Histo Eye and Ear

sebum, apocrine gland secretion of cirumen, and desquamated cells from epithelium; help to remove the cells from the external auditory canal and also helps to track microorganisms that go into the canal that can get removed.

ear wax

excess water may enter through the cuboidal cells and cause swelling of the cornea, and lead to opacity.

injury to corneal endothelium cells can lead to what?

1. refraction and focus: to refract entering light and focus image on retina - cornea, lens, ciliary muscles 2. color detection: to detect dark and color vision, retina 3. maintain shape of eyeball: AH and VH 4. intensity: to control the amount of light entering the eye - iris 5. resolution: to enhance acuity of vision and discriminative ability - fovea centralis

major functions of the eye and what does each

determines which wavelength of light is absorbed

opsin in rhodopsin

area of exit of optic nerve

optic disc

junction b/w non photosensitive and photosensitive neural retina

ora serrata

circular (sphincter) pupillae, and radial (dilator) pupillae. pupillary constriction, under parasympathetic stimulation, occurs when there is bright light. circular/constrictor muscle runs circularly and causes constriction. pupillary dilation, under sympathetic stimulation, occurs when there is dim light. radial muscles run radially and cause dilation.

smooth muscles of the iris

'old eye,' increase in farsightedness and loss of elasticity for accommodation due to aging.

presbyopia

stapes transmits vibrations to perilymph of bony labyrinth via the oval window; vibrations/pressure changes are set up in the perilymph that causes the round window to bulge into the middle ear; the pressure changes cause deflections in the basilar membrane, causing stereocilia to tip and resulting in depolarization

pressure pulses in perilymph

single layer of columnar cells held together by tight junctions; apex of RPE is very darkly stained in H&E and contains melanocytes, which absorb light and prevent glare. also has at apex a number of microvilli, which interdigitate with the photoreceptor cells. tight junctions on choroidal capillaries limit the quality and amount of nutrients that can diffuse into the sensitive layer of the retina - called the blood-retinal barrier.

retinal pigment epithelium

tensor tympani is attached to the eardrum itself; contraction of that muscle can put tension on the eardrum and make it less pliable/less sensitive to sound. the stapedius muscle (smallest muscle in the body) - contraction can cause rigidity in the stapes so its less responsive to chains of movement. both of these muscles act in the attenuation reflex - protects the inner ear from high decible sounds by making it less sensitive. loud sounds induce contraction of the muscles, making the ossicle chain more rigid and reducing movement

tensor tympani and stapedius muscles

utricle and saccule sense linear accelerations including gravity; cristae in semicircular ducts sense angular acceleration; organ of Corti senses sound. organ of Corti runs through the cochlea.

sensory structures

process by which the lens becomes rounder to focus on the image of a nearby object on the retina and flattens when image is distant object to focus it on retina; three components contribute to the accommodation process: 1. ciliary body 2. ciliary muscle 3. suspensory ligament: inserted at the equatorial region of the lens capsule.

accommodation

circular ciliary muscles contract, so suspensory fibers become more relaxed, and lens becomes more round. a round lens can help to focus the divergent light rays from a close object.

accommodation for close object

cochlear duct splits the cochlea into two parts: the scala vestibuli and the scala tympani. the scala vestibuli and tympani are connected at the tip of the helix (helicotrema) scala vestibuli begins at the oval window and ends at the helicotrema, scala tympani ends at the round window.

arrangement of cochlear duct

uneven curvature of cornea or lens, causing a scattering of light rays; occurs when light passes through football-shaped cornea and/or lens. usually treated with a combination of lenses.

astigmatism

pseudostratified ciliated epithelium - like respiratory tract - has goblet cells, cilia; aids in moistening this surface area but also in the beating of the cilia towards the pharynx and aids in removal of microorganisms. microorganisms can cause middle ear infections coming up through auditory tube; these infections can have long lasting impacts on sound b/c their impact on the ossicles present within the middle ear. auditory tube opens and closes when you swallow; relieves pressure.

auditory tube

structually heterogeneous; have different amounts of collagen and different degrees of stiffness from beginning to end. as a result, differentp arts of the membrane have a different sensitivity to deflection due to pressure pulses going through cochlea.

basilar membrane

consists of non-fenestrated capillaries of the retinal circulation and tight junctions b/w retinal epithelial cells preventing passage of large molecules from choriocapillaries into the retina.

blood-retinal barrier

amount and type of melanin found in the stromal layer of the iris can be linked to pigmentation of iris; darker eyes have more melanin and a higher eumelanin:pheomelanin ratio.

color of eyes/iris

in cornea, beneath the stratified squamous epithelia; consist of a basal layer of cells that are like stem cells, which proliferate and differentiate and reach into the surface to form the layer of epithelial cells. the stratified layer helps to protect the cornea. nonkeratinized epithelia bc do not want to obstruct incoming light.

