Sense OrgansSense Organs

Anatomy and PhysiologyAnatomy and Physiology

SensesSenses

Sense organs fall into two major Sense organs fall into two major categories; sense organs and special categories; sense organs and special sense organssense organs– Sense organs refer to receptors that Sense organs refer to receptors that

function to produce general senses such function to produce general senses such as touch, temperature, and pain to as touch, temperature, and pain to initiate reflexesinitiate reflexes

– Special sense organs function to Special sense organs function to produce vision, hearing, balance, taste, produce vision, hearing, balance, taste, and smelland smell

Sense OrgansSense OrgansSense organs are called sensory Sense organs are called sensory receptorsreceptorsThe general function of receptors are The general function of receptors are to respond to stimuli by converting to respond to stimuli by converting them to nerve impulsesthem to nerve impulsesReceptor potential occurs when an Receptor potential occurs when an adequate stimulus acts on a receptor; adequate stimulus acts on a receptor; when it reaches a threshold, it results when it reaches a threshold, it results in an action potential (impulse) in the in an action potential (impulse) in the sensory neuronsensory neuron

Sense OrgansSense OrgansReceptors can adapt to the stimuli, Receptors can adapt to the stimuli, meaning that the magnitude of the meaning that the magnitude of the receptor potential decreases over a receptor potential decreases over a period in response to a continuous period in response to a continuous stimulusstimulusReceptors are classified according to Receptors are classified according to their location in the body, the their location in the body, the specialized stimulus that causes specialized stimulus that causes them to respond, and their structurethem to respond, and their structure

Receptors Classified By LocationReceptors Classified By LocationExteroceptors are located near the body Exteroceptors are located near the body surface and respond to external stimuli; these surface and respond to external stimuli; these are sometimes referred to as cutaneous are sometimes referred to as cutaneous receptorsreceptorsVisceroceptors or interoceptors are located Visceroceptors or interoceptors are located internally; they function in response to internally; they function in response to internal organ stimuliinternal organ stimuli– Proprioceptors are specialized and are found in Proprioceptors are specialized and are found in

skeletal muscle, joints, and tendons. They provide skeletal muscle, joints, and tendons. They provide information about body movement, orientation, information about body movement, orientation, and muscle stretchand muscle stretch

Tonic receptors allow us to locate parts of our body Tonic receptors allow us to locate parts of our body without having to look at itwithout having to look at itPhasic receptors allow us to feel change in body positionsPhasic receptors allow us to feel change in body positions

Receptors Classified By Stimulus Receptors Classified By Stimulus DetectedDetected

Mechanoreceptors respond to Mechanoreceptors respond to mechanical stimuli that change mechanical stimuli that change position of the receptor itselfposition of the receptor itself– Pressure applied to skin, stretching Pressure applied to skin, stretching

muscles, etcmuscles, etc

Chemoreceptors are activated by the Chemoreceptors are activated by the amount or the changing amount or the changing concentration of certain chemicals concentration of certain chemicals – Taste, smell, pH, blood glucose Taste, smell, pH, blood glucose

levels,etclevels,etc

Receptors Classified By Stimulus Receptors Classified By Stimulus DetectedDetected

Thermoreceptors are activated by Thermoreceptors are activated by changes in temperaturechanges in temperatureNociceptors are activated by intense Nociceptors are activated by intense stimuli that results in tissue damage; stimuli that results in tissue damage; pain is producedpain is produced– May be caused by toxic chemicals, light, May be caused by toxic chemicals, light,

sound, pressure, heatsound, pressure, heat

Photoreceptors are only found in the Photoreceptors are only found in the eyes; they respond to lighteyes; they respond to light

Receptors Classified By StructureReceptors Classified By Structure

Free nerve endingsFree nerve endings are the simplest, most are the simplest, most common and most widely distributed common and most widely distributed sensory receptors; these include sensory receptors; these include exteroceptors, visceroceptors, and exteroceptors, visceroceptors, and nocioceptorsnocioceptors

Brain tissue lacks free nerve endings and Brain tissue lacks free nerve endings and is incapable of sensing painful stimuliis incapable of sensing painful stimuli

Slightly modified free nerve endings are Slightly modified free nerve endings are responsible for itching, tickling, touch, responsible for itching, tickling, touch, movement, and mechanical stretchingmovement, and mechanical stretching

