- contains melanocytes
- Bruchs (glassy) membrane)
- Acellular fused basal laminae of choriocapillaris and pigented retina epithelial
What is the Ciliary body?
- Wedge-shaped expansion of choroid peripheral to the lens
-
covered by a double layer of cells
- innermost layer is continous with pegmineted retina
- surgace layer is sensory layer of retina
- produces aqueous humor
- Suspensory ligaments (of Zinn) extend to just behind lens equator and anchor lens in place
-
Ciliary muscles
- smooth muscle that changes shape of lenses
- parasympathetic innervation
- flatten lens (one grp of muscles)
- Thickens lens (second)
-
Nonpigmented suraace layer of cells produce aqueous humor
- basal infolding secrete aqueous humor into posaterior chamber
- aqueous humor
- percolates through trabeular meshwork
- flows into canal schlemm
What is the Iris ?
- Apart of the vascular tunic (uvea)
- THe iris located anterior to the lens and separates the anterior posterior chambers
-
angle
- lateral borders of ant chamber
- loose CT
- Part of passageway for aqueous humor
- Surrounds pupil
-
Double layer of Epithelium
- inner layer = pigmented eputhelial cell
- outer layer of radially oriented myofilaments
- dilated pupillae muscle
- sympathetic
- dilates pup[il
- Concentric layer of myofilaments
- constricts the pupil
- parasympathetic innervation
-
Melanocytes
- More melanocytes the darker the iris
What is the inner tunic?
- Retina
- Two subdivsions divded by the ora serrata
-
Photosensitive region lies posterior to the ora serrata
- optic dic
- region on posterior aspect of eye where optic nerbe exits
- has no photosensitive retina and constitutes the blind spot
- Fovea centralis
- about 2.5 mm lateral to optic disc
- contains yellow pigment = macula lutea
- contains only cone type photoreceptors
- area of most acute vision
- optic dic
-
Photosensitive region lies posterior to the ora serrata
- Nonphotosensitive region liies anterior to the ora serrata
- consists of two cells covering iris , ciliary body, and ciliary processes
- Photosensitive region lies posterior to the ora serrata
- includes rods and cones
what are the chambers of the eye?
- Anterior chamber
- Posterior to cornea and anterior to iris
- Posterior chamber
- posterior to iris and anterior to lens
- Vitreal chamber
- Posterior to lens
- contains vitreous body
- gelatinous mass made up of 99% water, hyaluronic acid, and vitrein
- hyaloid canal is the site of a fetal artery
- Glaucoma
- Increased intraocular pressure due to compromised drainage of aqueous humor from anterior chamber
What is the pigmented epithelium?
Layer of the Reina
Adjacent to the choroid
dervivded form outer theinner layer of the optic cup
What are inner and outer segments of rods and cones
Outer segment consists of rhodopsin-containing lamellae
inner segment consists of areas of rods and cones possessing mitochondria, RER, golgi, and glycogen (metabolically active)
Layer of the Reina
What is the external limiting membrane?
area at junction of inner and outer segments of rods and cones and outer nuclear layer
includes adherens junctions between rods and cones and mueller cells
Layer of the Reina
What is the outer nuclear layer
cell bodies of rods and cones (1st order neurons)
Layer of the Reina
What is the Outer plexiform layer?
area of synapses between acons of rods and cons and dendrites of bipolar neurons and horzontal cells
Layer of the Reina
What is the inner nuclear layer?
cell bodies of bipolar cells (2nds order neurons ) , horizontal cells, amacrine cells, and mueller cells
Layer of the Reina
What is the inner plexiform layer?
Area of synapses between axons of bipolar cells and dendrites of ganglion cells
Layer of the Reina
What is the Ganglion cell layer
cell bodies of ganglion cells (3rd order Neurons)
Layer of the Reina
What is the optic nerve layer?
Axons of ganglion cells
Layer of the Reina
What is the internal limiting membrane?
Terminations of mueller cell processes for their basement membrane
Layer of the Reina
What are pigmented epithelial cells?
adjacent to choroid
synthesize melanin
apical processes surround and [rptect outer segments of rods and cones (photosensitive areas )
Phagocytose and segrade lamelae form rods and cones
connect via tight junctions to form blood retina barrier
esterify vitamin A used in formation of photosensitive pigments
Layer of the Reina
What are bipolar cells
condicting neurons that synapse with rods and cones
Layer of the Reina
What are horizontal cells ?