Bowman's membrane

consist of fibroblast cells (nuclei are visible in H&E stain), which secrete collagen fibers and ground substance. the collagen fibers have a unique layout - have one layer that runs parallel, another layer that runs perpendicular to that layer - called orthogonal array. this is critical for the transparency of the cornea. fibroblasts also secrete ground substance - made of lumican (keratan sulfate) and chondroiton sulphate. Ground substance also important to help in arrangement of these collagen fibers in the corneal stroma.

Stroma of cornea

single layer of cuboidal epithelium; cornea itself has no blood vessels, so has to have a mechanism by which nutrients diffuse into it; this is done by these endothelial cells - the plasma membrane of these cells help in diffusion of sodium and chloride from the fluid which is present in the aqueous humor. water, sodium, and chloride diffuse from the corneal endothelial cells into the stroma. essential for maintaining transparency of cornea.

corneal epithelia (or endothelium)

contains cupula - gelatinous structure into which the stereocilia project; cupula blocks lumen of the duct so that the movement of the duct relative to the fluid will cause a deflection.

cupula

cosists of the transparent cornea and the white, opaque sclera; cornea is the anterior 1/6th of the eye; sclera is made of DICT; limbus is the junction of cornea and sclera

describe the corneoscleral coat

auricle is vestigial - doesnt move around much, but still important in defining directionality of sound; covered with skin. continuing into the auditory canal (external acoustic meatus), the lining epithelium is very much like skin, has hairs and sebaceous glands and apocrine glands that produce cerumin. Sebum and apocrine glands together with desquamated cells from epithelium constitute ear wax. Wikipedia - Ceruminous glands are specialized sudoriferous glands (sweat glands) located subcutaneously in the external auditory canal, in the outer 1/3. Ceruminous glands are simple, coiled, tubular glands made up of an inner secretory layer of cells and an outer myoepithelial layer of cells. They are classed as apocrine glands

describe the outer ear

radial ciliary muscles relax, the suspensory ligaments become taut, and lens becomes flattened so that image of distant object can form on the retina. light rays from distant objects are nearly parallel and dont need as much refraction to bring them into focus.

distant object accommodation

shallow depression about 2.5 mm in diameter; fovea is the area where the vision is the sharpest and is crossed by the visual axis.

fovea centralis

1. transport of nutrients from choroidal vessels to the outer layers of the sensory retina 2. removal of metabolic waste products from sensory retina 3. active phagocytosis and recycling of photopigment shed from the disks of the outer segment of cones and rods 4. restoring the photo pigment rhodopsin bc the RPE brings enzymatic conversion of RETINOL to RETINAL (cis form). retinal then is returned to the photoreceptor cells by the interstitial retinal binding protein, IRBP

functions of retinal pigment epithelium

blockage of aqueous drainage canal, back pressure on optic nerve as well as pressure on blood vessels leads to loss of peripheral field of vision.

glaucoma cause

neurotransmitter vesicles right near the synapse; prelocalizes vesicles near the synaptic membrane via the synaptic ribbon. whenever the hair cell is depolarized, there are lots of calcium channels in the general region, so calcium enters and causes rapid exocytosis of neurotransmitters. those directly affect the postsynaptic membranes of the neurons.

hair cell synapse

inner hair cells (Type 1) primary sensors of basilar deflections; outer (type II) hair cells contract in response to depolarization and amplify the basilar membrane deflection in a frequency specific manner. this can produce middle ear movement and actually produce sound from the ear (called otoacoustic emission). CNS input modulates resting potential (sensitivity) and impact of outer cells on basilar stiffness.