Receptors Classified By StructureReceptors Classified By Structure

Stimulated free nerve endings almost Stimulated free nerve endings almost always result in the feeling of pain always result in the feeling of pain and is a first indication of injury or and is a first indication of injury or diseasedisease– Acute pain fibers mediate a sharp, Acute pain fibers mediate a sharp,

intense and localized pain sensationintense and localized pain sensation– Chronic pain fibers mediate a less Chronic pain fibers mediate a less

intense, but more persistent pain (dull/ intense, but more persistent pain (dull/ aching)aching)

Receptors Classified By StructureReceptors Classified By Structure

Root hair plexuses are free nerve Root hair plexuses are free nerve endings associated with the hair endings associated with the hair follicles and detect hair movementfollicles and detect hair movement

Merkel discs are responsible for Merkel discs are responsible for sensing light touchsensing light touch

There are six types of There are six types of encapsulated encapsulated nerve endingsnerve endings; they all have some ; they all have some type of connective tissue capsule type of connective tissue capsule that surrounds the dendritic endsthat surrounds the dendritic ends

Receptors Classified By StructureReceptors Classified By Structure

Meissner’s corpuscles are Meissner’s corpuscles are responsible for sensations of light responsible for sensations of light touch and low-frequency vibrationtouch and low-frequency vibration– These are concentrated in the hairless These are concentrated in the hairless

skin areas; lips, fingertips, etcskin areas; lips, fingertips, etc

Krause’s end bulbs respond to light Krause’s end bulbs respond to light touch and low-frequency vibrations; touch and low-frequency vibrations; it is also suggested that they are it is also suggested that they are stimulated in temperatures below stimulated in temperatures below 65°F65°F

Receptors Classified By StructureReceptors Classified By Structure

Ruffini corpuscles are located deep in Ruffini corpuscles are located deep in the dermis and mediate the sense of the dermis and mediate the sense of crude and persistent touch; these crude and persistent touch; these receptors are stimulated by receptors are stimulated by temperatures ranging from 85° to temperatures ranging from 85° to 120° F120° FPacinian corpuscles are found deep Pacinian corpuscles are found deep in the dermis and respond to deep in the dermis and respond to deep pressure, high-frequency vibrations pressure, high-frequency vibrations and stretchingand stretching

Receptors Classified By StrucureReceptors Classified By StrucureMuscle spindles consists of grouping Muscle spindles consists of grouping muscle fibers that are encapsulated and muscle fibers that are encapsulated and contain sensory nerve fibers; these are contain sensory nerve fibers; these are anchored to the connective tissue of anchored to the connective tissue of skeletal muscleskeletal muscle– these provide monitoring of the strength of these provide monitoring of the strength of

muscle contractions and stretching of musclesmuscle contractions and stretching of muscles

Golgi tendon organs are located between Golgi tendon organs are located between muscle tissue and tendons; they react to muscle tissue and tendons; they react to excessive muscle contraction and cause excessive muscle contraction and cause the muscle to relaxthe muscle to relax– This protects muscles from tearing and pulling This protects muscles from tearing and pulling

away from the tendinous points of attachmentaway from the tendinous points of attachment

OlfactoryOlfactoryThe olfactory neurons are bipolar and have The olfactory neurons are bipolar and have cilia that touch the surface of the cilia that touch the surface of the epithelium lining the nasal cavityepithelium lining the nasal cavityOlfactory receptor neurons are Olfactory receptor neurons are chemoreceptorschemoreceptorsOlfactory receptors are replaced on a Olfactory receptors are replaced on a regular basis by germinative basal cells in regular basis by germinative basal cells in the olfactory epitheliumthe olfactory epitheliumReceptor potentials are generated when Receptor potentials are generated when receptor neurons are exposed to gas receptor neurons are exposed to gas molecules or chemicals dissolved in the molecules or chemicals dissolved in the mucus covering the nasal epitheliummucus covering the nasal epithelium

OlfactoryOlfactory

Olfactory neurons rapidly adapt to Olfactory neurons rapidly adapt to continuous stimulation due to continuous stimulation due to inhibition of action potentials by inhibition of action potentials by specialized granule cells in the specialized granule cells in the olfactory bulbolfactory bulb

