eye & ear spr 2011. eye layers of the eye fibrous layer: anterior – cornea posterior –...
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Eye & Ear
SPR 2011
Eye
Layers of the Eye
Fibrous layer: Anterior – cornea Posterior – sclera
Middle vascular layer: Choroid Ciliary body Iris
Neural layer: Retina – outer pigment &
inner neural layer
Cornea Anterior transparent layer of the eye ( outer fibrous layer) Refractive structure of the eye. Avascular - but can heal by
diffusion of nutrients from the limbus. Has numerous free nerve endings – Very sensitive!
Structure of the CorneaAnterior corneal epithelium
Stratified squamous non keratinizedEpithelium capable of regeneration if damageddrying leads to ulceration
Bowman’s anterior limiting membraneBarrier for infection
Substantia proprialamellae of collagen fibers (lymphocytes & fibroblasts are interspersed in between the
fibers) in a ground substance.Regular arrangement, Regular spacing gives cornea the transparency
Descemet’s membraneIncreases in thickness with age
Endothelial layerActive pump located in the cells that maintains the dehydrated state of the cornea
(substantia propria)
Sclera Posterior 5/6th of outer fibrous layer Connective tissue with collagen fibers Relatively avascular Yellow in elderly because of accumulation of Lipofuscin
pigments
Also called as the Limbus Corneal epithelium becomes the bulbar conjunctiva
Contains 2 very important structures:1. Trabecular meshwork2. Canal of Schlemm
Sclerocorneal Junction
LimbusCanal of Schlemm:
Canal lined with endothelium situated at the inner aspect of the corneal stroma close to the iris
Trabecular Meshwork: Fine collagenous
trabeculae enclosing endothelium lined spaces
Merge & open into canal of Schlemm
Chambers of the Eye
Anterior chamber – between iris & cornea
Posterior chamber – between lens & iris
Vitreous chamber – lens & retina
Aqueous Humor Clear watery Non- Refractile fluid
secreted by the ciliary body into the posterior chamber.
Similar to plasma with just 0.1% protein (as compared to 7% plasma protein in blood)
Provides nutrition to the lens & cornea. Replaced every 2-3 hrs. Determines intra-ocular pressure ( 15-
20mm of Hg)
Disturbances in production or flow – Glaucoma!
Glaucoma
Rise in intra-ocular pressure due to increased production or impaired drainage of aqueous humor.
Needs to be treated as can affect vision.
Vitreous Chamber
Gelatinous mass with some fluid 99% water with small amount of collagen &
Hyaluronic acid Few cells called Hyalocytes synthesize the
contents of the vitreous. Contains the hyaloid canal
Uveal Tract
Middle vascular layer
1. Choroid
2. Ciliary body
3. Iris
Choroid Loose vascularized connective tissue present between the retina &
sclera in the posterior 5/6th of the eyeball.
Contains a choriocapillary layer for nutrition & oxygenation of the underlying retina.
Choroid & retina separated by Bruchs membrane - a hyaline glassy membrane, extends from the optic disc to the ora serrata.
Contains pigmented melanocytes which absorb light that passes through the retina.
Ciliary Body Extends from the iris to the ora
serrata. Attached to the suspensory
ligaments of the lens. Contains ciliary muscle which
is made up of meridoneal, circular & radial fibers.
When it contracts, tension on the suspensory ligaments is reduced, thus permitting the lens to acquire a more convex shape for accommodation.
Has parasympathetic innervation.
Stroma made up of elastic fibers, blood vessels & melanocytes.
Lining epithelium is double layered:
Deep pigmented layer continuous with the retina.
Superficial non pigmented layer continuous with the neural layer of retina. Involved in transport of ions/water. Have features of fluid transporting cells.
Ciliary Processes
Finger like extensions. Have a connective
tissue core rich in fenestrated capillaries.
Produce aqueous humor.
Iris
Forms a diaphragm anterior to the lens.
Circular in shape with a central opening called Pupil.