Interneurons that interconnect rods and cone with each other and with bipolar cells
Layer of the Reina
What are amacrine cells/
Interneurons that connect ganglion cells and bipolar neurons
layers of the retina
What are ganglion cells?
Conductiong neurons whose axons form the fibers of the optic nerve
What are muller cells
neuroglial cells that extend throughout retina
form external limiting membrane via zonulae adherens between muller cells and rods and cones
internal limiting membrane formed by the baement membrane of these cells
Layer of the Reina
What is the macula lutea ?
Yellow region surrounding fovea
highest visual acuity
Layer of retina
What is fovea centralis ?
depression of the visual axis
highest density of cone cells
lacks rods cells and capillaries
Layer of retina
What is the optic disc?
Lacks photoreceptors
point where ganglion cell axons turn into optic nerve
blind spot of retina
Layer of retina
What are the types of photo receptors?
- Rods - use rhodopsin as photopigment
-
Cones - 3 different kinds of iodopsons as photopigments
*
WHat is the general structure of photoreceptors?
- spherule (Rod) or pedicle (cone)
- cell body
- nucleus and short axon
- inner segmemt
- mitochondria and other organelles
- outer segment
- modified cilium
- connected by a stalk to inner segment
- site of stacks of disks contain photoreceptors
- Disks
- in rods cells
- disks detach from cell membrane and become free
- constantly renewed (older disks are phagocytosed)
- In cone cells
- disks remain sttached to cell membrane
*
- disks remain sttached to cell membrane
- in rods cells
What are the difference between rods and Cones
- Rods
- rhodopsin as photopigment
- sensitive to low light intensity
- responsible for black and white vision
- lamellae of outer segment are not continuous with plasmalemma
- axons of up to 100 rods synapse with sigle bipolar cell
- Cones
- 3 different kinds of iodopsons as photopigments
- sensitive to high intensity llight
- greater vsual acuity than rods
- lamellae of outer segment are continuous with plasmalemma
- each cone cell synapses with a single bipolar cell
What is rhodopsin?
Transmembrane glycoprotein
consists of opson and 11-cis-retinal
What happens when a photon strikes 11 cis retinal (vitmin A dervivtitive) ? LOW TESTABILITY
- Cis - retinal transforms into 11 trans retinal
- rhodopson becomes activated
- activated rhodopsin interacts with transducin (g protein)
- Activates cGMP phospodiesterase
- Closing of sodium channels
- Hyperpoalrization of hte rod cell
- reduction in calcium ion influx
- decline in calcium concentration activates recovering
- stimulates guanylate cyclase
- returns cGMP concntration to normal
What is does bleaching mean in relation to photopigments?
Disassembly of rhodopsin into opsin and retinal after light stimulation
What is the regeneration of photopigments
11- trans retinal converted back into 11 cis -retinal
11 cis retinal is transported back to photoreceptor
recombines with opsin
Rhodopsin is regenerated
What is the capsule?
Insertion point for suspensory ligament
glycoprotein and type 4 collagen
secreted by sub-capsular epithelial cells
layer of lens
What is the anterior epithelium?
simple cubodial epithelium
gives rise to cells that become lens fibers
layer of lens
What is the lens nucleus ?
Composed of lens cells that mature into fiber like structures that are devoid of nucleus and organelles and fileld with crystalline proteins
What is the anterior surface of the Eyelid?
- Covered with skin
-
Glands of Zeiss
- sebaceous glands associated with eyelids
-
glands of moll
- sweat glands
- ducts open into eyelash follicles
What is the palpebral fascia of the eyelid?
- fibrous core of eyelids
-
meibomian glands (tarsal)
- sebaceous glands
- open in front of free edge of eyelid
- secretion keeps tear film in eye
What is the palpebral conjuctive?
Stratfied columnar or squamous epithelium with goblet cells
lines inner surface of eyelids
continous with bulbar conjuctiva (covers eyeball)