Olfactory PathwayOlfactory Pathway1.1. Chemicals dissolved in mucus surrounds Chemicals dissolved in mucus surrounds

the olfactory cilia and a threshold is the olfactory cilia and a threshold is reachedreached

2.2. Receptor potential activatedReceptor potential activated3.3. Action potential of neuron generated and Action potential of neuron generated and

passed to the olfactory nerves in the passed to the olfactory nerves in the olfactory bulbolfactory bulb

4.4. Impulses pass through the olfactory tract Impulses pass through the olfactory tract to the thalamic and olfactory centers of to the thalamic and olfactory centers of the brain for interpretation, integration the brain for interpretation, integration and memory storageand memory storage

GustatoryGustatory

Gustatory receptors respond to taste Gustatory receptors respond to taste stimulistimuli

Most taste buds are associated with Most taste buds are associated with the elevated projections of the the elevated projections of the tongue called papillaetongue called papillae– Filiform papillae do not contain taste Filiform papillae do not contain taste

buds but allow you to experience food buds but allow you to experience food texturetexture

GustatoryGustatoryTaste buds are stimulated by chemicals Taste buds are stimulated by chemicals dissolved in saliva; taste buds house dissolved in saliva; taste buds house chemoreceptorschemoreceptorsEach taste bud contains gustatory cells Each taste bud contains gustatory cells that have cilia; cilia project into a taste that have cilia; cilia project into a taste pore that is bathed in salivapore that is bathed in salivaAll tastes can be detected in all areas of All tastes can be detected in all areas of the tongue; It is believed, however, that the tongue; It is believed, however, that each type of taste bud responds most each type of taste bud responds most effectively to one of the four primary effectively to one of the four primary taste sensations (bitter, sweet, sour, taste sensations (bitter, sweet, sour, and salty)and salty)

Gustatory PathwayGustatory Pathway1.1. Taste sensation begins with the creation Taste sensation begins with the creation

of the receptor potential in the gustatory of the receptor potential in the gustatory cellscells

2.2. The generation of an action potential The generation of an action potential then transmits sensory input to the brainthen transmits sensory input to the brain

1.1. Nerve impulses generated in the anterior 2/3 Nerve impulses generated in the anterior 2/3 of the tongue travel over the facial nerve of the tongue travel over the facial nerve

2.2. Nerve impulses from the posterior 1/3 of the Nerve impulses from the posterior 1/3 of the tongue are conducted by the tongue are conducted by the glossopharyngeal nerveglossopharyngeal nerve

3.3. The vagus nerve also plays a minor role in The vagus nerve also plays a minor role in taste; these sensations would begin in the taste; these sensations would begin in the walls of the pharynx and epliglottis walls of the pharynx and epliglottis

Gustatory PathwayGustatory Pathway

3.3. All three cranial nerves carry the All three cranial nerves carry the impulses to the medulla oblongataimpulses to the medulla oblongata

4.4. Relays carry impulses to the Relays carry impulses to the thalamus and then into the taste thalamus and then into the taste areas of the cerebral cortex in the areas of the cerebral cortex in the parietal lobe of the brainparietal lobe of the brain

Auditory and BalanceAuditory and Balance

The ear has a dual function; it plays a The ear has a dual function; it plays a role in hearing, but it also functions as role in hearing, but it also functions as the sense organ for balance and the sense organ for balance and equilibriumequilibrium

Specialized mechanoreceptors are Specialized mechanoreceptors are responsible for both functions; the responsible for both functions; the mechanoreceptors are called hair cellsmechanoreceptors are called hair cells

The ear is divided into three anatomical The ear is divided into three anatomical parts; external ear, middle ear, and the parts; external ear, middle ear, and the inner earinner ear

Auditory and BalanceAuditory and BalanceThe external ear has a flap called the The external ear has a flap called the auricle or pinnaauricle or pinnaThe tube leading from the auricle to the The tube leading from the auricle to the temporal bone is named the external temporal bone is named the external auditory meatus (ear canal)auditory meatus (ear canal)Modified sweat glands are located in the Modified sweat glands are located in the auditory canal; they secrete cerumen auditory canal; they secrete cerumen – When the glands become impacted it results in When the glands become impacted it results in

pain and temporary deafnesspain and temporary deafnessAt the end of the auditory canal is the At the end of the auditory canal is the tympanic membrane (eardrum) it tympanic membrane (eardrum) it stretches across the end of the ear canal stretches across the end of the ear canal separating it from the middle earseparating it from the middle ear