Stroma has pigment cells. Color of iris (eye) depends
on the pigment in the stroma.
Blue eyes have less pigment, brown eyes have more pigment.
Conjunctiva
Bulbar conjunctiva – covers exposed part of sclera
Palpebral conjunctiva – covers inner surface of eyelids.
Stratified columnar epithelium with goblet cells which secrete mucus.
Lacrimal Gland
Compound tubuloacinar gland.
Acini with a single layer of columnar to pyramidal cells (like parotid)
Secrete tears which is a watery secretion containing lysozyme & antibodies Ig A.
Eyelid
Hairy skin – thin & highly folded with a loose supporting tissue.
Skeletal muscle – orbicularis oculi & levator palpebrae.
Submuscular connective tissue – extremely lax, continuous with the loose areolar tissue layer of scalp.
Tarsal plate – thick fibroelastic plate with Meibomian glands (modified sebaceous glands) - CHALAZION
Conjunctiva
Lid margin has eye lashes associated with glands of Zeiss (sebaceous) & glands of Moll (modified sweat) - STYE
Retina Consists of an outer pigment layer & inner neural layer. Inner neural layer composed
Photoreceptors – rods & cones Conducting neurons – bipolar cells & ganglion cells Association neurons – horizontal cells & amacrine cells Supporting cells –Muller cells & neuroglial cells
Intraretinal space is cleavage plane.
Rods outnumber cones (120million to 7 million)
Rods more sensitive to light than cones.
Cones for color vision & high visual acuity.
RetinaComposed of 9+1 layers:
1. Outer pigment layer
2. Photoreceptor layer – rods & cones processes
3. Outer (external limiting membrane) – apical boundary of Muller cells, site of tight junction with photoreceptors.
4. Outer nuclear layer – nuclei of cell bodies of rods & cones
5. Outer plexiform layer – axodendritic synapses between axons of photoreceptors & dendrites of bipolar & horizontal cells.
6. Inner nuclear layer – cell bodies of horizontal, amacrine & bipolar cells
7. Inner plexiform layer – synapses between axons of bipolar cells & dendrites of ganglion cells
8. Ganglion cell layer – cell bodies of multipolar ganglion cells9. Optic nerve fiber layer – axons of ganglion cells 10. Inner limiting membrane – basal lamina of Muller cells – separates
retina from vitreous.
Rods & cones Have inner & outer segments,
a nuclear region & synaptic region.
Outer segment – contains flattened membranous discs which contain Rods - Rhodopsin. Cones- Iodopsin
- Eventually shed their discs which are phagocytosed by the pigment epithelium.
Inner segment – has organelles for rhodopsin & iodopsin production & numerous mitochondria.
Cones recognize – RED, GREEN, BLUE
Rods Rhodopsin or visual purple has two absorption
maxims: 350 and 500 nm. The spectral extinction curve for rods corresponds to that of rhodopsin, suggesting that rhodopsin is the chemopigment in rods.
Rhodopsin consists of a glycoprotein (opsin) and a chromophore group (11-cis-retinal).
Retinal is the aldehyde of vitamin A1 (retinol).
Photoisomerization in Rods Inside the rod a special amplification takes place.
Light absorption by a single rhodopsin molecule activates thousands of G-protein molecules (transducin), which then activate large quantities of cGMP phosphodiesterase in the discs.
With absorption, specifically, it is the 11-cis form of retinene, which, isomerizes to the all-trans form.
This isomerization converts the rhodopsin to its active form, metarhodopsin II.
This reconfiguration of the retinene molecule thus produces the same effect as if a neurotransmitter had suddenly bound to a receptor.
