Sense organs

Question 1

Eye intro
develop
brief intro on layers
eye chambers

Answer 1

eye is highly deveped photosensitive organ, analyse form, intensity, colour of light reflected fmo obj providing sense of sight.
- protected w orbit of skull, adipose cushions, tough fibrous globe to maintain shape, photosensitive cells + system of neurons (send ingo to brain)

develop:
- 4th week, OPTIC VESICLES bulge bilaterally from forebrain + elongate as OPTIC STALKS bearing OPTIC CUPS
- inductive interactions endoderm and optic cups, cause endoderm to INVAGINATE +detach as hollow LENS VESICLES
- optic stalk develops-> OPTIC N and in inferior groove= CHOROID FISSURE enclosed HYALOID VESSELS (supply lens and optic cup)
- next weeks head mesenchyme -> forms most tissue of eye- two outer and vitreous. Ectoderm of optic cup -> RETINA; surface of ectoderm forms CORNEAL EPI. lens fully forms, distal hyaloid a+ v DISSAPEARS leaving blood supply to retina

sensory epi: sensory+ supporting cells
sensory cells: convert external stimuli onto electrical impulse
classify ACC to stimulus
chemoreceptors: olfactory cells+ taste cells
mechanoreceptors: hair cells of inner ear (equilibrium+ hearing and balance)
photoreceptors: rods+cones of retina

according to structure:
1) primary: have axons: rods, cones and olfactory cells
2) secondary: no axons: hair and taste cells

3 layers
1) FIBROUS layer: tough external layer =
- post white SCLERA (0.5mm thickness, 5/6 of fibrous layer)
DENSE IRREG CT, FLAT COLLAGEN I BUNDLES+ microvasc; F: protects + origin for muscles.

• ant transparent CORNEA (1/6 of layer)= AVASC
  1) STRAT SQ EPI non keratinized (5-6 layer THICK , 10% cornal thickness) transport NA+ richest sensory n supply; NUCLEAR FERRITIN UV protection
• LIMBUS encircles cornea= corneoscleral junction epi;
  2) Bowman’s membrane: thick basement membrane beneath corneal epi (IRREG COLLAGEM FIBRES, protection against infection)
  3) thick stroma: 90%, 60 layers of LAMELLAE OF COLLAGEN DENSE CT, between lamellae flattened fibroblasts-like-cells= KERATINOCYTES. GS ground substance- keratan sulphate, chondroitin sulphate
  4) Descemet’s membrane: mesh of collagen fibers (another thick basement membrane supports corneal endothelium
  5) Corneal endothelium: SIMPLE SQ, low cuboidal EPI. transport Na/K to reg hydration state of corneal stroma for max transparency+ optimal light refraction)

2) VASCULAR/UVEA layer: = CHOROID, CILIARY BODY (loose CT, ciliary smooth m- accommodation; ciliary process: zonule fibres anchor lens; produce aqueous humor=clear fluid that fills ant chamber) and IRIS (opaque pigmented extension of vasc layer) w pupil (opening)

3) RETINA: innermost layer communicates w cerebrum though posterior OPTIC N
- pars optica: photosensitive
- pars ceaca: 2 cell layers line ciliary body + iris

Eye chambers
anterior: between cornea+ iris. filled w aqueous humor (excess reabsorbed by SCLERAL VENUS SINUS)
posterior: between posterior iris+ anterior lens. filled w aqueous humor (goes through pupil to reach ant)
vitrous: between post surface of lens and neural retina. VITREOUS BODY- chamber filled w CT (gelatinous mass w CT)

Question 2

in-depth of 2 layers
Lens

Answer 2

3 layers
1) FIBROUS layer: tough external layer =
- post white SCLERA (0.5mm thickness, 5/6 of fibrous layer)
DENSE IRREG CT, FLAT COLLAGEN I BUNDLES+ microvasc; F: protects + origin for muscles. encloses eyeball (22mm=d). ant muscle inserts; post thickens 1mm snf joins EPINEURIUM covering optic n+ surrounds choroid. SUPRACHOROID LAMINA (less collagen, more fibroblasts, ELASTIC fibres+ MELANOCYTES)
in children have slight blue tint/ yellowish in elderly bc of LIPOFUSCHIN ACCumulation in stroma