Auditory and BalanceAuditory and BalanceThe middle ear (tympanic cavity) contains The middle ear (tympanic cavity) contains three small bones called the auditory three small bones called the auditory ossicles; malleus (hammer), incus (anvil), ossicles; malleus (hammer), incus (anvil), and stapes (stirrup)and stapes (stirrup)

The malleus attaches to the inner surface The malleus attaches to the inner surface of the tympanic membrane, the other end of the tympanic membrane, the other end attaches to the incus, which then attaches attaches to the incus, which then attaches to the stapes; the stapes then connects to to the stapes; the stapes then connects to the oval windowthe oval window

Auditory and BalanceAuditory and BalanceThe middle ear has 4 openingsThe middle ear has 4 openings– The opening from the ear canal that is covered The opening from the ear canal that is covered

by the tympanic membraneby the tympanic membrane– The oval window which is a opening into the The oval window which is a opening into the

inner ear, this is also where the stapes fitsinner ear, this is also where the stapes fits– The round window which is an opening into the The round window which is an opening into the

inner ear, it is covered by a membraneinner ear, it is covered by a membrane– The eustachian tube (auditory tube) connects The eustachian tube (auditory tube) connects

the ear to the back of the throatthe ear to the back of the throat

The openings are routes for infection and The openings are routes for infection and are a concern of physiciansare a concern of physicians

Auditory and BalanceAuditory and BalanceThe inner ear is called the labyrinth The inner ear is called the labyrinth because of its shape; it consists of two because of its shape; it consists of two main parts the bony labyrinth and the main parts the bony labyrinth and the membranous labyrinthmembranous labyrinthThe bony labyrinth consists of three parts; The bony labyrinth consists of three parts; the vestibule, cochlea, and semicircular the vestibule, cochlea, and semicircular canalscanalsThe membranous labyrinth consists of the The membranous labyrinth consists of the utricle, saccule, cochlear duct, and the utricle, saccule, cochlear duct, and the semicircular canalssemicircular canals– The utricle, saccule, and semicircular canals The utricle, saccule, and semicircular canals

are involved in balanceare involved in balance– The cochlea is involved in hearingThe cochlea is involved in hearing

Auditory and BalanceAuditory and BalanceEndolymph refers to the fluid in the Endolymph refers to the fluid in the membranous labyrinthmembranous labyrinthPerilymph refers to the fluid that surrounds Perilymph refers to the fluid that surrounds the membranous labyrinth and fills the space the membranous labyrinth and fills the space between it and the bony walls around itbetween it and the bony walls around itCochlea means “snail”; it describes the shape Cochlea means “snail”; it describes the shape of this part; the cochlea consists of cell of this part; the cochlea consists of cell bodies for sensory neuronsbodies for sensory neurons– The cochlear duct is the only part of the internal The cochlear duct is the only part of the internal

ear concerned with hearingear concerned with hearing– The roof of the cochlear duct is known as the The roof of the cochlear duct is known as the

vestibular membrane or Reissner’s membranevestibular membrane or Reissner’s membrane– The floor of the cochlear duct is know as the The floor of the cochlear duct is know as the

basilar membranebasilar membrane

Auditory and BalanceAuditory and BalanceThe hearing sense organ, The Organs of The hearing sense organ, The Organs of Corti, rests on the basilar membrane along Corti, rests on the basilar membrane along the entire length of the cochlear ductthe entire length of the cochlear duct– Dendrites of sensory neurons are associated Dendrites of sensory neurons are associated

with the Organs of Corti; the axons of the with the Organs of Corti; the axons of the sensory neurons extend to form the cochlear sensory neurons extend to form the cochlear nervenerve

– Cochlear implants are used to assist deaf Cochlear implants are used to assist deaf persons if the Organs of Corti are damagedpersons if the Organs of Corti are damaged

Auditory PathwayAuditory Pathway

Sound is created by vibrations in Sound is created by vibrations in air, fluid, or solid materialair, fluid, or solid material

The amplitude of a sound wave The amplitude of a sound wave determines its perceived loudnessdetermines its perceived loudness