The photoisomerization of 11-cis retinal to all-trans retinal in photoreceptors is the first step in vision – occurs in the OUTER SEGMENT
in the LIGHT rhodopsin changes conformation (TRANS), which activated enzyme TRANSDUCIN;
Transducin activates a PHOSPHODIESTRASE, converts cyclic-GMP to GMP;
GMP closes the Na channels, and HYPERPOLARIZES rod cells (RECEPTOR POTENTIAL);
hyperpolarized rod cell stops releasing GLUTAMATE, allowing bipolar cells repsond*
Vitamin A & Rods
The Vitamin A that our bodies produce from the beta carotene in many of the foods we eat (including, most famously, carrots) is needed to synthesize the retinene bound to the centre of the rhodopsin molecule.
Indeed, a severe Vitamin A deficiency impairs night vision, because of the smaller amounts of retinene being produced.
During the daytime, however, there is generally enough light to allow relatively normal vision despite low levels of visual pigments
Cones In the cones, the photosensitive pigment is opsin,
a transmembrane protein that is very similar to rhodopsin
The fovea only contains cones.
Cones function in the daytime with maximal visual acuity and colour vision.
The human eye possesses three types of cones, each with a specific pigment related to the three basic colours: red (erythrolab), green (chlorolab) and blue (cyanolab).
The cones in the fovea do not contain cyanolab.
Colour blindness
Classic red/green colour blindness is the result of a lack of red cones in the retina.
Forms of colour blindness are usually classified according to the type of cone affected.
Thus there are three kinds of colour blindness, corresponding to the three kinds of cones.
Blindness to green, due to deficiency of the green pigment, is called deuteranopia, and is the most common form
Macula: Yellow pigment zone
(xanthophyll) surrounding the fovea
Retinal vessels are absent here
Ganglion cells heaped to the sides so that light can pass unimpeded to the fovea.
Fovea Depression in the inner layer of
retina. Located 2.5mm temporal to the optic
disc. High concentration of photoreceptors
(only cones) for maximal visual acuity.
Ophthalmoscopic examination reveals brownish choroid pigments.
Optic Disc:• Site where optic nerve
exits the retina ( Blind Spot as no photoreceptors there)
• Central artery of the retina pierces it.
Optic Nerve
Forms innermost strata of the retina.
Unmyelinated intra-retinally. Converge at optic disc
(blind spot) & then acquires myelin.
Exits through lamina cribrosa of the sclera.
Extraocular part is surrounded by meninges.
Lens It is an encapsulated, elastic,
biconvex transparent structure.
Suspensory ligament connects it to the ciliary body.
Consists of anucleated fibers derived from the anterior epithelium. The synthetic rate decreases with age.
Contains the protein crystallin. Subcapsular cuboidal
epithelium anteriorly. Opacity causes cataract
Ear
Ear
External Ear: Receives & transmits the
sound waves to the middle ear.
Middle Ear: Sound waves converted into
mechanical movement of the ossicles & this is transmitted to the inner ear
Inner Ear: Sound waves transduced into
nerve signals. Vestibular organ, responsible
for equilibrium, located in the inner ear.
External Ear
Pinna – Has plates of elastic cartilage covered by skin (except lobule). Has hair follicles & sebaceous glands.
External auditory meatus - outer 1/3rd is cartilage & inner 2/3rd is bony. Canal is lined by skin which is closely bound to the underlying
cartilage or bone by a dense collagenous tissue. Hair follicles have sebaceous glands associated with. Ceruminous glands (modified sweat glands) secrete earwax
(cerumen) into the lumen along with sebaceous glands. Meatal hair – protection from foreign bodies Cerumen – protects against moisture & infection
Middle Ear Cavity – Tympanic Membrane
It is a thin fibrous membrane the separates the external ear from the middle ear.
Pars flacida – loose transparent part in the superior quadrant with a thin connective tissue membrane called Sharpnell’s membrane.
Pars tensa – thick non-transparent membrane
Normal
perforated
Middle Ear Cavity – Tympanic Membrane
Has 3 layers:1. Outer cuticular layer – thin hairless skin with no epidermal
ridges, dermis contains a fine vascular network.