• ant transparent CORNEA (1/6 of layer)= AVASC
  1) STRAT SQ EPI non keratinized (5-6 layer THICK , 10% cornal thickness) transport NA+ richest sensory n supply; NUCLEAR FERRITIN UV protection
• LIMBUS encircles cornea= corneoscleral junction epi; bowmans membrane ends and epi more STRAT as CONJUCTIVA (covers abt part of clear).
  -stroma becomes vasc and less organized bc collagen merge w cornea’s
  -STEM cells renew basal cells (high proliferation). Limbus has MICROVILLI protrude into protective TEAR FILM of lipid, glycoprotein and water.
  • SCHELMM’S CANAL : drains fluid from ant chamber (receives from TRABECULAR meshwork= irreg ENDOTHELIAL lined channels )- fluid after schelmms canal-> small veins of sclera2) Bowman’s membrane: thick basement membrane beneath corneal epi (IRREG COLLAGEM FIBRES, protection against infection)
    3) thick stroma: 90%, 60 layers of LAMELLAE OF COLLAGEN DENSE CT, between lamellae flattened fibroblasts-like-cells= KERATINOCYTES. GS ground substance- keratan sulphate, chondroitin sulphate
    4) Descemet’s membrane: mesh of collagen fibers (another thick basement membrane supports corneal endothelium
    5) Corneal endothelium: SIMPLE SQ, low cuboidal EPI. transport Na/K to reg hydration state of corneal stroma for max transparency+ optimal light refraction)

2) VASCULAR/UVEA layer: = CHOROID, CILIARY BODY (loose CT, ciliary smooth m- accommodation; ciliary process: zonule fibres anchor lens; produce aqueous humor=clear fluid that fills ant chamber) and IRIS (opaque pigmented extension of vasc layer) w pupil (opening)

- choroid -on post 2/3 of eye LOOSE CT well vasc (fenestrated cap) + MELANOCYTES (form balc layer prevent light from entering anywhere but pupil, minize glare.     CHOROIDACAPILLARY LAMINA- first layer, loose CT, rich microvasc for outer retinal layers    BRUCH MEMBRANE- thin sheet, COLLAGEN+ELASTIC fibers surround adj microvasc and basal lamina of retina pigmented layer (attach choroid to retina- amorphous refractile area)

 -  ciliary body- internal to limbus    SMOOTH CILIARY M= accommodation (affect shape of lens to focus on obj far/near): MERIDIONAL (angle of IC??), RADIAL (distant) AND CIRCULAR (near)    CILIARY PROCESSES: covered w two layers of cells (CUBOIDAL/COLUMNAR).   - adj to process= PIGMENTED CELLS (on pigmented cells has inner non pigmented cells= acts as basal lamina F: give rise to ciliary zone)  - produce aqueous humor-> post chamber-> through pupil to ant chamber-> drains at angle formed by cornea-> iris -> trabecular meshwork and scleval venous sinus-> venules of sclera 
CILIARY ZONULE: w zonule fibres/ suspensory lig of lens FIBRILLIN rich fibers attach to capsule of lens.  vitreous chamber is post to lens and ciliary zonule

   - Iris: most anterior extension. ofuveal layer covers lens has pupil stroma: VASC LOOSE CT, MELANOCYTES, MACROPHAGE+ fibroblasts F: reg amount of light retina is exposed to; colour of eye- albino no pigment and its reflection of blood vessels    MYOEPI CELLS form PIGMENTED EPI layer which extend CONTRACTILE PROCESSES=DILATOR PAPILLAE M     POSTERIOR PIGMENT EPI- melanin to block light from entering eye except pupil; (give colour)
smooth m w circular bundle near pupil= SPHINCTER PAPILLAE M (smooth m- constriction). 

3) RETINA: innermost layer communicates w cerebrum though posterior OPTIC N
- pars optica: photosensitive
- pars ceaca: 2 cell layers line ciliary body + iris

Lens- suspended behind iris. 10um-d, 4mm thick
TRANSPARENT, BICONVEX, AVASC, highly ELASTIC (decrease w age=CATARACT)
capsule: thick, CARB rich basement membrane (COLLAGEN IV)
subscapular epi: SIMPLE CUBOIDAL- give rise to lens fibres undifferentiated cells. (mature: no nuclei/organelles. immature: still have nuclei, CRYSTALLINS protein in cyto.
lens fibers thin+flat 7-10mm long; tightly packed to be perfectly transparent for refraction
lens fixed by zonule fibres;
accommodation: focus on near/far obj by changing curvature
- eye at rest or looking far obj, ciliary m relax, ciliary body puts tension on zonule fibres= lens flatter.
- close obj: ciliary m contract, displaces ciliary body, releave tension on zonule fibres; lens in more rounded shape
PRESBYOPIA cause lens loose elasticity+ ability for accommodation in 40y

Question 3

retina
speciaised areas of retina

Answer 3

2 main layers (double epi):
- outer pigmented layer: epi resting on Bruch’s membrane inside choroid. PIGMENTED CUBOIDAL EPI also lines ciliary body+ posterior iris.
- inner neural retina: thick+stratrified; neurons+photoreceptor

4 types of cells
PHOTORECEPTOR CELLS: rods+cones
CONDUCTING NEURONS: bipolar n+ ganglionic cells
ASSOCIATION NEURONS: centrifugal, interplexiform, horizontal+ amacrine
SUPPORTING CELLS: muller, microglial and astrocyte cells

retinal pigmented layer

basal nuclei, junctional complex like gap j, invaginatins of basal membrane of mitochondria.
cells extend processes around photoreceptors rich in MELANOCYTES granules + apically. Also has phagocytotic vacuoles, secondary lysosomes (phagocytosis membrane has pump to increase acidity), peroxisome (single membrane no nuclei, metabolism of lipids, abundant smooth ER (vit A isomerization).