The number of sound waves during The number of sound waves during a specific period of time (frequency) a specific period of time (frequency) determines pitchdetermines pitch

Auditory PathwayAuditory Pathway1.1. Sound waves enter the external auditory canal Sound waves enter the external auditory canal

and strike the tympanic membraneand strike the tympanic membrane2.2. Vibrations from the tympanic membrane move Vibrations from the tympanic membrane move

the malleus, that then moves the incus, then the the malleus, that then moves the incus, then the stapesstapes

3.3. The stapes fits against the oval window, so when The stapes fits against the oval window, so when it moves it exerts pressure on it ; this causes a it moves it exerts pressure on it ; this causes a ripple effect in the perilymph of the scala ripple effect in the perilymph of the scala vestibulivestibuli

4.4. The ripple is transmitted through the vestibular The ripple is transmitted through the vestibular membrane to the endolymph inside the cochlear membrane to the endolymph inside the cochlear duct and then to the Organ of Corti and the duct and then to the Organ of Corti and the basilar membrane basilar membrane

5.5. The ripple then moves through the perilymph The ripple then moves through the perilymph (scala tympani side) to the round window (the (scala tympani side) to the round window (the end point)end point)

Auditory PathwayAuditory Pathway6.6. The movement of the hair cells and The movement of the hair cells and

thus the stimulation of the organ of thus the stimulation of the organ of corti results in an impulse being corti results in an impulse being conducted from the cochlear nerve conducted from the cochlear nerve to the brainstemto the brainstem

7.7. Auditory impulses go through relay Auditory impulses go through relay stations in the medulla, pons, stations in the medulla, pons, midbrain, and thalamus before it midbrain, and thalamus before it reaches the auditory area of the reaches the auditory area of the temporal lobe of the braintemporal lobe of the brain

BalanceBalanceSense organs involving balance, or Sense organs involving balance, or equilibrium, are found in the vestibule and equilibrium, are found in the vestibule and the semicircular canalsthe semicircular canalsThe utricle and the saccule function in The utricle and the saccule function in static equilibrium, a sense that explains static equilibrium, a sense that explains the position of the head relative to gravity the position of the head relative to gravity and the sense of acceleration and and the sense of acceleration and deceleration of the bodydeceleration of the bodyThe sense organs associated with dynamic The sense organs associated with dynamic equilibrium are the semicircular canals; equilibrium are the semicircular canals; they function to maintain balancethey function to maintain balance

Static EquilibriumStatic EquilibriumThe macula is a specialized epithelium The macula is a specialized epithelium containing receptor hair cells and supporting containing receptor hair cells and supporting cells that are covered with a gelatinous cells that are covered with a gelatinous matrixmatrix– Movement of the macula provides Movement of the macula provides

information relating to head position or information relating to head position or accelerationacceleration

– Otoliths are composed of calcium Otoliths are composed of calcium carbonate and are located in the maculas; carbonate and are located in the maculas; turning the head causes the otoliths to turning the head causes the otoliths to change position and thus stimulates hair change position and thus stimulates hair cells and neuronscells and neurons

Dynamic EquilibriumDynamic EquilibriumThe crista ampullaris is located in the The crista ampullaris is located in the ampulla of each semicircular canal. It is a ampulla of each semicircular canal. It is a specialized sensory epitheliumspecialized sensory epithelium– The crista is composed of hair cells that are The crista is composed of hair cells that are

embedded in a gelatinous cap, the cupulaembedded in a gelatinous cap, the cupula– The cupula serves as a float that moves with The cupula serves as a float that moves with

the flow of the endolymphthe flow of the endolymph– As the cupula moves it creates receptor As the cupula moves it creates receptor

potential, then an action potential. The potential, then an action potential. The impulse passes through the vestibular portion impulse passes through the vestibular portion of the 8of the 8thth cranial nerve. It reaches the medulla cranial nerve. It reaches the medulla oblongata and then to other areas of the brain oblongata and then to other areas of the brain and spinal cord for interpretation, integration, and spinal cord for interpretation, integration, and responseand response