2. Intermediate fibrous layer – outer layer of radiating collagen fibers, inner layer of circumferentially arranged fibers
3. Inner mucous layer – single layer of cuboidal cells with no cilia & goblet cells, thin lamina propria with its own blood supply.
Auditory Tube Connects middle ear with Nasopharynx & allows for
equalization of pressure in the middle ear. 2 parts – bony & cartilaginous (towards pharynx). Lined with simple columnar near tympanic cavity & respiratory
epithelium near the pharynx.
Ear Ossicles
Malleus – attaches to tympanic membrane
Incus – middle ear ossicle
Stapes – fixed to the oval (vestibular) window & is in contact with the perilymph of the inner ear.
Inner Ear
Vestibule Semicircular canals
CRISTA AMPULLARIS– ROTATIONAL MOVEMENT
Utricle & saccule MACULA – LINEAR
MOVEMENT
Cochlea
Vestibule
Structure: central, between cochlea and semicircular canals
Function: detect static equilibrium, linear acceleration
Maculae (inside utricle and saccule) contain receptor cells with hairs imbedded in membrane with otoliths (“ear stones” - CaCO3), position detected by pulling hairs
Inner Ear - vestibule
Bony Labyrinth: Intercommunicating periosteum lined
canals - semicircular canals, vestibule & cochlea.
Contains perilymph which is similar to CSF in composition.
Membranous Labyrinth: Closed sacs in the bony labyrinth.
Consists of the cochlear duct, saccule & utricle, semicircular ducts & endolymphatic sac.
Contains endolymph which is similar to intracellular fluid & is absorbed by the cells of endolymphatic sac.
Membranous Labyrinth
Saccule & Utricle – specialized receptors called Macula
Semicircular ducts 2 vertical & 1 horizontal, oriented at
right angles, communicate with utricle at both ends
one end of each duct dilated to form ampulla
Crista ampullaris specialized part of ampulla for balance & equilibrium
Cochlea – specialized structures called Organ of Corti for hearing.
Separated laterally from the middle ear by a thin bony plate with 2 openings in them
Oval window – closed by footplate of stapes
Round window – closed by a thin membrane called as secondary tympanic membrane that serves to dissipate spent sound waves from the internal ear.
Bony Labyrinth
Crista Ampullaris - ampulla of the semicircular canal
Receptor for angular (rotational) movement.
Rotation of the head causes movement of the semicircular canal & the duct contained in it.
2 types of cells: Hair cells – sensory
Type I – goblet like with basal nuclei, surrounded by basket like nerve endings at the base.
Type II – columnar cells with a central nucleus surrounded by many small dendrites.
Supporting cells – tall columnar cells with apical microvilli, nucleus at base of cell.
Crista Ampullaris Both types have long microvilli
called stereocilia & a single non motile kinocilium.
Surface is covered with a gelatinous glycoprotein called cupula (no otoliths – Ca deposits)
Hair processes are embedded in the cupula.
Macula – in saccule and utricle Detect linear movement Structurally resembles
crista ampullaris BUT has a gelatinous otolithic membrane with calcium carbonate crystals (otoliths or otoconia) on the surface of the membrane.
Function of Macula
Senses static position of head in space, especially when eyes closed or in water.
Hair cells in macula are oriented in different directions, thus in different positions of the head, different groups of hair cells are stimulated.
Vertigo – sense of rotation of head at equilibrium. Due to excessive stimulation of the crista ampullaris or compression of the vestibule by a growth (tumor)
Motion Sickness – excessive stimulation of the macula. ( going in a merry go round)
Defection towards kinocilium – depolarization
Defection away from kinocilium - hyperpolarization
Cochlea Central axis formed by a bony core called modiolus
which is perforated by nerve fibers.
Cochlea
Cochlear duct – a diverticulum of the membranous saccule within the cochlea. Follows the course of the bony cochlea.Divides the bony cochlea into:
1. Upper scala vestibuli 2. Lower scala tympani
In between the 2 is the scala media which contains the cochlear duct containing the endolymph.