hair cells in organ of corti

critical sensory cells of the ear; present within each of the cristae and maculae and throughout the organ of Corti. sit in an epithelium together with supporting cells; stereocilia are embedded in glycoprotein layer to reduce random noise; kinocilia next to longest stereocilia map asymmetry. hair cells are associated with afferent and efferent nerve endings; do not have axons. two types of hair cells. apical side of hair cells have stereocilia that extend from surface in a very discrete array - tall to short from one end to another. in the hair cells found in sensory structures other than cochlea, there is a structure called a kinocilium, and the stereocilia have a discrete orientation relative to this kind of cilia. stereocilia contain a number of ion channels, which are usually closed unless the stereocilia are tipped in a specific direction (from long to short). each of the stereocilia are connected to one another by proteins, and the distortion of stereocilia result in potassium channels in them opening, which depolarize the hair cell if tipped in one direction and hyperpolarize hair cell if tipped in the other direction. therefore, the hair cells ability to release neurotransmitter is totally dependent on stereocilia orientation in one direction or another.

hair cells structure, function

the pillar cells (which are stiffened by extensive microtubules) form a triangular tunnel as a pivot; the basilar membrane and tectorial membrnaes shear relative to eachother and cause shearing of the hair cell stereocilia (which are the only connection b/w the two); the hair cells then signal the afferent endings of the cochlear nerve. results in depolarization and release of neurotransmitter.

hearing transduction

from blood vessels in the retina called the retinal blood vessels.

how do the nuclei of the inner nuclear layer and ganglion layer of the retina receive nourishment?

farsightedness; difficulty wtih near vision. distance b/w cornea and retina too short. use convex lenses to correct this

hyperopia

1:1

in fovea centralis, what is the ratio of cones to ganglion cells?

cochlear hair cells

kinocilia are not found in the ___

1. photoreceptor cells 2. conducting neurons: bipolar and ganglion cells 3. association neurons: horizontal and amacrine 4. supporting neuroglial cells: muller cells

layers of photosensitive retina (brief):

refraction and focus; consists of a lens capsule (basal lamina), which is made up of elastic membrane and provides the flexibility to the lens to change its shape. this is made of type IV collagen. capsule does not contain elastic fibrils. inner layer of lens is lined by a single layer of epithelial cells - the subcapsular epithelium. Lens fibers - as these approach the equator of the lens, the cells begin to elongate and rotate so their longitudinal axes are parallel to the cortical surface. Cells slowly begin to lose their nuclei, and start to secrete a protein in their cytoplasm called crystallin. this is important for providing transparency to the lens. lens is suspended by suspensory fibers of the ciliary body

lens function and structure

yellow rim that surrounds the fovea centralis. provides accurate vision under normal and dim illumination

macula lutea

lined by simple epithelium; has 3 semicircular ducts, a cochlear duct, utricle, saccule, endolymphatic duct and sac. membranous labyrinth follows the contours of the bone, but creates two cavities within the bony area - one cavity has perilymph (ionic composition similar to extracellular, high in sodium but low in potassium); other cavity has endolymph, which has high potassium and low sodium.

membranous labyrinth

nearsightedness; difficulty with distance vision. distance b/w cornea and retina is too long. use diverging (concave) lenses for this

myopia

neuronal cell bodies are categorized into two groups: 1. conducting neurons, which are the bipolar and ganglion cells. bipolar cells have dendrites which collect the information from the photoreceptor cells to synthesize information and transmit it to the ganglion cells; these transmit signal through their axons to the visual cortex of the brain. 2. neuronal cell bodies - horizontal and amacrine cells, also known as association neurons. horizontal cells consist of a number of neurites which synapse with the photoreceptor cells; amacrine cells help in synthesizing information and sending it to the corresponding bipolar cells. Muller cell - involved in structural support as well as nourishment to the retina bc it stores glycogen in its cytoplasm. nuclei of conducting neurons as well as the association neurons together form the inner nuclear layer; synapse of dendrites along with the dendrites of the ganglion cell wall will form the inner plexiform cell layer. axons that arise from the ganglion cell layer reach from visual cortex and conduct information to the brain.

neurons of the retina

the drainage of aqueous humor is balanced by the rate of secretion; by this mechanism, the IP is maintained constant at 15-20 mm Hg. the pressure (normal IP) maintains the shape of the eyeball.