F: -BLOOD-RETINA BARRIER due to TIGHT junction: isolating photoreceptors from vasc choroid, reg ion transport;
-absorbs light passing through retina to prevent its reflection through neural layer-> choroid ;
-phagocytose of shed components from rods and cones;
-remove free radicals which supports neural retina by ATP, polypeptide growth factors and immunomodulary factors.
**Neural retina **

9 layers:
1) RETINAL PIGMENTED epi.
2) PHOTORECEPTORS. (outer + inner segs of rods+coins) recieve O2 from choroidocappilary of choroid.
3) OUTER LIMITING membrane: apical boundaries of MULLER CELLS
4) OUTER NUCLEAR layer: cell bodies of RODS+CONES
5) OUTER PLEXIFORM layer:processes of photoreceptors and connecting w process of amacrine+ bipolar+ horizontal cells
6) INNER NUCLEAR layer:cell bodies of bipolar n+ amacrine+ horizontal cells+ muller cells making specific connection w other neurons and integrade signals w photoreceptors.
7) INNER PLEXIFORM layer: same as outer
8) GANGLIONIC layer: near vitrous body, ganglionic cells+ longer axons. thickest near central macular region of retina; thins peripherally to one layer of cells
9) NERVE FIBER layer: axons of ganglionic cells converge to form OPTIC N
10) INNER LIMITING MEMBRANE: basal lamina of MULLER CELLS

specialised areas of retina
non-photoreceptive region: extends to ora serrata lining inner part of ciliary body and posterior iris. 11-cis-retinal bound MELANOPSIN. detect change of light/dark (signal pass through retinohypothalamic tract-> suprachiasmaic nucleas-> synapse at pineal gland.
photoreceptor region: lines inner surface of eye and post to ora serrata (except where its pierced by optic n)
OPTIC DISC/PAPILLAE is site where optic n joins retina (no photoreceptor=blind spot (but has NFL). 1.7mm=d. central a+v in optic nerve goes through NFL supply ganglionic cells.
FOVEA CENTRALIS shallow depression from 2.5mm lateral to optic disc (highest concentration and most precisely ordered arrangement of the visual elements) where retina cell bodies in periphery mainly cones(long, narrow+closely packed). 1.5mm=d;
Visual axis of eye passes through fovea MACULA DENSA surrounds fovea. yellowish due to CAROTENOIDS- antioxidant property=filter damaging short wavelength.

Question 4

Rods and cones

Answer 4

Rods
92 mil
sensitived to light (respond to single photon); thin elongated cells
- outer seg: modified primary CILIUM/microvilli, short rod, photosensitive
MEMBRANOUS DISC: stacked+ surrounded p.m. due to repetitive unfolding of p.m near connecting stalk+ insertion of rhodopsin.Disc detach from p.m displaced distally(90 disc/day) by new disc until reach the end, PHAGOCYTOSED, by cells of pigmented epi (10 days). Has RHODOPSIN protein 1 billion (bleached by light, initiate visual stimulus)
- inner seg: divided into outer ELLIPSOID and inner MYOID. mito, glycogen and polyribososmes
- connecting stalk: between both, part of primary cilium comes from ciliary body. CALYCEAL PROCESS from distal end of inner seg surround prox end of outer seg.

Cones
less #, less light sensitive, 4.6 mil produce colour vision. Elongated w inner (modified cilium connecting stalk+mito and polyribosomes. outer seg: shorter, more conical, in staked membranous disc= CONTINOUS invagination of p.m. ha rhodopsin; shed less than rods
- cones w IODOPSIN (photopsin): max sensitivity to light of diff wavelength (red, blue, green). mix neural input by pigments = colour image

phototransduction
stacked membranous disc +cone outer seg parallel w retina (max exposure to light). densely packed w rhodopsin/iodopsin proteins (membrane bound).
- each pigment has OPSIN (transmembrane protein) w small light sensitivity CHROMOPHORE bound to it.
- RETINAL (vit A derivative) acts as chromophore of rods
- phototransduction: (cascade of changes)
trigger light to hit+activate chromophore
absorption of photon-> conformation change 11-cis-retina to all-trans-retina.
cause conformational change in opsin; activate TRANSUCIN (membrane protein, heterotrimeric G protein). closes cGMP Na channels-> hyperpolarization reduce NT release. depolarizes bipolar n send AP to ganglionic cells of optic n