Histological Structure of Cochlear Duct
Reissner’s membrane: 2 layers of flattened
squamous epithelium held together by tight junctions to maintain ionic gradients between the perilymph & endolymph.
Histological Structure of Cochlear Duct
Stria Vascularis: A vascular epithelium that
lines the lateral aspect of the cochlear duct.
Contains ion & water transporting marginal cells that maintain the endolymph.
Histological Structure of Cochlear Duct
Basilar membrane: Separates cochlear duct
from scala tympani.
Resting on it is the Spiral Organ of Corti.
Organ of CortiHair cells:
Neuroepithelial cells that respond to sound.
Outer hair cells (3-5rows) W shaped stereocilia
Inner hair cells – linear stereocilia.- Both types of cells are associated with nerve endings.
Supporting cells: Inner & outer pillar cells
Inner & outer phalangeal / deiter cells
Tectorial membrane: Makes contact with the processes
of the hair cells.
A 10-month-old male infant is brought to the emergency department on a sweltering day in June. He is listless, cranky, and floppy as a dishrag. He has no hair or teeth. Over the past 2 weeks, he has not smiled, babbled, rolled over, sat up, or attempted to stand. The mother says that both she and her son cannot tolerate heat and that she has always had thin hair and still has some baby teeth. Which of the following skin structures is most likely to be absent or greatly decreased in number in the mother and the child?
A) Langerhans cells
B) Merkel's cells
C) Pacinian corpuscle
D) Sebaceous glands
E) Sweat glands
Sebaceous glands Present in all areas of hairy skin. Simple acinar glands with a duct that opens into the hair follicle. Nucleus shrinks and the cell bursts delivering contents into the
duct. ( Holocrine) Sebum is a complex mixture of triglycerides, waxes, cholesterol &
its ester. Is antibacterial & moisturizing. Stimulated mainly at puberty by sex hormones. When the duct is blocked, infection of the gland ensues,
accumulation of pus causes Acne
Sweat Glands Simple coiled tubular glands
with duct opening on the epidermal surface. (unrelated to hair follicle)
Merocrine (eccrine) distributed over the entire body.
Has 2 parts: secretory portion & duct
Secretory portion has simple cuboidal epithelium that has mainly 3 types of cells
Excretory ducts of sweat glands : stratified cuboidal epithelium
Sweat Glands Apocrine Sweat Glands
Duct – stratified cuboidal, cells smaller & darker. Absorb NaCl & glycoproteins.
Secretion includes NaCl, ammonia, urea & uric acid.
It is HYPOTONIC! Functions include
thermoregulation & waste excretion.
Present in the axillary, anal & areolar regions.
Secrete sweat into the hair follicle. Larger in diameter. Viscous secretion containing
proteins, carbohydrates and lipids. Bacteria act on lipids and produce
odoriferous compounds. (Pheromones)
Glands become functional at puberty influenced by sex hormones.
Under Adrenergic Sympathetic control!
Respond to emotional & sensory stimuli and NOT to heat.
Eccrine sweat glands – sympathetic cholinergic
Apocrine sweat glands – sympathetic adrenergic
Cystic fibrosisAnti-cholinergic drugs
Nail
Lunula – crescent shaped white area near root; cells are partially keratinized. (visible part of nail matrix)
Eponychium – formed by str corneum, keratinized edge of nail fold over lunula.
Hyponychium – thickened epidermis below free edge of nail
Summary Free Nerve Ending - basic sensations like pain, touch, temp & pressure
Merkel’s disc - Sense pressure & touch (deep dermis)
Meissner’s corpuscles - ‘two-point’ or discriminative touch
Pacinian - pressure, touch & vibration
Ruffini’s - Pressure & touch (dermis, hypodermis & joint capsules)
Krause end bulbs - receptors for cold
Muscle spindle - change in muscle length
Golgi tendon organ - Responds to muscle tension
GO THORUGH PICTURES OF THESE RECEPTORS