OpticOpticThe eyeball has three layers the The eyeball has three layers the sclera, choroid, and retinasclera, choroid, and retinaThe sclera is made up of tough white The sclera is made up of tough white fibrous tissuefibrous tissueThe anterior portion of the sclera is The anterior portion of the sclera is the cornea, it lies over the iris.the cornea, it lies over the iris.– The iris is the colored part of the eyeThe iris is the colored part of the eye– The cornea is transparent, whereas the The cornea is transparent, whereas the

rest of the sclera is white and opaquerest of the sclera is white and opaque

OpticOpticThe cornea and the lens lack blood vesselsThe cornea and the lens lack blood vessels

The Canal of Schlemm is a venous sinus The Canal of Schlemm is a venous sinus that drains the aqueous humor in the eyethat drains the aqueous humor in the eye– If the aqueous humor is produced faster than it If the aqueous humor is produced faster than it

can be drained, glaucoma resultscan be drained, glaucoma results

The choroid coat of the eye contains blood The choroid coat of the eye contains blood vessels and pigment. It is modified into vessels and pigment. It is modified into three separate structures; the ciliary body, three separate structures; the ciliary body, the suspensory ligament, and the iristhe suspensory ligament, and the iris

OpticOpticThe ciliary body contains small ciliary The ciliary body contains small ciliary muscles and ligaments that hold the lens muscles and ligaments that hold the lens suspended in the correct placesuspended in the correct place

The iris is the colored part of the eye; the The iris is the colored part of the eye; the hole in the middle of the iris is called the hole in the middle of the iris is called the pupilpupil– The iris is attached to the ciliary bodyThe iris is attached to the ciliary body

The retina is made up of three layers of The retina is made up of three layers of neurons; photoreceptor neurons, bipolar neurons; photoreceptor neurons, bipolar neurons, and ganglion neuronsneurons, and ganglion neurons

OpticOpticThe photoreceptor neurons are found in The photoreceptor neurons are found in the rods and conesthe rods and cones– Cones are more dense in the fovea centralis; Cones are more dense in the fovea centralis;

and become less dense outward from the fovea and become less dense outward from the fovea centraliscentralis

– Rods are absent from the fovea centralis and Rods are absent from the fovea centralis and increase density toward the periphery of the increase density toward the periphery of the retinaretina

Axons of the ganglion neurons extend Axons of the ganglion neurons extend back to the posterior eyeball into an area back to the posterior eyeball into an area called the optic disc; this is where the called the optic disc; this is where the optic nerve emerges from the eyeballoptic nerve emerges from the eyeball– The optic disc is also called the blind spot. It The optic disc is also called the blind spot. It

does not contain rods or conesdoes not contain rods or cones

OpticOpticThe eye is divided into two cavities;The eye is divided into two cavities;– The anterior cavity is filled with aqueous The anterior cavity is filled with aqueous

humor; a substance that is clear and humor; a substance that is clear and waterywatery

– The posterior portion is larger and it is The posterior portion is larger and it is filled with vitreous humor; a substance filled with vitreous humor; a substance with the consistency of a soft gelatinwith the consistency of a soft gelatin

– Both the aqueous and the vitreous Both the aqueous and the vitreous humors play a role in maintaining humors play a role in maintaining intraoccular pressure to prevent the intraoccular pressure to prevent the eyeball from collapsingeyeball from collapsing

OpticOpticThe aqueous humor is formed from capillaries in The aqueous humor is formed from capillaries in the ciliary bodythe ciliary body

Eyes have extrinsic and intrinsic musclesEyes have extrinsic and intrinsic muscles– The extrinsic eye muscles are skeletal muscles The extrinsic eye muscles are skeletal muscles

that attach the eye to the bones of the orbitthat attach the eye to the bones of the orbit– The intrinsic eye muscles are smooth muscles The intrinsic eye muscles are smooth muscles

located within the eye; these are the iris and located within the eye; these are the iris and the ciliary musclesthe ciliary muscles

The iris regulates the size of the pupil The iris regulates the size of the pupil

The ciliary muscles control the shape of the The ciliary muscles control the shape of the lenslens

OpticOpticThe eyebrows, eyelashes, eyelids, and The eyebrows, eyelashes, eyelids, and lacrimal apparatus are accessory lacrimal apparatus are accessory structures of the eyestructures of the eye– Eyebrows and eyelashes protect the eye from Eyebrows and eyelashes protect the eye from

entrance of foreign objects and they shade the entrance of foreign objects and they shade the eyes from direct lighteyes from direct light

The eyelash contains small glands that secrete The eyelash contains small glands that secrete lubricating fluid, if they become infected a sty lubricating fluid, if they become infected a sty developsdevelops

– Eyelids are lined with conjuctiva, which are Eyelids are lined with conjuctiva, which are mucous membranes, it continues over the mucous membranes, it continues over the surface of the eyeball. surface of the eyeball.

