LESSON 13 THE EYE AND EAR

INTRODUCTION

The eye and the ear are sensory organs. Both have receptor cells that may be activated by stimulus of light and sound. These sensitive cells in the eye and ear respond to stimulus by initiating nerve impulses along afferent sensory neurons that lead to the brain. When stimulus is applied to the sensory receptor cells of the eye and ear, there is a sensation produced that can be interrupted by the sight and sound areas in the brain that are connected to the receptor cells.

THE EYE

Anatomy and Physiology

Light rays enter the dark center of the eye, called the pupil. The conjunctiva is a mucous membrane that lines the inside of the eyelids and coats the outside portion of the eyeball covering the white of the eye. The conjunctiva is clear and colorless except when blood vessels are dilated. Dust, smoke, and allergies may cause the blood vessels to dilate and give the conjunctiva a reddish appearance commonly known as bloodshot eyes. When this membrane becomes infected by pathogens it becomes red and is known as conjunctivitis or pinkeye.

The cornea is a fibrous, transparent tissue that extends over the pupil and colored portion of the eye. The function of the cornea is to bend the rays of light so that they are focused directly on the sensitive receptor cells in the back of the eye. The cornea has no blood vessels directly into it but receives its nourishment from osmosis into its cells.

The sclera is a tough, fibrous, supportive, connective tissue that extends from the cornea on the front surface of the eyeball to the optic nerve in the back of the eye.

The choroid is a dark brown membrane inside the sclera. It contains many blood vessels that supply nutrients to the eye. The choroid is continuous with the pigmented iris and the ciliary body on the front surface of the eye.

The iris is the colored portion of the eye that surrounds the pupil. The iris can appear blue, green, hazel, gray, brown, or a combination of these colors. Muscles of the iris constrict the pupil in bright light and dilate the pupil in dim light, thereby controlling the amount of light entering the eye.

The ciliary body, connected to each side of the lens, contains muscles that adjust the shape of the lens. These changes in the shape of the lens aid in the bending of

light rays.

The lens is flattened for distant vision and thickened for close vision by the muscles of the ciliary body. The ability of the lens to change its shape is called accommodation.

Besides controlling the shape of the lens, the ciliary body secretes a fluid called aqueous humor. The aqueous fluid is constantly being produced and flows through the front chamber of the eye. This fluid leaves the eye through a canal that carries it into the bloodstream.

Another cavity of the eye is called the vitreous chamber which is a large region behind the lens filled with a Jello-like material called vitreous humor. Vitreous humor maintains the shape of the eyeball and is not constantly reformed. Its escape from the eye can cause blindness. Both the aqueous and the vitreous humors function to further refract light rays.

At the very back of the eye is the thin and delicate nervous tissue called the retina. Light waves traveling through the eye are refracted or bent so they focus on receptor cells of the retina called the rods and cones. There are approximately 7 million cones and over 100 million rods in the retina. The cones function in bright light and are responsible for color and central vision. There are three types of cones, each type stimulated by one of the primary colors, red, green, or violet. Color blindness generally affects either the green or red receptors so that the two colors cannot be distinguished from each other. Rods function at low levels of light and are responsible for black, white, and peripheral vision.

Light waves, when focused on the retina, cause a chemical change in the rods and cones, initiating nerve impulses that then travel from the eye to the brain via the optic nerve. The area in the eye where the optic nerve meets the retina is called the optic disk or blind spot of the eye. The macula is a small, oval, yellowish area to the side of the optic disk. It contains a central depression called the fovea centralis composed mostly of cones and is the location of the sharpest vision in the eye. If a portion of the fovea or macula is damaged, vision is reduced and central vision blindness occurs. The fundus is the most inner part of the eye that is visualized through the ophthalmoscope.

Light-stimulated nervous impulses, from the retina of both eye, travel to the visual areas of the right and left cerebral cortex creating images that are fused together into a single visual image. This is called binocular vision.

THE EAR

Anatomy and Physiology

Sound waves are received by the outer ears, conducted to receptor cells within the ears, and transmitted by those cells to nerve fibers that lead to the auditory region of the brain in the cerebral cortex. It is within the nerve fibers of the cerebral cortex that the sensations of sound are perceived and interpreted.

The ear can be divided into three separate regions: outer ear, middle ear, and inner ear. The outer and middle ears function in the conducting and intensifying of sound waves through the ear and the inner ear contains structures that receive the auditory waves and relay them to the brain.