• conformation change of retinal also cause chromophore to dissociate from opsin- BLEACHING.
  all-trasn-retinal transported back to rod-> pigmented epi cell to convert back to 11-cis-retinal -> photoreceptors for reuse
  process takes a min=slow adaptation of eye from bright to dim

Question 5

accessory structures of eye

Answer 5

3: conjuctiva, eyelid+ lacrimal gland
Conjuctiva: thin, transparent mucosa cover ant sclera. STRAT COLUMNAR EPI w small GOBLET CELLS. supported by thin LP loose vasc CT. mucous secretions added to tear film coats epi+cornea
conjuctivitis: bact infection in conjuctiva. inflamm increase mucous enlarging microvasc of sclera=reddish appearance. contacgeous but little affect on vision.

eyelid: pliable, protective structure: skin, muscle and conjuctiva. skin is loose elastic, flat, small hair follicles+hair exceptt large follicles of eyelashes =SABECOUS (ZIEL)+APOCRINE SWEAT glands (MOLL).
other glands: MEIBOMIAN: sabecous branched acinar, embedded in tarsal plate; GLAND OF ZEIS: sabecous empty to eyelash follicle. gland of MOLL: empty to edge of ACC LACRIMAL DUCT and ECCRINE gland: empty to skin
beneath has STRAT FASCICLES of orbicularis oris+ levator palpebrae m (folds eyelid).
adj to conjuctiva=dense fibroelastic plate=TARSUS. has 20-25 large sabecous glands w ACINI secretnug onto LONG CENTRAL DUCT opens into eyelashes. TARSAL glands= MEIBOMIAN GLANDS produce oils in sebum. forming surface layer on tear film, reducing state of evaporation to lubricate ocular surface.

lacrimal glands: produce film continously for tear film. moisten+lubricate cornea+conjuctiva+ supply O2 to corneal epi cells.
tear film also collects in LACRIMAL APPARATUS. floow through 2 small opening 0.5mm=d -> caniliculi (STRAT SQ EPI) at medial margin of lower+upper eyelid-> lacrimal sac (PSEUDO CILIATED EPI)-> nasal cavity via nasolacrimal duct (PSEUDO CILIATED EPI- like nasal cavity)
tear film= metabolytes, electrolyte, proteins of innate immun=lysosomes+ IgA.
Main lacrimal gland upper temporal portion of orbit, has several lobes drain through individual EXCRETORY DUCTS 12 into SUPERIOR FORNIX (conjuctiva lined recess between eyelids+ eye).
TUBULOACINAR SEROUS LOBULE lightly stained secretory granules w myoepi cells w sparse vasc stroma.
inter+intralobular ducts

Question 6

conjuctiva

Answer 6

lines space of inner part eyelid+ ant surface of eye
strat sq epi + goblet (mucous secretions added to tear film coats epi+cornea) + LP
below has lacrimal gland: tubuloacinar, secretes serous. myoepithelial cells
lacrimal gland: interlobular duct+ lacrimal duct and interlobular CT
conjuctivitis: bact infection in conjuctiva. inflamm increase mucous enlarging microvasc of sclera=reddish appearance. contacgeous but little affect on vision.

Question 7

retina

Answer 7

CHOROID- on post 2/3 of eye+ hyalin?

  SUPRACHOROIDAL lamina:part of sclera, loose pigmented CT MELANOCYTES (form balc layer prevent light from entering anywhere but pupil, minize glare. 
CHOROICAPILLARY layer: loose CT, fenestrated capillary supply O2 to retina
BRUCH'S membrane: 3-4um, elastic+collagen. separate blood from choroid to retina 

retina
1) retinal pigmented epi: cuboidal cell+melanin+
apical process under rods+cones (phagocytose by lysosomes, shed components)+ peroxisome
cells connect by gap j+occludens+adherens
blood-retina barrier: from choriocap
2) layer of rods+cones
3) outer limiting membrane: NOT TRUE membrane; tight+adherent junctions between apical boundary of MULLER cell
4) outer nuclear layer: cell bodies of rods+ cones
5) outer plexiform layer: axons rods+cones synapse w dendrites of cells in inner nuclear layer
6) inner nuclear layer: :cell bodies of bipolar n+ amacrine+ horizontal cells+ muller cells
7) inner plexiform layer: axons of inner nuclear cells synapse w dendrites of ganglionic cells
8) ganglionic cell layer: their cell bodies, large multipolar n, axons make 9 layer
9) nerve fiber layer: converge to make optic n
10: inner limiting membrane: basal lamina of MULLER cells