normal intraocular pressure

has about 16,000 inner and outer hair cells; 95% of inner hair cells are type 1; inner hair cell group is more towards the center of the entire cochlea, outer hair cell group is more removed; in both cases, hair cells are associated with inner and outer phalangeal (supporting) cells. These associate in such a way that they form tight junctions around every single hair cell so that perilymph and endolymph in other space do not mix. hair cells have stereocilia embedded in a glycoprotein matrix that is produced by cells above cochlear nerve; any movement of this basalar membrane will cause tipping of this structure and a shearing/movement of hair cells away from tectorial membrane, pulling and tugging the stereocilia resulting in sound perception. also pillar cells; hair cells sit upon the phalangeal cells, tectorial membrane is a glycoprotein-rich secretion of cells of the spiral limbus; tips of the stereocilia are embedded in the tectorial membrane.

organ of corti

pressure pulses in perilymph cause an oscillation in the basilar membrane; the location of the oscillation varies with the frequency of the sound; low frequencies cause oscillations closer to the apex (helicotrema) the spot of fluctuation in the BM is the spot that a specific frequency of sound affects. entire basilar membrane is mapped according to which frequency of sound can cause deflection; highest frequencies cause deflection closest to middle ear, lowest al lthe way to apex of basilar membrane. every single part of the hair cells along this basilar membrane are innervated with sensory neurons. any movement of any part of this membrane is picked up by a different group of sensory neurons

oscillation of basilar membrane

eye develops due to sequential inductions from three different tissues - 1. neural tube ectoderm 2. surface ectoderm 3. mesoderm Eye is an outgrowth from the brian; hence, develops from neural ectoderm

overview of eye development

ordinarily, operation of auditory ossicles causes the stapes to move in and out; when it moves in and out of oval window, it sets up sonic waves in the perilymph all around to the helicatrema and then to the round window. this puts pressure on the membranous structure of the organ of corti, causing it to vibrate. that vibration is what affects the hair cells located in that dark area resulting in sound perception

sound perception mechanism

in light, there is a decreased concentration of cGMP, which leads to sodium channels closing in outer segment. this leads to hyperpolarization of the cell. at the cell terminal, there are a number of calcium channels, which then close. this decreases the release of neurotransmitters into the corresponding layer.

step 2 of visual processing: change in concentration of internal messengers w/in the outer segment cytoplasm influences ionic permeability of plasma membrane

specialized region of cochlear duct, has vascularized epithelium (!), ultrastructural features indicating ion transport function and fluid transport function (many mitochondria), may condition/secrete endolymph.

stria vascularis

impact of force on hyperpolarization vs depolarization is different on the two sides of the striola; because the hair cells are at least 90 deg to one another, have at least four different fields being differentially affected by gravitational force or linear acceleration. brain can then interpret all of this and positioning of the body.

striola impact

roughly triangular, contains the scala media filled with endolymph; upper wall is vestibular membrane, side wall is the stria vascularis; lower wall is the basilar membrane, and then the organ of Corti rests on the basilar membrane.

structure of cochlear duct

present within temporal bone of the head; bc its present within this, have a bony labyrinth - this encases all of the sensory apparatuses of the inner ear: the three semi circular canals; a swollen cavity just below those called the utricle; and below that the sacuule, and then a helical structure called the cochlea. also the vestibule.

structure of inner ear bone

cuboidal epithelial cells; apical domain is sealed to form tight junctions. melanin granules are present in the apical cytoplasm and apical cell processes. melanin granules absorb excess light reaching the photoreceptors. apical surface contains microvilli that surrounds the outer segments of the photoreceptors. at this location, the sensory retina and RPE are attached to eachother through an amorphous extracellular material, the interphotoreceptor matrix.

structure of nonsensory retinal pigment epithelium

very darkly pigmented, has some spaces (fenestrated capillaries). dark pigment due to melanocytes, which absorb light and prevent glare, and help in transfer of nutrients from blood vessels to the layer of retina - the RPE - as well as the photoreceptor cells.

structure/function of choroid

rods are rod shaped and involved in vision in dark/dim lighting, have rhodopsin; cones are cone shaped and are color vision. there is an outer segment and an inner segment of photoreceptors- metabolic machinery lies in inner segment, which has a number of nuclei that represent the outer nuclear layer and are formed by rod and cone cells. the outer segment interdigitates with the RPE. the terminal ends of photoreceptors synapse with neuronal cells in the next layer, forming the outer plexiform layer.