Outer Ear

Sound waves enter the ear through the pinna, or auricle, which is the projecting part of the ear. The external auditory meatus leads from the pinna and is lined with numerous glands that secrete a yellowish-brown, waxy substance called cerumen. Cerumen lubricates and protects the ear. Build-up of the cerumen may cause hearing loss. When one puts items into the outer ear canal it causes the cerumen to be pushed closer to the tympanic membrane which, in turn, hardens and blocks the passage of sound waves.

Middle Ear

Sound waves travel through the auditorial canal and strike a membrane between the outer and the middle ear. This is the tympanic membrane, or eardrum. As the eardrum vibrates, it moves three small bones, or ossicles, that conduct the sound waves through the middle ear. These bones, in the order of their vibration, are the malleus, the incus, and the stapes. As the stapes moves, it touches a membrane called the oval window which separates the middle from the inner ear.

The eustachian tube is a canal leading from the middle ear to the nasal pharynx. It is normally closed but opens upon swallowing. This tube can prevent damage to the eardrum and pressure disturbance to the middle and inner ears by equalizing pressure. Normally the pressure of air in the middle ear is equal to the pressure of air outside. However, if you are flying in an airplane, climbing a high mountain, or riding a fast elevator, the atmospheric pressure will drop, while the pressure in

the middle ear remains the same. This inequality of air pressure in the inside and outside of the eardrum forces the eardrum to bulge outward and may eventually cause it to burst. Swallowing will open the eustachian tube so that air can leave the middle ear and enter the nasal pharynx until

the atmospheric and middle ear pressures are equal. The eardrum then returns to normal and the danger of its bursting is controlled.

Most middle ear infections result from the movement of bacteria containing mucous from the nasal pharynx through the eustachian tube into the middle ear. It is therefore important to teach proper methods of blowing your nose and of sneezing to prevent the movement of this mucous and bacteria into the middle ear. The proper method of blowing one’s nose is to leave at least one side of the nose and mouth open to equalize pressure. The proper method of sneezing is to not block the nasal opening while sneezing.

The Inner Ear

Sound vibrations, having been transmitted by the movement of the eardrum to the bones of the middle ear, reach the inner ear by the movement of air waves on the oval window that separates the middle and inner ears. The inner ear is called the labyrinth because of its circular structure. The part of the labyrinth that leads from the oval window is a bony, snail-shaped structure called the cochlea. The cochlea contains special auditory liquids called perilymph and endolymph through which the vibrations travel.

Also present in the cochlea is a sensitive auditory receptor area called the organ of Corti. The organ of Corti contains tiny hair cells that vibrate when sound waves strike them. The movement of these hair cells are received by auditory nerve fibers which relay the impulse to auditory nerve which then sends it to the auditory center of the cerebral cortex. It is in the cerebral cortex where these impulses are interpreted.

The ear is an important organ of balance as well as for hearing. Within the inner ear are several organs responsible for balance. These organs contain the fluid called endolymph as well as sensitive hair cells. The fluid and hair cells fluctuate in response to the movement of the body. This creates stimulus to nerve fibers that lead to the brain. Messages are then sent to all parts of the body to assure that balance is maintained.

LESSON 13 GRAPHICS

TERMS FOR LESSON 13:

THE EYE AND EAR

Parts of the Eye to Know:conjunctivascleracorneachoroidirisciliary bodypupillensretinarodsconesaqueous humorvitreous humormeibomian glandslacrimal glandsoptic nerve

Parts of the Ear to Knowexternal earauricleexternal auditory meatusmiddle eartympanic membraneeustachian tubeossiclesincusstapesanvilinner earoval window

cochleasemicircular canalsmastoid process

Word Parts to Know: Eye and Ear:blephar/oconjunctiv/ocor/ocore/opulpill/ocorne/okerat/odacry/olacrim/oirid/oocul/oophthalm/oopt/oretin/oscler/ocry/odipl/ophot/oton/oacou/oaudi/oaur/ilabyrinth/omastoidot/ostaped/otympan/o

