Lecture 22 Histology of the Eye II Flashcards
Layers of the Retina
Pigmented epithelium Inner and outer segments of rods and cones External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Optic nerve layer Internal limiting membrane
Pigmented epithelium
Adjacent to choroid
Derived from outer (thinner) layer of the optic cup
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)
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.
Outer nuclear layer
Cell bodies of rods and cones (1st order neurons)
Outer plexiform layer
Area of synapses between axons of rods and cones and dendrites of bipolar neurons and horizontal cells.
Inner nuclear layer
Cell bodies of bipolar cells (2nd order neurons), horizontal cells, amacrine cells, and mueller cells
Inner plexiform layer
Area of synapses between axons of bipolar cells and dendrites of ganglion cells
Ganglion cell layer
Cell bodies of ganglion cells (3rd order neurons)
Optic nerve layer
Axons of ganglion cells
Internal limiting membrane
Terminations of mueller cell processes and their basement membrane
Cells of the Retina
Pigmented epithelial cells Bipolar cells Horizontal cells Amacrine cells Mueller cells Ganglion cells
Pigmented epithelial cells
Adjacent to choroid
Synthesize melanin
Apical processes surround & protect outer segments of rods & cones
Phagocytose & degrade lamellae from rods & cones
Connected via tight junctions to form blood-retina barrier
Esterify vit. A used in formation of photosensitive pigments
Bipolar cells
Conducting neurons that synapse with rods and cones
Horizontal cells
Interneurons that interconnect rods and cones with each other and with bipolar cells
Amacrine cells
Interneurons that connect ganglion cells and bipolar cells
Mueller cells
Neuroglial cells that extend throughout retina.
Form external limiting membrane via zonula adherens between mueller cells and rods and cones .
Internal limiting membrane is formed by the basement membrane of these cells
Ganglion cells
Conducting neurons whose axons form the fibers of the optic nerve
Macula lutea
Yellow region surrounding fovea
Highest visual acuity
Fovea centralis
Depression of visual axis
Highest density of cone cells
Lacks rod cells and capillaries
Optic disc
Lacks photoreceptors
Point where ganglion cells turn into optic nerve
“blind spot” of retina
Types of Photoreceptors
Rods
Cones
Rods
Use 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 single bipolar cell
Cones
Use three different kinds of iodopsins as photopigment
Sensitive to high-intensity light
Greater visual acuity than rods
Lamellae of outer segment are continuous with plasmalemma
Each cone cell synapses with a single bipolar cell
General architecture of photoreceptors
Spherule (rod) and pedicle (cone)
Cell body
Inner segment
Outer segment
General architecture of Inner segment of photoreceptors
Mitochondria and other organelles
General architecture of Cell body of photoreceptors
Nucleus and short axons
General architecture of Outer segment of photoreceptors
Modified cilium
Connected by a stalk to inner segment
Site of stacks of disks containing photoreceptors
General architecture of disks of rod cells
Disks detach from cell membrane and become free.
Constantly renewed in rod cells
Older disks are phagocytosed by surrounding pigmented epithelial cells
General architecture of disks of cone cells
Disks remain attached to cell membrane
Rhodopsin
Transmembrane glycoprotein
Consists of opsin and 11-cis-retinal
When photon strikes the 11-cis-retinal (vitamin A derivative):
Cis-retinal transforms into 11-trans-retinal
Rhodopsin becomes activated
Activated rhodopsin interacts w/ transducin (G-protein)
Activates cGMP phosphodiesterase
Closing of sodium channels
Hyperpolarizaiton of the rod cell
Reduction in calcium ion influx
Decline in Ca concentration activates recoverin
Stimulate guanylate cyclase
Returns cGMP concentration to normal
Bleaching of photopigments
Disassembly of rhodopsin into opsin and retinal after light stimulation
Regeneration of photopigments
11-trans-retinal is converted back into 11-cis-retinal
11-cis-retinal is transported back to photoreceptor
Recombines with opsin
Rhodopsin is regenerated
Capsule of the Lens
Insertion point for suspensory ligament
Glycoproteins and type IV collagen
Secreted by subcapsular epithelial cells
Anterior epithelium of lens
Simple cuboidal epithelium
Give rise to cells that become “lens fibers”
Lens nucleus
Composed of lens cells that mature into fiber-like structures:
- Devoid of nucleus and organelles
- Filled with crystalline proteins
Anterior surface of the eyelid
Covered with skin
Glands of Zeiss
Glands of Moll
Glands of Zeiss
Sebaceous gland associated with eyelids
Glands of Moll
Sweat glants
Ducts open into eyelash follicles
Palpebral fascia of eyelid
Fibrous core of eyelids Meibomian glands (tarsal)
Meibomian glands
Sebaceous glands not associated with hair follicles
Open in front of free edge of eyelid
Secretion keeps normal tear film in eye
Palpebral conjunctiva of eyelid
Stratified columnar or squamous epithelium with goblet cells
Lines inner surface of eyelids
Continuous with bulbar conjunctiva (covers eyeball)