Inflammation of the conjuctiva is called pinkeyeInflammation of the conjuctiva is called pinkeye

OpticOptic

The lacrimal apparatus consists of The lacrimal apparatus consists of structures that secrete tears and structures that secrete tears and drain them from the surface of the drain them from the surface of the eyeballeyeball

The Process Of SeeingThe Process Of SeeingFour process focus light rays so that Four process focus light rays so that they form a clear imagethey form a clear image– Refraction means bending light rays. Refraction means bending light rays.

Rays are refracted by the cornea, Rays are refracted by the cornea, aqueous humor, lens, and vitreous aqueous humor, lens, and vitreous humorhumor

– If there are errors in refraction, If there are errors in refraction, nearsightedness (myopia), nearsightedness (myopia), farsightedness (hyperopia), and farsightedness (hyperopia), and astigmatism occursastigmatism occurs

Process of SeeingProcess of SeeingAccommodation for near vision Accommodation for near vision requires changes in the curvature of requires changes in the curvature of the lens, the constriction of the the lens, the constriction of the pupils and the convergence of the pupils and the convergence of the two eyestwo eyes– Curvature of the lens takes place to Curvature of the lens takes place to

achieve greater refraction (bending achieve greater refraction (bending light) for near vision because light rays light) for near vision because light rays from nearer objects are divergent and from nearer objects are divergent and not parallel (as in further vision)not parallel (as in further vision)

Process Of SeeingProcess Of SeeingContraction of the ciliary muscle pulls the Contraction of the ciliary muscle pulls the choroid layer closer to the lens and choroid layer closer to the lens and loosens tension of the suspensory loosens tension of the suspensory ligaments allowing the lens to bulgeligaments allowing the lens to bulge– Near vision the ciliary muscle is contracted so Near vision the ciliary muscle is contracted so

the lens will bulgethe lens will bulge– Far vision the ciliary muscle is relaxed so that Far vision the ciliary muscle is relaxed so that

the lens is flatterthe lens is flatter– Presbyopia is a condition where people become Presbyopia is a condition where people become

farsighted as the lenses lose their elasticity as farsighted as the lenses lose their elasticity as the person agesthe person ages

Process Of SeeingProcess Of SeeingThe iris constricts the pupil to prevent The iris constricts the pupil to prevent divergent rays from entering the eye divergent rays from entering the eye through the periphery of the cornea and through the periphery of the cornea and lens; if divergent light entered the pupil it lens; if divergent light entered the pupil it could not be bent enough to provide a could not be bent enough to provide a clear imageclear imageConvergence of eyes refers process where Convergence of eyes refers process where images must fall on the same location images must fall on the same location within each retina in order to see a clear within each retina in order to see a clear image. This is accomplished by moving the image. This is accomplished by moving the eyeball so that the visual axes are paralleleyeball so that the visual axes are parallel

Process Of SeeingProcess Of Seeing

Diplopia occurs when objects fall on Diplopia occurs when objects fall on noncorresponding points of the two noncorresponding points of the two retina; double visionretina; double vision

Strabismus (cross-eye or squint) is a Strabismus (cross-eye or squint) is a condition that cannot be corrected condition that cannot be corrected by neuromuscular effort. The person by neuromuscular effort. The person learns to suppress one of the imageslearns to suppress one of the images

PhotopigmentsPhotopigmentsPhotopigments can be broken down into a Photopigments can be broken down into a glycoprotein called opsin and a vitamin A glycoprotein called opsin and a vitamin A derivative called retinalderivative called retinalRods are named rhodopsin; they are highly Rods are named rhodopsin; they are highly sensitive to dim light and cause a rapid sensitive to dim light and cause a rapid breakdown of the photopigment into opsin and breakdown of the photopigment into opsin and retinal componentsretinal componentsCones are responsible for the ability to see colors; Cones are responsible for the ability to see colors; there are three different types of cones in the eyethere are three different types of cones in the eye– Neural input from a varying number of cones creates Neural input from a varying number of cones creates

color color – Cones produce vision in bright light Cones produce vision in bright light