Prefixes and Suffixes to Know: Eye and Earbi-bin--ician-opia-phobia-plegia

Diagnostic Terms to Know: Eye and Earblepharitisblepharoptosisconjunctivitiscorneoiritisdacryocystitisdiplopiairidoplegialeukocoriaoculomycosisophthalmalgiaophthalmorrhagiaphotophobiaphotoretinitissclerokeratitisscleromalacialabyrinthitismastoiditismyringitisotalgiaotomastoiditisotomycosisotopyorrheaotosclerosistympanitis

ceruminomaMenieren’s diseaseotitis externatinnitusvertigoastigmatismcataractchalazion (meibomian cyst)detached retinaglaucomahyperopiamyopianystagmuspresbyopiastrabismussty (hordeolum)

Surgical Terms to Know: Eye and Earblepharoplastycryoretinopexydacryocystorhinostomydacryocystotomyiridectomyiridosclerotomykeratoplastysclerotomylabyrinthectomymastoidectomymastoidotomymyringoplastymyringotomycryoextraction of the lensenucleation

iridencleisisphacoemulsificationretinal photocoagulationscleral bucklingstrabotomy

Diagnostic Procedural Terms to Know: Eye and EarkeratometerophthalmoscopeoptometeroptometryoptomyometerpupillometerpupilloscopetonometertonometryacoumeteraudiogramaudiometeraudiometryotoscopeotoscopytympanometryAdditional Terms to Know: Eye and Earbinocularcornealintraocularlacrimalnasolacrimalophthalmicophthalmologistophthalmologyophthalmopathy

opticopticianpupillaryretinalretinopathyaudiologistaudiologyauralotologistotologyotorhinolaryngologistmioticmydriatricoculus dexter (OD)oculus sinister (OS)oculus uterque (OU)optometristvisual acuity

PRACTICE EXERCISES FOR LESSON 13THE EYE AND EAR

MATCHING: Eye---- aqueous fluid a lies directly behind pupil---- choroid b gives eye color---- conjunctiva c middle layer of eye---- cornea d watery fluid in front of eye---- iris e mucous membrane of eye---- lacrimal glands f produces tears---- lens g transparent part of sclera

DEFINE: Eyeocul/oblephar/ocorne/olacrim/o

retin/opupill/oscler/oirid/oconjunctiv/ocor/oophthalm/okerat/oiri/ocore/oopt/odacry/ocry/odipl/ophot/oton/o

DEFINE: Eye-opiabi--plegia-ician-phobiabin-

DEFINE: Eyesclerokeratitisophthalmalgiacorneoiritisblepharoptosisdiplopiaophthalmorrhagiaconjunctivitis

leukocoriairidoplegiascleromalaciaphotophobiablepharitisoculomycosisphotoretinitisdacryocystitiscryoextraction of the lensenucleationiridencleisisphacomulsificationretina photocoagulationscleral bucklingstrabotomy

DEFINE: EarotomyocosistypanitisotomastoiditisotalgialabyrinthitismyringitisotosclerosismastoiditisotopyorrheavertigoceruminomatinnitusMeniere’s diseaseotitis externaotitis mediaaudiologist

audiologyauralotologistotologyotorhinolaryngologist

MATCHING: Ear

___ auricle a contains receptors of equlibrium___ cochlea b equalizes air pressure___ eustachian tube c separates outer ear from middle ear___ external auditory meatus d malleus, incus and stapes___ labyrinth e carries sound to inner ear___ mastoid bone f contains wax glands___ ossicles g external ear structure___ oval window h bony spaces in inner ear___ semicircular canals i skull bone behind ear___ tympanic membrane j contains organs for hearing

ASSIGNMENT FOR LESSON 13

Medical Terminology, HS 280The Eye and Ear

MATCHING: Ear May Be Used More Than Once

---- 1 audi/o a hearing---- 2 aur/i b ear---- 3 labyrinth/o c labyrinth---- 4 tympan/o d mastoid---- 5 staped e eardrum---- 6 oto/o f ear--- 7 myring/o g stapes---- 8 acou/o---- 9 mastoid/o

MATCHING: Eye---- 10 meibomian gland a outer layer of eye---- 11 optic nerve b inner layer of eye---- 12 orbit c jelly-like fluid behind lens---- 13 pupil d oil gland to lubricate eyeball---- 14 retina e hole in center of iris---- 15 sclera f bony protective cavity---- 16 vitreous fluid g leave eye near center of retina

DEFINE: Ear

17 otomycosis

18 typanitis

19 otomastoiditis

20 labyrinthitis

21 otorhinolaryngologist

DEFINE: Eye

22 nasolacrimal

23 ophthalmologist

24 mydriatric

25 retinopathy