structure/function of photoreceptors

part of vascular coat, consists of ciliary muscles and suspensory fibers that attach to the lens; ciliary muscles are both circular and radial. these regulate the tension on these suspensory fibers and indirectly helps to adjust the shape of the lens.

structures involved in accommodation

build up of ear wax that lies up against tympanic membrane can have a distinct negative effect on sound perception or even induce tinnitus

tinnitus due to ear wax

lined by simple cuboidal to simple squamous epithelium; origin is neural crest cells.

tympanic cavity structure

very thin structure with an epithelium on both sides; epithelium that faces middle ear is simple epithelium, cuboidal to squamous; epithelium that faces the auditory canal is typical of skin except no glands - stratified squamous epithelium. B/w these two layers is a layer of connective tissue. landmarks of tympanic membrane include manubrium of the malleus attached to the tense part of the membrane, umbo at the tip of the membrane, and projecting lateral process of the malleus. A small, flaccid part of the tympanic membrane is located above the lateral process of the malleolus. Generally see a cone of light (light reflex).

tympanic membrane structure/function

predominantly afferent nerve fibers, carries nerve impulses from hair cell to the brain. dendrite of neuron forms a challace around the hair cell. structure has the purpose of clustering neurotransmitters right near the synapse

type 1 hair cell

both afferent and efferent fibers, so brain is also sending info to the hair cell. considered modulators. the dendrite of the neuron is located mostly around the base of the hair cell.

type II hair cell

actin

type of filaments in stereocilia and kinocilia

vision is a process by which light striking the retina is converted into electrical impulses that are transmitted to the brain.

visual processing/phototransduction

the transparent, jelly-like substance that fills the space b/w the lens and retina; is a CT substance synthesized in the embryonic life. contains 99% water, hyaluronic acid and type II collagen. fully hydrated hyaluronic acid holds the collagen fibrils in place.

vitreous humor components

shrinking vitreous humor/detached vitreous humor, which tugs on retina and can cause retinal detachment. transient retinal detachments cause flashes.

what causes flashes in vision?

with age, vitreous humor becomes more fluid in nature, and as a result, collagen fibers that were once secure start moving freely. any other cellular debris also contribute to this.

what causes floaters?

neural retina - derived from inner layer of optic cup RPE - outer layer of optic cup lens vesicle - separates from surface ectoderm to form future lens. sclera - derived from surrounding mesoderm epithelium of ciliary body, iris - derived from optic cup (neuroectoderm) choroid, retinal vessels - derived from surrouding mesoderm vitreous body - neuroectoderm

what did the neural retina, RPE, and lens vesicle each derive from? also, sclera, epithelium of ciliary body and iris, choroid and retinal vessels, vitreous body?

rate of head rotation (angular acceleration), therefore are dynamic in fuction; when head is initially moved, the ampulla (and therefore hair cells) turns with it. the endolymph remains in its initial position due to inertia, causing movement of the stereocilia against the cupula and altering the receptor potential (could be depol or hyperpol, depending on direction); once head is moving at a constant velocity, the duct fluid moves at the same rate as the hair cells, and stereocilia are not deflected; when head stops moving, fluid keeps moving, and the receptor potential is again altered, this time in the opposite direction to what occured at the start. orientation of stereocilia in each canal is different, thus allowing depol or hyperpol in different cristae, and brain will be able to read and map what is happening to all three maculae at the same time, and as a consequence be able to interpret what is happening to the ehad in terms of rotation and even speed of rotation.

what do semicircular canals detect?

gravitational force and position of body in a horizontal vs vertical position; type 1 and type 2 hair cell's stereocilia are embedded in a gelatinous matrix, and also have otoconia (calcium carbonate crystals sitting on top of the gel) - otoconia create a density far greater than the density of the endolymph. otoconia are very sensitive to agitation, particularly to gravity. furthermore, within each patch are two populations of hair cells that have opposite polarities to one another - in a striola down the center of each the utricle and saccule - utricle: hair cells point towards striola, saccule: hair cells point away from it.

what do utricle and sacuule detect?

cochlear duct contains organ of corti, where the hair cells involved in hearing are located; coiled in a tube like a snail shell wthin the bone is the modiolus; cochlear nerve innervates the hair cells.

what organ is involved in hearing?