Neural Pathway For VisionNeural Pathway For Vision

Nerve fibers that conduct impulses Nerve fibers that conduct impulses from rods and cones reach the visual from rods and cones reach the visual cortex in the occipital lobes of the cortex in the occipital lobes of the brain via the optic nerves, the optic brain via the optic nerves, the optic chiasma, optic tracts, and optic chiasma, optic tracts, and optic radiationsradiations

Sense DisordersSense DisordersOtosclerosis is an inherited bone Otosclerosis is an inherited bone disorder that impairs conduction of disorder that impairs conduction of sound waves by causing structural sound waves by causing structural irregularities in the shape of the irregularities in the shape of the stapesstapesTinnitus is ringing of the ears and Tinnitus is ringing of the ears and could be a sign of otosclerosiscould be a sign of otosclerosisExcess cerumen can block sound Excess cerumen can block sound wave conductionwave conduction

Sense DisordersSense DisordersOtitis refers to a temporary ear infectionOtitis refers to a temporary ear infection

Presbycusis is the progressive loss of Presbycusis is the progressive loss of hearing associated with aging and hearing associated with aging and degeneration of nerve tissue in the ear degeneration of nerve tissue in the ear and vestibulocochlear nerveand vestibulocochlear nerve

Meniere’s disease is a chronic inner ear Meniere’s disease is a chronic inner ear disease with an unknown cause; it results disease with an unknown cause; it results in tinnitus, progressive nerve deafness and in tinnitus, progressive nerve deafness and vertigo (spinning sensations)vertigo (spinning sensations)

Sense DisordersSense Disorders

Myopia is nearsightedness; it can be Myopia is nearsightedness; it can be corrected using concave contact corrected using concave contact lenses, glasses or refractive surgerylenses, glasses or refractive surgery– The image focuses in front of the retinaThe image focuses in front of the retina

Hyperopia is farsightedness; it can Hyperopia is farsightedness; it can be corrected by convex lenses and be corrected by convex lenses and refractive eye surgeryrefractive eye surgery– The image focuses behind the retinaThe image focuses behind the retina

Sense DisordersSense DisordersAstigmatism refers to irregularity in the Astigmatism refers to irregularity in the curvature of the cornea or lens curvature of the cornea or lens Cataracts are cloudy spots in the eye’s Cataracts are cloudy spots in the eye’s lens that develop in the lens as we age, it lens that develop in the lens as we age, it can interfere with focusingcan interfere with focusingConjuctivitis is pink eye and is usually Conjuctivitis is pink eye and is usually caused by bacteriacaused by bacteria– Chlamydial conjuctivitis, or trachoma, is Chlamydial conjuctivitis, or trachoma, is

caused by the same bacteria that cause the caused by the same bacteria that cause the reproductive infectionreproductive infection

– Conjuctivitis can be caused by other bacteria Conjuctivitis can be caused by other bacteria such as Staphylococcus and Haemophiliussuch as Staphylococcus and Haemophilius

Sense DisordersSense DisordersRetinal detachment occurs when part of Retinal detachment occurs when part of the retina falls away from the tissue the retina falls away from the tissue supporting itsupporting it– Usually results from aging, tumors, or blows to Usually results from aging, tumors, or blows to

the headthe headDiabetic retinopathy is a disorder that Diabetic retinopathy is a disorder that causes small hemorrhages in the retinal causes small hemorrhages in the retinal blood vessels that disrupt the flow of blood vessels that disrupt the flow of oxygen to the photoreceptorsoxygen to the photoreceptorsGlaucoma results from excessive Glaucoma results from excessive intraoccular pressure intraoccular pressure Nyctalopia is night blindness that can be Nyctalopia is night blindness that can be caused by a vitamin A deficiency or caused by a vitamin A deficiency or degeneration of the retinadegeneration of the retina

Sense DisordersSense Disorders

Scotoma refers to the loss of only the Scotoma refers to the loss of only the center of the visual field often center of the visual field often associated with multiple sclerosisassociated with multiple sclerosis

Colored blindness is an inherited Colored blindness is an inherited condition where one of the condition where one of the photopigments in the cones are photopigments in the cones are missingmissing